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Fungi, Plant Pathogens

Ganoderma adspersum (Schulzer) Donk

 California Pest Rating for
Ganoderma adspersum (Schulzer) Donk
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On January 25, 2017, Dr. David Rizzo, Professor, Department of Plant Pathology, University of California, Davis, notified CDFA of his detection of Ganoderma adspersum in almond orchards in the San Joaquin Valley, during surveys which initiated during fall 2015, of almond trees for wood decay fungi. The fungus was noted to be very aggressive and had killed relatively young almond trees in some orchards.  Consequently, CDFA will collect official samples of the fungus for analysis at the CDFA Plant Pathology Laboratory, and for official record.  Ganoderma adspersum has not been reported earlier from California or North America (Rizzo, 2017a).  The potential risk of infestation of G. adspersum is assessed here and a permanent rating is proposed for the species.

History & Status:

Background:   Ganoderma adspersum is a wood-decaying fungus that occurs in a very wide range of tree species including deciduous trees and conifers throughout the world. The species has more frequently been detected in trees growing near human habitations, gardens, parks, and planted sites (Papp & Szabo, 2013; De Simone & Annesi, 2012).   Ganoderma adspersum is a pathogen of roots and butts of living trees causing white rot, and can continue to grow saprophytically on nonliving tissue such as, stumps of felled trees (De Simone & Annesi, 2012).  Ganoderma species often kill their hosts and frequently, a diseased tree breaks or is wind-thrown while still alive as a result of decay in the butt and base of the trunk (Sinclair & Lyon, 2005). Unlike other closely related species, G. adspersum is an aggressive species that is able to penetrate and break through intact reaction zones of infected wood causing progressive and extensive decay over a relatively short period of time (De Simone & Annesi, 2012).   In Italy, G. adspersum-infected pine stands were felled within two years of infection (De Simone & Annesi, 2012).

Ganoderma adspersum has been known by several names.  The fungus was originally found growing on Carpinus betulus (European hornbeam) in Croatia, and published by Schulzer 1878 as Polyporus adspersus, and later as P. linhartii Kalchbr. 1884, Ganoderma linhartii (Kalchbr.) Z. Igmándy 1968, and G. europaeum Steyaert 1961.  After studying all specimens under the different species names, in 1969, Donk concluded the correct name for the fungus, G. adspersum (Tortic, 1971). In European polypore monographs, G. adspersum was found under the name, G. australe (Fr.) Pat. 1889.  However, through molecular analysis, the European taxon (G. adspersum) was differentiated from the Australian taxon (G. australe).  Ganoderma adspersum is the name of the European species (Papp & Szabó, 2013).  Differentiation of species of Ganoderma is confusing and problematic with only seven species, including G. adspersum, being accepted in the European polypore monographs (Papp & Szabó, 2013).  Taxonomically, G. adspersum is a distinct species belonging to the G. applanatum – australe complex (Papp & Szabó, 2013).

The species was first reported from Europe and is primarily found in that continent. However, it has also been found in Argentina, Brazil, American Samoa, and recently in the USA (California) (see: ‘Worldwide Distribution’).

In California, Ganoderma adspersum was detected in nine and ten year old almond orchards trees in Kings County during surveys of almonds for wood decay fungi in February 2016 (Rizzo, 2017a)  Over a three-year period, the orchard had experienced almost 20% tree loss, resulting in its removal by the end of 2016.  This detection marked a first for the fungus in California and North America.  Another detection was made in August 2016, in a twelve-year old almond orchard in Fresno County, and in 2017, additional infections were detected in Tulare, Kern, and Madera Counties (Rizzo, 2017b).  Presently, in California, the fungus has been found only in almond, prune and peach. All surveyed almond trees were planted on peach rootstock (Rizzo, 2017b).

Disease development:  Generally, most infections are initiated by airborne basidiospores that enter wounds on roots and trunk bases.  Basidiocarps (fruiting bodies or conks containing numerous spore producing structures or basidia) usually grow from the vicinity of old wounds.  Basidiospores are produced in great numbers during evening hours when the air is humid.  Experimentally, infection by root contact with previously colonized wood is also possible, although tree-to-tree spread has not been indicated by field observations (Sinclair & Lyon, 2005).

Dispersal and spread: Primarily by airborne basidiospores (De Simone & Annesi, 2012).

Hosts: Abies sp. (fir), A. alba (silver fir), Acer saccharinum (silver maple), Aesculus hippocastanum (horse chestnut), Betula pendula (European white birch), Broussonetia papyrifera (paper mulberry), Carpinus betulus (European hornbeam), Cedrus deodara (deodar cedar), Celtis occidentalis (common hackberry), Cercis siliquastrum (Judas tree), Fagus sylvatica (European/common beech), Fraximus sp. (ash), F. angustifolia subsp. danubialis (narrow-leafed ash), F. ornus (manna ash), Gleditschia triacanthos (honeylocust), Gymnocladus dioicus (Kentucky coffeetree), Juglans nigra (black walnut), Laurus nobilis (bay laurel), Picea abies (Norway spruce), Pinus sp. (pine), P. pinea (Italian stone pine), Platanus sp. (sycamore/plane trees), Populus alba (white poplar), P. nigra (black poplar), Prunus avium (wild cherry), P. padus (European bird cherry), P. cerasus (sour cherry), P. domestica (European plum), P. dulcis (almond), P. persica (peach), Prunus sp. (plum), Robinia sp. (locusts), R. pseudoacacia (black locust),  Quercus sp. (oak), Q. cerris (Turkey oak), Q. petraea (sessile oak), Q. pubescens (downy oak ), Q. robur (English oak), Q. ilex (holly oak), Morus sp. (mulberry), Salix sp. (willow), Tilia sp. (basswood), T. cordata (littleleaf linden), Ulmus laevis (European white elm), Zelkova serrata (Japanese zelkova) (De Simone & Annesi, 2012; Farr & Rossman, 2017; Gottlieb et al., 1998; Papp, 2013; Rizzo, 2017b; Tortic, 1970);

Symptoms:  In general, trees affected by Ganoderma develop widespread decay of sapwood in the butt and major roots.  Other symptoms include loss of vigor, undersized and sometimes yellowing or wilting leaves, thin crowns, and dead branches.  Some infected trees may die while others are weakened and fall by windstorms as a result of decay.  In advanced stages of decay, wood is light colored and stringy or spongy.  Large, reddish brown basidiocarps of G. adspersum grow from roots or butts (Sinclair & Lyon, 2005).  Progression of decay may be favored by predisposing conditions such as wounds, excessive stem density, or water stress (De Simone & Annesi, 2012).

Damage Potential:  Ganoderma adspersum causes wood decay and root rot thereby decreasing structural strength, growth and stand of infected trees.  In California, Rizzo (2017b) reported 50% to 70% infection rates in almond and prune orchards, with tree loss being exponential over time. Very high infection levels were observed in 9-12 years old almond orchards.  The life span of a typical almond orchard is about 25 years.  However, extensive infections may be terminal for almond orchards.  Few orchards were removed entirely due to high infections of Ganoderma adspersum.

Worldwide Distribution: Europe: Belgium, England, Germany, Hungary, Italy, Yugoslavia; North America: USA (California); South America: Argentina; Brazil; Oceania: American Samoa (CABI, 2017; De Simone & Annesi, 2012; Farr & Rossman, 2017; Gottlieb et al., 1998; Tortic, 1971)

Official Control: No official controls are reported for Ganoderma adspersum.  However, Ganoderma spp. is on the “Harmful Organism Lists” for Colombia and Jamaica.  Shipments of Ganoderma spp.-free Phoenix dactylifera, (date palm) plants is required by Colombia (USDA PCIT, 2017).

California Distribution: Ganoderma adspersum has been found in almond and prune orchards in Fresno, Kings, Tulare, Kern, and Madera Counties (Rizzo, 2017b).

California Interceptions: None reported.

The risk Ganoderma adspersum would pose to California is evaluated below. 

Consequences of Introduction: 

1) Climate/Host Interaction: Presently, Ganoderma adspersum has been found in almond and prune orchards within the San Joaquin Valley.  It has therefore demonstrated its capability to establish under suitable climates for those hosts within the State.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Ganoderma adspersum has a wide host range which includes deciduous and confer trees reported worldwide.  However, in California, the fungus has presently been detected in almond, prune and peach (almond on peach root stock) (Rizzo, 2017b). Those fruit hosts are cultivated in significant acreage in California.

Evaluate the host range of the pest.

Score: 3

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Numerous basidiospores are produced by the fungus but are dependent on wind currents for dispersal and spread to non-infected trees. Therefore, a Medium rating is given for high reproductive potential.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 2

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Rizzo (2017b) reported 50% to 70% infection rates in almond and prune orchards in California, with tree loss being exponential over time.  Ganoderma adspersum causes wood decay and root rot resulting in decreased structural strength, growth and stand of infected trees.  Few orchards were removed entirely due to high infections.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Ganoderma adspersum has been reported on several hosts that are found in California environments.  Internationally, the fungus has more frequently been detected in trees growing near human habitations, gardens, parks, and planted sites.  However, in California, the fungus has only been detected in cultivated almond and prune. Other hosts may be threatened if the almond isolate in California is able to infect them.  However, as presently this is not known, the fungus is given a Medium score for potentially impacting urban gardens and plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Ganoderma adspersum: High (13).

Add up the total score and include it here.

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Evaluation is Medium (-2).  Ganoderma adspersum has been reported (Rizzo, 2017a, 2017b) from Fresno, Kings, Tulare, Kern, and Madera Counties.

Score: (-2)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11.

Uncertainty:  

Presently, in California, Ganoderma adspersum has only been found in almond, prune, and almond on peach rootstock.  The fungus has a wide host range, but it is not known if other hosts, in particular those in natural environments of California, have been infected or will be infected by the almond isolate of the fungus.  Future information on its distribution may alter the numerical score but less likely, the proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ganoderma adspersum is B.

References:

Agrios, G. N.  2005.  Plant Pathology Fifth Edition.  Elsevier Academic Press.  922 p.

De Simone, D., and T. Annesi.  2012. Occurrence of Ganoderma adspersum on Pinus pinea.  Phytopathologia Mediterranea 51: 374-382.

CABI.  2017.   Ganoderma adspersum basic datasheet. http://www.cabi.org/cpc/datasheet/24922

Farr, D. F., and A. Y. Rossman.  2017.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved March 8, 2017, from http://nt.ars-grin.gov/fungaldatabases/

Gottlieb A. M., B. O Saidman, and J. E. Wright, 1998. Isoenzymes of Ganoderma species from southern South America. Mycological Research 102, 415‒426.

Papp, V. and I. Szabó.  2013.  Distribution and host preferences of poroid Basidiomycete in Hungary I. – Ganoderma.  Acta Silv. Lingn. Hung. 9: 71-83.  DOI: 10.2478/aslh-2013-0006

Rizzo, D.  2017a. Email from David Rizzo, University of California, Davis, to Cheryl Blomquist, CDFA, sent Wednesday, January 25, 2017 6:09 am, forwarded to John Chitambar, CDFA, Wednesday, January 25, 2017 8:03:08 am.

Rizzo, D.  2017b. Email from David Rizzo, University of California, Davis to John Chitambar, CDFA, Tuesday, March 7, 2017 12:33 pm.

Sinclair, W. A., and H. H. Lyon.  2005.  Diseases of trees and shrubs second edition.  Comstock Publishing Associates, a division of Cornell University Press, Ithaca and London.  660 p.

Tortic, M.  1971.  Ganoderma adspersum (s. Schulz.) Donk (Ganoderma europaeum Steyaert) and its distribution in Yugoslavia.  Acta Botanica Croatica. 30: 113-118.

USDA PCIT.  2017.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Calonectria pseudonaviculata (Crous, J. Z. Groenew. & C. F. Hill) L. Lombard, M. J. Wingf. & Crous, 2010

California Pest Rating for
Calonectria pseudonaviculata (Crous, J. Z. Groenew. & C. F. Hill) L. Lombard, M. J. Wingf. & Crous, 2010
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On November 22, 2016, non-official samples of diseased boxwood plants collected by a landscaper from a private property in Hillsborough, San Mateo County, were sent through the San Mateo County Agricultural Commissioner’s office to the CDFA Plant Pathology Lab for diagnosis.  The samples were examined by Kathy Kosta CDFA plant pathologist, and the associated pathogen was cultured and identified by Cheryl Blomquist CDFA plant pathologist, as Calonectria pseudonaviculata (Kosta, 2016).  Subsequently, on November 29, 2016, official samples were collected from the same private property by Kathy Kosta (CDFA) and Fred Crowder (San Mateo County) and processed at the CDFA Plant Pathology Lab for pathogen diagnosis.  The official identification of Calonectria pseudonaviculata was made by Cheryl Blomquist on December 7, 2016.  This detection marked a first record of the pathogen in California.  Consequently, the pathogen was assigned a temporary ‘Q’ rating.   The risk of introduction and establishment of the pathogen is assessed here and a permanent rating is proposed.

History & Status:

Background:  Calonectria pseudonaviculata is the fungal pathogen that causes boxwood blight or box blight disease.  The pathogen is also known by its asexual (anamorph) stage as Cylindrocladium pseudonaviculatum.  The disease was first reported in the United Kingdom in the early to mid-1990s and the pathogen was given the name Cylindrocladium buxicola.  The origin of C. pseudonaviculatum is not known.  The pathogen was considered an exotic species that had been introduced to the UK and by 1998, it had spread to Europe and New Zealand.  (CABI, 2016; Crous et al., 2002; Dart et al., 2012).  While most published literature refers to the fungus as C. buxicola, this pathogen was not formally reported in the literature until 2002 as Cylindrocladium pseudonaviculatum which later became synonymous with Calonectria pseudonaviculata, the sexual (teleomorph) stage of the fungus (Lombard et al., 2010).  The current scientific name of the pathogen is Calonectria pseudonaviculata (CABI, 2016; Crous et al., 2002; Ivors & LeBude, 2011).

