The Septoria Diseases of Wheat - IBSA

The Septoria Diseases of WheatConcepts and methods of disease managementCentro Internacional de Mejoramiento de Maíz y TrigoInternational Maize and Whea t Improvement Center

The International Maize and Wheat Improvement Center (C1MMYT) is an internationallyfunded, nonprofit scientific research and training organization. Headquartered inMexico, the Center is engaged in a worldwide research program for maize, wheat, andtriticale, with emphasis on food production in developing countries. It is one of 13nonprofit international agricultural research and training centers supported by theConsultative Group on International Agricultural Research (CGIAR), which is sponsoredby the Food and Agriculture Organization (FAO) of the Un ited Nations, theInternation al Bank for Reconstruction and Development (World Bank), and the UnitedNations Development Programme (UNDP) . The CGIAR consists of 40 donor countries,international and regional organizations, and private foundations.C1MMYT receives support through the CGIAR from a number of sources, including theinternational aid agencies of Australia, Austria, Brazil, Canada, China, Denmark,Federal Republic of Germany, France, India, Ireland, Italy, Japan, Mexico, theNetherlands, Norway, the Philippines, Saudi Arabia, Spain, Switzerland , the UnitedKingdom and the USA, and from the European Economic Commission, FordFoundation, Inter-American Development Bank, Intemational Development ResearchCentre, OPEC Fund for International Development, Rockefeller Foundation, UNDP, andWorld Bank. Responsibility for this publication rests solely with C1MMYT.Correct Citation: Eyal, Z., A.L. Scharen, J.M . Prescott, and M. van Ginkel. 1987. TheSeptoria Diseases of Wheat: Concepts and methods of disease management. Mexico,D.F.: CIMMYT.ISBN 968-6127-06-2

The Septoria Diseases of WheatConcepts and methods of disease managementZ. EyalTel-Aviv UniversityA.L. ScharenAgricultural Research Service,USDAMontana State UniversityJ.M. PrescottM. van GinkelInternational Maize an d WheatImprovement Center (CIMMVnEditing: Gene P. HettelDesign and layout: Miguel Mellado E.,Jose Manuel Fouilloux, Rafael De laColina, and Bertha Regalado M .Typesetting: Silvia Bistrain R. andMaricela A. de Ramos .Abstract(Correct citation: Eyal, Z., A.L. Scharen,J.M. Prescott, and M. van Ginkel. 1987.The Septaria Diseases of Wheat: Conceptsand methods of disease management.Mexico, D.F.: CIMMYT. 52 pp., 17figures, 20 color plates)In the last 25 years, attention to theseptaria diseases of wheat has intensified.The two pathogens of the septaria groupthat have the greatest impact on globalwheat production are Septaria tritici andSeptaria nodarum. Annual yield lossesworldwide due to both diseases areestimated at about 9 million metric tons.Breeding for resistance has obtained apreeminent place in a number of researchand crop improvement programsworldwide.In this introduction, emphasis is placedon summarizing the more pertinentscientific reports for managing the twomajor septoria pathogens. Research dataare interpreted into concepts andprocedures. Topics include the biology ofthe fungi, infection process, collectionand handling of infected material,isolation and maintenance of the fungi,inoculum product ion, artificialinoculation, disease assessment,epidemiology, pathogen specialization ,breeding for resistance, and means ofcultural and chemical control.Each treatment of a topic or group ofalternative methods is followed by therecommendation of one or more preferredtechniques or approaches. Thisinformation is intended for wheatscientists in developed and developingcountries who are unfamiliar with thesediseases.iii

Contentsvi Preface1 Introduction1 Distribut ion1 Economic Importance to Wheat Growers2 Nomenclature3 Identification4 Processes Associated with Infection4 Septoria tritici4 Introduction4 Biology5 Environmental conditions required for germination, penetration, and infection5 Symptom expression and disease development6 Septoria nodorum6 Introduction6 Biology7 Environmental conditions required for germination, penetration, and infection7 Symptom expression and disease development8 Infection Process Com parison of Septoria tritici and Septoria nodorum10 Methodology10 Collection and Handling of Infected Plant Material10 Isolation of the Fungi10 Isolation of Septaria triticiDirect methodIndirect method12 Isolation of Septaria nodorutnDirect methodFrom symptomless leavesFrom seeds12 Single-spore method13 Summary and recommendations13 Maintenance of Septaria Cultures13 Short-term maintenancePycnidial formConidial formSeptaria triticiSeptaria nodotumSummary and recommendations14 Long-term maintenanceSoilLyophilizationCold storageSummary and recommendations15 Production of Inoculum15 Solid media15 Liquid media16 Kernel media16 Summary and recommendations

16 Inoculation Procedures16 Greenhouse inoculationRevolving inoculation techniqueIntact leaf techniqueDetached leaf techniqueAdult plant techniqueSummary and recommendation17 Field inoculationInfested crop debrisSpore suspensionSummary and recommendations18 Disease Assessment24 Saari-Prescott 0-9 scale, double digit 00-99 scale25 Bronnimann's Septaria nodarum leaf and head evaluation scale25 Rosielle 's Septaria tritici scale26 Eyal's septaria tritici disease evaluation methodsSeptoria progress coefficientDiagrammatic scaleDisease severity classesPCD/SPC27 James' septoria foliar key27 Gough 's pycnidiospore production method28 Summary and recommendations28 Summary of recommendations29 Epidemiology and Cult ural Practices29 Septoria tritici30 Septoria nodorum31 Pathogen Specialization31 Septoria tritici31 Septoria nodorum32 Summary33 Breeding for Disease Resistance34 Septoria tritici34 Septoria nodorum35 Summary36 Chemical Control36 Foliar Applications36 Protectants36 SystemicsMethyl benzimidazole carbamate (M BC) groupErgosterol-biosynthesis inhibitors37 Seed Treatments38 Summary40 Literature Cited45 GlossaryColor Plates, pp. 19-22

PrefaceThe econo mic impact of the septa riadiseases of cereals on wheat productionin certain parts of the world has caughtthe attention of increasing numbe rs ofgrowe rs, scientists, pol icy makers, andadmi nistrators. This inten sified interest haslead to more funds allocated to plantpatho logica l research and cultivardevelopment programs. Thi s in turn haslead to a better understanding of thedi seases and the release of a number ofhigh-yielding, disease-resistant cultivars forthe septaria-prone areas. Though muchscientific literature has accumulated, nopubl ication , to date, has gathered togetherthe basic information necessary for apractical approach to understanding thediseases, the methodology for screeningresistance, and other control measures.In this publication, we have reviewed thelite rature and presented it in a formatconcentrating on the bio logy of thepathogens, processes associated wi thinfection, isolation and mainten ance ofthe fungi, inocu lum production,inoculation, disease assessment,epide miology, breeding for resistance andmeans of cultural and chemica l contro l.We have not intend ed to present anintensive, detail ed overall review of theliterature, but to bring attentio n to themore relevant scientific reports pertainingto the various top ics covered. Theinforma tion elaborates on concepts andmethods employed in septoria researchand their implementation .The practical information is intended forw heat scientists who are unfami liar withthese diseases in both developed anddeveloping countries.

Introdu ctionSeptaria is the name commonly appliedto more than 1,000 species of fungi,most of which are plant parasites.Approximately 100 species are parasiticon cereals and grasses. Many areeconomically important on crops otherthan cereals (123).DistributionThere are two major septaria diseases thatcause problems in wheat in many parts ofthe world. These are septaria tritici blotch(Plate 1, p.19) (syn. septaria leaf blotch,speckled leaf blotch of wheat) incited bythe fungus Septaria tritici (sexual state:Mycosphaerella graminicala) and septarianodorum blotch (syn. septaria glumeblotch of wheat) caused by the fungusSeptoria nodorum (sexual state:Leptosphaeria nadorum). The worlddistribution of these diseases is shown inFigure 1.Economic Importance toWheat GrowersBoth diseases cause serious yield losses(35, 54, 97, 111, 137, 139). Yield lossesattributed to heavy incidences of septariatritici blotch and septoria nodorum blotchof wheat have been reported to rangefrom 31% (4) to 53% (35). In 1982,worldwide loss was estimated to be 9million metri c tons w ith a value of overU.S. $1 billion (123). The average yearlylosses in yield in the United States due toseptaria tritici blotch and septarianodorum blotch were estimated at 1% in1965 (2). The other few available nationalloss estimates range between 1 and 7%annually (35). Both diseases are capableof reducing yields by as much as 30-40%,values usually obtained from numerousfungicide control comparisons (18). Undersevere epidemics, the kernels ofvulne rable wheat cultivars are shrivelledand are not fit for milling (Figure 2).Sn*.aJ0!b'~

