Alternaria The dark brown spores are borne in simple or branched chains from the tips of simple dark conidiophores and are divided into several cells by transverse and vertical walls. New spores are produced by the extrusion of wall material through a pore at the tip of the previous spore. Commonly isolated from decaying plant materials; also causing plant diseases. Spores of Alternaria species are dispersed by air currents and are usually a major component of outdoor air. Holomorphs: Clathrospora, Leptosphaeria, Pleospora, Pyrenophora. Refs: Ellis 1971, 1976; Joly 1964.
Aspergillus The U.S. Government's Occupational Safety and Health Administration [OSHA] lists the following Aspergillus species as all being allergens and irritants and a cause of Hypersensitivity pneumonitis and Dermatitis: Aspergillus flavipes, Aspergillus flavus, Aspergillus fumigatus, Aspergillus glaucus, Aspergillus nidulans, Aspergillus niger, Aspergillus ochraceus, and Aspergillus versicolor.
Aureobasidium Aureobasidium is a known Type I and Type III allergen that can sometimes cause infections in the human skin, nails, and eyes. The U.S. Government's Occupational Safety and Health Administration [OSHA] lists both Aureobasidium and Aureobasidium pullulans as an allergen and irritant, and as a cause of Hypersensitivity pneumonitis and Dermatitis.
Chaetomium Chaetomium is a dematiaceous filamentous fungus found in soil, air, and plant debris. As well as being a contaminant, Chaetomium spp. are also encountered as causative agents of infections in humans. Some species are thermophilic and neurotropic in nature. Chaetomium spp. are among the fungi causing infections wholly referred to as phaeohyphomycosis. Fatal deep mycoses due to Chaetomium atrobrunneum have been reported in an immunocompromised host. Brain abscess, peritonitis, cutaneous lesions, and onychomycosis may also develop due to Chaetomium spp. [from http://www.doctorfungus.org ]
Cladosporium The U.S. Government's Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Cladospotium mold: Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis. Cladosporium is a dematiaceous (pigmented) mold widely distributed in air and rotten organic material and frequently isolated as a contaminant on foods. Some species are predominant in tropical and subtropical regions. Also, some Cladosporium spp. were isolated from fish and were associated with findings of infection.
Exserohilum Exserohilum species are common environmental molds found in soil and on plants, especially grasses. Several species have been reported as agents of phaeohyphomycosis, notably E. rostratum (= E. halodes), E. meginnisii and E. longirostratum. Clinical manifestations include mycotic keratitis, subcutaneous phaeohyphomycosis, endocarditis, osteomyelitis and sinusitis in both normal and immunosuppressed patients.   The U.S. Government's Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Exserohilum mold: Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis.
Fusarium Fusarium is a filamentous fungus widely distributed on plants and in the soil. It is found in normal mycoflora of commodities, such as rice, bean, soybean, and other crops. While most species are more common at tropical and subtropical areas, some inhabit in soil in cold climates. Some Fusarium species have a teleomorphic state. As well as being a common contaminant and a well-known plant pathogen, Fusarium species  may cause various infections in humans. Fusarium is one of the emerging causes of opportunistic mycoses.
Microsporum Microsporum species particularly infect the hair and skin, except for Microsporum persicolor which does not infect the hair.  The pathogenesis of the infection depends on the natural reservoir of the species in such a way that the geophilic species are acquired through contact with soil, zoophilic species are transmitted from the infected animal, and direct or indirect human – to – human transmission is of concern for anthropophilic species. Infections involving the nails are rare.  Immunocompromised patients are infected as well as the otherwise healthy hosts.
Mucor The U.S Government’s Occupational Safety and Health Administration [OSHA] lists the following as the health effects of Mucor: Allergen, Irritant, Hypersensitivity pneumonitis, Dermatitis. Mucor is a dangerous mold that can adversely affect one's respiratory system. It is a possible cause of the dangerous mold disease zygomycosis.  For those of you who watched the very disturbing feature on the Ripley's Believe It or Not cable TV show about a man's face [eyes, nose, cheeks, and everything else between his mouth and his forehead] having been eaten away by a mold that began to grow in the man's sinus cavities, the flesh-eating mold that ate his face was actually the very unhealthy mold Mucor!
Penicillium Penicillium spp. are occasional causes of infection in humans and the resulting disease is known generically as penicilliosis. Penicilliosis is an infection caused by Penicillium marneffei, a dimorphic fungus endemic to Southeast Asia and the southern part of China. Persons affected by penicilliosis usually have AIDS with low CD4+ cell count of typically <100 cells/cu mm. The average CD4 count at presentation is 63.5 cells/cu mm. Penicillium marneffei infections have also been reported in non-AIDS patients with hematological malignancies and those receiving immunosuppressive therapy.
Rhinocladiella Rhinocladiella is a cosmopolitan fungus which can be found in soil, herbaceous substrates, and decaying wood.  To date, there are only three cases of subcutaneous infection that have been reported as caused by Rhinocladiella aquaspersa.
Rhizopus Rhizopus is a cosmopolitan filamentous fungus frequently isolated from soil, decaying fruit and vegetables, animal feces, and old bread. Aside from being known as common contaminants, Rhizopus species are also occasional causes of serious, and often fatal, infections in humans.  Certain species are plant pathogens as well. Rhizopus species are among the fungi causing the group of infections referred to as zygomycosis.  Zygomycosis is now the preferred term over mucormycosis for this angio – invasive disease.  Rhizopus arrhizus is the most common cause of zygomycosis and is followed by Rhizopus microsporus var. rhizopodiformis. Zygomycosis infection includes mucocutaneous, rhinocerebral, genitourinary, gastrointestinal, pulmonary, and disseminated infections.  The most frequent predisposing factors for zygomycosis include diabetic ketoacidosis and immunosuppression due to various reasons, such as organ transplantation and other factors such as desferoxamine treatment, renal failure, extensive burns, trauma, and intravenous drug use which may also predispose to development of zygomycosis.  Heatstroke has been described as a risk factor for disseminated zygomycosis as well.  Contaminated adhesive tapes and wooden tongue depressors have been reported to lead to nosocomial outbreaks of zygomycosis.  Vascular invasion that causes necrosis of the infected tissue, and perineural invasion are the most frustrating features of these infections. Zygomycosis is frequently considered as fatal infection.	(Image Courtesy of www.doctorfungus.org @ 2005) Rhinocerebral zygomycosis caused by Rhizopus oryzae extensive involvement of the orbit and associated MRI image.
Trichoderma   Trichoderma species are usually considered as non – pathogenic, on the other hand, Trichoderma viride has been reported as a causative agent of pulmonary infection, peritonitis in a dialysis patient, and perihepatic infection in a liver transplant patient.  Trichoderma infections are opportunistic in nature and develop in immunocompromised patients, such as neutropenic cases and transplant patients, as well as those with chronic renal failure, chronic lung disease, or amyloidosis.  Disseminated infections due to Trichoderma have also been reported.

Similar Species

There are approximately 227 species and subspecies in this genus. Here are just 100 of them: U. achnatheri · U. agropiyri · U. agropyri · U. agropyri-campestris · U. agropyri-juncei · U. agrostidis · U. alaskana · U. allii · U. alopecuri · U. alstroemeriae · U. americana · U. andina · U. anemones · U. anemones f. aconiti · U. anemones f. anemones · U. anemones f. cassubici · U. anemones f. repentis · U. anemones var. adonis · U. anemones var. andina · U. anemones var. anemones · U. anemones var. japonica · U. anemones var. kerguelensis · U. anemones var. pulsatillae · U. antarctica · U. antipolitana · U. aquilegiae · U. aristidicola · U. arrhenatheri · U. asphodeli · U. atragenes · U. atropidis · U. aurea · U. avenae-elatioris · U. avenastri · U. beckmanniae · U. behboudii · U. beijingensis · U. bolivari · U. bolivarii · U. bomareae · U. bornmuelleri · U. brassicae · U. bromi · U. bulbigera · U. bulbocodii · U. calamagrostidis · U. callianthemi · U. camassiae · U. carcinodes · U. castellana · U. cepulae · U. ceratocephali · U. cholerae · U. cholerae-asiaticae · U. chorizandrae · U. circaeasteri · U. clintoniae · U. colchici · U. colchici f. colchici · U. colchici f. narcissi · U. colchici var. colchici · U. colchici-lutei · U. coralloides · U. corsica · U. cortusae · U. corydalis · U. dactylidina · U. delphinii · U. destruens · U. dioscoreae · U. elymi · U. eranthidis · U. eriospermi · U. erythronii · U. ferrarisiana · U. festucae · U. ficariae · U. filipendulae · U. fischeri · U. fischeri var. fischeri · U. fischeri var. littoralis · U. floccosa · U. flowersii · U. frasarii · U. fraseri · U. fraserii · U. gageae · U. galanthi · U. gei · U. giliae · U. gladiolicola · U. granulosa · U. hederae · U. helanensis · U. helvetica · U. herteriana · U. heucherae · U. hierochloae · U. hieronymi · U. hispanica

Members of the genus Uredo:

There are approximately 1,700 species and subspecies in this genus. Here are just 100 of them: U. segetum hordei · U. segetum panici-miliacea · U. segetum segetum · U. abdita · U. aberrans · U. abietina · U. abietis-pectinatae · U. abri · U. abscondita · U. aburiensis · U. acaciae · U. acaciae-bursariae · U. acaciae-concinnae · U. acaenae · U. acalyphae · U. acalyphae-fruticosae · U. acherois · U. achyranthicola · U. achyranthis · U. achyroclines · U. acori · U. acriuli · U. acuta · U. adapertilis · U. adenocalymmatis · U. adenocauli · U. adenocaulonis · U. adoxae · U. aeluropodina · U. aeschynomenes · U. affinis · U. aframomi · U. africana · U. agerati · U. aggregata · U. agnostoica · U. agrimoniae-eupatoriae · U. agropyrina · U. agrostidis · U. agrostidis-myrianthae · U. agrostidis-rupestris · U. agrostis-palustris · U. akaisiensis · U. alabamensis · U. alafiae · U. alaskana · U. albertensis · U. albiziae · U. alchorneae · U. alemquerensis · U. alibertiae · U. alismacearum · U. alismatis · U. allii-fragilis · U. allmaniae · U. allophili · U. aloës · U. alocasiae · U. alpestris · U. alstroemeriae · U. alternantherae · U. alysicarpi · U. amagensis · U. amami-oshimaensis · U. amaniensis · U. amapaensis · U. amazonensis · U. amazonica · U. americana · U. amicosa · U. amitostigmatis · U. ammopiptanthi · U. amomi · U. amphiosporae · U. amsoniae · U. amygdalinae · U. anacardii · U. ancylanthi · U. andicola · U. andina · U. andromedae · U. andropogonicola · U. andropogonis-gabonensis · U. andropogonis-gayani · U. andropogonis-lepidi · U. andropogonis-schoenanthi · U. andropogonis-zeylanici · U. androsaemi · U. andryalae · U. aneimiae · U. angeae · U. angiosperma · U. anguillariae · U. angusii · U. anilis · U. anodae · U. antarctica · U. antarctina · U. anthephorae · U. antherarum a silenes-nutantis

 

 

 

 

 

 

 

 

 

 

 

 

Fusarium conidia

 

 

 

• Fusarium oxysporum f.sp. albedinis
• Fusarium oxysporum f.sp. asparagi
• Fusarium oxysporum f.sp. batatas
• Fusarium oxysporum f.sp. betae
• Fusarium oxysporum f.sp. cannabis
• Fusarium oxysporum f.sp. cepae
• Fusarium oxysporum f.sp. ciceris
• Fusarium oxysporum f.sp. citri
• Fusarium oxysporum f.sp. coffea
• Fusarium oxysporum f.sp. cubense
• Fusarium oxysporum f.sp. cyclaminis
• Fusarium oxysporum f.sp. herbemontis
• Fusarium oxysporum f.sp. dianthi
• Fusarium oxysporum f.sp. lentis
• Fusarium oxysporum f.sp. lini
• Fusarium oxysporum f.sp. lycopersici
• Fusarium oxysporum f.sp. medicaginis
• Fusarium oxysporum f.sp. melonis
• Fusarium oxysporum f.sp. nicotianae
• Fusarium oxysporum f.sp. niveum
• Fusarium oxysporum f.sp. passiflorae
• Fusarium oxysporum f.sp. phaseoli
• Fusarium oxysporum f.sp. pisi
• Fusarium oxysporum f.sp. radicis-lycopersici
• Fusarium oxysporum f.sp. ricini
• Fusarium oxysporum f.sp. tulipae
• Fusarium oxysporum f.sp. vasinfectum

 

 

 

MILDÚS.

1.- Describa las características de signos y síntomas en las muestras proporcionadas.

• Cucumis sativus (pepino).Síntomas: manchas circulares rodeadas por un halo clorótico. Signos: en el envés de la hoja aspecto velloso.

• Lactuca sativa (lechuga).Síntomas: manchas cloróticas. Signos: aspecto vellosos por el envés de la hoja.

• Espinaca. Síntomas: manchas cloroticas circulares. Signos: aspecto vellosos por el lado del envés.

• Maleza. Síntomas: manchas circulares rodeadas por un halo clorotico. Signos: en el envés de la hoja aspecto velloso.

2.- Describa las características microscópicas de los esporangios observados.

• Bremia presenta haustorios globosos y ramificación en una sola dirección, los esporangios germinan de forma directa o indirecta.

• Perosnospora las terminaciones de las ramas de los esporangios son agudos, no presenta papila apical, presenta haustorios claviformes.

• Plasmopara presenta haustorios piriformes, las ramificaciones de los esporangios son en ángulo recto, presenta una papila apical.

• Pseudoperonospora la ramificación de los esporangios es dicotomica, presenta papila, las puntas son romas, presenta haustorios claviformes.

3. - ¿Cuál es la forma y color de los esporangios de los hongos observados?

Son hilanos.

Forma: Bremia Plasmopara

Peronospora Pseudoperonospora

4.- ¿Por qué no se emplea un medio de cultivo para el aislamiento de los hongos que producen Mildiús?

Por que son parásitos estrictos.

5. - ¿Qué estructura fungosa nos permiten establecer la identificación a nivel de género de los Mildiús?

Los haustorios.

6.- ¿Qué estructuras son las encargadas de adsorber los nutrientes de las células vegetales?

Los haustorios y el micelio intracelular.

7.- ¿Por qué no es conveniente usar lactófenol con azul de algodón para observar las estructuras fúngicas?

Por que el azul de algodón va a teñir las estructuras del hongo y no se va a poder apreciar si el hongo presenta color por si mismo, además que el color de las estructuras es un criterio para la identificación del hongo, sobretodo si las oosporas o conidios presentan color.

8.- Comentarios y discusión.

Los mildiús son parásitos estrictos por lo cual no se van a aislar en medios de cultivo por lo que va a ser necesario que se realicen cortes de los tejidos infectados para la observación de esporangioforos y esporangios para su identificación.

Para una buena identificación se hace uso del material vegetal ya que se tiene establecido que patógenos son los más frecuentemente encontrados en el material vegetal que nos interesa o que estamos trabajando.

El diagnostico de mildiús es rápida ya que como se menciono anteriormente son parásitos estrictos y con una observación microscópica en fresco se realiza la identificación.

Para la diferenciación de los mildiús se hace uso de sus estructuras tales como: esporangios, el tipo de ramificaciones y la presencia de papila apical en los esporangios.

En cuanto el tipo de lesiones producidas por los diferentes hongos son similares, por lo que no se puede hacer un diagnostico diferencial como lo es con las bacterias que algunas de ellas presentan lesiones características en el hospedante.

De los aspectos más importantes para la identificación del parásito en el tejido vegetal es saber diferenciar las células vegetales de las estructuras fungosas y para que se realice una buena observación se necesita de un buen corte vegetal que sea delgado y representativo.

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First Report of Powdery Mildew of Ligustrum japonicum (Japanese Privet) Caused by Microsphaera syringae (Erysiphe syringae) in North America

Jennifer S. Falacy, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser 99350-8694; and Dean A. Glawe, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998

Corresponding author: Dean A. Glawe. glawe@wsu.edu

Falacy, J. S., and Glawe, D. A. 2003. First report of powdery mildew of Ligustrum japonicum (Japanese privet) caused by Microsphaera syringae (Erysiphe syringae) in North America. Online. Plant Health Progress doi:10.1094/PHP-2003-1210-01-HN.

The woody shrub Ligustrum japonicum Thunb. (Japanese privet) is used widely as a landscape plant. The only published report (4) of powdery mildew on this host in North America was based on an anamorphic fungus in Louisiana regarded as a possible species of Microsphaera. The Plant Clinic at Oregon State University houses an unpublished record, dated August 30, 1961, of a powdery mildew on this host in Portland, Multnomah County, Oregon (Jay Pscheidt, personal communication); that fungus was recorded as Microsphaera alni but no voucher specimen or morphological description exists. In August 2002, powdery mildew was collected by Master Gardener Marilyn Tilbury from L. japonicum in Seattle, King County, Washington. The authors determined the causal agent to be Microsphaera syringae (Schw.) Magn. The present report documents for the first time the occurrence of M. syringae on L. japonicum in North America, and presents information on the taxonomy and identification of this fungus.

Signs of the fungus included white mycelium consisting of hyphae, conidiophores bearing single conidia, and brown to black ascocarps. Distinguishing characteristics included lobed appressoria (Fig. 1); ascocarps (85-) 90-113 (-116) µm with dichotomously branched appendages (Fig. 2), short-stipitate asci (Fig. 3) 50-60 (-64 ) × 27-42 (-45) µm each with 4 to 8 oval to phaseoliform ascospores 18-22 (-23) × 10-11  (-12) µm; conidiophores with short cylindrical foot cells and cylindrical conidia (Fig. 4) (26-) 27-35 (-41) × (11-) 12-14 (-15) µm. A voucher specimen (WSP 70743) was deposited with the Mycological Herbarium, Department of Plant Pathology, Washington State University.

	Fig. 1. Appressorium of Microsphaera syringae formed on Ligustrum japonicum.		Fig. 2. Ascocarp appendages of Microsphaera syringae formed on Ligustrum japonicum.