Disease cycle:  The pathogen infects host plants rapidly in warm (18-25°C) and humid conditions and has a life cycle that is completed in one week (Henricot, 2006; Henricot et al., 2008).  The primary inoculum of spores are sticky and therefore, are best transmitted to healthy host plants by water-splash or carried by insects, birds or infested plants.  Spores germinate three hours after inoculation and penetrate leaves in as little as five hours (Henricot, 2006).  Hyphae penetrate through stomata on lower surface of leaves, or directly through the cuticle on upper surface of leaves without appressorium formation (specialized attachment and penetration structure).  The fungus continues to grow intercellularly in the mesophyll layers of the plant (Henricot, 2006).  Two to three days after infection, the fungus produces conidiophores and conidia (asexual spores) through stomata and after seven days, these cover the lower surface of the leaf.  Leaves are eventually killed (Henricot, 2006).   The fungus can form resting structures (microsclerotia) which can survive on leaf material and in the soil in the absence of a susceptible host (Henricot, 2006).  However, in a 5-year study on the survival of the fungus on decomposing plant material, Henricot et al., (2008) did not detect the presence of microsclerotia.  Apparently, the pathogen is able to survive as mycelium within decomposing plant tissue.   No sexual stage structures have been observed in nature or in culture (CABI, 2016).

C. pseudonaviculata is a low temperature fungus that can grow below 10°C but is inhibited at 30°C and killed at 33°C (Henricot, 2006).

Dispersal and spread: The pathogen is spread by wind-driven rain and splashing water over short distances.  Long distance spread occurs by movement of infected plants/nursery stock, infested plant debris, soil, contaminated tools and equipment, insects or birds.  The pathogen can survive in leaf debris on or beneath the soil surface for up to 5 years (Dart et al., 2012; Henricot, 2006; Henricot et al., 2008).  The disease may also be spread is through the movement of asymptomatic (or with very limited outward symptoms) boxwood plants or plants treated with fungicides that suppress but do not kill or eliminate the inhabiting pathogen (Douglas, 2011).

Hosts: Buxaceae: Buxus microphylla (little-leaf box), B. microphylla var. japonica, B. sempervirens (syn. B. colchica; common boxwood), B. sinica (Chinese box), B. sinica var. insularis (Korean boxwood), Buxus sp. (box), Pachysandra procumbens, P. terminalis (Japanese spurge), Sarcococca sp. (sweet box) (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016).

The full host range of this pathogen is not currently known however, none of the Buxus species are immune to boxwood blight and susceptibility to the pathogen may vary among cultivars (Henricot et al., 2008).  Sarcococca sp. (sweet box) and Pachysandra terminalis (Japanese spurge) are experimental hosts (Henricot et al., 2008; LaMondia et al., 2012).

Symptoms:  Infections by Calonectria pseudonaviculata result in the production of dark brown or lighter brown leaf spots surrounded by a dark border.  Stems are also infected exhibiting characteristic black streaks.  Eventually severe defoliation and dieback occur.  The fungus does not infect the roots.  Entire foliage typically becomes blighted causing the leaves to turn ‘straw’ to light brown in color and defoliate.  Stems of blighted plants may remain green under the outer bark until infected by secondary or opportunistic pathogens and diseases resulting in decline and eventual death of entire plants.  Young seedlings can be killed by this pathogen (Henricot, 2006; Henricot et al., 2008; USDA-NCSU).

Damage Potential:   The disease has been described as ‘devastating’ to boxwood plants (Henricot et al., 2008). Foliage of infected plant is eventually killed and blighted plants are predisposed to infections by secondary pathogens also resulting in their eventual death.  At particular risk are boxwood plants grown in nurseries, commercial landscapes, parks and gardens, and at private residences under warm and wet climates conducive for the development and spread of the pathogen.  Rapid and widespread infection including over 10,000 American boxwood plants and 150,000 plants in production nurseries in North Carolina and Connecticut were reported (Ivors et al., 2012).  Buxus spp. (boxwood) are not native to the United States, and are widely cultivated as ornamental plants.  In California, depending on plant species and cultivar, boxwood is commonly grown throughout the State except in cold, mountainous regions, and are likely to prefer cooler climates in the State (Sunset Western Garden Book, 1992).  Three main species are grown as ornamentals in the USA, B. sempervirens, B. microphylla, and B. sinica var. insularis, all which are known hosts of C. pseudonaviculata (USDA-NCSU).

Worldwide Distribution: Asia: Iran, Republic of Georgia, Turkey; North America: Canada (restricted distribution in British Columbia, few occurrences in Ontario and Quebec), USA; Europe: Austria, Belgium, Croatia, Czech Republic, Denmark, France, Germany, Ireland, Italy, Netherlands, Norway, Slovenia, Spain, Sweden, Switzerland, United Kingdom; Oceania: New Zealand (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016).

In the USA, C. pseudonaviculata has been reported from Alabama, Connecticut, Delaware, Kentucky, Maryland, Massachusetts, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, Rhode Island, Virginia (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016), and by this report from California.

Official Control:  Cylindrocladium buxicola (synonym C. pseudonaviculata) is on the ‘Harmful Organism Lists’ for the Republic of Korea (USDA PCIT, 2016).  Presently, it has a temporary Q rating in California.

California Distribution:   San Mateo County.

California Interceptions:  None reported.

The risk Calonectria pseudonaviculata would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: The boxwood blight pathogen, Calonectria pseudonaviculata rapidly infests host plants under humid and warm (18-25°C) climates – being inhibited at 30°C and killed at 33°C. Spores are transmitted to healthy host tissue under wet conditions, requiring wind-driven rains and water splash from overhead irrigation systems. Depending on species and cultivar selection, Buxus are grown throughout California, except in mountainous regions, and are likely to do best in cool climates, such as coastal regions of the State.  Plants grown in warm and humid climates are at possible risk of infection by the pathogen.  The pathogen may be able to establish in a larger but limited region in the State, suitable also to the growth of its host plants.  Therefore a ‘medium’ rating is given to this category.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The host range of Calonectria pseudonaviculata is currently limited to few Buxus species (boxwood) and several cultivars, as well as Sarcococca (sweet box) and Pachysandra spp. (Japanese spurge).

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Calonectria pseudonaviculata has high reproductive potential.  Although its dispersal and spread over short distances to non-infected plants depends on wind-driven rain and water-splash, long distance spread occurs by movement of infected plants/nursery stock, infested plant debris, soil, contaminated tools and equipment, insects or birds. The disease may also be spread through the movement of asymptomatic (or with very limited outward symptoms) boxwood plants or plants treated with fungicides that suppress but do not kill or eliminate the inhabiting pathogen.  These modes of spread, plus the ability of the pathogen to survive in leaf debris on or beneath the soil surface for up to 5 years, places it as a ‘high risk’ in this category.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Boxwood blight disease could result in lower crop value, loss of foliage and plants, increased production costs, loss of markets, and changes in delivery of irrigation water so to avoid water splash and wetness of foliage.  Also, insects and birds could aid in spread of the pathogen to non-infected plants.  Therefore, economic impact, caused by the boxwood blight pathogen, is given a ‘High’ score.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C, D, E.

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Infections of Calonectria pseudonaviculata could significantly affect private and commercial plantings of boxwood plants commonly used as hedge and shrub ornamentals and result in additional treatments against the pathogen.  Therefore, risk on environmental impact is scored as ‘High’.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: D, E.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Calonectria pseudonaviculata: Medium (11)

Add up the total score and include it here.

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Presently, the boxwood blight pathogen has only been officially reported from one region, namely, San Mateo County. California.

Score: (-1)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = Medium (10)

Uncertainty:  

None.                              

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Calonectria pseudonaviculata is B.

References:

CABI, 2016.  Calonectria pseudonaviculata (buxus blight) full datasheet. http://www.cabi.org/cpc/datasheet/17414.

Crous, P.W., J. Z. Groenewald, and C. F. Hill.  2002.  Cylindrocladium pseudonaviculatum sp. nov. from New Zealand, and new Cylindrocladium records from Vietnam. Sydowia 54: 23-34.

Dart, N., M. A. Hansen, E. Bush, and C. Hong.  2012.  Boxwood blight: a new disease of boxwood found in the eastern U.S.  Virginia Cooperative Extension, Virginia State University Publications and Educational Resources PPWS-4.  http://pubs.ext.vt.edu/PPWS/PPWS-4/PPWS-4.html

Douglas, S. M.  2011.  Boxwood blight – a new disease for Connecticut and the U. S.  The Connecticut Agricultural Experiment Station.  www.ct.gov/caes .

Farr, D.F., and A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved December 1, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Henricot, B., C. Gorton, G. Denton, and J. Denton. 2008. Studies on the control of Cylindrocladium buxicola using fungicides and host resistance. Plant Disease, 92(9):1273-1279.  http://www.apsnet.org

Ivors, K. and A. LeBude.  2011.  A new pest to the U. S. ornamental industry: the “box blight” pathogen Cylindrocladium pseudonaviculatum = Cylindrocladium buxicola.  NC Pest Alert. http://plant-clinic.bpp.oregonstate.edu/files/plant_clinic/webfm/NC_pest_alert_box_blight1-1.pdf

Ivors, K. L., L. W. Lacey, D. C. Milks, S. M. Douglas, M. K. Inman, R. E. Marra, and J. A. LaMondia.  2012.  First report of boxwood blight caused by Cylindrocladium pseudonaviculatum in the United States.  Plant Disease.  96: 1070. http://dx.doi.org/10.1094/PDIS-03-12-0247-PDN.

Kosta, K.  2016.  Personal communication to J. Chitambar, CDFA Primary Plant Pathologist/Nematologist via email on November 30, 2016, 5:03:15 pm.

LaMondia, J. A., D. W. Li, R. E. Marra, and S. M. Douglas.  2012.  First report of Cylindrocladium pseudonaviculatum causing leaf spot of Pachysandra terminalis.  Plant Disease 96: 1069. http://dx.doi.org/10.1094/PDIS-03-12-0235-PDN.

Lombard, L., P. W. Crous, B. D. Wingfield, and M. J. Wingfield.  2010.  Phylogeny and systematics of the genus Calonectria.  Studies in Mycology. 66: 31-69.  www.studiesinmycology.org , doi:10.3114/sim.2010.66.03

USDA-NCSU.  (Date not known).  The ‘box blight’ pathogen: Cylindrocladium pseudonaviculatum = Cylindrocladium buxicola (Teleo.  Calonectria pseudonaviculata).  Datasheet developed by USDA-APHI-PPQ-CPHST and NCSU Department of Plant Pathology, Mountain Horticultural Crops Research and Extension Center (MHCREC) staff. caps.ceris.purdue.edu/dmm/1603

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

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♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Coleophoma empetri (Rostr,) Petr. 1929

California Pest Rating for
Coleophoma empetri (Rostr,) Petr. 1929
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On April 27, 2016 a mail shipment containing cut foliage of Galax sp. was intercepted by the Santa Barbara County Dog Team, at the FedEx Service Center in Goleta, Santa Barbara County.  The shipment had originated in Florida and was destined to a nursery in Carpinteria, Santa Barbara County.  Samples of diseased leaves exhibiting leaf spots were collected by the County and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  On April 29, 2016 Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Coleophoma empetri, as the cause for the disease.   The pathogen has not been previously reported in California and therefore, was assigned a temporary Q rating.  Subsequent action taken by the County resulted in the destruction of the intercepted shipment of Galax sp. foliage (CDFA, 2016). The risk of infestation of Coleophoma empetri in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Originally described as Septoria empetri, the fungal pathogen Coleophoma empetri is also known by other synonyms, Rhabdostromina empetri, Sporonema oxycocci, and Coleophoma rhododendri, and Coleophoma ericae.  The pathogen is widely distributed and found on living and dead leaves and fruit of many different plant species (Farr & Rossman, 2016; Sutton, 1980).

Disease cycle:   There is a paucity of specific information on Coleophoma empetri.  However, it is likely that the development of disease caused by the pathogen would be similar to other pycnidia-forming fungal pathogens.   The pathogen overwinters as mycelium or immature pycnidia in infected fruit and diseased plant debris. Under high moisture and cool temperature conditions, pycnidia swell and release conidia which are spread by splashing rain, irrigation, water, and so on.  Seed transmission is not known for C. empetri.  Infection of host plants and severity of disease development is likely to require high moisture and cool temperatures.  In the development of fruit rot of berries, conidia initiate infection during bloom and early berry development.  As infected fruit mature, hyphae continue to invade the fruit and rot symptoms do not develop until the late growing season and mostly in storage (Kusek, 1995).

Dispersal and spread: Splashing rain and irrigation water, air currents, infected plants, infected plant debris, cultivation tools, animals, and contaminated clothing.

Hosts:  Archontophoenix alexandrae (Alexander palm), Arctostaphylos sp. (Manzanita), A. uva-ursi, Arctous alpine (bearberries), Betula sp. (birch), Camellia sp., Cajanus cajan (pigeon pea), Canavalia ensiformis (Jack bean), Capsicum annuum (bell peppers), Croton sp., Diapensia sp., D. obovata (pincushion plant), Elaeagnus sp. (oleaster), E. macrophylla, Empetrum sp., E. nigrum (black browberry), Erica carnea (winter heath), Eucalyptus sp. E. tereticornis (forest red gum), Ficus sp., Fraxinus sp. (ash), Galax aphylla (beetleweed/coltsfoot), Gaultheria shallon (shallon), Gaylussacia brachycera (box huckleberry), Juniperus sp. (juniper), Kalmia angustifolia (sheep laurel), Laurus sp., L. nobilis (sweet bay), Leucothoe sp., Loiseleuria sp., L. procumbens, Lonicera sp. (honeysuckle), L. periclymenum, Malus sylvestris (European crab apple), Paxistima canbyi (Canby’s mountain-lover), Plea europaea, Prunus laruocerasus (cherry laurel), P. ponticum, Rhododendron sp., R. maximum, Solanum tuberosum (potato), Stransvaesia sp., Taxus baccata (English yew), Vaccinium sp. (blueberry), V. macrocarpon (American cranberry), V. ovatum (California huckleberry), V. oxycoccos (bog cranberry), V. vitis-idaea (lingonberry) (Farr & Rossman, 2016; Kusek, 1995; Sutton, 1980).