Table 1. Classification and nomenclature of the sexual states of S. trifid and S.nodorumOrderFamilyGenusSpeciesDiseaseEUMYCOPHYTA (True Fungi)Class: Ascomycetae (Ascomycetes)Subclass: Loculoascomycetes (asci bitunicate,perithecioid pseudothecium)S. triticiDothidealesDothideaceaeMycosphaerellaM . graminicola[FOckel] SchroeterSeptoria tritici blotchS. nodorumPleosporalesPleosporaceaeLeptosphaeriaL. nodorum MOllerSeptaria nodorum blotchNomenclatureWithin the Fungi Imperfecti, fungi of thegenus Septaria are classified among theorder Sphaeropsidales, characterized bythe production of conidia, termedpycnidiospores, which are produced invariously shaped, semiclosed fruitingbodies known as pycnidia. The sexualstates of S. tritici and S. nodorum areassociated with the class Ascomycetes(Table 1).During the 2nd International SeptoriaWorkshop (123), a motion was passedstating that "the taxonomic names of thefungi involved in the septoria diseasecomplex would be based on their sexualstate, namely, Leptosphaeria nodorum E.MOiler, Leptosphaeria avenaria Weber f.sp. triticea T. Johnson, andMycosphaere/la graminicola (fuckel)Schroeter, and the common names of thediseases would be septaria nodorumblotch of wheat, septoria avenae blotch ofwheat, and septaria tritici blotch of wheat,Table 2. Descriptive comparison of the septoria wheat pathogensSexual state Pseudothecium (p'> Ascospore (p'> Number of LesioncellsMycosphaere/la 70-100 10-15 x 2-3 2 Irregular tograminicolarectangular, elongatedbetween veinsLeptosphaeria 120-200 23-32 x 4-6 4 Lens shaped,nodorumwith chlorotic borderAsexual state Pycnidium (p'> Pycnidiospore (p'> Number of LesionseptaSeptorie 60-200 35-98 x 1-3 3-5 Irregular totriticirectangular, elongatedbetween veinsSeptoria 160-210 15-32 x 2-4 0-3 Lens shaped,nodorumwith chlorotic border

espectively. The lower case's' will beused for septoria, septoria nodorumblotch, etc. which are not written initalics."Leptosphaeria avenaria, which is notdiscussed in this manual, is the mostrecent Septoria species to becharacterized on wheat and is probably oflesser importance than those previouslymentioned. The intermediate size of thepycnidiospores often leads to confusionwith S. nodorum.in differentiation and identification. In theUnited Kingdom, northern U.S.A., Brazil,Uruguay, western Australia, and otherareas, septoria tritici blotch and septorianodorum blotch are often found together,many times with fruiting structures ofboth organisms on the same leaf.Moreover, other fungi that form similarfruiting structures, spores, and othersymptoms are often present to complicateidentification (Figure 3). Thus, fieldidentification without confirmation in thelaboratory is often difficult if notimpossible; however, with the preparationof a few slides and microscopicexamination at lOOx or 400x, identities ofthe pathogens can usually be confirmed.Although the sexual state has beenreported in several countries and willmost likely be found elsewhere, it is theasexual state that causes most diseasesymptoms and associated yield losses.Therefore, throughout this text thepathogens will generally be designated bytheir asexual state.~~ ,~~~~~ \i ~~~~~~ ~~~~}}~~ S. avenae f.sp. avenae oatThe descriptive comparisons of S. triticiand S. nodorum are presented in Table 2(123).IdentificationSymptoms vary according to cultivar,cultural practices, and geographic location(44). Under Mediterranean conditions,where spring wheats are grown during thecool and rainy winter months (NovemberMay) of the year, S. tritici is mostimportant. It is important to note that thesexual state has not been reported as yetin the literature from this region. Usuallymany pycnidia are produced makingidentification relatively simple. In thesoutheastern United States and northernEurope, S. nodorum is most common,usually producing an abundance ofpycnidia allowing identification with ease;however, under certain environmentalconditions, pycnidia of S. nodorum maynot occur readily within the necroticlesions. In many other wheat-growingareas, both S. tritici and S. nodorumoccur, thus introducing some difficultiesMycosphaerella graminicolaI[' ~f~ ~~OO~ ,B:~ ~M~~~ ~~~ s avenae f.sp triticea wh••leptosphaeria nodorumS. nodorum barleyCalonectria nivalisD~~~~L microscopica188(/Ascochyta tritidDidymella exitialis888BB~8gBeA. sorghi8888eS. avenae f.sp, triticea barley[" ,m~~! ~Hendersonia sp.88898A. hordeiFigure 3. Fungi that produce spores similar to those of Septaria spp. on cereals.

Processes Associatedwith Infection4 _ ~-;:: ~~.--Septoria triticiIntroductionThe asexual state of M. graminicola,namely S. tritici Rob. ex Desm., wasfound on wheat and described byDesmazieres in 1842 (133). The sexualform M. graminicola (Hickel) Schroeterwas described by Sanderson in 1972 inNew Zealand (113). The sexual state hasalso been identified in Australia, Brazil,the Netherlands, the United Kingdom,and the U.S.A. Pycnidia bearingpycnidiospores of the asexual state werefound on plant specimens of wild emmer(Triticum turgidum dicoccoides) collectedin Israel in 1906. Only occasional yieldlosses of economic impact were reportedprior to the 1960s.The increase in the economic importanceof septaria tritici blotch was largely due tothe widespread and rapid replacement oflocal wheat cultivars with early-maturing,semidwarf cultivars that were susceptibleto the pathogen. Cultivars with adequateresistance are now replacing the originalintroductions. Changes in culturalpractices have also significantlycontributed to the increase in diseaseincidence. Severe outbreaks of septoriatritici blotch have occurred in high-rainfallareas such as South America. Epidemicsalso occur in semiarid countries along theMediterranean Coast and in Australia.\Perilllid oid pii:u dotllecium).#. tlFigure 4. Pseudothecium, asci, and ascospores of Mycosphaerella graminicola.BiologyA pseudothecium, asci, and ascospores ofM. graminicola are presented in Figure 4and Plate 2. A pycnidium andpycnidiospores of the asexual state, S.tritici, are presented in Figure 5.Ascospores of M. graminicola have twocells which are unequal in size. Septoriatritici farms slender, elongatedpycnidiospores enclosed within aFigure 5. Pycnidium and pycnidiospores of Septoria tritici.

pycnidium. The pycnidia are embeddedin the epidermal and mesophyl tissue onboth sides of the leaf with an opening(ostiole) on top.The pycnidiospores of 5. tritici can bepresent in two forms within thepycnidium: macropycnidiospores (35-98 x1-3 p,m) with 3-5 septa (Plate 3) ormicropycnidiospores (8-10.5 x 0.8-1 p,m)without septa (114,137,138). Both sporeforms are equally able to infect wheat(137).Environmental conditions required forgermination, penetration, and infectionPycnidiospores germinate on a suitablesubstrate, following release from thepycnidium, when the plants are wet.Germination occurs either by elongationof the apical cell or by budding. In thelaboratory, spores begin to germinatewithin 12 hours and leaf penetrationoccurs after 24 hours. The fungus maypenetrate the .leaf through the stomata ordirectly through the cell walls of theepidermis.and pycnidia development by lengthen ingthe time required for each. Symptomsgenerally appear after 14-21 days. Thetime from infection to production ofpycnidia depends, however, onenvironmental conditions (moisture,temperature, and light), the cultivar, andthe septaria isolate. It appears that there isa compensation effect between moistureand temperature in susceptible wheats.Where the moist period is short, anincrease of temperature up to 25°C maystill result in severe levels of disease.With long moist periods and lowtemperatures, high disease levels areagain observed (57). Spore germinationand mycelial growth of 5. tritici areoptimum at 8-12,000 lux (8). Pycnid ialformation is most rapid at 2,000 lux. Itmay be concluded that the infectionprocesses occur best on rainy, cloudydays with temperatures between 20 and25°(,Symptom expressionand disease developmentThe life cycle of 5. tritici is shown inFigure 6. First symptoms of infection onwheat leaves are expressed as irregularchlorotic lesions that usually appear 5-6days after inoculation. However, the timeof first expression is highly dependent onthe cultivar and environmental cond ition sduring the infection process. Three to sixdays later, at 18-24°C and high relativehumidity, necrotic (dead tissue) lesionsdevelop at the chlorotic sites (plates 4 and5). The necrotic lesions appear sunkenand grayish-green at first. By holding theleaf up against the light, the beginning ofpycnidia formation (when occurring) canoften be seen, usually after 15 days(Plates 6, 7, and 8). The pycnidia, rangingin color from light to dark brown,develop in the necrotic lesions. Thepycnidia are scattered within the lesion,and can be on both the upper and lowerMoisture is required for all stages ofinfection: germination, penetration,development of the mycelium within theplant tissue, and subsequent pycnidialformation (21, 60, 130). Periods of 72and 96 hours in a moisture chamberresult in similar levels of disease, whileonly 48 hours may produce significantlyless disease. A moist period of only 24hours is generally insufficient to producedisease symptoms (57).Wind-blown ascospores~RainactivatessporedisposalRain- splashedpycnidiosporesCardinal temperatures reported forgermination of 5. tritici conidia are aminimum of 2-3°C and a maximum of33-37°C, with an optimum of 20-25 °(,Infection can be delayed in the field if thetemperature falls below 7°C during 2consecutive nights (129, 130). Lowtemperatures (4°C) affect sporegermination, myceli al growt h, and lesionSecondary cyclesFigure 6. life cycle of Septoria tritici CMrcosphaereila graminicola).