	Fig. 3. Asci with ascospores formed by Microsphaera syringae on Ligustrum japonicum.		Fig. 4. Conidium of Microsphaera syringae formed on Ligustrum japonicum.

A Survey of Ascomycetous Holomorphs
 

 

Series Unitunicatae-Inoperculatae

The Microbial World: Biotrophic plant pathogens Produced by Jim Deacon Institute of Cell and Molecular Biology, The University of Edinburgh

Biotrophic plant pathogens

Quite a lot of plant-pathogenic fungi establish a long-term feeding relationship with the living cells of their hosts, rather than killing the host cells as part of the infection process. These pathogens are termed biotrophic [from the Greek: bios = life, trophy = feeding].

Typically, these fungi grow between the host cells and invade only a few of the cells to produce nutrient-absorbing structures termed haustoria. By their feeding acitivities, they create a nutrient sink to the infection site, so that the host is disadvantaged but is not killed. This type of parasitism can result in serious economic losses of crop plants, and in natural environments it can reduce the competitive abilities of the host; indeed, a few biotrophic pathogens have been used successfully as biological control agents of agricultural weeds.

In many ways, this type of parasitism is very sophisticated - keeping the host alive as a long-term source of food. This has led some people to suggest that biotrophic parasitism is evolutionarily advanced. But this is clearly not the case in general, because an almost identical type of parasitism is found in the arbuscular mycorrhizal fungi (see Mycorrhizas) which are thought to have developed on the earliest land plants.

Here we consider the two most important groups of biotrophic plant pathogens:

• the rust fungi (Basidiomycota)
• the powdery mildew fungi (Ascomycota).

A parallel can be made between the behaviour of these fungi and the biotrophic mycoparasites (see Verticillium biguttatum)

 

 

[DOC]

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Tomato plants showing typical signs of powdery mildew were received in April 2006 from a hydroponic greenhouse situated in western Turkey. Dense, irregular white patches observed on the upper surfaces of the leaves and on the stems of the plants (Fig. 1) could be easily differentiated from the symptoms caused by Leveillula taurica.  L. taurica is known as the unique agent of tomato powdery mildew in Turkey up to now and causes white powdery masses appearing just under the chlorotic spots that are produced on the adaxial surface of the leaves.

Figure 1: Symptoms of powdery mildew on stalks and upper leaf surfaces of tomato	Figure 2: Conidiophore with false chain of conidia (A), conidium developing singly on conidiophore (B), and germinating conidia (C) of Oidium neolycopersici (bar represents 30 µm)

To determine the morphological characteristics of the pathogen, surface mycelium was removed with small strips of clear adhesive tape and examined using light microscopy. Microscopic observations revealed ellipsoid-ovoid or doliform conidia that measured 31-57 x 15-27 µm (mean: 33.7 x 17.4 µm; n=50) germinating with one short germ tube terminating in simple apices. Conidiophores were straight, with cylindrical foot-cells measuring 47-78 µm (mean: 53.8 µm), followed by two or three short cells. The total length of the conidiophores measured 73-104 µm (mean: 87.4 µm). Conidia were solitary or sometimes in short pseudo-chains of 2-4 conidia (Fig. 2). Based on these characteristics the fungus was identified as Oidium neolycopersici (Kiss et al., 2001).

To confirm the pathogenicity of the fungus, disease free tomatoes plants (20 plants of each cultivars SC 2121 and H 2274) were inoculated at the five to six true-leaf stage with conidia falling from diseased tomato leaves hanging above them. Plants were kept in a polyethylene chamber placed in a greenhouse cabinet at 21 ± 1⁰C and a 14-h photoperiod for five days. The polyethylene chamber was then removed and the plants were grown in the greenhouse. The first white fungal colonies appeared on the leaves of the inoculated plants 7 days after inoculation and after 14 days, a powdery mildew, exhibiting the same morphological features, was observed on all of the tomatoes plants.

This is believed to be the first report of powdery mildew caused by Oidium neolycopersici on tomatoes in Turkey. This disease has the potential to cause economic losses (Jones et al., 2001) and may become a problem in greenhouse-grown tomatoes in the near future.

Figure 2: Conidium, mycelium and conidiophore of Oidium piperis. Top left: close-up of conidium; Top right: close-up of mycelium showing the indistinct to slightly nipple-shaped apressoria; Bottom: close-up of conidiophore. Note that oil droplets attached to the surface of the fungal structures originated from the host-plant tissue.

Based on these characteristics the fungus was identified as Oidium piperis. A specimen was deposited in the herbarium of the Universidade Federal de Viçosa (VIC 27825). The description of O. piperis provided in Braun (1987) states that conidia of this fungus are 20–74 x 6–23 µm (mostly 34–47 x 13–20 µm). Although our specimen had smaller conidia it was otherwise identical to Braun’s description. Previously reported only in India on Piper betle (Uppal et al., 1946) and in Denmark on Peperomia verticillata (Anon., 1981), there is no previous record of this fungus occurring in Brazil. This new finding suggests a much wider distribution and perhaps a more common occurrence than previously thought. Only minor was observed damage on isolated plants and the threat to medicinal use of P. aduncum appears small.

 

INTRODUCTION TO THE ASCOMYCOTA

The Ascomycota (as-ko-mi-KO-ta) is derived from two Greek roots that mean wineskin or bladder (aski -ασκί); and fungus (mykes -μύκης).  The reference is to the structure (ascus) within which the sexual meiospores are formed.

The ascus-bearing fungi include a very diverse and economically-important collection of organisms.  Asci (Figure A) and ascocarps (Figure B), the structures that bear the asci, are among the important structural themes in this phylum.  Asci contain the sexual meiospores, which may be agents of dispersal, but most taxa disperse themselves asexually by means of conidiospores contained on conidia (Figure C).  The phylum itself is extraordinarily diverse formed of free-living, parasitic, and symbiotic taxa (Figures D-T).  Many are parasites of agricultural plants and cause diseases like: apple scab, apple bitter rot, brown stone rot, strawberry stem rot, etc.  Some, like Endothia parasitica, have by their introduction altered the Eastern Deciduous Forest in North America by the effective elimination of one of its dominant plants, the American Chestnut (Castanea dentata).  Similarly, American Elms (Ulmus americana) have disappeared due to the introduction of another ascomycete that causes Dutch Elm Disease.  

Ascomycete-caused diseases are not restricted to plants.  For example, skin ailments (e.g. ringworm, athlete's foot), and histoplasmosis, a pneumonia-like disease, are caused by ascomytogenous fungi.  Household molds (toxic molds, black molds, and green molds) tend to be from this phylum, though many have lost the ability to produce sexual spores.  Ergot, a disease brought on by ingesting rye infected with Claviceps purpurea, causes hallucinations and uncontrolled contractions of certain muscles, especially the uterus.  The active agent in ergotized grain seems to be a compound similar to LSD.

All ascomycetes are not dangerous or detrimental.  Truffles and morels produce much-prized edible ascocarps.  Yeast (Saccharomyces and related taxa) is perhaps the most economically-important fungus of all and is responsible for the alcoholic fermentation of beer, wine, etc. as well as the fermentation necessary for the production of leavened bread.

Some species of the Orbiliomycetes are associated with dry wood and are the causative agents of dry rot. These thrive in the xeric environments of dry dead wood on a tree (where they can be exposed to drying winds and sun) or the semi-arid soil associated with plants like Yucca. However, when the hyphae of their sparse mycelia come into contact with nematodes, they begin to elaborate hyphal loops, which function as nematode traps.  When a nematode sticks its head into a snare, the hydrostatic pressure of the hyphal loop increases suddenly, and the worm is caught.  The fungus then elaborates a feeding haustorium into the nematode and quickly digests the animal. The fungus, with the added nutrition from the nematode, elaborates conidia for dispersal.  Not only do they lead a double life as wood eaters and nematode trappers, but some have lost the ability to make asci.  The most well-known nematode-eating fungus, Arthrobotrys, is the anamorph (asexual form) of some taxa within the sexual genus Orbilia.  Thus, these same fungi can consume the trim wood on my garden shed door, recycle wood and its elements in the brush pile at the bottom of my yard, and consume soil nematodes in the garden bed where I grow tomatoes.  Clearly, the benefits to me far outweigh the costs.

Many species of the ascomycetes perform ecological functions that are quite valuable in the long run.  Indeed, the environmental role of most ascomycetes cannot be overstated.  Apart from their roles as "decomposers", many of them enter into symbiotic relationships with plants to form a fungus-plant mycorrhizal associations.  Similar fungus chimeras include the lichens, most of which have an ascomycete as the mycobiont.

The typical ascomycete life cycle involves the association of haploid, monokaryotic branched filaments.  In the case of morel (Morchella), hyphae of two compatible mating types associate and begin to weave the ascocarp.  Then, in the hymenial layer, each filament has cells that enlarge.  The functional female grows a long structure called a trichogyne that fuses with an enlarged cell in the compatible filament.  The result is the emergence of a filament that remains haploid with two distinct nuclei (dikaryotic).  As it divides, the terminal end makes a crook (called a crozier) that sequesters one of the nuclei to insure that each daughter cell has the full complement of haploid nuclei.  This dikaryon is short-lived and after a few cell divisions leads to the development of the ascus, within which the haploid nuclei fuse and then undergo meiosis to form the ascospores on the surface of the ascocarp.  