Symptoms:  Coleophoma empetri causes leaf spot, fruit rot and tuber skin spot disease on numerous hosts in numerous families.  Symptoms of ripe rot on cranberry fruit initially appear as a small soft area which expands over the entire fruit.  Diseased fruit appear off-red or reddish orange, and internally watery, squirting a watery fluid when squeezed.  However, as not all watery-soft fruit is caused by the pathogen, the latter must be isolated from the diseased fruit to confirm an association with the symptoms (Kusek, 1995).

Disease Potential:  Specific information on quantitative crop losses caused by Coleophoma empetri has not been reported. Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected. Symptomatic host plants infected with the pathogen may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California.  The disease could negatively impact value and marketability of nursery-grown plants including ornamental and landscape plants such as Manzanita, Camellia, Rhododendron, and Eucalyptus. The pathogen causes fruit rot that is apparent during late growing season and mainly in storage.

Worldwide Distribution: Coleophoma empetri is globally widely distributed.  Asia: India, USSR; Europe: Finland, Lithuania, Poland, USSR, United Kingdom, Ukraine, Scotland, Germany; North America: Alaska, Maryland, Massachusetts, Maine, Michigan, New Jersey, Oregon, Tennessee, Virginia, Washington, Wisconsin, and Northwestern states (Farr & Rossman, 2016).

Official Control:  Currently, has a temporary Q rating in California.

California Distribution:  is not established in California.

California Interceptions: A single shipment of Coleophoma empetri-infected Galax sp. foliage was intercepted on April 27, 2016 at the FedEx Service Center in Goleta, Santa Barbara County (see ‘Initiating Event’).

The risk Coleophoma empetri would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): Coleophoma empetri may be able to establish on suitable host plants growing in high moisture and cool to warm climate conditions.  These conditions would likely limit natural establishment to northern coastal regions of California.

2) Known Pest Host Range: Evaluate the host range of the pest:

Score: 2

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2):  Coleophoma empetri has a moderate host range that includes many host species in different plant families.  Most hosts grow under cool and wet climates.  In California, main hosts include ornamental, landscape, and fruit berry plants such as, Manzanita, Camellia, Rhododendron, Eucalyptus, blueberry, and cranberry.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest:

Score: 2

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (2): Coleophoma empetri has high reproduction and dispersal potential.  The pathogen can be spread over short and long distance by splashing rain and irrigation water, air currents, infected plants, infected plant debris, cultivation tools, animals, and contaminated clothing.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Score: 2

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2):  The pathogen may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California.  The disease could negatively impact value and marketability of nursery-grown plants including ornamental and landscape plants.  Also, the pathogen may cause fruit rot that is apparent during late growing season and mainly in storage.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

Score: 3

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

 Risk is High (3): Severe infections caused of Coleophoma empetri could impact ornamental plantings.  Under suitable conditions that result in severe disease, threatened or endangered plant species, namely, manzanita (Arctostaphylos spp.) could be affected and disrupt critical habitats.  

Consequences of Introduction to California for Coleophoma empetri:

Add up the total score and include it here:

-Low = 5-8 points

–Medium = 9-12 points

        -High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 11 (Medium).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included:

Score: 0

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not Established (0).  Coleophoma empetri is not established in California.   

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11 (Medium).

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Coleophoma empetri is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

CDFA.  2016.  Santa Barbara County Dog Team Interception.  CDFA AQW Pest Report No. 18-2016, weekly AQW report: for the week of April 28 to May 04, 2016.

Duan, J. X., W. P. Wu, and X. Z. Liu.  2007.  Reinstatement of Coleonaema for Coleophoma oleae and notes on Coleophoma.  Fungal Diversity 26: 187-204.

Farr, D. F. and A. Y. Rossman.  2016.   Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 24, 2016 from http://nt.ars-grin.gov/fungaldatabases/.

Kusek, C. C.  1995.  Cranberry Ripe Rot.  In Compendium of Blueberry and Cranberry Diseases Edited by F. L. Caruso and D. C. Ramsdell.  APS Press, The American Phytopathological Society, page 43.

Sutton, B. C. 1980. The Coelomycetes. Fungi Imperfecti with pycnidia, acervuli and stromata. Commonwealth Mycological Institute, Kew, Surrey, England, 696 pages

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Phytoplasmas, Plant Pathogens

Candidatus Phytoplasma pruni

California Pest Rating for
Candidatus Phytoplasma pruni
(= Peach X-disease, Peach Rosette, Peach Red Suture, and Little Peach Phytoplasmas)
Pest Rating: C
PEST RATING PROFILE
Initiating Event: 

CDFA regulations require imported peach nursery stock to be certified free from Peach Rosette, Peach Yellows, Little Peach and Red Suture Diseases.  These diseases are caused by phytoplasmas which are named accordingly.  Presently, all four phytoplasmas are A-rated pathogens in California.  However, research has shown that these phytoplasmas are actually strains of Candidatus Phytoplasma pruni.  Therefore, the status of the four phytoplasmas and their current rating in California are reviewed herein and a new permanent rating is proposed.

History & Status:

Background:  In 1933, a disease of peach was discovered in Connecticut and called the “X-disease of Peach” because of its unknown cause and mysterious nature.  For several years following its discovery, X-disease was believed to be caused by a virus that was mainly vectored by insects from nearby forests to peach orchards and seldom passed from tree to tree in the eastern USA.  Wild chokecherry (Prunus virginiana), growing in forests, was found to be an important natural host of the pathogen.  By the early 1950s, X-disease was also discovered in several US north eastern states and western states, including California, as well as in Canada (Stoddard, et al., 1951).   Subsequently, based on slightly different symptoms, two forms of peach X-disease were initially distinguished in the USA, namely, eastern X-disease and western X-disease, however, based on serological, nucleic acid and graft-transmission studies the eastern and western forms were found to be similar and recognized as strains of the pathogen. The pathogen was soon discovered to be widely distributed in fruit trees in the USA and can be transmitted by species of leafhopper.  X-disease is now known to be caused by a phytoplasma (formerly, mycoplasma-like organism or MLO).  In Eastern USA, peach rosette, peach yellows (also called little peach) and peach red suture were associated with the presence of peach X-disease phytoplasma.  Cherry albino disease, once found in the Rogue River Valley of Oregon in 1937 but now no longer found, was suspected to be caused by a strain of peach X-disease phytoplasma.  In California, Cherry buckskin disease on cherry had been known since the early 1920s and later the pathogen that caused this disease was also discovered to cause lethal decline disease of peach or “lethal casting yellows’.  Both diseases were later considered to be caused by strains of peach X-disease. Also in California, peach yellow leaf roll disease is caused by several genetically unrelated phytoplasmas of which only one is similar to, and a strain of peach X-disease phytoplasma (CABI, 2016; Davis et al., 2013; Kirkpatrick, 1995; Larson & Waterworth, 1995; 1995 Kirkpatrick et al., 1995).

Based on gene analysis, namely, restriction fragment length polymorphism (RFLP) analysis of 16S rRNA gene sequences, strains of peach X-disease phytoplasma from eastern and western USA and eastern Canada were classified in phytoplasma 16S rRNA gene RFLP group 16 SrIII, subgroup A.  Davis et al., (2013) found gene sequences of peach X-disease phytoplasma strains to be distinct from other previously described Candidatus Phytoplasma species and therefore, formally described Candidatus Phytoplasma pruni (Ca. Phytoplasma pruni) as a new species group or taxon of phytoplasma associated with X-disease of stone fruits to include geographically diverse X-disease phytoplasma strains that shared similar nucleotide sequence (16S rRNA gene sequences) alignments.  These strains include X-disease phytoplasma (cause of peach yellows disease), peach rosette, peach red suture, and little peach phytoplasmas.

Hosts: Peach (Prunus persica) is the principal host of the pathogen.  Other hosts include species of the genus Prunus, including, cherry (P. avium and P. cerasus), Japanese plum (P. salicina), almond (P. dulcis), apricot (P. armeniaca), nectarine (P. persica var. nectarine), Chinese bushcherry (P. japonica), Bessey cherry (P. besseyi), wild American plum (P. americana), wildgoose plum (P. munsoniana) and European plum (P. domestica). Common chokecherry (P. virginiana) is a wild host species that serves as an important natural reservoir of peach X-disease phytoplasma in many states of USA.  Bur clover (Medicago polymorpha) is also a wild host of the pathogen.  Also, switch sorrel (Dodonaea viscosa) and lucerne (Medicago sativa) (CABI, 2016; EPPO, 2014; Davis et al., 2013; Douglas, 1986; Stoddard et al., 1951).

Symptoms: Symptoms of X-disease on peach (Ca. Phytoplasma pruni) include: tattered, shot-holed leaves, chlorosis, loss of severely affected leaves leaving a cluster of leaves at the terminal tips of shoots (rosettes), dieback of branches and death of trees (Davis, et al., 2013; Douglas, 1986; Stoddard, et al., 1951).  Younger peach trees die within 1-3 years after the first appearance of symptoms.  The first symptoms of X-disease in peach on leaves of some or all branches appear as reddish purple spots which later die and fall out (shot-holes). The leaves turn reddish and curl upwards.  Older trees may survive longer but bear little or no fruit.  Fruit usually shrivel and drop, but those remaining on the trees ripen prematurely, have an off-taste and are not marketable. No seeds develop in infected fruit.  The phytoplasma can be irregularly distributed in the trees therefore fruit on healthy-appearing parts of a tree do not show signs of disease (Agrios, 2005; CABI, 2014).  Infected cherry trees on resistant Prunus mahaleb rootstock die rapidly due to hypersensitive reaction that occurs at the graft union. Other rootstocks die slower (Kirkpatrick et al., 1995).

Damage Potential:  Peach X-disease is one of the most important diseases of peach.  Infected trees become commercially useless in 2-4 years (Agrios, 2005). The degree of damage depends on the strain of the pathogen and development stage of the infected host.  Also, it can cause serious losses to cherry production.

Transmission: The pathogen is transmitted by several species of leafhopper, including Colladonas clitellarius, C. montanus, C. geminatus, Euscelidius variegates, Fieberiella florii, Graphocephala confluens, Gyponana lamina, Keonella confluens, Norvellina seminude, Osbornellus borealis, Paraphlepsius irroratus, and Scaphytopius delongi (S. acutus) (CABI, 2014; Davis, et al., 2013).  The leafhopper vectors overwinter on herbaceous weeds that act as reservoir of the pathogen in orchards, and infect trees in spring and summer. The latency period, or the time between when a vector acquires the pathogen while feeding on an infected host and when the vector is able to inoculate the pathogen into a non-infected, susceptible host, is 22-35 days for Colladonas geminatus and 45 days for Scaphytopius delongi (S. acutus) (CABI, 2016).

The pathogen is also transmitted over long distances through infected plant materials that were propagated by budding and grafting of infected plant material.  Infected plant parts at risk of spreading the phytoplasma include all plant parts with the exception of fruit (CABI, 2016).

Worldwide Distribution: Asia: India (EPPO, 2016); North America: Canada, USA (California, Colorado, Connecticut, Georgia, Hawaii, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New York, North Dakota, Oregon, Pennsylvania, South Carolina, South Dakota, Utah, Virginia, Washington, West Virginia) (CABI, 2016; EPPO, 2016; Thakur et al., 1998).

Official Control: Currently, the listed diseases and strains of Ca. Phytoplasma pruni are on the ‘Harmful Organism Lists’ for the respective countries.  Peach X-disease phytoplasma: Argentina, Brazil, Canada, Chile, China, Colombia, Guatemala, Japan, Jordan, Republic of Korea, Mexico, Morocco, Norway, Paraguay, Peru, and Turkey; Peach X-disease mycoplasma: European Union, Holy See (Vatican City State), Monaco, San Marino, and Serbia; Peach X phytoplasma: Israel and Japan; Peach rosette mycoplasma: European Union, Holy See (Vatican City State), Monaco, San Marino, and Serbia; Peach rosette phytoplasma: Argentina, Brazil, Guatemala, Israel, Japan, Mexico, Morocco, Paraguay, and Turkey; Peach yellow MLO: Mexico; Peach yellows mycoplasma: European Union, Holy See (Vatican City State), Madagascar, Monaco, San Marino, Serbia, and Ukraine; Peach yellows phytoplasma: Brazil, Chile, Colombia, Israel, Japan, Jordan, Republic of Korea, Mexico, Morocco, Paraguay, Peru, and Turkey (PCIT, 2016).

Ca. Phytoplasma pruni is an EPPO A1 quarantine pest.  It is a quarantine pest in Israel, and Norway (EPPO, 2016).

Currently, diseases and strains of Ca. Phytoplasma pruni, namely, X-disease phytoplasma causing cherry buckskin, cherry albino and peach western X diseases are already present in California and rated ‘C’, while peach red suture, peach rosette, little peach and X-disease (causing peach yellows disease) phytoplasmas are quarantine pathogens rated ‘A’.

California Distribution:  Western X-disease phytoplasma (now, Ca. Phytoplasma pruni) is generally distributed throughout California and has been detected on plum, cherry, apricot, peach, nectarine, almond and celery (California Plant Disease Host Index by French, A. 1989, Updated 2014).

California Interceptions: The risk Ca. Phytoplasma pruni would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is High (3) – Strains of Ca. Phytoplasma pruni are already established and widespread within California.