surfaces of the leaf. The size of pycnidiamay vary among cultivars and is alsoaffected by the number of pycnidiapresent. As the number of pycnidia on theleaf increases, the pycnidia themselvesmay become smaller (37). The size of thepycnidia and pycnidiospores is notsignificantly affected by changes in thepercentage of the leaf area covered bylesions bearing pycnidia, or by the isolateof S. tritici (133). Pycnidiosporeproduction may be related to cultivarresponse, with lower pycnidiosporeproduction occurring on the resistantcultivars (51). It is important to state thatimmunity in Triticum species is rare.Pycnidiospores can remain viable inpycnidia on infested stubble tor severalmonths (58). Nevertheless, there arereported instances of epidemics ofseptoria tritici blotch develop ing in fieldplantings following several years ofnonwheat cropping. The primaryinoculum could possibly have arisen fromwindblown infested crop debris, airborneascospores, volunteer wheat, othersusceptible grass species, or from latentseptoria mycelium in crop residues(though the last is not proven).Information on some of these parametersis scarce. The sexual state, M .graminicola, is a source of primaryinoculum wherever it occurs. Themorphological appearances of asexualpycnid ia and sexual pseudothecia arequite similar. This may lead to the falseconclusion that the pycnidiospores are thesole source of primary inoculum. As aresult, the sexual forms can be and oftenare overlooked.Pycnidiospores are released from pycn idiawhen the leaf has been wet for 30minutes or more. The spores areproduced in a thick, sticky matrixcontaining a high concentration ofpreserving sugars and proteins (48). This"preserving medium" or ooze permits thepycnidiospores to remain viable duringperiods of dry weather. An oozing drop,or cirrhus , containing pycnidiosporesexudes through the ostiole at the top ofthe pycnidium following sufficient leafwetting. After drying, part of the oozingdrop may return into the pycnidium orremain on top of the ostiole for additionalrewetting.There are reports that S. tritici does notform new pycnidia on dead tissue, andthat pycn idia are not capable ofregenerating new pycnidiospores aftereach release of spores. Fewerpycnidiospores are released after eachwetting, with the bulk of the sporesreleased on the first wetting (34).However, in Tunisia, regeneration ofpycnidiospores did occur when pycnidiathat had been dried and emptied weremoistened by autumn rains (32). Thisregeneration of pycnidiospores continuedin a cyclic manner and formed theprimary inoculum to infect autumn-sownwheat.Septoria nodorumIntroductionThe asexual state of L. nodorum MUlier,namely, S. nodorum (Berk.), wasdescribed by Berkeley in 1845 as apathogen affecting mainly the glumes andnodes of wheat. Pseudothecia were foundin cultures of S. nodorum as early as1904. But it was not until 1952 thatMUlier described L. nodorum as thesexual state of the septoria nodorumblotch fungus. Septoria nodorum has beenisolated from hosts in 17 genera, and ithas recently been identified as a diseaseof barley in Britain, Ireland, andScandinavia (47). Cross-inoculation studieshave shown that wheat isolates are moreharmful to wheat than barley. Both wheatand barley isolates are capable ofinfecting many grasses w ithout causingobvious symptoms.Septoria nodorum is especially importantin warm, moist growing areas such as thesoutheastern U.S.A., Europe, and southernBrazil (122). It can occur and causedamage in relatively dry areas such asMontana, U.S.A., as well (75). In theFederal Republic of Germany and theGerman Democratic Republic , headinfection was stated to be the main causeof yield reduction (70), yet foliar infectioncan be as detrimental to yield as headinfection. In both cases, infection resultsin shrivelled seeds.The highest reduction in number ofheads/plant, number of kernels/head, andthou sand kemel weight occurred withartificial inoculation of S. nodorum afteremergence, followed by reinoculationwhen the second node was formed (49).Susceptibil ity is generally expressed at itsmaximum during heading-floweringmaturity(132).BiologyA pseudothecium, asci, and ascospores ofL. nodorum are presented in Plates 9 and10. A pycnidium and pycnidiospores ofthe asexual state, S. nodorum, are shownin Figure 7.Pseudothecia, formed on host tissue,contain numerous club-shaped asciholding eight ascospores (Plate 11). Theascospores are straight to slightly curvedand have three septa (Plate 12). Thesecond cell from the apex is the largest.These sexual spores are known to play anactive role in over-seasoning. It is also asource of primary inoculum in many areasof the world. Its full role in the diseasecycle is still not understood completely.The mycelium of S. nodorum is usuallybranched, has dividing walls of tissuecalled septa, and is transparent. Later,however, it may turn dark in color.Pycnidia and pycnidiospores developquickly in artificial culture (unlike S.tritici) and on host tissue. The pycnidiaappear under the epidermal layer of cells

and are dark. Pycnidiospores releasedthrough the ostiole are cyli ndrical,transparent, with 0-3 septa, and 15-32 x2-4 p,m in size (114,137 ,138) (plate 13).Each spore cell contain s one nucleus(137). Infective micropycnidiospores(3-6 x 0.7-1 p'-m) may also be present(56). An atypical form of pycnidiospores(12-27 x 2-3 p,m) with no or one septumhas been isolated in Pennsylvania, U.S.A.(55).The organism on wh eat can attack allplant parts above ground. It can infectany tim e from seed germination to plantmaturity. The mycelium of S. nodorumalso can be seedborne and can causeseedling infection. Brown lesions oncoleoptiles of wheat seedli ngs grown frominfected seed were first described in 1945in Canada (82).Environmental conditions required forgermination, penetration, and infectionPycnidiospores germinat e in a moi stenvi ronment, usually free water, followingexudation from the pycnidium on rainyand/or dewy days. They w ill germinatew ith in a temperature range of 5-37°Cw ith an optimum between 20-25°C. Thepycnidiospores germinate in thelaboratory within 2 hours after emergingfrom the pycnidium. Spore germinationand penetration are greatest between15-25 °C, with a min imum of 6 hours ofwetness (high relative humidity) necessaryfor good infection (121).Infection of S. nodorum is best at22-24°C, with symptoms appearing after7-14 days. Infection in Wales occurredwh en relative hum idity was greater than63% (63). In addit ion, in the 24 hoursthat followed ino culation, at least 4 hourshad to be at a temperature above 6° Cand a relative hum idi ty greater than 69%.The period from inoculation to theproduction of mature pycnidia (latentperiod) was as short as 6 days afterinoculation was achieved at 22°C onplants kept in a conti nuously watersaturatedatmosphere..The latent periodextended to 10 days wh en plants werekept at 20°C under a regime of 12 hou rsof complete saturation alternating with 12hours at 85-90% relative humidity (134).A dry period of 8 hours every 16 hoursresulted in lower disease levels than withcontinuous wetting. A dry interruption ofthe wet period occurring within 24 hoursof the appl ication of spores may result ineven less di sease development (142). Inthe field, an increase in temperature,duration of leaf wetn ess, and highinoculum density cause a decrease in thelatent period (1 35).The pycnidiospores are spread bysplashing or windblown rain. Dispersal ofpycnidiospores in a droplet was found tooccur when at least 5 mm of rainfall anda temperatur e greater than 10°C wasfollowed by at least 10 mm more rainfalling during a 48-hour period andreaching an intensity of 2 mmlhour (65,66). Pycnidiospore s of S. nodorum weredispersed by rain at a height up to 2 mand to a di stance greater than 92 cm frominfected plant s (53, 150). Airborne S.nodorum spores were coll ected at aheight of 40 cm at distances up to 10mdownwind of a target spore suspensionon which simulated rain fell (12). Windgreatly increases the dispersal of smallerdroplets and spores in the downwinddirection.pycn idium.' . 1" ~~\ I\'.: . • - , ~,~,>Figure 7. Pycnidium and pycnidiospores of Septoria nodorum.Symptom expressionand disease developmentThe life cycle of S. nodorum is shown inFigure 8. Septoria nodorum lesions areoften lens-shaped w ith a yellow-greenborder surroundin g the dead tissue area(plates 14 and 15). Pycnidia may or maynot appear withi n the center of the lensshapedlesions on the leaves, but aremore common on nodes and stems, leafsheaths, and glumes (Plates 16 and 17).Whenever nodes are infected, it maycause distortion and bending of the straw

1.8with a possibility of lodging and breakageof the straw at the node with subsequentlosses in yield. Cyclic regeneration ofpycnidia and pycnidiospores in deadwheat tissue has been reported in S.nodorum (116). The pycnidia initiatednew pycnidiospores in 10-33 days,depending upon the wheat cultivar.Infected seed has been the primary sourceof septoria nodorum blotch inoculum inGermany (92). Seed infection ranging ashigh as 80% has been reported inGeorgia, U.S.A. (26). Several authors havediscussed the relationship of seedinfection to symptoms on glumes (26, 53,91). Just one infected seedling among5,000 plants in a field may be enough toinitiate an epidemic (54). The extent towhich S. nodorum colonizes wheat seedsmight be more important than thepercentage of infected seeds (26). In thesoutheastern U.S.A., infected seeds ofsusceptible wheat cultivars often exceed40-50%, even when septoria nodorumblotch is not severe. As the incidence ofseed infection at planting increases from 1to 40%, the intensity of subsequentdisease increases (BO). However, 10%seed infection can supply sufficientinoculum to cause a severe epidemic, andhigher levels of seed infection onlyslightly increase the disease levels in thecrop. Disease infection may occur incrops grown in areas where wheat hasnot been cultivated for a number of yearsif infected seed is used. This' clearlydemonstrates the role of seed as one ofthe potential sources of primary inoculum.Septoria nodorum produces variousphytotoxic compounds such as septorinand ochracin when grown in liquidculture (10, 11, 33). Some of them mayplaya role in symptom development (6B).For example, septorin reduces seedlinggrowth of the susceptible wheat cultivar,Etoile de Choisy. In mitochondria isolatedfrom the same cultivar, septorin inducedchanges in respiratory activities similar tothat of 2,4-D (10). Ochracin is aphytotoxin that inhibits photosynthesisand leads to a decrease in the opening ofthe stomata. It may affect stomatalbehavior indirectly by inhibiting C02assimilation (33).Histological studies have shown thatduring mycelial invasion, the hyphalcolonization in the leaf was both betweenWi"d~low" ascospores ~PeritheciaRainactivatessporedisposal~Rain-splashedpycnidiosporesand within the cells and the host cellwalls seemed disorganized (5). On wheatleaves during the infection process, aswell as in an artificial medium containingwheat cell walls, S. nodorum releasesdigestive enzymes that break down cellwall material (B3).Infection ProcessComparison of Septoria triticiand Septoria nodorumThe processes associated with infection ofS. tritici and S. nodorum are summarizedin Table 3.~~OffiSeedSecondary cyclesFigure 8. Life cycle of Septoria nodorum (Leptosphaeria nodorum).