One of the oddest members of this phylum is Laboulbenia, an obligate parasite of insects, especially beetles, with a distinctive non-mycelial and determinate growth pattern. The fungus body, the receptacle, attaches to the host by a basal cellular holdfast and a single, simple haustorium penetrates the insect.  Lateral filamentous appendages and one or more sessile or stalked perithecia arise on the receptacle after feeding on the insect.  The ascus wall deliquesces (begins to gelatinize) prior to spore discharge. 

SYNOPTIC DESCRIPTION OF THE ASCOMYCOTA

The following description comes from Alexopoulos and Mims (1979), Alexopoulos et al (1996), Bold et al. (1987), and Scagel et al., (1984).

I. SYNONYMS: ascomycetes, sac fungi. II. NUMBER: >15,000 species. III. PHYLUM CHARACTERISTICS: A. ASEXUAL REPRODUCTION:  Conidia. B. SEXUAL REPRODUCTION:  Ascospores produced within an ascus and often enclosed within an ascocarp. Nuclear fusion followed by meiosis (and usually a mitosis) to produce 8 ascospores in an ascus.  Distinctive gametangia and stages of ascospore formation. C. VEGETATIVE HYPHAE:  Haplophase dominant; dikaryophase produces ascogenous hyphae and ascus mother cells. D. CELL WALLS: Chitin and glucan. E. ECOLOGY: These are fungi that are free-living saprobes or parasites.  Some of them make chimeroid entities like mycorrhizal associations and lichens.

SYSTEMATICS OF THE ASCOMYCOTA

The taxonomy of the Ascomycota has been in flux for some time ( e.g. Hudson 1984, Alexopoulos and Mims 1979, Bold et al. 1987, and Scagel et al. 1984).  First, the practice of separating the lichens and imperfect fungi (those that do not exhibit sexual reproduction) was abandoned and more natural taxonomic systems began to appear.  This trend can be seen in the systems of Margulis and Schwartz (1982, 1988, and 1998).  Then, Nishida and Sugiyama (1994) discovered a distinct group that they called the Archiascomycetes according to their SSU rRNA analysis of fungi. Thus, they and others including Liu et al. (1999), defined the Ascomycota as having 3 classes: Archiascomycetes, Saccharomycetes, and the Euascomycetes.  Both the Saccharomycetes and the Euascomycetes groups seemed to be well defined and monophyletic.  The "Archiascomycetes" seemed to be paraphyletic and comprised the broad grouping from which the other two groups sprang.  I feel that the diversity of the Ascomycota is too great to be reflected in a system of 3 classes.  Thus, I have adopted the system of Eriksson et al (2001) which has 3 subphyla and 14 classes.  The analysis of Lutzoni et al. (2004) confirms the monophyly of the Ascomycota but calls into question the monophyly of some of the Taphrinomycotina.  Adl et al. (2005) seem to separate the ascomycotes into four taxa at the level of Taphrinomycotina (which I interpret as 4 subphyla).  Thus, the system of Eriksson et al. (2001) likely will be modified.

HIERARCHICAL CLASSIFICATION OF THE ASCOMYCOTA

This system is a modification of Eriksson et al (2001) which has 3 subphyla and 14 classes.