2) Known Pest Host Range: Evaluate the host range of the pest:

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – The host range is limited to Prunus spp. of which peach (P. persicae) is the principal host.  Peach is a major stone fruit crop in California, cultivated in significant acreage throughout the State.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest:

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – The pathogen is artificially transmitted mainly by a number of leafhopper species thereby marking it as having a high potential for increase and spread.  It is also spread in infected plant materials through grafting and budding operations.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3) – Ca. Phytoplasma pruni has the potential to seriously damage peach (and stone fruit) production by lowering crop yield and value, requiring changes in cultural management practices to maintain disease free plants, trigger loss of markets possibly through further impositions of quarantines by importing countries and increase costs in production of clean crops.  The pathogen is vectored by many species of leafhopper.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2) – There is a medium impact to the environment expected. The pathogen is limited to Prunus spp. of which a few serve as wild hosts.  These wild hosts may also serve as reservoirs from which the vectors can acquire and transmit the pathogen to non-infected main hosts.  Home grown peach trees may be infected thereby requiring specific treatment measures.

Consequences of Introduction to California for X-disease phytoplasma:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of X-disease phytoplasma to California = (12).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included:

Score: 3

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is High (3). 

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9.

Uncertainty:

Continued survey of stonefruit production for all strains of Ca. Phytoplasma pruni will lend more knowledge to the distribution of this pathogen in California.  This information can result in further lowering the overall score but will not lower the proposed C rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ca. Phytoplasma pruni (containing peach X-disease, peach rosette, peach red suture, and little peach strains) is C.

References:

Agrios, G. N.  2005.  Plant Pathology fifth edition.  Elsevier Academic Press, Massachusetts, USA.  922 p.

CABI.  2016.  Phytoplasma pruni (peach X-disease) full datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/ .

Davis, R. E., Y. Zhao, E. L. Dally, Ing-Ming Lee, R. Jomantiene and S. M. Douglas.  2013.  ‘Candidatus Phytoplasma pruni’, a novel taxon associated with X-disease of stone fruits, Prunus spp.: multilocus characterization based on 16S rRNA, secY, and ribosomal protein genes.  International Journal of Systematic and Evolutionary Microbiology, 63:766-776.

EPPO.  2016.  Phytoplasma pruni (PHYPPN).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm .

Douglas, S. M.  1986.  Detection of mycoplasma-like organisms in peach and chokecherry with X-disease by fluorescence microscopy.  Phytopathology 76:784-787.

Kirkpatrick, B. C.  1995.  Diseases caused by mycoplasma-like organisms: Cherry Albino, Peach Rosette, Peach Yellows.  In Compendium of Stone Fruit Diseases.  Edited by J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu and J. K. Uyemoto.  APS Press, The American Phytopathological Society, Minnesota, USA, pg. 55-59.

Kirkpatrick, B. C., J. K. Uyemoto and A. H. Purcell.   1995.  Diseases caused by mycoplasmalike organisms: X-Disease.  In Compendium of Stone Fruit Diseases.  Edited by J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu and J. K. Uyemoto.  APS Press, The American Phytopathological Society, Minnesota, USA, pg. 57-59.

Larsen, H. J., and H. E. Waterworth.  1995.  Diseases caused by mycoplasmalike organisms: Peach Red Suture.  In Compendium of Stone Fruit Diseases.  Edited by J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu and J. K. Uyemoto.  APS Press, The American Phytopathological Society, Minnesota, USA, pg. 55-56.

PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Stoddard, E. M., E. M. Hildebrand, D. H. Palmiter and K. G. Parker.  1951.  X-disease.  In Virus Diseases and Other Disorders with Viruslike Symptoms of Stone Fruits in North America, United States Department of Agriculture Handbook, Washington: US Government Printing Office. 10:37-42.

Thakur, P. D., A. Handa, S. C. Chowfla, and G. Krczal.  1998.  Outbreak of a phytoplasma disease of peach in the northwestern Himalayas of India.  Acta Horticulturae, No. 472: 737-739.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health@cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

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♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

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♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: C

Posted by ls

Fungi, Plant Pathogens, Ratings

Pseudocercospora purpurea (Cooke) Deighton 1976

California Pest Rating for
Pseudocercospora purpurea (Cooke) Deighton 1976
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On November 17, 2016, USDA APHIS PPQ inquired if CDFA had conducted a pest risk assessment of the fungal pathogen, Pseudocercospora purpurea on avocados in California.  Subsequently, the risk of infestation of P. purpurea in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Pseudocercospora purpurea is a fungal plant pathogen that causes Pseudocercospora (Cercospora) spot (blotch) disease exhibiting leaf and fruit spot symptoms in Persea spp., including avocado (P. americana) plants. The pathogen was originally known as Cercospora purpurea. In South Africa, the disease is known as black spot or Cercospora spot and is the most serious pre-harvest disease affecting all cultivars of avocado, particularly, cv. Fuerte (Crous et al., 2000; Pohronezny et al., 1994).  The disease occurs in warm, humid and rainy climates and is found in southeastern USA, South America, northern Australia, Asia, Africa, and the Caribbean (CABI, 2016; Menge & Ploetz, 2003).  The pathogen has not been reported from California.

Disease cycle:  Initial inoculum of conidia (asexual spores) mostly comes from infected leaves.  New shoot tissues are infected wherever this disease occurs.  The pathogen penetrates host tissue either directly or through wounds. Conidia are easily detached and blown by wind often over long distances.  On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host.  In South Africa, the pathogen remains latent for about 3 months after penetration.  Infected plants produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia successively.  Substomatal stroma (compact mycelial structure) may form from which conidiophores develop.  Fruit are susceptible when developed to a quarter to three-quarter of their full size.  Very small fruit (< 4 cm diameter) and those at or near maturity are almost immune.  Disease development is severe during warm, rainy weather when fruit are about a quarter size (Agrios, 2005; Menge & Ploetz, 2003; Pohronezny et al., 1994).  High relative humidity is necessary for conidial germination and plant infection.  The pathogen can overwinter as mycelium (stromata) in old infected leaves (Agrios, 2005).  

Dispersal and spread: Wind, rain, irrigation water, infected nursery plants, infected leaves, insects (Menge & Ploetz, 2003).

Hosts: Avocado is the main host; Persea spp. in the family Lauraceae, namely, P. americana (syn. P. gratissima, avocado), P. borbonia (redbay), P. drymifolia (Mexican avocado), P. palustris (swamp bay), and Persea sp. (Farr & Rossman, 2016).

Symptoms: Symptoms occur on leaves, stems, and fruit (Pohronezny et al., 1994).  On leaves, lesions initially appear as small (1-5 mm) angular, purple to purplish brown flecks or spots near leaf margins.  Over time, chlorotic halos surround older spots and are visible on both leaf surfaces.  The fungus sporulates under high humid conditions, appearing as gray, felty mycelial growths in the center of lesions. Individual lesions may coalesce forming larger regions of necrotic tissue.  Leaves become curled, deformed and may fall.

On fruit, lesions initiate as small flecks which later become slightly sunken, expand or coalesce becoming somewhat circular, and turn brown to brownish black in color.  Fissures or cracks usually develop in fruit lesions and serve as avenues for infection by other pathogens.  In certain cases, if the disease is temporarily arrested, the lesions appear as minute, raised, shiny, black specks associated with the corking of lenticels.  While blotch is usually confined to the rind of fruit, in advanced cases, the flesh may be invaded.  Once defoliation occurs, fruit may turn chlorotic, shrivel and drop.  Dark brown to black, 2-10 mm lesions may also form on green twigs and fruit pedicels (Pohronezny et al., 1994; Menge & Ploetz, 2003).

Damage Potential:  Pseudocercospora spot (blotch) is one of the most common diseases of avocado in Florida (Pohronezny et al., 1994).  Losses in avocado production may be severe and have been reported to be up to 69% in non-sprayed orchards in South Africa (Pohronezny et al., 1994; Menge & Ploetz, 2003).  Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected.  In California, avocado production is a major industry producing 75% and 92% of the nation’s avocado fruit supplies (Lazicki et al., 2016).  Therefore, losses due to this pathogen is of particular concern.

Worldwide Distribution: Pseudocercospora purpurea is widespread in subtropical and tropical regions.  Asia:  India, Japan, Philippines; Africa: Cameroon, Democratic Republic of Congo, Côte d’Ivoire, Guinea, Kenya, South Africa; North America: Bermuda, Mexico, USA; Central America and Caribbean: Dominica, El Salvador, Honduras, Jamaica, Nicaragua, Panama, Puerto Rico, Trinidad and Tobago, United States Virgin Islands; South America: Argentina, Bolivia, Brazil, Chile, Guyana, Peru, Venezuela; Oceania: Australia, Palau (CABI, 2016; Farr & Rossman, 2016).

In the USA, the pathogen has been found in the states of Florida, Georgia, and Mississippi (CABI, 2016).

Official Control:  Presently, Cercospora purpurea (syn. Pseudocercospora purpurea) is on the ‘Harmful Organism Lists’ for Namibia and South Africa and P. purpurea is on the ‘Harmful Organism Lists’ for French Polynesia and New Caledonia (USDA PCIT, 2016).

California Distribution: Pseudocercospora purpurea has not been reported from California.  The pathogen is not known to be established in California.

California Interceptions:  None reported.

The risk Pseudocercospora purpurea would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): In California, Pseudocercospora purpurea may be able to establish on avocado, under high moisture and warm climate conditions.  In the State, avocados are grown mostly along the southern coast (Lazicki et al., 2016).

2) Known Pest Host Range: Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  The host range for Pseudocercospora purpurea is limited to Persea spp. with avocado being the main host.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Pseudocercospora purpurea has high reproductive potential resulting in the successive production of conidia which are mainly dependent on wind, rain, and infected plants for dispersal and spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3):  Infected host plants with leaf and fruit spot symptoms caused by Pseudocercospora spot (blotch) disease could lower value and yield of commercially produced avocado plants as well as affect nursery productions resulting in loss of markets.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2):  The pathogen could significantly impact avocado plants grown for fruit and aesthetic value in private residential and public environments.

Consequences of Introduction to California for Pseudocercospora purpurea:

Add up the total score and include it here:

-Low = 5-8 point

–Medium = 9-12 point

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 11

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Score: 0

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0):  Pseudocercospora purpurea is not established in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score:

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pseudocercospora purpurea is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

CABI.  2016.  Pseudocercospora purpurea (spot blotch) (basic) datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/12266 .

Crous, P.W., A. J. L. Phillips, A. P. and Baxter.  2000.  Phytopathogenic fungi from South Africa. University of Stellenbosch, Department of Plant Pathology Press, 358 pages (referenced by Farr & Rossman, 2016).

Farr, D. F., & A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 18, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Lazicki, P., D. Geisseler, and W. R. Horwath.  2016.  Avocado production in California. https://apps1.cdfa.ca.gov/FertilizerResearch/docs/Avocado_Production_CA.pdf. (Last updated April, 2016.)

Menge, J. A., and R. C. Ploetz.  2003.  Disease of Avocado.  In Diseases of Tropical Fruit Crops, Edited by R. C. Ploetz, CABI Publishing, CAB International, UK, USA, 527 p.

Pohronezny, K. L., G. W. Simone, and J. Kotzé.  1994.  Pseudocercospora spot (blotch).  In Compendium of Tropical Fruit Diseases, Edited by R. C. Ploetz, G. A. Zentmeyer, W. T. Nishijima, K. G. Rohrbach, and H. D. Ohr, APS Press, The American Phytopathological Society, 79-80 p.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Cercospora coniogrammes Crous & R. G. Shivas 2012

California Pest Rating for
Cercospora coniogrammes Crous & R. G. Shivas 2012
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On June 14, 2016, a shipment of silver lady fern (Blechnum gibbum) plants from Florida, destined to a nursery in Nippomo, San Luis Obispo County, was intercepted by San Luis County officials.  Diseased plants exhibiting leaf spot symptoms were collected and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Cercospora coniogrammes, by culturing and multigene sequencing.  On July 19, 2016, the pathogen was detected in another shipment of silver lady fern plants from Florida and destined to the same nursery in San Luis Obispo County. The identity of the pathogen was confirmed on August 19, 2016 by the USDA PPQ PM National Identification Services in Beltsville, Maryland.  This detection marked a new US record and is reportable/actionable by the USDA (Bowers, 2016).    The pathogen was given a temporary Q rating and consequently, the shipment of Blechnum gibbum was placed on hold, treated with fungicides, and is currently undergoing 30-day inspections (Schnabel, 2016).  The risk of infestation of C. coniogrammes in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Cercospora coniogrammes is a fungal pathogen that causes leaf spots on fern.  The pathogen was first reported in 2012 from infected bamboo fern, Coniogramme japonica var. gracilis, in Brisbane, Queensland, Australia (Groenewald et al., 2012), and in 2016 from Brazil (Guatimosim et al., 2016).  The detection of C. coniogrammes in California marked a new record of the pathogen in the USA (Bowers, 2016; see ‘Initiating Event’).  Presently, not much is known about the distribution and ecology of the pathogen.

Disease cycle:  In general, in infected plants, Cercospora species produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia (asexual spores) successively.  Conidia are easily detached and blown by wind often over long distances.  On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host.  Substomatal stroma (compact mycelial structure) may form from which conidiophores develop.  Development of the pathogen is favored by high temperatures and the disease is most destructive during summer months and warmer climates.  High relative humidity is necessary for conidial germination and plant infection.  The pathogen can overwinter in or on seed and as mycelium (stromata) in old infected leaves (Agrios, 2005).  

Dispersal and spread: air-currents, infected nursery plants, infected leaves, seeds (Agrios, 2005).

Hosts: Fern species, namely, Blechnum gibbum, Coniogramme japonica var. gracilis, Hypolepis mitis, Macrothelypteris torresiana (Groenewald et al., 2012; Guatimosim et al., 2016).