· . - 9Table 3. Comparison of the processes associated with infection by S. tritici and S. nodorumCausal agentSeptoria tritici blotchSeptoria nodorum blotchAsexual stateClassOrderFruiting bodyPycnidiosporeSexual stateClassFruiting bodySporeSymptomsPycnidia found on:EpidemiologyPrimary source ofinoculumSpore disseminationInfection requirementsSymptom appearance(days after inoculation)Septaria tritici Rob. ex Desm.Deuteromycetes (Fungi Imperfecti)SphaeropsidalesPycnidiumFiliformMycosphaerella graminicola (Hickel)SchroeterAscomycetesPerithecioid pseudothecium8 ascospores in bitunicate ascus, 2-celled,cells of unequal sizeRectangular lesions (numerous lessions maymerge); pycnidia mayor may not appearin lesionLeaves, sheaths, culms, glumes, awnsInfected debrisSplashing of pycnidiospores, mechanicaltransmission, wind-blown ascosporesProlonged, high relative humidity,temperatures higher than 7°C. Nodesiccation during process.15-21 days at 20-24°CSeptaria nadarum (Berk.)Deuteromycetes (Fungi Imperfecti)SphaeropsidalesPycnidiumCylindricalLeptasphaeria nadarum MUlierAscomycetesPerithecioid pseudothecium8 ascospores in bitunicate ascus, 4-celled,with second cell from tip enlargedLens-shaped lesions; pycnidia mayor maynot appear in lesionLeaves, nodes, sheaths, glumes, awns,seedsInfected debris, seedSplashing of pycnidiospores,mechanical transmission, wind-blownascosporesProlonged, high relative humidity,temperatures higher than 7°C. Nodesiccation during process.7-14 days at 22-24°C

If the pycnidia do not ooze after severalhours, they should be kept longer andchecked for oozing later in the day. Donot allow the leaves to remain in themoist petri dish for an extended period(more than 8 hours), because secondaryorganisms (Alternaria, etc.) may grow onthe leaf surface. This will interfere withthe isolation procedure since theantibiotics will exclude many bacteria butnot other fungi. If oozing does not occurwithin the day, open the cover of thepetri dish and let it dry overnight. Rewetand repeat the process the following dayor days. Often , this wetting-drying processwill initiate oozing in difficult specimens.If oozing does not occur, repeat the entireprocedure with other leaf samples.Whenever pycnidia do not produceoozing drops after repeated wetting anddrying, it is possible to transfer theIVIIIIIVVIIIVII. Collection of leaf samplesII. Mounting leaf on glass slidewith pycnidia facing upIII. Incubation of leaf withpycnidia in moist environmentIV. Transfer of ooze to media w ithantibioticV. Transfer of septaria colony toslant and storage at SOCVI. Growth of S. nodorum colonyon YMA under light at 20°CVII. Agitation of S. tritici culture inliquid medium at 18-20°CVIII.Observation of conidialsuspension and spore countingIX. Spraying of conidial sporesuspension in field on rainydays or dewy nightsFigure 9. Sequence of events from sample collection to artificial inoculation of septoria field trials (direct method).

content of a pycnidium, that is thepycnidiospores, directly from wettedleaves. This is done by digging with asterile needle inside the pycnidium andtransferring the contents to a mediumcontaining antibiotics. The chances oftransferring pycnidiospores by this methodare smaller, yet the technique is muchsimpler.The inoculated petri plates are kept at18-20 oe for 7-10 days. Following this, thesmall, pinkish-orange colonies thatdevelop are transferred to PDA or yeastmalt agar (YMA) without antibiotics.Yeast-malt agar (YMA):Yeast extractMalt extractSucroseAgarDistilled water4 g4 g4 g15 g1000 ml(1 liter)The success of isolation depends on: 1)the condition of the leaves, 2) keeping theenvironment sterile, and 3) proceduresand methods used during the isolation .Indirect method-A different method forisolating bulk 5. tritiei isolates may alsobe used (46). Active leaf lesions (greenleaves with pycnidia) caused by 5. tritieiare washed for 1 hour in running tapwater, then immersed in 5% sodi umhypochlorite for 2-3 minutes, and blotteddry on sterile filter paper. The leaf piecescontaining pycnidia are moved across thesurface of an agar plate (PDA + 50mg/liter Rose Bengal + 125 mg/literstreptomycin). Where pycnidiosporesooze out onto the agar surface, smallcolonies develop.Isolation of Septoria nodorumDirect method-The pathogen is isolatedafter surface sterilizing of the infectedplant material, leaves or kernels. Thefollowing surface sterilizing solution hasbeen used: 0.5% sodium hypochloriteplu s 5.0% ethanol (95%) in 100 ml ofdistilled water . One or two drops of asurfactant (Ivory Liquid, Tween 20,glycerine) are added to the suspension inorder to reduce the surface tension. Plantmaterial is completely immersed for 3minutes. Then the leaves or kernels areput on water agar plates containing oneor more of the antibiotics mentionedabove for S. tritiei to avoid bacterialcontamination. The plates are kept at19-20 oe , about 10-15 cm below a coolwhitefluorescent tube and, if possible, inan incubator. After 1 week, single or massspore transfers are made by removing thecirrhi with a needle from pycnidia formedon the leaf or kernels onto YMA, PDA,oatmeal agar, or Czapek Dox V-8 agar(23). All the above procedures should beperformed using a stereoscopicmic roscope under microbe-freeconditions.From symptomless leaves-A method ofdetecting S. nodorum in symptomlessleaves of wheat is described as follows(7). The medium used contains 20 mgparaquat, 200 mg chloramphenicol, 200mg fentin hydroxide, and 5 g agar in1,000 ml of distilled water. Paraquat,chloramphenicol, and fentin hydroxideare added to the agar after autoclaving.Leaves from the field are surface-sterilizedwith 0.5% sodium hypochlorite for 1minute and washed three times indistilled water to remove any excesssodium hypochlorite. Leaf segments arethen placed in contact with the specialmedium in the plastic petri dishes. Thelower surface must be in contact with theagar. The segments are inoculated andthen are kept under 12 hours darknessand 12 hours near-ultraviolet (NUV)irradiation at 18-20°e. Pycnidia firstappear after 6 days.From seeds-Seeds are plated on amedium (10 g dextrose, 10 g peptone, 15g oxgall, and 20 g agar in 1,000 ml ofdistilled water) in 9-cm petri dishes, 10seeds per dish, and incubated for 6 daysat 20 0e under 12-hour altemating cyclesof NUV light and darkness. The light issupplied by two black light tubes (PhilipsTL 40W/80) mounted 20 cm apart and 40cm from the dishes. Keep the dishes withthe covers facing up for the first 3 days.On the remaining days, turn them upsidedown. Fluorescence of the S. nodorumcolonies may be observed after severaldays' incubation (85).A modification of this fluorescence test isdescribed as follows (69). A doublethickness of filter paper is moistened withsterile water and placed in plastic trays.Seeds are placed equidistant on eachpaper pad. The samples are enclosed inpolyethylene bags to prevent drying outand are incubated at 20 0e in darkness for3 days to permit imbibition and initialgermination. They are then transferred toa deep freeze at -20 oe for 3 hours to killthe seedlings and are then removed andincubated in darkness at 28°e for 4 days.The trays are removed from thepolyethylene bags and the seeds areexamined under a 100-watt NUV light at360 nm.A modified blotter test for checking seedsinfected with 5. nodorum involvespretreating the seed in sodiumhypo chlorite on moist blotters in 9-cmpetri dishes which are kept at 20 0e for 1day to allow imbibition. The samples aretransferred to a deep freeze at -20 oe for 1day and then incubated for 5 days incycles of 12 hours darkness and 12 hoursNUV light at 350 nm. Seeds are observedunder the stereoscopic microscope(x25-50) for production of pycnidia (103).Single-spore MethodIf cultures derived from singlepycnidiospores are desired, this can beachieved by attaching a surface-sterilizedwet leaf segment with pycnidia on theinterior surface of a petri plate shouldcontain 1.0% water agar (lOg agar perliter of water) with or without therecommended antibiotics. Oozing cirrhiwill fall onto the agar surface. After about

· .1324 hours, view with a stereoscopicmicroscope, pick up single pycnidiosporeswith a sterile needle under microbe-freeconditions, and transfer to PDAcontaining antibiotics. Be sure to transferapproximately 10 spores to each petriplate. The success rate is usually low. Ifthe water agar petri plates are left forlonger than about 24 hours, colonies willstart growing which may have beenderived from a single pycnidiospore. Themycelium then can be transferred to PDA.Summary and recommendationsThe easiest and most effective method toisolate both S. tritiei and S. nadarum isthe direct method, in whichpycnidiospores are directly transferred toan appropriate artificial medium. Whenvery specific studies are to be carried out,the single-spore method may be necessaryto ensure absolute uniformity of theinoculum source.Maintenance ofSeptoria CulturesSeveral methods have been suggested formaintaining Septaria spp. isolates for shortor long periods. Isolates can be preservedeither in the pycnidial or in the conidialforms.Short-term maintenancePycnidial form-Short-term maintenanceof isolates of both S. tritici and S.nadarum can be achieved by storinggreen leaves with pycnidia which wereseparately inoculated with the specificisolates. The leaves are placed in amarked paper envelope (isolate, cultivar,date, etc.) for drying during several daysat room temperature. Then the envelopesare placed in a sealed plastic bag in therefrigerator at 5-10°(, The pycnidiaremain viable for several months andoften up to 1 year if kept dry and cold.This method is useful if the pathogenicityof the fungal cultures on artificial mediabecomes attenuated. Then reisolation ofthe culture from pycnidia will be requiredto recover pathogenicity.Pycnidia of S. tritici and S. nodorum onsolid media may be obtained on amodified Czapek Dox V-8 medium: 200ml V-8 juice, 109 agar, 800 mldeionized water (24). Irradiation issupplied with a black light (NUV) tube(Philips TL40 W/80) mountedapproximately 45 cm above the petriplates inside an enclosed cabinet that iskept at 20°(, The inner walls of thecabinet are covered with aluminum foil togive a more uniform radiation .Sporulation of S. nadarum may beinduced with high relative humidity in acabinet fitted with a water bath, a vent,and an air fan (59).Septaria nodorum may also producepycnidia directly on YMA (75, 76). Whenat regular intervals only spores aretransferred, pathogenicity is maintained .Conidial form-Septoria tritlci. Theproduction of slanted S. tritlci cultures isas follows: 3-5 ml of medium (PDA orYMA) in liquid form is placed into testtubes. These are closed with plastic capsor cotton plugs. Immediately followingautoclaving, the test tubes are placed atan angle and the medium allowed tosolidify. Thus, so-called "slants" areobtained. When the slants are cool, S.tritiei spores can be transferred to themunder microbe-free conditions. Septariatritici grows well on such slants, whichcan be easily handled.On artificial medium , S. tritici reproducesmainly by the product ion of conidiathrough budding. Such cultures of S. triticiusuall)\remain pathogenic followingrepeated monthly transfers of spores overseveral years. Their relative ability tocause infection may decline somewhat,although they continue to grow well onslants. Therefore, the cultures should berenewed periodically by reisolatingpycnidiospores from newly infectedseedling leaves of a susceptible cultivar.At some laboratories, this procedure isbeing followed every 4-6 month s. Forroutine laboratory work, reculturing onagar slants is performed at 14- to 21-dayintervals. When a fungal culture is usedto inoculate a liquid medium, fresh 5- to10-day old cultures should be used.Cultures of certain isolates may form amycelial mat (usually dark) in the slant asthey become older . The cultures varygreatly in their sporulating (budding) ormycelial formation characteristics. Aculture whi ch tends to form myceliumafter a rather short period requires morefrequent transfers. By increasing thefrequency of transfers, conidial productionis maintained. The cultures should betransferred in their conidial form if theyare to be used for inoculations. This isespecially true if sprayers with finenozzles are used to apply inoculum in thefield since the mycelium may block theapparatus.Conidial form-Septoria nodorum.Septaria nodarum is maintained on agarslants or petri plates with appropriateartificial medium on which it usuallyforms pycnidia. Cirrhi on top of pycnidiamay be directly used for transfer of sporesfrom the original medium to a freshmedium . Alternatively, the followingprocedure may be employed , whichallows the collection of a larger numberof spores. Sterile water (2-5 rnl) istransferred with a sterile Pasteur pipette ina microbe-free environment to the slant orpetri plate containing the fungal culture.Cirrhi w ith pycnidiospores are mixed w iththe water on the surface of the mediumby gently rubbing with a glass rod