SUBPHYLUM TAPHRINOMYCOTINA = CLASS ARCHIASCOMYCETES  This is the group that Nishida and Sugiyama (1994) called the class Archaeascomycetes.  I have raised it to subphylum level according to the system of Ericksson (2000) who claims that they are the sisters to all of the other Ascomycota, and they appear to be the groups from which the other Ascomycotes arose.  However, the following classes differ from each other structurally and, according to Ericksson (2000), on the basis of their SSU rRNA sequences.    Thus, the diversity of the group of four classes really indicates that they are defined by exclusion from the well-defined and natural groupings: Saccharomycotina and Pezizomycotina.  Also, I am troubled by their apparent primitiveness.  All of these taxa (except the fission yeasts) are parasites and, therefore, may only appear to be primitive through reduction.  Clearly, the book is not closed on the taxonomy of the Ascomycota. CLASS NEOLECTOMYCETES These are fungi that produce large fruiting bodies (ascocarps up to 9 cm tall).  The ascogenous hyphae do not have crosiers.  The asci open by a slit.  The ascospores germinate to form yeast-like conidia.  The mycelia and fruiting bodies are associated with spruce roots and may be parasitic.   ORDER NEOLECTIALES Neolecta  CLASS PNEUMOCYSTIDOMYCETES These live as parasites in the alveoli of certain vertebrates and, therefore, are of significant medical importance.  They grow as yeasts that divide by fission (not budding).  They fuse to form asci of 8 banana-shaped ascospores.   ORDER PNEUMOCYSTIALES Pneumocystis CLASS SCHIZOSACCHAROMYCETES  = OCTOSPOROMYCES These are the fission yeasts.  They fuse to form asci of four or eight ascospores.  They live as saprobes in fruit juice.   ORDER SCHIZOSACCHARIALES Schizosaccharomyces CLASS TAPHRINOMYCETES Biotrophic parasites of seed plants and ferns causing galls, leaf curls, deformed fruits and witches brooms. Intercellular or subcuticular dikaryophase mycelium in parasitic phase with terminal chlamydospores or ascogenous cells, each forming a single ascus in a hymenium-like layer; after nuclear fusion and mitosis, ascogenous cells often divide to give a basal stalk cell with ascus at the apex; ascospores may bud within ascus so that it appears multispored; saprotrophic phase of budding monokaryotic cells; can be cultured in the yeast state.   ORDER TAPHRINALES) Taphrina, Protomycetes. SUBPHYLUM SACCHAROMYCOTINA = HEMIASCOMYCETES These are the budding yeasts.  Vegetative phase unicellular yeast-like or filamentous; asci one-walled, naked, not borne on ascogenous hyphae, produced singly, following karyogamy; no ascocarps.   CLASS SACCHAROMYCETES ORDER SACCHAROMYCETALES = ENDOMYCETALES Saccharomyces, Dipoascus. SUBPHYLUM PEZIZOMYCOTINA These comprise most of the ascomycota.  The organisms form mycelia that make ascocarps (ascus-bearing structures also called ascomata) with hymenia.  Some of the taxa are lichenized (enter into a symbiotic relationship with algae to form lichens).  Some of the taxa have lost the ability to undergo meiosis and, although they might fuse, they can not produce ascospores or asci.  Such taxa were once called the Fungi Imperfecti or Deuteromycota.  Such a distinction is decidedly artificial.  On the other hand, symbiotic entities like lichens do not easily fit into a natural system unless the fungal symbiont (mycobiont) is given complete preference.  To be consistent with current fungal taxonomic systems, I will include the lichenized fungi in this system and describe the lichens in a separate page.  This subphylum follows that of Ericksson (2000), but I have added a 9th class, Laboulbeiomycetes, a group of uncertain status in Ericksson's system. CLASS ARTHRONIOMYCETES  This class appears to be monophyletic. Most of them are lichenized and produce asci with double walls and slits.  The asci elongate to a rostrum when discharging spores.   The ascocarps are apothecia with a naked hymenium.   ORDER ARTHRONIALES Arthonia, Chrysothrix, Melaspilea, Roccella, Arthrophacopsis. CLASS CHAETOTHYRIOMYCETES This class appears to be monophyletic. Most species are saprobes on vascular plants, dead wood, lichens, etc.  Some are human pathogens.  The ascocarps are small perithecia that contains paraphyces.   ORDER CHAETOTHYRIALES Chaetothyrium, Capronia, Adelococcus, Verrucaria. CLASS DOTHIDIOMYCETES  Typically, these form bitunicate asci within perithecia (members of the order Patellariales produce apothecia).  The asci usually are associated with paraphyses-like structures (pseudothecia).  The spores are septate.  This class and the Chaetothyriomycetes corresponds to Loculoascomycetes in some earlier systems and is often referred to as "bitunicate ascomycetes".  Five orders are recognized in this system (after Ericksson, 2000). Some families will probably have to be transferred to the Chaetothyriomycetes when more molecular data are available. ORDER CAPNODIALES Capnodaria, Capnodium, Achaetobotrys, Antennulariella, Coccodinium, Metacapnodium. ORDER DOTHIDIALES Asci ovoid, club-shaped or cylindrical, grouped in small locules without pseudoparaphyses in pseudothecia; pseudothecia separate or grouped on or in stroma; ascospores usually uniseptate. Dothidea, [Mycosphaerella, Guignardia both incertae sedis]. ORDER HYSTERIALES On dead woody branches and bare wood; with distinct boat-shaped, carbonaceous pseudothecia opening by longitudinal slit and appearing apothecium-like when moist. Hysterium. ORDER MYRIANGIALES Mostly tropical or subtropical, epiphytes, parasites or hyperparasites on fungi or scale insects on living leaves and stems; asci globose, scattered individually throughout ascocarp. Myrangium, Elsinoe. ORDER PATELLARIALES Asci in apothecia. Patellaria ORDER PLEOSPORALES Asci long, cylindrical, separated by pseudoparaphyses in relatively large, uniloculate, usually solitary pseudothecia; ascospores commonly phragmosporous or dictyosporous, pigmented. Venturia, Delitschia, Leptosphaeria, Lophiostoma, Melanomma, Montagnula, Phaeosphaeria, Phaeotrichum, Pleospora, Sporormia, Teichospora. CLASS EUROTIOMYCETES This class appears to be monophyletic. Two orders are accepted. The Elaphomycetaceae form a monophyletic group with Eurotiales and are not treated as a separate order, but should perhaps be placed in a separate suborder in Eurotiales.  Asci are small, evanescent and are produced at different levels within the ascocarp which may vary from a loose weft of hyphae bearing asci to a well organized structure with a definite wall; the ascocarp is often enclosed by a cleistothecium (but osteolate in some); conidia common; widespread and often associated with seeds, soils, and as animal parasites. "The blue and green molds".  Some like Aspergillus and Penicillium are form-taxa.  That is, sexual structures are not known.  The class has 2 orders. ORDER EUROTIALES Eurotium, Eupenicillium. ORDER ONYGENIALES Gymnoascus, Eremascus, Onygena, Ascosphaera, Arthroderma CLASS LECANOROMYCETES This class contains most of the lichenized fungi.  Most produce asci in apothecia with a naked hymenium.  Asci usually thin-walled with a thicker wall at the distal end.  Dehiscence is rostrate.  This class  is used for most of the discolichens, but it is not strongly supported in phylogenetic analyses.  This is a large and diverse class of 5 orders and 500 genera. ORDER AGYRIALES Agyrium, Lithographa, Anamylopsora, Elixia. ORDER GYALECTALES Coenogonium, Gyalecta. ORDER LECANORALES Acarospora, Hymenelia, Anzia, Arctomia, Anthroraphis, Biatorella, Calicium, Calycidium, Catillaria, Cetradonai, Cladonia, Coccocarpia, Collema, Crocynia, Dactylospora, Gypsoplaca, Haematomma, Arctopeltis, Lecanora, Lecidea, Loxospora, Megalaria, Macarea, Miltidea, Micoblastus, Ophioparma, Pachyascus, Pannaria, Parmelia, Physcia, Porpidia, Psora, Ramalinia, Rhizocarpon, Sphaerophorus, Stereocaulon, Lobaria, Nephroma, Peltigera, Placynthium, Fuscidea, Letrouitia, Teloschistes. ORDER LICHINALES Gloeoheppia, Heppia, Lichina, Peltula. ORDER PERTUSARIALES Megaspora, Pertusaria. CLASS LEOTIOMYCETES They have thin-walled asci that are inoperculate.  The mildews are part of this class (as indicated by molecular studies).  Most produce apothecia (the mildews produce reduced cleistothecia). ORDER CYTTARIALES Cyttaria. ORDER ERISIPHALES Biotrophic parasites; ascocarps with 1 to several oval-shaped to club-shaped explosive asci; ascospores unicellular, colorless; chains of conidia arising in basipetal succession from mother cell on superficial colorless mycelium; penetration of host by haustoria confined to epidermal cells. "Powdery mildews." Erysiphe, Microsphaera, Uncinula. ORDER HELIOTIALES (HELOTIALES) Asci inoperculate in distinct hymenium in apothecia of varying form; mostly saprotrophic but with a few plant pathogens. Monilinia, Bulgaria, Dermea, Geoglossum, Hemiphacidium, Hyaloscypha, Leotia, Loramyces, Phacidium, Rustroemia, Sclerotinia, Vibrissea, Ascocorticium. ORDER RHYTISMATALES Ascodichaena, Cryptomyces, Cudonia, Rhytisma. ORDER THELEBOLALES Thelebolus. CLASS ORBILIOMYCETES This class contains dry rot fungi, as well as taxa that feed on other plants.  When in the presence of nematodes, some will elaborate capture mechanisms with which they can significantly reduce the populations of soil nematodes.  Arthrobotrys is the anamorph (asexual form) of small cup fungi, in the genus Orbilia. ORDER ORBILIALES Orbilia, Hyalorbilia CLASS PEZIZOMYCETES Thin-walled asci operculate in distinct hymenium.  Most produce apothecia of varying shapes, large to minute; saprophytic on soils, dung, wood and plant debris.  Others (truffels) produce subterranean (hypogeal)  ascocarps that are modified apothecia in which the acsi have become inoperculate.  This large class has a single order (PEZIZALES) ORDER PEZIZALES Anthracobia, Ascolobus, Ascodesmis, Caloscypha, Carbomyces, Gyromitra, Glaziella, Helvella, Karstenella, Acervus, Pyronema, Sphaerosoma, Peziza, Morchella, Rhizinia, Sarcoscypha, Sarcosoma, Tuber. CLASS SORDARIOMYCETES These have unitunicate asci in perithecia.  The asci open by a pore  This assemblage is supported by SSU rRNA as a natural group.  The 8 orders are distributed among 3 subclasses: Hypocreomycetidae, Xylariomycetidae, and Sordariomycetidae.  This is a large and diverse class of nearly 800 genera. ORDER HALOSPHAERIALES Halosphaeria. ORDER HYPOCREALES Perithecial fungi with unitunicate asci; perithecia usually in a well-developed stroma which is usually light-colored; asci are long and cylindrical, with a thickened apex; 8 ascospores which are filiform, hyaline, septate and break apart easily; mainly parasitic on grasses, insects, spiders and other fungi. Bionectria, Melanospora, Claviceps, Hypocrea,Nectria, Niesslia. ORDER MICROASCALES Chadefaudiella, Microascus. ORDER BOLINIALES Endoxyla, Catabotrys. ORDER DIAPORTHALES Melanoconis, Valsa. ORDER OPHIOSTOMATALES Kathistes, Ophiostoma. ORDER SORDARIALES Perithecia are ostiolate with persistent, unitunicate asci; asci usually embedded in a stroma which may be composed of both host and fungus tissue or fungus tissue only: ascocarps are usually dark and carbonaceous. Annulatascus, Batistia, Cephalotheca, Chaetomium, Chaetosphaeria, Coniochaeta, Helminthosphaeria, Lasiosphaeria, Nitschkia, Neurospora, Sordaria.  ORDER XYLARIALES Amphisphaerella, Clypeosphaerella, Diatrype, Graphostroma, Hyponectria, Xylaria. CLASS LABOULBENIOMYCETES Mainly obligate parasites of insects, especially beetles, with distinctive non-mycelial and determinate growth pattern. With main body of the fungus, the receptacle, attached to host by basal cellular holdfast; single, simple haustorium penetrating host; receptacle varies in size and complexity, in some row of 3 cells, in others large number of cells superimposed in tiers. Lateral filamentous appendages and 1 or more sessile or stalked perithecia arise on receptacle; asci usually 4-spored; ascospores usually colorless, elongated and more or less spindle-shaped, 2-celled with large basal cell, each surrounded by a colorless envelope thickened at the lower end; ascus wall deliquesces prior to spore discharge.  ORDER LABOULBENIALES Laboulbenia.

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Downy Mildew in Greenhouse Cucumber

Author:	Gillian Ferguson - Greenhouse Vegetable IPM Specialist/OMAFRA; Ray Cerkauskas - Plant Pathologist/Agriculture and Agri-Food Canada; Michael Celetti - Plant Pathologist/OMAFRA.
Creation Date:	03 April 2007
Last Reviewed:	03 April 2007

Table of Contents

1. Introduction
2. Symptoms
3. Disease Cycle
4. Management Strategies
5. References

Introduction

Downy mildew is a disease caused by the fungus-like water mold, Pseudoperonospora cubensis, which attacks only cucumbers and related crop species (gourds, pumpkin, squash, melons) . This disease primarily affects the foliage and can cause severe yield losses in a short period of time.

Symptoms

Symptoms are usually seen first on the lower, older leaves. Initial symptoms of downy mildew typically consist of angular, yellow spots on the upper leaf surfaces (Figure 1). On the undersides of such spots, a purplish grey fungal (Figure 2) growth may be visible when there is high relative humidity or moist conditions. As the disease progresses, the yellow spots enlarge, become necrotic or brownish in the centre, with the browning spreading to the margins of the spots (Figure 3). Such spots may merge to form large brown areas on the leaves (Figure 4). This kills leaves if the disease is allowed to develop unchecked. Lack of photosynthetic tissue results in stunting of plants, reduced fruit size, and poor fruit set.

Figure 1: Yellow angular spots defined on upper surface of cucumber leaf

Figure 2: Fungal growth of Pseudoperonospora cubenis on lower surface of cucumber leaf

Figure 3: Typical papery brown spots of downy mildew

Figure 4: Coalescing of many infected spots in downy mildew infection

Disease Cycle

Pseudoperonospora cubensis is an obligate parasite requiring living host tissue to survive and does not live in debris in the soil. The pathogen does not survive over winter in Canada. However, occasionally under optimum environmental conditions, the pathogen may develop thick-walled spores (called oospores) that are resistant to low temperatures and dry conditions, but this is rare and not considered an important source of inoculum. Infections in greenhouses likely originate from another type of spore (called sporangia), that enter the facilities from the outside. Local field infections are usually established by spores that are carried by moist air currents blowing northwards from southern regions during the summer.