Symptoms: Infected host plants exhibit leaf spots on upper and lower sides of leaves and are sub-circular to angular, 1-3 mm in diameter, grey to pale brown, surrounded by a broad brown margin up to 4 mm in diameter (Groenewald et al., 2012).

Damage Potential: Quantitative losses due to Cercospora coniogrammes have not been reported.  Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected.  However, damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005).

Worldwide Distribution: Australia: Queensland; South America: Brazil; North America: USA (Groenewald et al., 2012; Guatimosim et al., 2016).

Official Control: None reported particularly for Cercospora coniogrammes, however, the following countries have Cercospora spp. on their ‘Harmful Organism Lists’: French Polynesia, Madagascar, South Africa, and Sri Lanka (USDA PCIT, 2016).

California Distribution: Cercospora coniogrammes is not known to be established in California.  Interceptions of infected plants in a San Luis Obispo nursery were placed on hold, treated with fungicide, and is currently undergoing 30-day inspections (see, ‘Initiating event’).

California Interceptions:  Cercospora coniogrammes was detected in only two shipments of Blechnum gibbum intercepted by San Luis Obispo County officials during June and July 2016.

The risk Cercospora coniogrammes would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2):  Cercospora coniogrammes may be able to establish in large but limited regions in California wherever fern plants are able to grow naturally under high humid and cool to warm temperatures. Silver lady fern, Blechnum gibbum, is cultivated indoors and outdoors in coastal parts of California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1): Presently, the host range for Cercospora coniogrammes is limited to few species of fern, namely, Blechnum gibbum, Coniogramme japonica var. gracilis, Hypolepis mitis, and Macrothelypteris torresiana.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Cercospora coniogrammes has high reproductive potential resulting in the successive production of conidia which are dependent on air currents and infected plants and seed for dispersal and spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2):  Infected host plants with leaf spot symptoms could result in lowered value and loss of markets of nursery-produced fern host plants.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Low (1): The pathogen could significantly impact ornamental plantings in home/ urban and commercial gardens and recreational environments.

Consequences of Introduction to California for Cercospora coniogrammes:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 9

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0):  Cercospora coniogrammes is not established in California and has only been detected in intercepted shipments of fern to the State. 

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Cercospora coniogrammes is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

Bowers, J. H.  2016.  Email from J. H. Bowers, USDA, to H. R. Wright, USDA APHIS, forwarded to U. Kodira, CDFA on September 2, 2016.

Farr, D.F., & A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved September 22, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Groenewald, J. Z., C. Nakashima, J. Nishikawa, H. D. Shin, J. H. Park, A. N. Jama, M. Groenewald, U. Braun, and P. W. Crous.  2013.  Species concepts in Cercospora: spotting the weeds among the roses. Studies in Mycology 75: 115-170.

Guatimosim, E., P. B. Schwartsburd, R. W. Barreto, and P. W. Crous.  2016.  Novel fungi from an ancient niche: cercosporoid and related sexual morphs on ferns.  Persoonia 37: 106-141.

Schnabel, D. L.  2016.  Email from D. L. Schnabel, CDFA Pest Exclusion, to J. Chitambar, CDFA on September 28, 2016.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System. Sept. 23, 2016.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Pest Rating: B

Posted by ls 

Fungi, Plant Pathogens

Podosphaera xanthii (Castagne) U. Braun & Shishkoff 2000

Watermelon leaf showing an even distribution of powdery mildew (Podosphaera xanthii) over the entire leaf surface. June 1995 Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org
Watermelon leaf showing an even distribution of powdery mildew (Podosphaera xanthii) over the entire leaf surface. June 1995.  Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org
California Pest Rating for
Podosphaera xanthii (Castagne) U. Braun & Shishkoff 2000
Pest Rating:  C
PEST RATING PROFILE
Initiating Event:

On July 13, 216, diseased leaves of Calibrachoa sp. plants exhibiting powdery mildew symptoms were collected during a regulatory nursery inspection, from a nursery in San Luis Obispo County, by San Luis Obispo County officials and sent to the CDFA Plant Pathology Laboratory for diagnoses.  Suzanne Latham, CDFA plant pathologist, identified the powdery mildew pathogen, Podosphaera xanthii, as the cause for the disease.  The pathogen was assigned a temporary “Z” rating as it has been reported earlier in California and is considered widely distributed.  That rating is reassessed here and a permanent rating is proposed.

History & Status:

Background: Podosphaera xanthii causes powdery mildew disease primarily in cucurbits under field and greenhouse conditions.  The pathogen has a wide host range which includes several ornamental plants, including Verbena. There are several pathogenically distinct races of P. xanthii, and plant resistance-breaking races are present in California.  The pathogen is widely distributed throughout the world (see ‘Worldwide Distribution’ below) as well as in California.  Within California, powdery mildew may be common in coastal and desert production areas, but is more common in fall in the San Joaquin Valley and Sacramento Valley (Davis, et al., 2012).

Podosphaera xanthii was previously known by several names including Sphaerotheca fuliginea and S. fusca.  In 2012, P. caricae-papayae was synonymized with the morphologically similar species P. xanthii (Braun & Cook, 2012) however, the synonymy of P. xanthii and P. caricae-papayae is in question given the molecular work of Takamatsu et al., (2010) who also inferred that further molecular and morphological studies would help to determine the correct taxonomic position of P. caricae-papayae within the genus Podosphaera in the family Erysiphaceae of the order Erysiphales.  (The CDFA risk assessment and rating for P. caricae-papayae is published separately.)

Hosts: Podosphaera xanthii has a wide host range which includes agricultural crops, ornamentals, few fruit, and weed plant species within eight or more families. Hosts include, Citrullus lanatus (watermelon), Cucumis melo (melon), C. sativus (cucumber), Cucurbita (pumpkin), C. maxima (giant pumpkin, C. moschata (pumpkin), C. mixta (pumpkin), C. pepo (synonym: C. ovifera; ornamental gourd), C. vulgaris, Lagenaria siceraria (bottle gourd), Luffa acutangula (angled luffa), L. aegyptiaca (loofah), L. cylindrica, Momordica charantia (bitter gourd), M. cochinchinensis (gac), Sechium edule (chayote), Cyamopsis tetragonoloba (guar), Phaseolus aconitifolius (synonym: Vigna aconitifolia; moth bean), P. coccineus (runner bean), P. vulgaris (common bean), Vigna mungo (black gram), V. radiata (mung bean), V. umbellata (rice-bean), V. unguiculata (synonym: V. catjang; cowpea), Cajanus cajan (pigeon pea), Sesamum indicum (sesame), Capsicum frutescens (chili), Solanum melongena (eggplant),  Hibiscus mutabilis (cottonrose), H. syriacus (shrubby althaea), Hoheria lyallii (synonym: H. populnea; lacebark), Malva pusilla (round-leaved mallow), Carica papaya (papaya), Coriaria arborea (tree tutu), Kalanchoe blossfeldiana (flaming katy), Petunia x hybrid, , Verbena bonariensis (purpletop vervain), V. brasilensis (Brazilian verbena), V. canadensis (clump verbena), Verbena x hybrida (synonym: V. hortensis; garden verbena), V. incisa, V. lasiostachys (western vervain), V. litoralis (blue vervain),V. macdougalii (MacDougal verbena), V. officinalis (common verbena), V. phlogiflora, V. rigida rigid verbena), Calendula sp. C. arvensis (field marigold), C. officinalis (pot marigold), C. palaestina (Palestine marigold),  Cosmos bipinnatus (garden cosmos), Calibrachoa sp.,  Cephalotus follicularis (Albany pitcher plant), Farfugium japonicum (leopard plant), Glandularia pulchella (South American mock vervain), Gynostemma pentaphyllum (jiagulan), Gerbera jamesonii (African daisy), Gynura bicolor (Okinawan spinach), Helianthus annuus (sunflower), Heteropogon contortus (black speargrass), Jatropha gossypiifolia (bellyache bush), Ligularia sibirica, Medusagyne oppositifolia (jellyfish tree), Melampyrum nemorosum (wood cow-wheat), Melothria japonica (Japanese wild cucumber), Melothria sp. Parasenecio hastatus subsp. tanakae, Pericallis cruenta (common cineraria), Physalis alkekengi (Chinese lantern), Pisum sativum (pea), Pulicaria dysenterica (meadow false fleabane), Senecio chrysanthemoides , S. grahamii, S. hercynicus, S. nemorensis, Impatiens hawker (New Guinea impatiens), Ageratum conyzoides (billy goat weed), Bidens bipinnata (Spanish needles), B. cernua (nodding beggarticks), B. frondosa (devil’s beggartick), B. pilosa (blackjack), B. tripartita (three-lobe beggarticks), Boehmeria nivea (Chinese grass), Buddleja brasiliensis, B. salviifolia, Xanthium californicum (synonym: X. strumarium var. canadense; Canada cocklebur), Xanthium italicum, X. pensylvanicum, X. spinosum, X. strumarium (common cocklebur), X. spinosum (spiny cocklebur) Zinnia elegans (zinnia), (CABI, 2016; Farr & Rossman, 2016).

Symptoms:  Powdery mildew symptoms on cucurbits: the disease first appears as pale yellow spots on stems, petioles, and leaves.  These spots enlarge as white powdery fungal growth comprising primarily of asexual spores (conidia) develops on upper and under leaf surfaces, petioles, and stems of infected plants, usually developing first on crown leaves, shaded lower leaves, and leaf undersurfaces.  Affected leaves become dull, chlorotic and may wilt and eventually turn brown and papery (Davis et al., 2012).  Older plants are initially infected and infected leaves usually wither and die.  Premature senescence may occur.  Fruit infection occurs rarely in cucumber and watermelon.  Minute dark brown chasmothecia (sexually produced, closed fruiting structures) have been rarely observed in infected cucurbits in the USA and may be easily overlooked. They may develop late in the season, and the sexual spores within the structures are protected from adverse conditions.  Symptoms are less common on cucumber and melon as many commercial cultivars are resistant to the pathogen (McGrath, 2011).

Disease cycle:  Podosphaera xanthii is an obligate parasite.  Primary sources of inoculum include conidia which can be dispersed over long distances and remain viable for 7-8 days.  The fungus grows on the surface of plant tissue and invades by sending feeding organs (haustoria) into the plants epidermal cells only in order to obtain nutrients.  Mycelium produces conidiophores on the plant surface.  Each conidiophore produces chains of conidia (spores) that are dispersed by air currents.  Powdery mildew develops quickly under favorable conditions of dense plant growth and low light intensity.  High relative humidity is favorable for infection and conidial survival, and infection can occur as low as 50% relative humidity.  Dry conditions favor colonization, sporulation, and dispersal, however, rain and free moisture on plant surfaces are unfavorable.  Optimum temperature for disease development is 20-27°C with infection occurring at 10-32°C.  Powdery mildew development is arrested at 38°C and higher temperatures.  As an obligate parasite, P. xanthii requires living host plants for survival, however, it may also survive as chasmothecia which have been reported rarely in the United States (CABI, 2016; McGrath, 2011).

Damage Potential:  Powdery mildew can diminish the photosynthetic regions of cucurbit leaves. Severely infected leaves turn brown and shriveled.  Fruit quality and yield are reduced.  In squash, fruit quality is reduced by sunscald and premature ripening resulting in poor storability, in melon, incomplete ripening and poor flavor occurs, and pumpkin fruit may be shriveled and discolored (CABI, 2016).  Late fruit usually fail to mature and are small and misshapen.  Stress from disease can result in speckling and oedema on fruit rind.  Powdery mildew-infected plants can be weakened and predisposed to other diseases.  Podosphaera xanthii can be a major production problem of cucurbits in field and greenhouse conditions (McGrath, 2011).

Transmission:  Conidia (spores) are airborne and dispersed by wind currents.  Laboratory studies have shown that conidia remain viable for 7-8 days. On cucurbits in greenhouses conidia are released and spread from plant to plant via irrigation or air currents.  Conidia can overwinter on cucurbit plants in a greenhouse and then be dispersed from greenhouse to field crops during spring and summer.  Non-cucurbit hosts are not a major source of inoculum due to pathological specialization (CABI, 2016; McGrath, 2011).

Survival:  During cool weather, conidia production ceases and powdery mildew fungi overwinter as chasmothecia and mycelium in weeds and dormant plant tissue. However, the sexual (teleomorph) stage has only been found in California greenhouses and reported for the first time in greenhouse grown squash and melons in Salinas, California (Ramos et al., 2010-2011).  Constant greenhouse growth conditions could perpetuate the asexual stage of the fungus.

Worldwide Distribution: Asia: Armenia, Azerbaijan, Bangladesh, China, Republic of Georgia, India, Iran, Iraq, Israel, Japan, Republic of Korea, Kyrgyzstan, Lebanon, Myanmar, Oman, Pakistan, Saudi Arabia, Singapore, Taiwan, Turkey, Turkmenistan Uzbekistan, Vietnam; Africa: Egypt, Ethiopia, Libya, Somalia, South Africa, Sudan, Tunisia; North America: Canada, Mexico, USA; Central America and Caribbean: Cuba, Puerto Rico; South America: Argentina, Bolivia, Brazil, Nicaragua, Uruguay, Venezuela; Europe: Austria, Bulgaria, Czech Republic, (former) Czechoslovakia, Denmark, Estonia, Finland, Former USSR, Romania, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Norway, Poland, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom, Ukraine, Yugoslavia (Serbia and Montenegro); Oceania: Australia, New Zealand, Samoa (CABI, 2016; Farr & Rossman, 2016).

Official Control: Podosphaera xanthii is on the ‘Harmful Organism List’ for Guatemala (USDA-PCIT, 2016).

California Distribution: San Luis Obispo, Solano, and Yolo (CDFA Pest and Damage Records); San Joaquin Valley and Sacramento Valley counties, coastal and desert cucurbit production areas (Davis, et al., 2012).

California Interceptions:  None reported.