previously sterilized in ethy l alcohol andflamed. A sterile Pasteur pipette is thenused to transfer the suspension ofpycnidiospores to a fresh medium.Summary and recommendations-Thesimp lest short-term maintenance methodfor either fungus is proper storage ofleaves infected with pycnidia as describedin the "Pycnidia l form" section above. Ifthe fungi are to be maintained on artificialmedi a, the respective methods descri bedin the "Conid ial form" section above arepreferred.long-term maintenanceSoil- Septoria tritici can be increased onEll iot V-8 juice agar (133). Five-gramsamples of a coarse sandy loam soil at1% moist ure are placed in bottle s. Thebottles are autoclaved twice (20 min utesat a 12-hour interval). Conidialsuspensions (2 rnl) are transferred to thebottles. The inoculated soil-spore bottlesare sealed, thoroughly shaken to evenlydistribute the spores thro ughout the soil,and immediately stored in the dark at4° C. Soil from soil-spore preparations issuspended in 2 ml of sterile deionizedwater and spread on the surface ofnutrient agar for conid ial increase.lyophilization-Both f reezing andlyophil ization have been studied asmethods for long-term storage. Freezin gresults in loss of pathogenicity. How ever,IyophiIization proved very successfuI(109, Ubels, personal communication).Procedu res for lyophil ization of S. triticiconidia and S. nodorum pycnidiosporesare as follows : Pyrex test tubes (10- x0.6-cm) and Pasteur pipettes should besteril ized in an autoclave or in an oven(48 hours at 90 °C). A skimmed-m ilksuspension (12%) is steamed for 15minutes, three ti mes, preferably during3 separate days in an autoclave withoutpressure buildup. Spores of S. tritici andS. nodorum grow n in liquid. shakecultures (S. tritici) or on solid media (S.tritici and S. nodorum) are transferred totest tubes to which 2.5 ml of theskimmed milk suspension was previouslyadded. A sterile paper label with anisolate identification code and the date isplaced in each test tube. Cotton plugs areinserted and pressed dow n the tubeabove the spore suspension and the tubelabel. The test tubes are then freeze driedat -20 °C in a dry ice-acetone bath forseveral minutes. After the contents arefrozen (this only takes a few min utes), thetubes are then placed into a vacuumchamber, and subjected to 20 mm Hgvacuum for about 4-5 hours (Ubels,personal comm unication) .The freezing and vacuuming are not doneunder sterile conditions. Steri le conditionsshould be maintaine d before and wh ilethe cotton plugs are inserted into thetube. Some investigators prefer to flamesealthe test tubes. Thi s requi res a set upin w hich the test tubes are attached to avinyl or rubber hose capable ofwithstanding the vacuum . Then the tubeis sealed under vacuum with anoxygen/gas torch. If test tube sealing isnot performed, the following procedu resshould be used: after 2 hours, the dry-iceacetone bath is removed and the drying isco ntinued at room temperature. As longas the tubes are still evaporating, they willfeel cool to the touch. After they reachroom temperature let them dry foranother hour. The tubes maintain sterilitydue to previous sterile conditio ns and thecotton plu g. Both the sealed and theunsealed tubes should be kept at 4°C ina refrigerator. Whenever cultures arewi thdrawn from cold storage, thefollowing procedures are necessary forsealed and unsealed tubes:• Sealed tubes are opened at roomtemperature by scoring the tube witha file and breaking it open near thecenter of the cotton plug. The who leconte nts of the test tube (milk,conidia, powder, plug, and label) aretransferred to an agar plate withantibiotics under microbe-freeconditions.• Unsealed tubes should be markedwith a file under the cotton plug,flamed, and broken in half. Add 0.2ml of sterile water to each test tubew ith a steri le pipette under microbefreeconditio ns to resuspend the mil kand the spores and then transfer thecontents to an agar plate.W hen high spore concentrations, 1 x 106spores/ml or higher, are used, germinatio nof spores and pathogenic ity areindisting uishable from "fresh" fungalcul tures. Especially for S. nodorum , aslightly modified method of lyophilizationhas been published (109).Cold storage- Cultures of septoria onPDA or YMA slants can be kept in coldstorage (4°C) or in regular refrigerators.The test tubes should be carefully sealed,especially if cotton or foam rubberstoppers are being used. Cultures storedin this manner tend to dry up but keepviability for several months. This methodis useful in providing a backup storage ofspecific isolates under study. It alsoprovides the needed backup if cultures inuse get contaminated or lost for somereason.Summary and recommendations- Thelyophilization method is recomm endedfor we ll-equipped laboratories thatconduct long-term studies on virul ence orother studies w here the originalcharacteristics of the isolates need to bemaintai ned. However, the short-termmaintenance method recommended forthe pycnidial form, in wh ich infected

· . 15leaves are stored under dry conditions ina refrigerator, is often applicable as wellfor long-term maintenance. In that case,as an additional precaution, spores shouldbe obtained from the stored materialevery 6 months, multiplied, and used forinoculation of new seedlings. Thus,freshly infected leaves are available forcontinued storage.Production of InoculumArtificially cultured conidia of S. triticiand pycnidiospores of S. nodorum areoften used for greenhouse and field trials(102, 122). These types of trials call for ahigh concentration of live spores pervolume (rnl), High concentrations of S.tritici pycnidiospores can be produced ineither solid or liquid media. Septorianodorum can be increased on solidmedium or on kernels.Solid mediaSolid media on which S. tritici and S.nodorum grow well and develop manyspores (PDA + 4-5% of yeast extract, orYMA) are good for inoculum increase.Large numbers of petri plates containingmedium are inoculated with either fungiby streaking the spores from a 5- to10-day-old slant or petri plate across thesurface. They can also be inoculated bytransferring a spore suspension to thefresh plates in microbe-free conditions.These suspensions are obtained by adding2-5 ml sterile water with a sterile Pasteurpipette to 5- to 10-day-old slants or petridishes containing the fungus. The surfaceof the culture is then scraped with a glassrod in order to suspend the spores intothe surface water. Then 2 ml of thecloudy suspension are transferred to petriplates with the help of a sterile pipette. Aspore suspension of S. tritici can also beobtained from liquid shake cultures wherean aliquot of 1-2 ml is transferred to thesolid medium plates. The petri plate isrotated to ensure that the suspension isdistributed evenly. The plates areincubated at 18-22°C in growth chambersor on the laboratory bench withillumination. After 5-10 days, pinkishreproductive spores or pycnidia (S.nodorum) should occur. The petri platesare flooded with sterile water (or tapwater if deionized sterile water is notavailable) and scraped lightly with a glassslide or other utensil without damagingthe surface of the agar. To avoid cloggingthe inoculation equipment with agar orfungus mycelium, filter the suspensionthrough 2-3 layers of cheesecloth or othercoarse cloth.liquid mediaThis method is applicable only to S. triticisince S. nodorum cannot be produced onliquid shake culture. Small amounts offresh reproductive agar cultures arescraped from the petri plate or slant andtransferred to liquid medium. Thefollowing liquid media can be used (inorder of preference):a) Yeast sucrose liquid mediumSucrose10.0 gYeast extract10.0 gDistilled water 1000 ml(1 liter)b) Modified Fries liquid medium (146)NH4 tartarate5.0 gNH4N031.0 gMgS04.7H200.5 gKH2P0411.3 gK2HP042.6 gGlucose20.0 gYeast extract5.0 gDistilled water 1000 ml(1 liter)c) Potato dextrose yeast liquid mediumDecant from cookedpotatoes (15 minutes in steameror 20 minutes in autoclave) 200 gDextrose200 gYeast extractDistilled water20 g1000 ml(1 liter)All liquid media are prepared in largeErlenmyer flasks or beakers, 2 liters orlarger if needed. The liquid medium istransferred to smaller Erlenmyer flasks andthen autoclaved. For greenhouse seedlinginoculations, usually involving only asmall number of plants, about 100-125 mlof medium is placed in a 250-mlErlenmyer flask. This ratio of 1:2.5 formedium volume to flask volume is alsokept for flasks of other sizes.The flasks are shaken on a shaker (wrist,rotary, horizontal movement, etc.) for5-10 days at 20°C, depending on thecultures. Some cultures grow fast andneed less shaking time (5 days). Othersgrow slowly and need more shaking time(7-10 days). When shaking is done eitherby wrist or rotary movement, the shakingspeed should not be too fast. Slowershaking prevents the flask plugs fromgetting wet with media. If they do getwet, contamination, especially bybacteria, may follow. At the end of theshaking period, the inoculum is filteredthrough several (2-3) layers of cheeseclothto remove any mycelia. Countingchambers, usually a hemacytometer, areused to determine the sporeconcentration. Cloudy liquid culturesmight have a spore concentration rangingfrom 1 x 105 to 1 x 107 spores/ml. Ifconcentration is important, it should bechecked and counted for each isolate insuspension. For inoculum increase, eachisolate should be grown in several flasks.