Moisture on the leaf surfaces is necessary for infections to occur. When spores land on a wet leaf surface, they can either germinate and infect through the breathing pores (stomates) on leaves, or release many smaller spores (called zoospores) that swim in the film of water on leaves during humid or wet conditions, and infect leaves through stomates. Optimum temperatures for infection range between 16° to 22°C. Infection occurs more rapidly at the warmer temperatures. The period of wetness needed for infection on cucumber leaves are about 12 hours at 10 to 15°C, 6 hours at 15 to 19°C, and 2 hours at 20°C. About 4 to 5 days after infection, new spores are produced and released into the air primarily during the morning period. Spores can quickly spread within the greenhouse via moist air currents, contaminated tools, equipment, fingers, and clothing. Fortunately, the spores become less infective under conditions of high temperatures and low humidity in the greenhouse.

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Management Strategies

Cultural Practices

1. Management of the greenhouse environment - Avoid dew formation by providing adequate heating and ventilation. This is critical to reducing incidence of downy mildew. Special attention must be paid to purging moist air out of the greenhouses during the evenings, and keeping the plant foliage dry, particularly during the night. At normal greenhouse temperatures, relative humidity should generally not be allowed to exceed 70-75%.
2. Sanitation - All sources of infection should be removed and discarded away from the greenhouse so that spores are not blown back into the greenhouse. This could include burial of plant debris. Infected leaves or plants should be carefully removed and placed in a garbage bag before disposal to ensure that spores do not escape and infect nearby commercial cucurbit fields (pumpkin, zucchini, cucumber, squash). All cucurbit plants should be removed from the immediate surroundings of the greenhouse because they may serve as reservoirs for the downy mildew fungus. Surfaces in infested greenhouses should be thoroughly disinfected.
3. Adequate canopy aeration - Ensure that plants are sufficiently spaced and that the canopy is well pruned and thinned to provide for adequate air-circulation.
4. Avoid over watering - Over-watering not only leads to overly soft, more vulnerable plants, but also to guttation or production of droplets of moisture at the margins of leaves early in the morning. This moisture at the leaf margins provides perfect infection sites for the downy mildew pathogen.
5. Avoid overhead watering or humidification - Any cultural practice (e.g. misting) that increases leaf moisture will increase disease development when spores are present in the air.

Chemical Controls

Apply chemical controls in a timely manner - If only a few spots are evident on a few leaves of one plant, then the disease is in the early stages of development. Appropriate chemical control procedures should be implemented immediately because the spores are readily dispersed by air currents. Further disease development may be very rapid under favourable environmental conditions as previously described.

Rotate products - Where possible, it is best to rotate fungicides to reduce chances of development of resistance in the fungus to the material applied. Generally, systemic fungicides should be used in combination with protectant fungicides to reduce the chances of development of resistance in the fungus. As for all crop protection chemicals, growers must always read and follow label recommendations.

Anthracnose of Cucumber

Karen Rane, Plant Disease Diagnostician

These leaf spots on cucumber are the symptoms of anthracnose, caused by the plant pathogenic fungus Colletotrichum orbiculare. The round, tan lesions are 2-10 mm in diameter, and often develop holes or cracks in the center. Lesions can form on leaf blades, petioles, stems and fruit. The spore-bearing structures (acervuli) of the causal fungus are found in the necrotic lesions. They are tan or light orange in color and contain numerous spores in a slimy matrix. A diagnostic feature of this disease is the presence of dark brown hairs, or setae, in the acervuli. The setae are visible with a hand lens or dissecting microscope.

The fungus can infect muskmelon and watermelon in addition to cucumber. The pathogen survives the winter in infected plant residues. The fungus can also be associated with seed. As with most fungal diseases, long periods of leaf wetness favor disease development. Spores are splashed from leaf to leaf, and plant to plant, during irrigation or rain events. Several disease cycles can occur in a single growing season, resulting in defoliation of severely infected plants.

Management of anthracnose in cucurbits involves both cultural and chemical measures. There are several cucumber cultivars that are resistant to anthracnose –this information is usually listed in the descriptions found in seed catalogues. Remove infected plant debris from the vegetable garden to reduce the amount of spores available for causing infection the following season. Purchase new seed each year, since the fungus can overwinter on seed from infected fruit. Avoid overhead irrigation, which promotes long leaf wetness periods and aids in the spread of the fungus from plant to plant. If anthracnose has been a problem in the past, consider using a protectant fungicide to protect uninfected leaves. Remember, fungicides will not cure leaves with lesions. Always follow label directions when using any pesticide.

Click on the small image to view a larger image.

Anthracnose, caused by Colletotrichum orbiculare, on cucumber leaves (Photos by Peggy Sellers)	Close-up of anthracnose leaf lesions (Photos by Peggy Sellers)
Setae (dark hair-like structures) of Colletotrichum orbiculare in an anthracnose leaf lesion (magified 100X) (Photos by Peggy Sellers)

Pathovars

Following ribotypical analysis several pathovars of Pseudomonas syringae were incorporated into other species^[12] (see P. amygdali, 'P. tomato', P. coronafaciens, P. avellanae, 'P. helianthi', P. tremae, P. cannabina, and P. viridiflava). The remaining pathovars are as follows:

Pseudomonas syringae pv. aceris attacks maple Acer species.

Pseudomonas syringae pv. aptata attacks beets Beta vulgaris.

Pseudomonas syringae pv. atrofaciens attacks wheat Triticum aestivum.

Pseudomonas syringae pv. dysoxylis attacks the kohekohe tree Dysoxylum spectabile.

Pseudomonas syringae pv. japonica attacks barley Hordeum vulgare.

Pseudomonas syringae pv. lapsa attacks wheat Triticum aestivum.

Pseudomonas syringae pv. panici attacks Panicum grass species.

Pseudomonas syringae pv. papulans attacks crabapple Malus sylvestris species.

Pseudomonas syringae pv. pisi attacks peas Pisum sativum.

Pseudomonas syringae pv. syringae attacks Syringa and Phaseolus species.

Note that Pseudomonas savastanoi was once considered a pathovar or sub-species of P. syringae, and in many places continues to be referred to as Pseudomonas syringae pv. savastanoi, although as a result of DNA-relatedness studies it has been instated as a new species^[13]. It itself has three host-specific pathovars, fraxini which causes ash canker, nerii which attacks oleander and oleae which causes olive knot.

Diseases of Alsike clover

Mosaic

Causal organism: Bean yellow mosaic virus (BYMV), Cucumber mosaic virus (CMV)

Most individuals are infected at the second or third year from seeding in the warm regions. The symptoms begin to appear in spring and are various such as yellow mosaic, geen mosaic, chlorotic spots, rugose, etc. according to the varieties of plants and environmental conditions. The virus is transmitted by sucking of the various aphids. symptom

Witches' broom

Cause of a disease: Phytoplasma (PLO)

Mycoplasm-like organism disease causing shrinkage of the plant. A lot of small leaves at first appear from the center part of the plant. These leaves turn to reddish brown or fade. The plant gradually begins to rosette and wither. The causal organism is transmitted by some kinds of leafhoppers. symptom

Pepper spot

Causal organism: Leptosphaerulina trifolii (Rostrup) Petrak, Ascomycotina

Spot-causing fungal disease occurring in the cool regions. The blackish brown, small lesions of about 1 mm in diameter are produced a lot and the whole leaf looks like sprinkled with black pepper. The surroundings of the lesion turn to yellow gradually and the leaf withers finally. It occurs severely in the cool condition with frequent rain. Black small grains (perithecia) are formed on the old lesions. The species of the causal organism is different from pepper spot fungus of alfalfa. symptom

Rust

Causal organism: Uromyces hybridi Davis, Basidiomycotina

Rust disease occurring in Hokkaido, Tohoku Dist. and etc., the northern part of Japan. The causal organism can infect subterranean clover, but infect neither red clover nor white clover. symptom causal organism (urediniospores)

Sclerotinia crown rot and root rot

Causal organism: Sclerotinia trifoliorum Eriksson, Ascomycotina

Important fungal disease which causes plant death occurring in cool and wet regions. The small spots appears at first and then the leaf and stalk turn to yellow and wither. The disease progresses gradually under the snowfall. The stem, leaf and root rot to ash white according to increase of the temperature after snow-melting in the spring of next year. White and fluffy hyphae are produced on the surface of the withering plant and large black sclerotia of irregular types and about 8-10mm in size are produced before long. They germinate in autumn and produce light brown stroma of 3-8 mm in diameter. The ascospores spread from the stroma and the infection happens again. The host range of the causal organism is wide including alfalfa and vetches. symptom

Sooty blotch

Causal organism: Cymadothea trifolii (Persoon) Wolf, Ascomycotina

Leaf blight causing fungal disease occurring in the cool region. Black sooty molds are produced in the back side of the leaf. These are like black, irregular shaped, small lesions bristly in the leaf. The infected leaf keeps green at first but gradually turns to yellow. It occurs in other clovers. symptom

Summer black stem and leaf spot

Causal organism: Cercospora zebrina Passerini, Imperfect fungi

Spot-causing fungal disease mainly occurring in the leaf and stalk. The lesions are grayish brown devided by leaf veins, fuse mutually and cause leaf blight. They become purple brown stripes when occurring in the stalk and the damage enlarges. The causal organism can infect other kinds of clovers, but the pathogenicity is considered to be differentiated. symptom

 

Cucumber, Squash, Melon & Other Cucurbit Diseases

HGIC 2206

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Many diseases of cucurbits can be prevented or minimized in the home vegetable garden by using the following simple cultural controls:

• Plant certified disease-free seeds.
• Select varieties recommended for South Carolina, especially those with some degree of disease resistance (Table 1).
• Keep the garden and surrounding area free of weeds that harbor insects, which can spread viruses and bacterial wilt.
• Remove plant debris from the garden after harvest, since many diseases survive on plant debris from year to year.