The risk Podosphaera xanthii would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2) – Powdery mildew of cucurbits Podosphaera xanthii can occur in coastal and desert production regions, and is common in fall in the San Joaquin Valley and Sacramento Valley. Powdery mildew thrives in warm and humid environments. Low light levels, high humidity, and moderate temperature enhance disease development.  Dry conditions favor conidia production and dispersal.  The pathogen is already widely distributed within cucurbit production regions of the state.   

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is High (3) – Podosphaera xanthii has a wide host range that includes agricultural crops – primarily cucurbits, ornamentals, few fruit and weed plants.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Under suitable climate conditions, airborne conidia are produced in abundance and readily spread by wind currents to non-infected sites.  Within and outside greenhouse environments, the pathogen is capable of rapidly spreading to non-infested host plants as well as other sites where host plants are grown.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3) – The pathogen can potentially cause significant losses in plant growth and crop yield. Powdery mildew infections could lower crop yield and value causing significant losses in production – especially with use of protective and eradicative fungicides.  It could result in loss of markets, and change in cultivation practices to prevent the spread of inocula to non-infected, healthy plants.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2) – The powdery mildew pathogen could significantly impact home/urban gardening and/or ornamental plantings.  

Consequences of Introduction to California for Podosphaera xanthii:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

Total points obtained on evaluation of consequences of introduction of P. xanthii to California = (13).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is High (-3).  Powdery mildew of cucurbits caused by Podosphaera xanthii is widely distributed in California. 

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10

Uncertainty:

None.

Remark:

The assessment of risk of Podosphaera xanthii distinctly documents its economic importance to California agriculture and environment and its widespread distribution within cucurbit production regions of the State.  Due to its biological capacity for rapid spread and its current widespread instate status, it is highly unlikely that the powdery mildew pathogen of cucurbits can be eradicated from California.  However, control measures, including use of protectant fungicides and resistant varieties, have proven successful in significantly reducing disease intensities and spread (CABI, 2016).  Therefore, a ‘C’ rating is proposed for this pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Podosphaera xanthii is C.

References:

Braun, U. and R. T. A. Cook.  2012.  Taxonomic manual of the Erysiphales (Powdery Mildews).  Centraalbureau voor Schimmelcultures, vol. 11, 707 p.

CABI.  2016.  Podosphaera xanthii (powdery mildew of cucurbits) full datasheet.  http://www.cabi.org/cpc/datasheet/50922.

Davis, R. M., T. A. Turini, B. J. Aegerter, and J. J. Stapleton.  2012.  Cucurbits powdery mildew pathogens: Sphaerotheca fuliginea (=Podosphaera xanthii) and Erysiphe cichoracearum (=Golovinomyces cichoracearum).  UC IPM Pest Management Guidelines: Cucurbits UC ANR Publication 3445. http://ipm.ucanr.edu/PMG/r116100711.html .

Farr, D.F., and A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

McGrath, M. T.  2011.  Vegetables: powdery mildew of cucurbits.  Vegetable MD Online, Cooperative Extension, New York State, Cornell University.  Fact sheet Page: 732.30 Date: June 2011.  http://vegetablemdonline.ppath.cornell.edu/

Ramos, C. B., K. Maruthachalam, J. D. McCreight, and R. S. Garcia Estrada.  2010-2011. Podosphaera xanthii but not Golovinomyces cichoracearum infects cucurbits in a greenhouse at Salinas, California.  Cucurbit Genetics Cooperative Report 33-34: 24-28.

Takamatsu, S., S. Ninomi, M. Harada and M. Havrylenko.  2010.  Molecular phylogenetic analyses reveal a close evolutionary relationship between Podosphaera (Erysiphales: Erysiphaceae) and its rosaceous hosts.  Persoonia, 24, 38-48.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

 PEST RATING:  C

Posted by ls

Fungi, Plant Pathogens

Phyllosticta yuccae Bissett 1986

California Pest Rating for
Phyllosticta yuccae Bissett 1986
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

On June 17, 2016 Yucca elephantipes (Adam’s needle) plants exhibiting leaf spot symptoms were intercepted at a nursery in San Diego County by San Diego County officials.  The shipment had originated in Florida.  Samples of symptomatic leaves were collected by the County and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  On July 17, 2016 Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Phyllosticta yuccae, as the cause for the disease.   The pathogen has not been previously reported in California and therefore, was assigned a temporary Q rating.  Subsequent action taken by CDFA resulted in prevention of the shipment from introduction to California. The risk of infestation of Phyllosticta yuccae in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Phyllosticta yuccae causes leaf blotch disease in Yucca plants.

Disease cycle:  It is likely that Phyllosticta yuccae has a similar life cycle to that of other Phyllosticta species and overwinters as conidia (asexual spores) in pycnidia (asexual fruiting structures) and ascospores (sexual spores) in perithecia (sexual fruiting structures) in infected plant leaf debris. Conidia and ascospores are only released when the fruiting structures become thoroughly wet.  Conidia are exuded from pycnidia in mucoid mass and are washed down or splashed away by rain or overhead irrigation water.  Ascospores are shot out forcibly from perithecia and carried by air currents.  On landing on host leaf surfaces, conidia or ascospores are germinate and infect plant tissue of young leaves.  Pycnidia are produced within lesions and provide conidia for secondary infections of plants (Agrios, 2005).

Dispersal and spread: rain/water splash, air currents, infected plant material and debris.

Hosts:  Yucca sp., Y. aloifolia, Y. elephantipes, Y. filamentosa (Farr & Rossman, 2016).

Symptoms:  Phyllosticta yuccae infections result in production of leaf spots in Yucca plants.  Initial symptoms include dark brown, elliptical, and scattered lesions which later become grey at the center with a reddish brown margin, irregular and coalesced (Silva et al., 2013).

Disease Potential:  Symptomatic Yucca plants infected with Phyllosticta yuccae may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California.  The disease could negatively impact value and marketability of nursery-grown Yucca plants.

Worldwide Distribution: Asia: Iran; Caribbean: Dominican Republic; North America: Canada, USA (Florida), Guatemala; South America: Brazil; Oceania: New Zealand (Farr & Rossman, 2016; Silva et al., 2013).

Official Control:  Currently, Phyllosticta yuccae has a temporary Q rating in California.

California Distribution:  Phyllosticta yuccae is not established in California.

California Interceptions: Phyllosticta yuccae was detected once in a shipment of Yucca elephantipes plants from Florida and destined to a San Diego nursery.

The risk Phyllosticta yuccae would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): Yucca plants. grow naturally under dry conditions in southern California.  Under those natural conditions, Phyllosticta yuccae may not receive adequate wet conditions for infection and spread.  However, certain species of the host plant may be grown as residential and commercial landscape ornamentals in coastal regions of southern and central California under favorable environments for disease development.     

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  The host range is limited to Yucca spp.   

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is Medium (2): Phyllosticta yuccae has high reproductive potential, however, the dispersal of spores from fruiting structures is dependent on wet conditions.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1): Nursery grown Yucca plants infected with Phyllosticta yuccae and exhibiting leaf blotch/spot symptoms could lower crop value and marketability.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

 Risk is Medium (2):  Under favorable conditions for disease development, Phyllosticta yuccae may significantly impact ornamental plantings of commercially and home grown Yucca plants.     

Consequences of Introduction to California for Phyllosticta yuccae:

Add up the total score and include it here. (Score)

–Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 8 (Low).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not Established (0).  Phyllosticta yuccae is not established in California.   

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8 (Low).

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phyllosticta yuccae is C.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

Farr, D. F. and A. Y. Rossman.  2016.   Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 24, 2016 from http://nt.ars-grin.gov/fungaldatabases/.

Ingram, S.  2008.  Cacti, Agaves and Yuccas of California and Nevada.  Pacific Horticulture, 69 (3): http://www.pacifichorticulture.org/articles/cacti-agaves-and-yuccas-of-california-and-nevada/

Silva, A.D.A., Pinho, D.B., Jr., Hora, B.T., and Pereira, O.L. 2013. First Report of Leaf Spot Caused by Phyllosticta yuccae on Yucca filamentosa in Brazil. Plant Disease 97: 1257.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

PEST RATING:  C

Posted by ls

Fungi, Plant Pathogens

Pseudocercospora smilacicola U. Braun, 2014

California Pest Rating for
Pseudocercospora smilacicola U. Braun, 2014
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On July 21, 2016, a shipment of lance leaf greenbrier (Smilax sp.) plants from Texas, destined to a wholesale plant company in Santa Barbara, was intercepted by the Santa Barbara County officials.  Diseased plants exhibiting leaf spot symptoms were collected and sent the CDFA Plant Pathology Laboratory for disease diagnosis.  The fungal pathogen, Pseudocercospora smilacicola, was identified as the cause for the leaf spots, by Cheryl Blomquist, CDFA plant pathologist.  This pathogen was also detected on March 23, 2016 and September 30, 2015, from Smilax sp. plant shipments that had originated in Texas and were destined for wholesale plant companies in Santa Barbara and Riverside Counties respectively.  The pathogen was given a temporary Q rating.  The risk of infestation of P. smilacicola in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Pseudocercospora smilacicola is a fungal plant pathogen that belongs to a larger group of Cercospora-like fungi most of which cause leaf spot symptoms in host plants. The pathogen has previously been referred to as Ceracospora petersii and C. (or Pseudocercospora) mississippiensis, which are synonym species of Exosporium petersii which is morphologically distinguished from P. smilacicola (Braun et al., 2014; Farr & Rossman, 2016).  However, Braun et al., (2014) reported that Pseudocercospora mississippiensis on Smilax riparia from Korea is morphologically indistinguishable from the Cuban and North American collections of P. smilacicola.

Disease cycle: Infected plants produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia (asexual spores) successively.  Conidia are easily detached and blown by wind often over long distances.  On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host.  Substomatal stroma (compact mycelial structure) may form from which conidiophores develop.  Development of the pathogen is favored by high temperatures and the disease is most destructive during summer months and warmer climates.  High relative humidity is necessary for conidial germination and plant infection.  The pathogen can overwinter in or on seed and as mycelium (stromata) in old infected leaves (Agrios, 2005).  

Dispersal and spread: air-currents, infected nursery plants, infected leaves, seeds.

Hosts: Smilax auriculata (earleaf greenbrier), S. laurifolia (laurel greenbrier), S. pseudochina (bamboo vine), S. riparia, S. rotundifolia (roundleaf greenbrier), Smilax sp. (Braun et al., 2014).

Symptoms:  Infected host plants exhibit leaf spots on both leaf surfaces and are sub-circular to angular or irregular, 1-10 mm in diameter, initially pale then turn dark brown and later develop a paler center, brownish to greyish brown, occasionally somewhat zonate with darker brown to black margin.  Lesions or spots may be slightly raised and occasionally surrounded by a diffuse lighter halo (Braun et al., 2014).

Damage Potential: Specific losses due to Pseudocercospora smilacicola have not been reported.  Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected.  However, damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005).  In California, Smilax californica and S. jamesii grow indigenously in the northern mountain and valley regions (Calflora, 2016).  Smilax sp. vines and foliage are used in floral decorations and therefore, diseased plants could be of concern to greenbrier floral/ornamental production nurseries.

Worldwide Distribution: Asia: Japan, Korea; North America: USA, Cuba. (Braun et al., 2014).  In the USA, Pseudocercospora smilacicola has been found in Georgia, Florida, Louisiana Mississippi, and Pennsylvania (Braun et al., 2014).

Official Control: None reported.

California Distribution: Pseudocercospora smilacicola has not been reported from California.  The pathogen is not known to be established in California.

California Interceptions:  Pseudocercospora smilacicola was detected shipments of Smilax sp. plants intercepted thrice from September 2015 to July 2016 (see ‘Initiating Event’).

The risk Pseudocercospora smilacicola would pose to California is evaluated below.

 Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): In California, host plants (Smilax spp.) grow indigenously in warm and humid conditions in northern mountain and valley regions.  If introduced, the pathogen could establish in those limited areas.    

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  The host range for Pseudocercospora smilacicola is limited to Smilax spp.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Pseudocercospora smilacicola has high reproductive potential resulting in the successive production of conidia which are dependent on air currents and infected plants and seed for dispersal and spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1):  Infected host plants with leaf spot symptoms could lower value of nursery-produced Smilax plants used in floral/ornamental decorations.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is High (3):  Two plant species, namely, Smilax californica and S. jamesii, are native to California and grow under warm, humid conditions in northern mountain and valley regions of the State.  The plants grow as under story plants in pine and mixed evergreen forest communities and provide food for wild animals and birds. Climate conditions may be conducive for the development of the pathogen if introduced.  In severe infections, available food could be reduced for wildlife.  Smilax jamesii is included in the California Native Plant Society Inventory of Rare and Endangered Plants on List 1B.3 7th/8th edition.  Also, the pathogen could significantly impact nursery production of ornamental greenbrier foliage and vines.

Consequences of Introduction to California for Pseudocercospora smilacicola:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 10

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0):  Pseudocercospora smilacicola is not established in California and has only detected in intercepted plant shipments to the State.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pseudocercospora smilacicola is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

Braun, U., Crous, P.W., and Nakashima, C. 2014. Cercosporoid fungi (Mycosphaerellaceae) 2. Species on monocots (Acoraceae to Xyridaceae, excluding Poaceae). IMA Fungus 5: 203-390.

Calflora.  2016.  Information on California plants for education, research and conservation. [Web application].  Berkeley, California: The Calflora Database [a non-profit organization]. http://www.calflora.org/

Farr, D.F., & A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 1, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

 Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Sclerophthora rayssiae var. zeae Payak & Renfro 1967

California Pest Rating for
Sclerophthora rayssiae var. zeae Payak & Renfro 1967
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

Sclerophthora rayssiae var. zeae was recently proposed by the USDA to be removed as a select agent from the 2016 updated Select Agents Registration List and Select Agent Regulations.  Currently, the pathogen is not rated in California.  Therefore, the risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is proposed herein.