This assures that if growth is poor in oneflask, other flasks of the same isolate canserve as substitutes.For germplasm evaluation of field trials,grow each S. tritici isolate in a separateflask instead of growing the isolates inmixed cultures. Just before inoculation,the separately grown isolates are mixedtogether.Kernel mediaThis method has been most successfullyapplied to S. nodorum. A culture of S.nodorum grown on V-8 juice/Czapek Doxagar or YMA incubated at 17°C underNUV light is flooded with sterile distilledwater. The surface of the culture isscraped to remove air bubbles and allowthe water to reach the pycnidia. Thepycnidiospores are then discharged intothe water. After 30 minutes, about 3 mlof the resulting spore suspension aretransferred with a sterile Pasteur pipette toa 250-ml flask containing sterile wheatkernels (6). Prior to transfer, these flasksare prepared by autoclaving 25 g ofwheat seed and 30 ml of water for 20minutes at 1.5 kg/cm-' pressure and126°C. During this time, all free water istaken up by the seed. The inoculatedflasks are incubated in the dark at 5°C forabout 4 months. More than one flask isprepared for each isolate, so substitutesare available in case of contamination orpoor growth.To prepare inoculum for a field trial,flood each flask with 150 ml distilledwater. This breaks up the mat of infectedgrain in the bottom of the flask. Thepycnidia are then allowed to dischargetheir spores over a 30-minute period. Thespore suspension is filtered throughcheesecloth to remove fragments offungus, pycnidia, and grain. The sporeconcentration of each isolate isdetermined with a counting chamber andadjusted to 1 x 106 spores/ml.Summary and recommendationsFor S. tritici the liquid media method isrecommended for large-scale productionof spores. Although the kernel method forS. nodorum is very successful, it requiresa lot of time and thus is less flexible.Therefore, when large-scale increase isrequested on short notice, the solid mediamethod is used for S. nodorum.Inoculation ProceduresGreenhouse inoculationSeedlings can be inoculated with a sporesuspension by using quantitative ornonquantitative methods. The methodused depends on the objectives of thestudy. Seedlings can be inoculated bygently rubbing the leaves with cottonswabs that have been soaked in a sporesuspension. One drop of a surfactant is ahelpful additive since it reduces surfacetension and increases the creation of auniform suspension. This method doesnot provide good control of the varioussteps involved in the inoculation process,such as the number of spores reachingthe leaves. But if other more quantitativemethods are difficult to use, the resultsfrom rub inoculation can serve as apreliminary evaluation method.Quantitative inoculation methods allowthe researcher to determine the number ofspores/ml, and the volume of sporesuspension sprayed onto the plants.Special techniques, such as the use of aturntable or a settling tower, can controlthe delivery of a known number of sporesper volume during a given time.Revolving inoculation technique-Amethod using rotary motion (a turntable)devised by Eyal and Scharen (38) hassuccessfully been used for evaluatingseedling-host response to both S. triticiand S. nodorum (38, 40, 148).The increase of inoculum for this methodwas described in the section onproduction of inoculum. Inoculum isprepared from 5- to 7-day old septoriacultures. A 15-ml spore suspension (1 x10 6 to 1 x 107 spores/rnl) is sufficient toinoculate about 200 10- to 12-day oldseedlings. Ten to twenty seedlings shouldbe used per cultivar when host responseis to be evaluated. Seedlings are grown inrows in a square container. The containeris placed on a turntable and, whilerotating at 45 rpm, seedlings are sprayinoculated with a 15-ml spore suspensionper container during about a 2-minuteperiod (Plate 18). A drop of a surfactantshould be added to the spore suspension.After inoculation, the container withseedlings is placed into an incubationchamber with a saturated atmosphere for48-72 hours at 18-22°C (Plate 19). Asaturated atmosphere can be made byputting very fine tap water mist nozzles inthe chamber which is enclosed with clearplastic film. It can also be made bycreating high relative humidity within thechamber with water pans, wet cloth, etc.(122). At the end of the incubationperiod, the plants in the seedlingcontainers are left to air dry. They shouldnot be removed while wet because theinoculum might be spread or mixed bycontact with other containers. They arethen transferred to a greenhouse bench orto controlled environment chambers.Septaria tritici trials are kept there from14 to 30 days (usually 21) at 22 °C beforerecording disease infection. After 10-15days (usually 14), infection of Septarianodorum can be evaluated. Symptomdevelopment may be poor at hightemperature,high-irradiation, and lowhumidityconditions (summer).

Intact leaf technique-Intact wheat leavescan be tested for thei r reaction to Septoriaspp. while still functioning as parts ofliving plants (147). Several leaves arepartially inserted into a plastic "humiditybox" above water placed on the bottom.They are then inoculated with a drop ofspore suspension. Subsequently, the lid isclosed. Thus, while still part of normalplants, the leaves are enclosed in a humidchamber conducive to disease infection.. Detached leaf technique-To test hostresponse to S. tritici, the cut ends ofseedling first leaf segments may be placedin a benzimidazole solution (96, 128).The leaves are sprayed with a freshreproductive suspension of S. ttitici in a0.5% gelatin solution and kept moist for 4days. The greatest amount of difference inresistance is obtained at 40 mg/literbenzimidazole concentration, at 21 DC,and with a 12-hour day or 24 hoursunder weak illumination. Uninoculatedleaves are green and vigorous for about20 days under these conditions. Loss ofgreen coloring of susceptible cultivarsappears about 6 days after inoculation.Sporulation of the pathogen occurs inabout 12 days.Agar containing benzimidazole has alsobeen used for S. nodorum. Leaf sectionsare placed on the medium, inoculated,incubated, and subsequently evaluated forinfection (5, 9, 18, 67). This methodshows a fairly good correlat ion with fieldassessments (9, 67).Adult plant technique-It may bedesirable to evaluate germplasm beyondthe seedling stage in the greenhouse.Wheat plants have been inoculated atdifferent growth stages, from jointing tomedium milk, by spraying the sporesuspension onto plants on a greenhousebench (131). The plants should besprayed as uniformly as possible from alldirections. After inoculation, enclose theplants in a moist chamber consisting ofwet cloth hung on a frame around theplants and covered with clear plastic. Thisreduces solar radiation and will keep thechamber at 100% relative humidity forthe required 7 days. During the first 3nights, keep the leaves wet by sprayingthem with water. Following the 7-daywetting period, place the plants on anopen greenhouse bench. Disease can beassessed after about 14-21 days.Summary and recommendation-Thechoice of inoculation method will dependon the degree of accuracy required in theexperiment and on equipment availability.Where quantitative inoculations arerequired, the revolving inoculationtechnique method, widely used for bothpathogens, is recommended.Field inoculationInfested crop debris-Nurseries, yieldtrials, and chemical control studies, etc.,can be readily inoculated with the twoseptoria pathogens. After seedlingsemerge, usually about 2-3 weeks afterplanting, they are covered with pycnidiabearingstraw. There is a danger thatseeds remain present in loose or baledstraw and thus render genetic studiesuseless. Therefore, straw spread over theplants should have all seeds removed andbe finely chopped . Chopped straw can bespread throughout the season. Do notspread straw on a windy day. Infectedstraw is most effective as a primaryinoculum source in the evenings whendew forms. Infected straw with viablepycnidia or pseudothecia should becollected and stored in a dry placeimmediately after harvest for the nextyear's trials.Spore suspension-Spore suspensions canoriginate from liquid media (5. triticii,solid media (5. tritici and S. nodorurm,and/or kernel media (5. nodorum). Thesespore suspensions can be used forartificial inoculation. Septoria isolates ofdifferent origins are grown separately,filtered, and mixed just beforeinoculation. Inoculations done underfavorable weather conditions achieve thebest results (rainy days, temperatures notless than 8-10°C nor higher than 28°C,low velocity winds, etc.). The locationand condition of the field, transportation,and equipment are important in decidingwhen to mix cultures for field inoculation.Evidence shows that bench life of coldstored spores after mixing with water isshort, not longer than 12 hours. Bacteriaor other microorganisms mightcontaminate mixed cultures and reducethe life of the spore suspension. Ifconditions are not good for inoculation, itmight be better to continue to grow thecultures for a few more days beforemixing and inoculating. It is best toprepare several batches of inoculum atregular intervals. That way, freshinoculum will always be available . Ifsprinkler or nozzle irrigation is availablefor use in the field, inoculation canproceed even on days without rain, ifother conditions are favorable. The sporesuspension is mixed with a few drops of asurfactant (Tween 20, 0.5% gelatin, or amild soap such as Ivory Liquid) andsprayed with low-volume, low-pressuresprayers during high-humidity days (lightrain or irrigation) (plate 20) or on dewynights, once or twice a week dur ing theinoculation period.