More information about growing cucurbit plants is available in the fact sheets: HGIC 1304, Cantaloupe and Honeydew Melon; HGIC 1309, Cucumber; HGIC 1321, Summer Squash; and HGIC 1325, Watermelon. See also Fact Sheet CE-6 Cucurbit Diseases, an Aid to identification.

Bacterial Wilt

The main symptom of this disease is severe wilting of the vines, followed by rapid death of the plant. The disease is caused by the bacterium Erwinia tracheiphila, and at first may only affect a few vines on a plant. However, as the disease progresses, more leaves wilt, and eventually the entire vine is affected. Bacterial wilt is most severe on cucumber and cantaloupe and less severe on squash, pumpkin and watermelon.

Prevention and Treatment: There is no chemical control for bacterial wilt once plants become infected. The bacteria are carried from plant to plant by striped or spotted cucumber beetles. The beetles spread the wilt bacterium by feeding on infected vines and then feeding on healthy plants.

Bacterial wilt can be reduced in your garden if the beetles are kept under control at the first sign of activity. Insecticides that control striped and spotted cucumber beetles in the home vegetable garden include carbaryl and esfenvalerate (see HGIC 2207, Cucumber, Squash, Melon and Other Cucurbit Insects). Bees pollinate many of these vegetables, so spray all insecticides in the late afternoon. Apply all chemicals according to directions on the label.

Powdery Mildew

Powdery mildew causes a white powdery growth on the upper surfaces of leaves and on the stems of infected plants. Infected areas are often stunted and distorted and may drop prematurely from the plant. Fruits are usually not directly affected, but their size and growth may be stunted. Powdery mildew is caused by the fungi Erysiphe cichoracearum and Sphaerotheca fuliginea. Infection can occur when temperatures are between 50 and 90 °F, during dry weather with high relative humidity. The disease can be a particular problem on late-planted squash.

Powdery mildew on watermelon leaves.
David B. Langston, University of Georgia, www.insectimages.org
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Prevention and Treatment: Powdery mildew-resistant varieties (Table 1) are available for most cucurbits, thus with proper planning, chemical control should not be necessary. Preventative fungicide treatments are available (Table 2) if disease becomes severe enough to warrant chemical control.

Downy Mildew

Downy mildew is one of the most important leaf diseases of cucurbits. Typically, symptoms begin as small yellow areas on the upper leaf surface. As lesions expand, they may become brown with irregular margins. Affected areas may grow together, and the entire leaf may wither and die. Infected plants also develop a gray mold on the lower leaf surface. The fruit is not affected, but in the case of cantaloupes, it will be less sweet. This disease is caused by the fungus Pseudoperonospora cubensis and is favored by moist conditions.

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Downy Mildew on top (left) and bottom (right) of cantaloupe leaf.
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Symptoms on watermelon are different than symptoms on other curcurbits. Leaf spots on watermelon are dark brown and irregular in shape, ranging from oval to angular to retangular. Slight yellowing may be seen around the edges of the spots or in small patches in other parts of the leaf. Leaves infected with downy mildew curl inward as the leaf dies. As on other crops, spores usually are found on the bottom of the leaf, although spores may be formed on top of the leaf in severe infections or foggy weather.

Prevention and Treatment: Use varieties that are resistant to this disease (Table 1). Fungicides are available for the home vegetable garden if disease becomes severe enough to warrant chemical control (Table 2).

Gummy Stem Blight

Gummy stem blight is a stem and leaf disease of cucumber, cantaloupe, pumpkin and watermelon caused by the fungus Didymella bryoniae. This fungus also causes a fruit rot called black rot.

Symptoms include leaves with brown or tan spots of various sizes that may eventually cover the entire leaf. The stems may split to form open wounds called cankers. A brown, gummy substance may be evident on the surface of these open wounds. Infected vines usually wilt after the middle of the season. Infected stems die one after another, and seedlings and entire individual vines may be killed. Affected fruit have irregular circular spots, and a wet rot occurs where the fungus penetrates the rind.

Leaf spots caused by gummy stem blight on watermelon leaf.
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
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To distinguish gummy stem blight on watermelon from downy mildew, look at the size, shape, and position of leaf spots. Leaf spots of gummy stem blight are larger than individual spots of downy mildew. Some leaf spots of gummy stem blight have a ringed or target look. Gummy stem blight also can be found on the petioles (leaf stems) and the mid vein of leaves as a water-soaked or reddish-brown wet spot.

Prevention and Treatment: There are no varieties that are resistant to this disease. This disease may be seed-borne, so purchase seed from a reputable source. Remove and destroy all plant debris in the garden, since the disease can survive on plant debris from year to year. Rotate crops with nonhost plants, such as corn, for two or more years as an effective way of reducing the incidence of this disease. Avoid wetting the leaves when watering. If disease is severe enough to warrant chemical control, preventative fungicides are available (Table 2).

Symptoms of anthracnose on watermelon.
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
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Anthracnose

Anthracnose is caused by the fungus Colletotrichum obiculare, and requires rainy, cool weather for several days for the disease to develop. The first symptoms of anthracnose are spots on the leaves that begin as yellowish or water-soaked areas. Spots enlarge and turn brown to black. The diseased tissue dries and the center of the spots fall out giving a “shot-hole” appearance. Infected fruits have black, circular, sunken cankers of different sizes.

Prevention and Treatment: Remove and destroy old cucurbit vines and residues, since this is where the fungus survives the winter. Rotation of crops in the garden is also important to minimize disease. Purchase seeds from a reputable source, since the disease can be seed-borne. If the disease is severe enough to warrant the use of fungicides, several are available for home garden use (Table 2).

Alternaria Leaf Spot

This disease is caused by the fungus Alternaria cucumerina and causes small, circular, tan spots to appear on the leaves, which later enlarge to 1½ inches or more in diameter. Definite concentric rings and margins appear that give the area a “bull’s eye” appearance. Leaf drop can be severe. Bright sunshine, frequent dews or rain, and temperatures between 60 and 90 °F favor disease development.

Alternaria leaf spot on cantaloupe.
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
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Prevention and Treatment: Remove and destroy all infected plant residues at the end of the gardening season, since the fungus survives thewinter on plant residue. The disease is easily spread by tools, wind, splashing water or insects. Rotation of crops and seed treatment will also help. When this disease occurs consistently in the garden, a preventative fungicide program can be followed (Table 2).

Fusarium Wilt

This disease is caused by the fungus, Fusarium oxysporum forma specialis melonis. It attacks the roots of the plant and moves into the stems. Older, established plants that are infected become stunted, wilt and eventually die. Wilt symptoms develop in one or more laterals, usually starting at the vine tips. A white mold may develop on dead vines. Affected seedlings will damp-off (rot at the soil line), wilt and die. On runners near the crown of the plant, brown streaks may be evident. Roots will have a honey brown discoloration inside.

Prevention and Treatment: This fungus can survive in the soil for many years. Planting resistant varieties (Table 1) is critical in preventing this disease. Careful water management is also important in minimizing root stress. There are no chemical treatments available for control.

Viruses

There are several common viruses that can affect cucurbits, including cucumber mosaic virus (CMV) and watermelon mosaic virus (WMV). Infected plants may be stunted or have leaves that are mottled, crinkled, or a light green color. Fruits may be irregular in shape, mottled or warty. Various insects transmit these viruses.

Cucumber mosaic virus (CMV) on squash.
Division of Plant Industry Archive,
Florida Department of Agriculture and Consumer Services, www.insectimages.org
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Prevention and Treatment: There are no chemicals available to kill viruses. Chemical control of the insects that spread the viruses may minimize the disease. This control method is difficult, because infection occurs immediately after an insect feeds, and insects migrate freely between plants. A good control strategy is to maintain healthy and vigorous plants, plant recommended varieties and monitor your garden for any unusual symptoms as they occur. Keep the area clear of weeds that can harbor insects. Choosing separate areas for early and late plantings may help to reduce virus severity in the late plantings.

Blossom-End Rot

Blossom-end rot appears as a dark-colored dry rot on the end of the fruit where the flower was. The problem is caused by a lack of calcium in the developing fruit. It is an indication that calcium is lacking in the soil or that the plant does not have the ability to take up enough calcium. When growth is rapid, not enough calcium may be delivered to the blossom end of the developing fruit.