History & Status:

Background: Sclerophthora rayssiae var. zeae is an oomycete pathogen that causes brown stripe downy mildew disease of maize.  The disease was first observed in several maize-growing regions of India in 1962, and the pathogen was described by Payak and Renfro in 1967.  Since its initial discovery, the disease has spread through India has also been reported from Mynmar, Nepal, Pakistan, and Thailand (CABI, 2016; Putnam, 2007; EPPO, 2016).

Sclerophthora rayssiae var. zeae has not been reported within the USA (CABI, 2016; USDA, 2013).  In 2002, the USDA designated the pathogen a ‘select agent’ deemed to be very damaging to susceptible maize and sources of resistance, if any, had not been established for U. S. maize varieties (USDA, 2013).  However, on January 14, 2016, after its fourth biannual review, the USDA proposed to remove S. rayssiae from the updated Select Agents Registration List and Select Agent Regulations.  Removal of select agents, by the USDA, was based on either the absence of viable samples present in the U.S., no climate conducive to growth, or the availability of adequate treatments for the agents (USDA, 2016).

Hosts: Zea mays (maize), Z. mays var. indurata; Digitaria sanguinalis (large crabgrass), D. bicornis (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016; Putnam, 2007).

Symptoms: Characteristic symptoms of Sclerophthora rayssiae var. zeae infection are expressed only in leaves as vein-delimited narrow chlorotic or reddish to purple stripes, 3 to 7 mm wide, depending on maize genotype, extending parallel with the leaf veins. Other parts of the plant including leaf sheaths, husk leaves, ears or tassels do not exhibit symptoms even though all the leaves may be symptomatic.  Early infections appear as vein-delimited chlorotic flecks which enlarge and coalesce to form stripes. At first the stripes are chlorotic or yellowish but later turn yellowish-tan to reddish-brown and necrotic.  The disease initially appears on the lowermost leaves which have a high level of striping, and appear pale-brown and burnt.  Severely affected leaves may be shed prematurely.  In comparison, leaves around the ear shoot show a lesser amount of striping and the leaves above show the least.  The veins are not affected, but in severe infections, leaves tear apart near the apices and become tattered.  Greyish-white downy growth develops on the upper and lower surfaces of the stripes on leaves.  The downy growth disappears as the stripes become necrotic.  Sporangia disappear as the lesions become necrotic and oospores are produced only in necrotic tissue.  Unlike other downy mildews of maize, brown stripe downy mildew does not result in malformation of floral and vegetative tissues (CABI, 2016; Putnam, 2007).

Disease cycle:  The disease cycle involves both sexual and asexual reproduction.  Oospores (sexual spores) germinate to produce sporangia (sac-like structures containing spores), which then release zoospores (motile spores) that penetrate leaf tissue.  Moisture is critical for infection.  A twelve-hour wetting period of a free film of moisture on a leaf surface is essential for infection to occur.  Longer wetting periods increase the amount of infection (Singh et al., 1970).   Once primary infection occurs, the disease becomes established and lesions are formed in leaves.  Sporangia are produced and a cyclic chain of secondary infections occur that eventually result in the spread of the disease throughout an entire crop (CABI, 2016). High levels of moisture and warm temperatures are required for disease development and spread.  Asexual reproduction, resulting in the production of sporangia is most abundant at 22 to 25°C.  Sporangia production, germination, and infection require a film of water (Putnam, 2007; CABI, 2016). Oospores are produced in necrotic leaf tissue and form the survival stage of the pathogen in soil or in plant debris.

Dispersal and spread:  The pathogen survives as oospores in soil or plant debris.  Oospores serve as primary inoculum for infections of plants, where the lower leaves show greater disease intensity than the upper leaves, and can survive in soil or plant debris for several years (CABI, 2016; Fry & Grűnwald, 2010).  Experimentally, oospores were shown to be viable for up to 3 years when powdered infected leaf debris was placed around each seed at the time of sowing, resulting in heavy infection of the emerging seedlings (Singh et al., 1970). Seed transmission may also occur, although the initiation of new infections is less likely through seed transmission than infected leaf debris (Putnam, 2007).  The pathogen may be found on the seed surface and within the embryo (CABI, 2016; Putnam, 2007).  The pathogen is dispersed short distances by wind and rain splash or physical contact with infected plants.  Long distance transmission by wind is unlikely (Singh & Renfro, 1971).

Damage Potential: Brown stripe downy mildew of maize causes severe infections in areas of high rainfall.  In India, 20 to 90% in crop losses are reported.  Losses above 70% occur in highly susceptible maize cultivars grown under disease-favorable conditions (CABI, 2016).  In California, the required warm temperature and long wet periods (heavy rain durations) for disease development and spread are not present.  Therefore, the potential for damage caused by the pathogen to California’s maize production, can be considered to be minimal, if at all.

Worldwide Distribution: Asia: India, Mynmar, Nepal, Pakistan, Thailand (CABI, 2016).

Official Control: Presently, Sclerophthora rayssiae var. zeae is on the ‘Harmful Organism Lists’ of the following countries: Honduras, Namibia, New Zealand, Peru, and South Africa (USDA-PCIT, 2016).  The USDA designated S. rayssiae var. zeae a select agent in 2002, however, on January 14, 2016, the USDA proposed to remove S. rayssiae from the updated Select Agent Registration List and Select Agents Regulations (see ‘Background’.

California Distribution: Sclerophthora rayssiae var. zeae is not present in California.

California Interceptions:  There are no reports of the detection of Sclerophthora rayssiae var. zeae in plant and soil shipments imported to California.

The risk Brown stripe downy mildew of maize would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas. 

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Low (1):   Sclerophthora rayssiae var. zeae is not likely to establish in California as the required warm temperature and long wet periods (12 hours or more) for disease development and spread are not present.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1): Maize and crabgrass are the only reported hosts of the pathogen.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Under favorable wet conditions, Sclerophthora rayssiae var. zeae has high reproductive potential.  The pathogen is dispersed primarily through infected soil, plant debris, and maize seeds.  Short distance spread is by wind and rain splash or physical contact with infected plants.  Long distance transmission by wind is reported to be unlikely.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1):  In California, the required warm temperature and long wet periods (heavy rain durations) for disease development and spread of the pathogen, are not present, thereby, making it most unlikely for the pathogen to establish and cause infections to the State’s maize cultivation. However, within contained and artificially controlled conditions as in greenhouses, it is possible for pathogen infections to occur.  The economic impact is therefore, regarded low.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Low (1):  No environmental impacts due to the pathogen are expected to occur in California.

Consequences of Introduction to California for Brown stripe downy mildew of maize:

Add up the total score and include it here. (Score)

–Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 7

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is ‘Not established’ (0):

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 7

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Sclerophthora rayssiae var. zeae is C.

References:

CABI.  2016.  Sclerophthora rayssiae var. zeae (brown strip downy mildew of maize) full datasheet.  http://www.cabi.org/cpc/datasheet/49244

EPPO.  2016.  Sclerophthora rayssiae var. zeae ().  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  http://www.newpqr.eppo.int.

Farr, D.F., and A. Y. Rossman.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Fry, W. E. and N. J. Grűnwald.  2010.  Introduction to Oomycetes.  The Plant Health Instructor.  DOI:10.1094/PHI-I-2010-1207-01

Payak, M. M., and B. L. Renfro.  1967.  A new downy mildew disease of maize.  Phytopathology, 57:394-397.

Putnam, M. L.  2007.  Brown stripe downy mildew (Sclerophthora rayssiae var. zeae) of maize.  Plant Management Network International Plant Health Progress, published 8 November 2007. http://www.plantmanagementnetwork.org/pub/php/diagnosticguide/2007/stripe/

Singh, J. P., and B. L. Renfro.  1971.  Studies on spore dispersal in Sclerophthora rayssiae var. zeae.  Indian Phytopathology, 24:457-461.

Singh, J. P., B. L. Renfro, and M. M. Payak.  1970.  Studies on the epidemiology and control of brown stripe downy mildew of maize (Sclerophthora rayssiae var. zeae).  Indian Phytopathology, 23:194-208.

USDA.  2013.  Recovery plan for Philippine downy mildew and brown stripe downy mildew of corn caused by Peronosclerospora philippinensis and Sclerophthora rayssiae var. zeae, respectively.   http://www.ars.usda.gov/SP2UserFiles/Place/00000000/opmp/Corn%20Downy%20Mildews%20Recovery%20Plan%20Revised%202013.pdf

USDA, 2016.  Stakeholder announcement: USDA proposes updates to select agents registration list and select agent regulations.  USDA APHIS. Published January 14, 2016.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Peronosclerospora philippinensis (W. Weston) C. G. Shaw, 1978

peronosclerospora philippinensis | photo by Bob Kemerait, Univ of Georgia, Bugwood.org
California Pest Rating for
Peronosclerospora philippinensis (W. Weston) C. G. Shaw, 1978
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

Peronosclerospora philippinensis was recently proposed by the USDA to be removed as a select agent from the 2016 updated Select Agents Registration List and Select Agent Regulations.  Currently, the pathogen is not rated in California.  Therefore, the risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is proposed herein.

History & Status:

Background: Peronosclerospora philippinensis is an oomycete pathogen that causes Philippine downy mildew disease.  The disease is destructive mainly to corn in tropical Asia, endemic to the Philippines, and has also been reported from China, India, Indonesia, Nepal, Pakistan, Taiwan, and Congo, Mauritius, and South Africa (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016).  The pathogen has not been reported within the USA (Farr & Rossman, 2016; USDA, 2013).

In 2002, the USDA designated Peronosclerospora philippinensis a ‘select agent’ deemed to be very damaging to susceptible maize and sources of resistance, if any, had not been established for U. S. maize varieties (USDA, 2013).  However, on January 14, 2016, after its fourth biannual review, the USDA proposed to remove P. philippinensis from the updated Select Agents Registration List and Select Agent Regulations.  Removal of select agents, by the USDA, was based on either the absence of viable samples present in the U.S., no climate conducive to growth, or the availability of adequate treatments for the agents (USDA, 2016).

Hosts: Hosts include species within the family Poaceae.  Zea mays (maize) is the main host.  Other hosts include, Andropogon sorghum (Sorghum bicolor, sorghum), Avenae sativa (oats), Euchlaena luxurians, Saccharum officinarum (sugarcane), S. spontaneum (wild sugarcane), Sorghum halepense (Johnson grass), Zea mays subsp. mexicana (teosinte) (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016).

Symptoms: Systemic symptoms are expressed in the first true leaf stage as stripes or overall yellowing of an entire leaf.  Local symptoms are expressed as long chlorotic streaks with downy growth of conidia (spores) and conidiophores.  This downy growth is the site of spore production and may be present on both upper and lower leaf surfaces, but is more common on the lower surface.  Tassels may be malformed and produce less pollen, and ears may be aborted.  Early infected plants are stunted and may die.  Infected stems do not show external symptoms, but may be stunted (CABI, 2016).  The pathogen invades the stem, and becomes established in the shoot apex producing chlorotic areas, which are initially confined to the base of the lower leaf but later increase in size in succeeding leaves.  The youngest leaf emerging from the whorl becomes completely chlorotic.  The pathogen becomes established within seed, as mycelium in the pericarp layer, and also within the embryo and endosperm.  However, no external symptoms on seed are expressed and seed quality is not affected (CABI, 2016).

Disease cycle:  Although the Philippine downy mildew pathogen was reported to produce oospores (overwintering sexual spores) on corn leaf, there have been no subsequent reports.  Even though the Philippine downy mildew pathogen was reported in 1967 to produce overwintering sexual spores (oospores), on corn leaf, there have not been any subsequent reports since then and therefore, the role of oospores has not been established in the life cycle or disease caused by this pathogen (USDA, 2013). Airborne conidia (spores) released from infected crops or weeds form primary source of inoculum for infection. Germinating conidia produce germ tubes which penetrate stomata of leaves.  The optimum temperature for germination and germ tube growth is 18-30°C.  Penetration is followed by invasion of the mesophyll.  Soon the disease becomes established and lesions are formed in leaves.  Conidia are produced under night temperatures ranging from 21 to 26°C and free moisture.  Moisture is critical for infection.  Secondary infections occur that eventually result in the spread of the disease throughout an entire crop.  Seed transmission can occur at low rates from seeds harvested with higher moisture content (CABI, 2016).

Dispersal and spread:  Peronosclerospora philippinensis is commonly spread by wind and rain.  Production of conidia requires night temperatures ranging from 21 to 26°C and free moisture.  Disease severity is highest in areas that receive 39-78 inches of rain annually and in tropical climates.  The pathogen is dispersed short distances by wind.  Although the pathogen is present within infected seed, it has been demonstrated that once the seed or grain is dried to below 14% it will not produce an infected plant (Adenle & Cardwell, 2000; USDA 2013).

Damage Potential: Before resistant varieties became widely available in the Philippines, annual yield losses of maize were often 40 to 60%.  Yield losses of sweet corn were 100%. Disease severity is highest in areas that receive 39-78 inches of rain annually and in tropical climates (USDA, 2013).  In California, the required warm temperature and long wet periods (heavy rain durations) for disease development and spread are not present.  Therefore, the potential for damage caused by the pathogen to California’s maize production, can be considered to be minimal, if at all.  Furthermore, the pathogen is seed transmissible, but transmission will not occur once the seed has been dried to the moisture content required for storage.  Seed treatments are available to eradicate the pathogen (CABI, 2016).

Worldwide Distribution: Asia: China, India, Indonesia, Japan, Nepal, Pakistan, Philippines, Taiwan, Thailand; Africa: Mauritius, Congo, South Africa (CABI, 2016; Farr & Rossman, 2016).