The inoculation should begin at thetillering growth stage and may continueuntil the later maturing cultivars reach thepost-flowering growth stage. Establishingseptoria epidemics in the field requiresrepeated inoculations (usually at least 3-4)throughout the inoculation period underproper conditions (rain, temperature).These efforts will reduce escape andfaci Iitate the proper selection of resistantgermplasm. Loss-severity trials also requireadequate and uniform levels of disease.However, when inoculum is artificiallyapplied from the top (spray inoculated)after head emergence, the upward spreadof the disease is limited making selectionfor genetic factors difficult or impossible.Inoculated trials in semiarid countriesneed special attention. If possible, diseaseprogress during the season should bepromoted by 15-30 minutes of sprinkleror nozzle irrigation over the crop once ortwice a day. Irrigation should be done inthe mornings before the dew dries toextend the dew period or in the eveningsafter the dew forms to promote splashingof the oozing pycnidiospores. A wetperiod of at least 24-48 hours followinginoculation is best to ensure infection inthe field.An increase in humidity can be achievedby wetting the soil prior to inoculation.Also, portable plastic humidity chamberscan be placed over the plantsimmediately after inoculation with a sporesuspension. If pressurized water isavailable, increased relative humidity canalso be obtained by fitting the chamberwith a dewspraying nozzle. Inoculation ofa limited number of entries (crossingblock, segregating populations, etc.) canbe carried out in a nethouse or in otherpermanent housing covered withtransparent plastic or fitted with dewsprayingwater nozzles connected to atimer.Summary and recommendationsSpreading infected straw, collected at theright time in the previous season andstored in a dry place, is the simplest fieldinoculation procedure, but adequatelevels of disease for selection can notalways be guaranteed. Repeatedinoculations using spore suspensions willensure good infection in most situations.However, if inoculation is continued intothe adult plant stage, certain resistancecomponents that, under natural infection,would limit the upward spread of thedisease from lower to upper leaves maybecome difficult, if not impossible, toselect for. It may be advisable toinoculate repeatedly only during thetillering stage, and no longer once stemelongation commences .Disease AssessmentAssessment of disease infection isessential for evaluating germplasmresponse to pathogens in genetic andepidemiological studies and for studyingother aspects of the interaction of thehosts and pathogens.Septoria diseases of wheat are usuallyevaluated on the basis of plant tissueaffected by the pathogen. Estimates ofdisease severity are made two ways: 1)evaluating how dense the pycnidia are,and 2) determining the area of dead tissueon the affected plant, the nongreen leafarea or the remaining green leaf area. Theformer method estimates the totalpresence and direct manifestation of thepathogen. The latter takes into accountinteractions between the host and thepathogen . Thi s interaction is not alwaysdirectly related to the effect of thedisease. The host does not always showobvious loss of quality because of thepresence of the disease. In these cases, acombination of both approaches may benecessary. The presence of disease mayalso be evaluated by quantifying mycelialor spore production.Although research workers usuallyevaluate the presence of disease, thenonaffected area or the absolute greenleaf area is likely to be more closelyrelated to yield potential than the diseaseindex (the sum of the percentage ofnongreen leaf area on the top four leavesof diseased plants minus the sum forhealthy plants) (50).Host response may be greatly influencedby the growth stage of the host. Severalinvestigators studied the relationshipsbetween host growth development anddisease severity (35, 124, 126). Theserelationships are strongly affected by hostgenotype and phenotype. It is thus ofgreat importance to record the growthstage of the host at the time of diseaseassessment.The decimal code of Zadoks et al (154),which was developed from the Feekesgrowth stage scale (78), is used by manycereal workers (Figure 10). It appl ies to allsmall grain cereal species growing in awide range of environments.When the effects of infection on yield arestudied, disease evaluations are usuallymade between medium milk (growthstage 75) and late milk (growth stage 77).This is the period when the kernels areaccumulating dry matter most rapidly andcompensation for diseased plants byadjacent healthier plants is least likely to

Plate 1. Septaria tritici on durum wheat.Plate 2. Pseudothecium, asci, and ascospores ofMycosphaerella gramin icala.Plate 3. Macropycnidiospores of S. tritici.Plate 4. Typical symptoms of septoriatritici blotch.Plate 5. Necrotic and chlorotic lesions ofS. tritici.

Plate 6. Advanced symptoms of septoriatritici blotch on bread wheat.Plate 7. Pycnidia formation of septoriatritici blotch.Plate 8. Mature pycnidia of septoria triticiblotch.-.

Plate 11. Mature pseudothecia of L.nodorum.Plate 12. Ascospores of L. nodorum arestraight to slightly curved, and have 3septa.Plate 13. Pycnid iospores of S. nodorumare cylindrical and transparent, with 0-3septa.Plate 14. Leaf symptoms of septoria nodorum blotch.Plate 15. Septoria nodorum lesions areoften lens-shaped, with a yellow-greenborder surrounding the necrotic area.

Plate 16. Symptoms of septoria nodorumblotch on a bread wheat glume.Plate 17. Head infection of septo rianodorum blotch .Plate 18. Revolving inoculation techn iqu efo r evaluating seedli ng-host repon se tos. tritici and S. nodorum.Plate 19. M ist chamber for inc ubatinginoculated seedli ngs.Plate 20. Spraying of co nidial spor e suspension in the fie ld .

Key to figure 10. Descriptions of the principal and secondary growth stages of the Zadoks scale, as modified byTottman and Makepeace (143).Code Stage Code Stage Code Stage0 Germi nation 3 Stem elongation 7 Milk development00 Dry seed 30 Pseudo stem erection 71 Kernel water ripe01 Start of imb ibition (wi nter cereals on ly) 73 Early mi lk03 Imbibition complete 31 1st node dete ctab le 75 M ediu m mi lk05 Radicle emerged from seed 32 2nd nod e det ectable 77 Late mi lk07 Co leoptile emerged from seed 33 3rd nod e detectabl e 8 Dough development09 Leaf just at coleoptile tip 34 4th nod e detectable 83 Early dough1 Seedling growth 35 5th node detectab le 85 Soft dough (fing ernail10 First leaf th rough coleoptile 36 6th nod e det ectab leimpressio n not held )11 Fir st leaf un folded 37 Flag leaf ju st vi sibl e87 Hard dough (finrcern ail12 2 leaves unfol ded 39 Flag leaf ligule ju st visible impression he d; head13 3 leaves un folded 4 Booting losing chlorophyll)14 4 leaves un fol ded 41 Flag leaf shea th extend ing 9 Ripening15 5 leaves un fo lded 43 Boots just visible swo llen 91 Kernel hard (d iffic ult to16 6 leaves unfolded 45 Boot s swo llen divide by thumbnail)17 7 leaves unfold ed 47 Flag leaf sheath opening92 Kernel hard (can no lon ger18 8 leaves unfolded 49 First aw ns visibl e be dent ed by thumbna il)19 9 or mor e leaves unfolded 5 Ear emergence 93 Kerne l loosenin g in2 Tilleri ng 51 First spik elet of ear just visib le daytime20 Main shoot only 53 One-fourth of ear e mer~ e d 94 Ove rri pe; straw dead and21 Main shoo t and 1 ti ller 55 One- half of ear emerge collapsing22 Main shoo t and 2 tillers 57 Thr ee-fo urt hs of ear emerged 95 Seed dormant23 Ma in shoo t and 3 ti llers 59 Emergence of ear co mple te 96 Viab le seed giving 5024 M ain shoo t and 4 till ers 6 Flowering percent germ ination25 Main shoo t and 5 tille rs 61 Beginning of fl owerin g 97 Seed not dormant26 Ma in shoot and 6 tillers 65 Flowering halfway complete 98 Second ary dormancy27 Ma in shoot and 7 tiller s 69 Flowering complete ind uced28 Main shoo t and 8 tillers 99 Second ary dormancy lost29 M ain shoot and 9 or more tillersr4---------------- 1. Seedling growt h ------------___+,_ 2. Tillerin g3. Ste m elongation ----------+j+- 4. Boot ingStage12On eshoot;2 leavesunfold edStage21Tilleringbegins:main' hootand1 tillerStage22leafsheathslengthen;mainshootand2 tillers--'T+---- ---Stage30PseudostemerectStage31FirstnodedetectableStage32Secondnodedetect·ableStage37FlaglearjustvisibleStage39FlagleafligulejustvisibleStage45Bootsswollen5. Earemerge nce16.Flow eringStage Stages53 6 1·691/4 ofearemerged9. RipeningIStages91 ·94IIIFigure 10. Zadoks scale of cereal growth stages.

occur (70). Yet, in many cases, diseaseassessment is conducted throughout thegrowing season starting with the onset ofthe disease. Evaluation of disease progresswith time may provide some explanation sas to relationships between disease andplant development and its reflection onyield . Moreover, various types of diseaseprotection (slow disease progress, etc.)can only be evaluated by followingdisease development over time.Several methods used to assess disease foreach of the pathogens will be presentedand discussed. There is not a singleuniform assessment method accepted byall septaria workers for either controlledstudies in the greenhouse or for fieldevaluation .Saari-Prescott 0-9 scale,double digit 00-99 scaleThe Saari-Prescott 0-9 scoring scale (110)for evaluating the intensity of foliardiseases other than rusts in wheat,triticale, and barley is most commonlyused for both septaria diseases whentaking notes in the field (Figure 11).The method was recently improved byusing two digits, representing the verticaldisease progress and an estimate ofseverity (Figure 12). The first digit givesthe relative height of the disease using theoriginal 0-9 Saari-Prescott scale as ameasure. The second digit shows thedisease severity as a percentage but interms of 0-9. Because it is difficult toevaluate diseases on dead leaves, diseasenotes should be taken when at least fourleaves are still alive and green (soft tomid-dough growth stage). Then visuallyevaluate the average percentage severityon only those leaves of the uppermo stfour that are infected (Figure 12). Inpractice, the percent severity is estimatedby looking at 10-20 plants and decidingon an overall score. The following formatis used for scoring severity:10% coverage = 1 60% coverage = 620% coverage = 2 70% coverage = 730% coverage = 3 80% coverage = 840% coverage = 4 90% coverage ~ 950% coverage = 5The score of 10 is not used.For example, a certain line of wheat isinfected by S. tritici. If the height of thedisease is at about the mid-point of theplant, the score on the 0-9 Saari-Prescottscale for relative height is 5. The averagecoverage with S. tritici on only thoseleaves of the uppermost four that areinfected, that is, those at and below themidpoint, is 10%. Then the numericaldisease description is 51 (Figure 12). Thisscale is called the double-digit 00-99scale and can be used for many foliardiseases that "climb up" the plant,including the septaria blotches, butshould not be used to evaluate the rusts.1 3 5 7 9Figure 11. Saari-Prescott (0-9) scale for appraising the intensity of foliar diseases in wheat and barley.