Blossom end rot on watermelon.
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
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Prevention and Treatment: Help prevent blossom-end rot by having your soil tested before planting through your local county Extension office, and lime according to recommendations. Always maintain an adequate supply of moisture, especially during fruit growth. Mulch plants to prevent rapid drying of the soil and water plants during extended dry periods. Use gypsum (1-2 pounds per 100 square feet) as a supplement to liming on calcium deficient soil. Lime and/or gypsum should be applied before planting. Do not overfertilize plants with excessive nitrogen or potassium. Excess amounts of these nutrients reduce the uptake of calcium in the plant. When plants are dark green, extra fertilizer should not be applied.

Treatment of affected plants includes applying a calcium solution to prevent additional fruits from being damaged. Spray or drench the foliage with a calcium nitrate or calcium chloride (three tablespoons per gallon of water) solution. Premixed solutions are also available. Follow the instructions on the label. Removing fruit with symptoms is recommended.

RIPing in an asexual fungus

Posted on March 23rd, 2008 by Jason Stajich · 2 Comments

Powdery Mildew on Vegetables Published 11/01 In this Guideline:
Identification and damage Life cycle Management About Pest Notes Publication Glossary

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Powdery mildew is a common disease on many types of plants. There are many different species of powdery mildew fungi (e.g., Erysiphe spp., Sphaerotheca spp.) and each species only attacks specific plants. A wide variety of vegetable crops are affected by powdery mildews, including artichoke, beans, beets, carrot, cucumber, eggplant, lettuce, melons, parsnips, peas, peppers, pumpkins, radicchio, radishes, squash, tomatillo, tomatoes, and turnips (Table 1). Powdery mildews generally do not require moist conditions to establish and grow, and normally do well under warm conditions; thus they are more prevalent than many other leaf-infecting diseases under California's dry summer conditions.

Table 1. Host Plants and Control Measures for Powdery Mildew Species.

Hosts	Fungus species	Controls
cucumbers, endive, lettuce, melons, potato, pumpkin, squash	Erysiphe cichoracearum	resistant varieties of lettuce, cucumber; water sprays; fungicides if necessary on squash and pumpkin
broccoli, Brussels sprouts, cauliflower, and other cole crops; radicchio, radishes, turnips	Erysiphe cruciferarum	not usually required
tomatoes	Erysiphe lycopersici	fungicides if necessary
peas	Erysiphe pisi	resistant varieties; sprinkler irrigation
carrots, parsley, parsnips	Erysiphe heraclei	tolerant varieties
beets	Erysiphe polygoni	tolerant varieties
artichoke, eggplant, peppers, tomatillo, tomatoes	Leveillula taurica	rarely required; fungicides if necessary
beans, black-eyed peas, cucurbits, okra	Sphaerotheca fuliginea	resistant varieties for some; fungicides if necessary

IDENTIFICATION AND DAMAGE
Powdery mildew first appears as white, powdery spots that may form on both surfaces of leaves, on shoots, and sometimes on flowers and fruit. These spots gradually spread over a large area of the leaves and stems. An exception is one of the powdery mildews that affects artichokes, onions, peppers, and tomatoes: it produces yellow patches on leaves but little powdery growth.

Leaves infected with powdery mildew may gradually turn completely yellow, die, and fall off, which may expose fruit to sunburn. On some plants, powdery mildew may cause the leaves to twist, buckle, or otherwise distort. Powdery mildew fungal growth does not usually grow on vegetable fruits, although pea pods may get brownish spots. Severely infected plants may have reduced yields, shortened production times, and fruit that has little flavor.

LIFE CYCLE

All powdery mildew fungi require living plant tissue to grow. Year-round availability of crop or weed hosts is important for the survival of some powdery mildew fungi. Special resting spores are produced, allowing overwinter survival of the species that causes the disease in cucurbits, lettuce, peas, and certain other crops.

Most powdery mildew fungi grow as thin layers of mycelium (fungal tissue) on the surface of the affected plant part. Spores, which are the primary means of dispersal, make up the bulk of the white, powdery growth visible on the plant's surface and are produced in chains that can be seen with a hand lens; in contrast, spores of downy mildew grow on branched stalks that look like tiny trees.

Powdery mildew spores are carried by wind to new hosts. Although humidity requirements for germination vary, all powdery mildew species can germinate and infect in the absence of free water. In fact, spores of some powdery mildew fungi are killed and germination is inhibited by water on plant surfaces for extended periods. Moderate temperatures (60° to 80°F) and shady conditions generally are the most favorable for powdery mildew development. Spores and fungal growth are sensitive to extreme heat (above 90°F) and direct sunlight.

MANAGEMENT

The best method of control is prevention. Planting resistant vegetable varieties when available, or avoiding the most susceptible varieties, planting in the full sun, and following good cultural practices will adequately control powdery mildew in many cases (Table 1). However, very susceptible vegetables such as cucurbits (cucumber, melons, squash, and pumpkins) may require fungicide treatment. Several least-toxic fungicides are available but must be applied no later than the first sign of disease.

Resistant Varieties

In some cases, varieties resistant to powdery mildew may be available. If available, plant resistant varieties of cantaloupe, cole crops, cucumber, melons, peas, pumpkins, and squash. If you plant more susceptible varieties, you may need to take control measures.

Cultural Practices

Plant in sunny areas as much as possible, provide good air circulation, and avoid applying excess fertilizer. A good alternative is to use a slow-release fertilizer. Overhead sprinkling may help reduce powdery mildew because spores are washed off the plant. However, overhead sprinklers are not usually recommended as a control method in vegetables because their use may contribute to other pest problems.

Fungicide Application

In some situations, especially in the production of susceptible cucurbits, fungicides may be needed. Fungicides function as protectants, eradicants, or both. A protectant fungicide prevents new infections from occurring whereas an eradicant can kill an existing infection. Apply protectant fungicides to highly susceptible plants before the disease appears. Use eradicants at the earliest signs of the disease. Once mildew growth is extensive, control with any fungicide becomes more difficult.

Fungicides. Several least-toxic fungicides are available, including horticultural oils, neem oil, jojoba oil, sulfur, potassium bicarbonate, bicarbonate of soda (baking soda), and the biological fungicides AQ10 and Serenade. With the exception of the oils, these materials are primarily preventive, although potassium bicarbonate has some eradicant activity. Oils work best as eradicants but also have some protectant activity.

Oils. To eradicate mild to moderate powdery mildew infections, use a horticultural oil such as JMS Stylet Oil, Saf-T-Side Spray Oil, Sunspray Ultra-Fine Spray Oil or one of the plant-based oils such as neem oil (e.g., Powdery Mildew Killer) or jojoba oil (e.g., E-rase). Be careful, however, to never apply an oil spray within 2 weeks of a sulfur spray or plants may be injured. Also, oils should never be applied when temperatures are above 90°F or to drought-stressed plants. Some plants may be more sensitive than others, however, and the interval required between sulfur and oil sprays may be even longer; always consult the fungicide label for any special precautions. Of the horticultural oils, JMS Stylet Oil is the most highly refined and therefore the least likely to damage plants, but it may be more difficult to obtain than the others.

Sulfur. Sulfur products have been used to manage powdery mildew for centuries but are only effective when applied before disease symptoms appear. The best sulfur products to use for powdery mildew control in gardens are wettable sulfurs that are specially formulated with surfactants similar to those in dishwashing detergent (e.g., Safer Garden Fungicide). However, sulfur can be damaging to some squash and melon varieties. To avoid injuring any plant, do not apply sulfur when air temperature is near or over 90°F and do not apply it within 2 weeks of an oil spray. Other sulfur products, such as liquid lime sulfur or sulfur dust, are much more difficult to use, irritating to skin and eyes, and limited in terms of the plants they can safely be used on. Copper is also available to control powdery mildew but is not very effective.

Bicarbonates. Also available is a fungicide product containing potassium bicarbonate (e.g., Kaligreen) and a fungicide that can be made at home by combining 2-1/2 tablespoons of horticultural oil (Sunspray Ultra-Fine, Saf-T-Side, etc.) in a gallon of water and adding 4 teaspoons baking soda. This solution is sprayed on plants to prevent powdery mildew infections. Sprays of both potassium bicarbonate and baking soda can injure the plant, so use these materials with caution. Also, baking soda sprays can have deleterious effects on soil structure and should be used sparingly.

Biological Fungicides. Biological fungicides (AQ10 and Serenade) are commercially available beneficial microorganisms formulated into a product that, when sprayed on the plant, destroys fungal pathogens. AQ10 is a parasitic fungus, Ampelomyces quisqualis, that actively attacks and destroys the powdery mildew fungus. The active ingredient in Serenade is a bacterium, Bacillus subtilis, that helps prevent the powdery mildew from infecting the plant. While both products function to kill the powdery mildew organism and are nontoxic to people, pets, and beneficial insects, they have not proven to be as effective as the oils or sulfur in controlling this disease.

How to Use. Apply protectant fungicides to susceptible plants before or in the earliest stages of disease development. The protectant fungicides are only effective on contact, so applications must provide thorough coverage of all susceptible plant parts. As plants grow and produce new tissue, additional applications may be necessary at 7- to 10-day intervals as long as conditions are conducive to disease growth.

If mild to moderate powdery mildew symptoms are present, the horticultural oils and plant-based oils such as neem oil and jojoba oil can be used.

WARNING ON THE USE OF CHEMICALS