Official Control: Presently, Peronosclerospora philippinensis is on the ‘Harmful Organism Lists’ of the following countries: Colombia, French Polynesia, Guatemala, Honduras, Indonesia, Japan, Republic of Korea, Morocco, Namibia, New Caledonia, New Zealand, Peru, South Africa, and Timor-Leste  (USDA-PCIT, 2016).  The USDA designated S. rayssiae var. zeae a select agent in 2002, however, on January 14, 2016, the USDA proposed to remove S. rayssiae from the updated Select Agent Registration List and Select Agents Regulations (see ‘Background’).

California Distribution: Peronosclerospora philippinensis is not present in California.

California Interceptions:  There are no reports of the detection of Peronosclerospora philippinensis in plant and soil shipments imported to California.

The risk Philippine downy mildew disease would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas. 

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Low (1):   Peronosclerospora philippinensis is not likely to establish in California as the required warm temperature and long wet periods (12 hours or more) for disease development and spread are not present.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1): The host range is limited to include species within the family Poaceae.  Maize is the main host, cultivated sugarcane, oats, sorghum cultivars, and weedy grass species including Euchlaena luxurians, wild sugarcane, Johnson grass, and Zea mays subsp. mexicana (teosinte).

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Under favorable wet conditions, Peronosclerospora philippinensis has high reproductive potential.  The pathogen is dispersed primarily through infected soil, plant debris, and maize seeds.  Short distance spread is by wind and rain splash or physical contact with infected plants.  Long distance transmission by wind is reported to be unlikely.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1):  In California, the required warm temperature and long wet periods (heavy rain durations) for disease development and spread of the pathogen, are not present, thereby, making it most unlikely for the pathogen to establish and cause infections to the State’s maize cultivation. However, within contained and artificially controlled conditions as in greenhouses, it is possible for pathogen infections to occur. Seed transmission of the pathogen will not occur once the seed has been dried to the moisture content required for storage and the pathogen can be eradicated from seed through seed treatments. The economic impact is therefore, regarded low.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Low (1):  No environmental impacts due to the pathogen are expected to occur in California.

Consequences of Introduction to California for Brown stripe downy mildew of maize:

Add up the total score and include it here. (Score)

  -Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 7

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is ‘Not established’ (0):

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 7

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Peronosclerospora philippinensis is C.

References: 

Adenle, V. O., and K. F. Cardwell. 2000.  Seed transmission of maize downy mildew (Peronosclerospora sorghi) in Nigeria. Plant Pathology 49:628-634.

CABI.  2016.  Peronosclerospora philippinensis (Philippine downy mildew) full datasheet.  http://www.cabi.org/cpc/datasheet/44646

EPPO.  2016.  Peronosclerospora philippinensis (PRSCPH).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  http://www.newpqr.eppo.int.

Farr, D.F., and A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Fry, W. E. and N. J. Grűnwald.  2010.  Introduction to Oomycetes.  The Plant Health Instructor.  DOI:10.1094/PHI-I-2010-1207-01

Payak, M. M., and B. L. Renfro.  1967.  A new downy mildew disease of maize.  Phytopathology, 57:394-397.

USDA.  2013.  Recovery plan for Philippine downy mildew and brown stripe downy mildew of corn caused by Peronosclerospora philippinensis and Sclerophthora rayssiae var. zeae, respectively.   http://www.ars.usda.gov/SP2UserFiles/Place/00000000/opmp/Corn%20Downy%20Mildews%20Recovery%20Plan%20Revised%202013.pdf

USDA, 2016.  Stakeholder announcement: USDA proposes updates to select agents registration list and select agent regulations.  USDA APHIS. Published January 14, 2016.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

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♦  Comments may not be posted if they:

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Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Calonectria pteridis Crous, M. J. Wingf. & Alfenas, 1993

California Pest Rating for
Calonectria pteridis Crous, M. J. Wingf. & Alfenas, 1993
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On April 19, 2016, diseased Ravenea rivularis (majesty palm) plants exhibiting leaf spots were intercepted by San Luis Obispo County Agricultural officials. The shipment of plants had originated in Florida and was destined to a nursery in San Luis Obispo County.  Symptomatic leaves were sent to the CDFA Plant Pest Diagnostics Branch for diagnosis.  Suzanne Latham, CDFA plant pathologist, identified the associated pathogen as Calonectria pteridis.  Then on May 23, 2016, C. pteridis was detected again in a different shipment of majesty palm plants destined to the same nursery in San Luis Obispo.  In both detections, the pathogen was assigned a temporary Q rating by the CDFA and consequently, all infected plant materials were destroyed. The risk of infestation of C. pteridis in California is evaluated and a permanent rating is proposed here.

History & Status:

Background:  Calonectria pteridis is the sexual (telemorph) stage of the fungal pathogen, while its asexual (anamorph) stage is Cylindrocladium pteridis.  Calonectria pteridis causes leaf spot and blight, stalk and root rot diseases in various hosts.  In the continental United States, Calonectria pteridis primarily causes symptoms of leaf spots and blights in palm.  Symptoms are indistinguishable from those caused by three other species in the genus (Yu & Elliot, 2013).  In Brazil, C. pteridis is one of the most common species associated with eucalyptus trees causing Calonectria leaf blight disease (Alfenas et al., 2013). In China, C. pteridis caused serious damage to Serenoa repens – an important medicinal and ornamental garden plant (Yang, et al., 2014).  In the USA, C. pteridis has been found on several hosts including palm from Tennessee, Georgia, Florida, and Hawaii (Uchida, 2004; Farr & Rossman, 2016). Recently, the pathogen was detected in infested majesty palm plants shipped from Florida to California.  The pathogen is widespread especially in subtropical and tropical regions.

Disease cycle:  The disease cycle generally involves the pathogen’s anamorphic or asexual stage resulting in the production of conidia (spores) and telemorphic or sexual stage resulting in perithecia (fruiting structure) and ascospores. Conidia, produced on infected plants are dispersed by insects, tools, gloves, plant handling, wind and splashing water, while ascospores are discharged from fruiting bodies by air currents and splashing water.  Discharged spores land on plant host tissue and germinate and penetrate tissue when leaves are wet or under high relative humidity.  The pathogen grows within the host and after about one week produces conidiophores and conidia.  Perithecia and ascospores are formed on infected tissue (Uchida, 2004; Yu & Elliot, 2013).

Hosts: Calonectria pteridis can attack a number of hosts including ornamentals, forest and environmental trees and shrubs, and few agricultural crops.  In the USA, palms have been reported as the main host attacked by the pathogen.  Hosts include: Arachis hypogaea (peanut), Arachnoides adiantiformis  (syn. Rumohra adiantiformis, Polystichum adiantiformis; leatherleaf fern), Arecastrum romanzoffianum (syn. Sygarus romanzoffiana; queen palm); Asparagus plumosus (asparagus fern), Callistemon citrinus (crimson bottlebrush), C, rigidus (erect bottlebrush), Chamaedorea elegans (syn. Collinia elegans; neanthe bella palm/parlor palm), C. cataractarum (cat palm), Chrysalidocarpus sp. (syn. Dypsis sp.; palm); Cissus rhombifolia (grape ivy), Cocos nucifera (coconut), Crassula sp., C. argentea (jade plant), Dictyosperma album (princess palm), Dracaena marginata (Marginate Dracaena), Drosera sp. (sundews), Dryopteris sp. (woodfern), Elaeis guineensis (African oil palm), Eucalyptus spp.,(eucalyptus), Guzmania wittmackii (bromeliad/Guzmanea), Heliconia bihai (macawflower), Howeia belmoreana, H. forsteriana (kentia palm/curly palm), Laccospadix australasica (Atherton palm), Leucadendron sp., Livistona chinensis (Chinese fan palm), Lupinus sp., (lupine), Mauritia flexuosa (moriche palm), Melaleuca leucadendra (weeping paperback), M. quinquenervia (broad-leaved paperback), Musa sp. (banana), Nephrolepis sp., Nephrolepis exaltata (sword fern), Phoenix canariensis (Canary Island date palm), Pinus sp., P. caribaea (Caribbean pine), P. caribbaea var. hondurensis,  P. oocarpa (Mexican yellow pine), Pouteria dulcifica (syn. Synsepalum dulcificum; miracle fruit/sweet berry), Ravenea rivularis (majesty palm), Rhapis humilis (slender lady palm), Rhododendron obtusum (Hiryu azalea/Kurume azalea), Serenoa repens (saw palmetto), Scolopendrium sp., Solanum tuberosum (potato), Strelitzia reginae (bird of paradise), Tillandsia wagneriana (bromeliad), Washingtonia sp., W. filifera (California or desert fan palm), W. robusta (Mexican fan palm) (Crous et al., 1993; Crous & Wingfield, 1993; Farr & Rossman, 2016; Yu & Elliot, 2013).

Symptoms:  Symptoms caused by Calonectria pteridis in palm begin as flecks of small, water-soaked lesions that develop to irregular shades of gray, yellow, reddish brown, brown, or black.  Newly formed lesions are circular or elliptical, 3-5 mm long, and on enlarging develop a tan or gray center surrounded by a brownish halo. The rachis and petiole may become infected with small flecks and eventually leaves and leaflets dry as the disease progresses and lesions coalesce.  Leaf spots may appear on leaves of all ages, although mature leaves are most susceptible (Yu & Elliot, 2013).

Spread:   Conidia are readily spread by insects, pruning tools, plant handling, air currents, rain or splashing irrigation water, while ascospores can be released from their fruiting bodies and spread by air currents and splashing water (Uchida, 2004; Yu & Elliot, 2013).

Damage Potential:  Leaf spot and blight disease caused by Calonectria pteridis can result in reduced plant growth, quality, and marketablility.  Estimates of yield/crop loss due to this pathogen have not been reported.  However, under nursery controlled environments, production of palms, ferns, eucalyptus, and other ornamental host plants may be at heightened risk for pathogen infection and reduced plant production. Seedling and immature palms without trunks are likely to be most susceptible to this leaf spot disease (Yu & Elliot, 2013).  Infection of outdoor growths of palm and eucalyptus trees require warm and humid to wet climate for disease development.  In Brazil, C. pteridis is one of the most important causal agents of Calonectria leaf blight disease of Eucalyptus spp. and has significantly reduced eucalyptus growth (Alfenas, et al., 2013).  In China, up to 100% incidence of leaf spot disease in Serenoa repens, medicinal plant, often lead to plant death (Yang, et al., 2014).

Worldwide Distribution: Asia: China, India, Malaysia, Singapore; Africa: Cameroon, Ivory Coast, Mauritius, South Africa; Europe: Spain, North America: USA (Florida, Hawaii), West Indies; South America: Brazil, Costa Rica, Martinique, Venezuela (Crous & Wingfield, 1993; Farr & Rossman, 2016).

Official Control: None reported.  Currently, Calonectria pteridis is a quarantine, actionable pathogen with a Q rating in California.

California Distribution: Calonectria pteridis is not known to be established in California.  Diseased plants detected in a San Luis Obispo nursery were destroyed (see “Initiating Event).

California Interceptions:  There have been two interceptions of Calonectria pteridis- infested Ravenea rivularis (majesty palm) plants that originated in Florida (see ‘Initiating Event’).

The risk Calonectria pteridis would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2):  Calonectria pteridis requires humid, wet, rainy and warm climates to infect plants and develop.  Therefore, the pathogen may only be able to establish in limited parts of California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is High (3): Calonectria pteridis has a very wide host range and can attack a number of diverse hosts including ornamentals, forest and environmental trees and shrubs, and few agricultural crops.  In the USA, palms have been reported as the main host attacked by the pathogen.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  The pathogen has high reproductive potential.  Conidia and ascospores are transmitted by wind, wind-driven rain and splashing irrigation water, cultivation tools, and plant handling.  However conidial germination and plant infection require long, wet periods.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2): Infections of Calonectria pteridis could lower crop value and cause loss of markets.  Under controlled wet and warm environments, nursery productions of palms and other ornamental host plants may be at particular risk for pathogen infection and reduced plant production.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2):  Under conducive climate for development, the pathogen could significantly impact cultural practices or home garden plantings.  Its overall impact on California’s environment is assessed as ‘medium’. 

Consequences of Introduction to California for Calonectria pteridis:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Calonectria pteridis to California = (12).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not established (0):  Interceptions of Calonectria pteridis-infected nursery plants were destroyed and therefore, the pathogen is not considered established in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

 Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 12.

Uncertainty:  

Periodic surveys and/or subsequent detection may confirm the presence/absence of C. pteridis in commercial and private production regions within California.  Subsequent results may alter the herein proposed rating for the pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Calonectria pteridis is B.

References:

Alfenas, R. F., O. L. Pereira, R. G. Frietas, C. S. Freitas, M. A. D. Dita, and A. C. Alfenas.  2013.  Mass spore production and inoculations of Calonectria pteridis on Eucalyptus spp. under different environmental conditions.   Tropical Plant Pathology, 38:406-413.

Crous, P. W., M. J. Wingfield, and A. C. Alfenas.  1993. Additions to Calonectria.  Mycotaxon 46:217-234.

Crous, P. W., and M. J. Wingfield. 1993.  Calonectria pteridis.  IMI Descriptions of Fungi and Bacteria. No. 116 pp. Sheet 1153.

Farr, D.F., & A. Y. Rossman.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Uchida, J. Y.  2004.  Calonectria leaf spot (Cylindrocladium leaf spot).  In ‘Compendium of Ornamental Palm Disease and Disorders’ Eds. M. L. Elliott, T. K. Broschat, J. Y. Uchida, and G. W. Simone.  The American Phytopathological Society, pgs. 12-14.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Yang, W., L. Zheng, C. Wang, and C. -P. Xie.  2014.  The first report of Calonectria pteridis causing a leaf spot disease on Serenoa repens in China. Plant Disease. 986: 854.

Yu, J. and M. L. Elliott.  2013.  Calonectria (Cylindrocladium) leaf spot of palm.  University of Florida Institute of Food and Agricultural Sciences.  http://edis.ifas.ufl.edu/PP302.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: (916) 262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posting by ls