Bronnimann's Septoria nodorumleaf and head evaluation scaleSeptoria nodorum blotch is usuallyevaluated by estimating dead leaf tissueor loss of color, and by the amount ofglume infection if that symptom occurs(15) (Figure 13). Pycnidia are almostalways present in lesions when thedisease is severe, but they are notconsidered separately from the othersymptoms (26, 122).Rosielle's Septoria tritici scaleRosielle developed a six-point scale for S.tritici (105):a - Immune (Imm) - No pycnidialformation, no symptoms or occasionalhypersensitive fleck.1 - Highly Resistant (HR) - No or onlyoccasional isolated pycnidia formed,particularly in older leaf tissue,hypersensitive flecking in younger leaftissue.1) relative disease 1) relative diseaseheight-5 height- 52) 10% of infected 2) 90% of infected0 1 5 10 25 50 75 % 100leaves isleaves isdiseased = 1 diseased -91) relative disease 1) relative diseaseheight-8 height- 82) 10% of infected 2) 90% of infectedleaves isleaves isdiseased- 1 diseased -9Figure 12. Double-digit (00-99) scalerepresenting the vertical diseaseprogress (first digit) and severityestimate (second digit).o1 5 10 25 50 75 % 100Figure 13. Percentage of wheat leaf or head area affected by Septoria nodorum.Source: Bronnimann, A. (15)

2 - Resistant (R) - Very light pycnidialformation. Some coalescing of lesionsmainly toward the leaf tip and in olderleaf tissue.3 - Intermediate (I) - Light pycnidialformation. Coalescing of lesions normallynoticeable towards the leaf tip andelsewhere on the leaf.4 - Susceptible (S) - Moderate pycnidialformation, lesions coalescingconsiderably.em'90Plant height ~ 8070605 - Very Susceptible (VS) - Large,abundant pycnid ia, lesions coalescingextensively.Eyal's Septoria tritiddisease evaluation methodsSeptoria progress coefficient-Toovercome some of the difficultiesassociated with plant growth habit(maturity and height) and the expressionof symptoms, Eyal and Ziv (43) have usedthe Septoria Progress Coefficient (SPC)together with an evaluation of diseaseseverity (Figure 14). Plant and diseaseheight (em) are determined. Diseaseheight is the maximum height (em) fromthe ground where pycnidia of thepathogen are found on the plant.SPC =Disease height (cm)/Plantheight (em)The coefficient indicates the position ofpycnidia relative to plant height regardlessof pycnidial coverage. It allows thecomparison of infection placement oncultivars with different plant stature.Despite plant stature, the vertical progressof the pathogen from the ground levelmight be the same. Variation in how highthe pathogen is on the plant might be dueto the characteristics of the plant and howthese relate to the spread of the disease.This variation might also be due togenetic factors that determine the upwardprogress of the disease over time . Thespread of disease cannot be measured byonly looking at the uppermost leaf (flagleaf). If this were done, taller plantswould generally show less susceptibilityto disease and vertical disease spreadwould not be taken into account.Diagrammatic scale-Disease severity canbe evaluated according to the Eyal andBrown diagrammatic scale (37), wh ich isused to evaluate the actual pycnidialdensity per unit leaf area (Figure 15).Disease severity classes-In the screeningand evaluation of germplasm for breedingprograms, disease severity classes, basedon infection of the four uppermost leaves,have been made as follows:VR - Very Resistant - Average pycnidialdensity of 0-5%.R - Resistant - Average pycnidial densityof 5-15% .40302010Figure 14. Septoria ProgressCoefficient (SPO. SPC = Diseaseheight (em)/Plant height (em). Diseaseheight = the maximum height (em)above ground level at whichthe pycnidia of So tritici could befound on green plant tissue.AB2.74125.722511.445017.157519.8987Figure 15. The Eyal-Brown scale estimating coverage of wheat leaves by pyenidiaof Septaria tritlci. A = actual observed pyenidial coverage (%). B = scaledpossible pyenidial coverage (%).Source: Eyal, Z. and M.B . Brown (37)

MR - Moderately Resistant - Averagepycnidial density coverage of 15-30%.MS - Moderately Susceptible - Averagepycnidial density coverage of 30-40%.S - Susceptible - Pycnidial density greaterthan 40%.The septoria infection classes (VR, R, MR,MS, S) are strongly affected by the overalldisease level in the trial. The level ofdisease in the trial can be shown byincluding wheat cultivars of known andvarying host response (susceptible,moderately resistant), plant stature, andmaturity.PCD/SPC-Eyal et al (42) categorized therelationships between the percentcoverage of disease (PCD) or coverage ofpycnidia (Figure 16) on the fouruppermost leaves and the vertical diseaseplacement or Septoria Progress Coefficient(SPC) into four distinct cultivar responseclasses:Class A PCD c::::: 15% I SPCs0.40Class BPCD -e::: 15% I SPC=0.40-0.65Class C .... PCD ~ 15-40% I SPC0.40-0.70Class D PCD :::>40% I SPC :::>0.70James' septoria foliar keysJames' key (62) is an illustrated series ofevaluation keys for plant leaf diseases,their preparation, and usage. The standardarea diagrams were accurately preparedwith an electronic scanner (Figure 17).Cough's pycnidiosporeproduction methodOther methods have used pycnidiosporeor mycelial production to evaluate hostresponse. A method based onpycnidiospore production is presented.Gough (51) has reported on a method toevaluate cultivar response to S. triticibased on pycnidiospore production. Leafsegments (1-3 cm long) with thickpycnidia coverage are removed fromwheat cultivars and soaked in deionizeddistilled water for about 15 seconds towet them and the pycnidia. They are thenmounted in petri dishes containing filterpaper moistened with deionized distilledwater. The petri dishes are kept at18-25°C One-half milliliter (about 4drops) of deionized distilled water isdeposited into spot glass depressions.Spores are then harvested after 24-26Septaria Leaf Blotchof Cereals (Leaf symptoms)Septaria Glume Blotchof Wh eat5 20 50 70 100 1 5 25 50 10 25 50Percentage leaf area covered Percentage spike area coveredFigure 16. The Ziv-Eyal rough scalefor estimating pycnidial coverage ofSeptoria tritici.Figure 17. James' key for assessing the intensity of symptoms of septoria tritidblotch and septoria nodorum blotch of wheat.Source: James, W.C (62)

hours by dipping each leaf segment 10times into the distilled water and countedusing a hemacytometer. After the firstharvest, the dishes are left for 30 hours.Then they are rewetted. After another24-26 hours, a second spore harvest andcounting take place. The total number ofspores produced is determined from thetwo hemacytometer counts.Summary and recommendationsThe nine assessment methods include twodistinct approaches:1) One is designed to evaluategermplasm response on a comparative orrelative basis, thus allowing the largecollection of cultivars usually sown indisease evaluation nurseries to beevaluated in a relatively short time.Examples are the Saari-Prescott 0-9 scaleand its modification, the double-digit00-99 scale. These are widely used byplant breeders and pathologists. Theinclusion of the disease severityassessment of the area of the plantaffected adds a quantitative parameter tothe method.2) When more precise evaluation ofgermplasm is required, then thequantitative scales designed byBronnimann (15), Eyal et al (42), Eyal andBrown (37), and James (62) can be usedor other quantitative assessment methodsmay be employed, such as quantificationof pycnidiospore production (51).Summary of RecommendationsFor both S. tritici and S. nodorum, theprocedures outlined in this methodologychapter are summarized in Table 4 in theform of recommendations.Table 4. Summary of recommended methodologies discussed in this chapterSeptoria triticlSeptoria nodorumIsolation Pycnidiospore transfer Pycnidiospore transferfrom leaf (directfrom leaf or kernel (directmethod) 1method)MaintenanceShort-term Storage of infected Storage of infectedleaves (pycnidial form) leaves or kemels (pycnidialform)On yeast-malt agar (YMA)(conidial form)On yeast-malt agar (YMA)(conidial form)Long-term Storage of infected Storage of infectedleaves (pycnidial form) leaves or kernels (pycnidialform)Freeze dry(lyophilization)Freeze dry(lyophilization)Inoculum production In suspension On agar media(liquid media)(solid media)InoculationGreenhouse Quantitative method Quantitative method(revolving inoculation (revolving inoculationtechnique)technique)Field Straw (infested crop Straw (infested cropdebris)debris)Spraying spores (sporesuspension)Spraying spores (sporesuspension)Disease assessmentGreenhouse Coverage of disease Coverage of disease(necrosis) or presence (necrosis) or presenceof pycnidia (disease of pycnidia (diseaseassessment)assessment)Field Combination of relative Combination of relativedisease height and'disease height andseverity (Saari-Prescott severity (Saari-Prescott0-9 scale, double digit 0-9 scale, double digit00-99 scale) 00-99 scale)1 Boldface terms in parentheses refer to sections in the Methodology chapter.

Epidemiology andCultural PracticesEpidemics of septoria tritici blotch andseptoria nodorum blotch of wheat areassociated with favorable weatherconditions (frequent rains and moderatetemperatures), specific cultural practices,availability of inoculum, and the presenceof susceptible wheat cultivars.The splashing dispersal mechanismaffected by rain limits distances to whichpycnidiospores can be spread. The usualvertical progress of septoria from lower toupper leaves is affected by the distancebetween consecutive leaves-the "laddereffect." The distances between the firstemerging three to four leaves are similarfor short and tall cultivars. On tallvarieties, the distance between each leafis greater toward the flag leaf. In thedwarf cultivars (70-90 cm), the closenessof the upper leaves to the lower leavesfacilitates contact between newlyemerging leaves and splashedpycnidiospores. Movement of thepathogen from infected lower leaves isthereby made simpler . As a result,pycnidia often appear earlier on upperplant parts of dwarf cultivars than they doon leaves of taller cultivars. Thus bothresistance- and morphology-relatedgenetic factors influence disease spreadand resulting severity. Under severeepidemics, the differences in plantarchitecture and stature of susceptiblecultivars are of no importance to thepathogen. In moderate to light epidemics,however, upper plant parts of dwarfcultivars are more receptive to thepathogen than taller wheats as they arenearer to inoculum sources (34). Inwheat-growing regions where septoriapathogens are a potential danger, plantarchitecture, especially leaf placement,should be taken into account when newwheat cultivars are to be released.Because of the splashing dispersalmechanism, exposed plants are ofteninfected to a higher degree than plantsclosely surrounded . Therefore, observingdisease levels on plants on field bordersusually indicates the greatest infectionlevel at a particular time during plantgrowth. Open areas within the field thatresult from skips during machine sowingare also good areas to observe diseaseoccurrence. In areas facing the rain, thesplashing effect is increased because thepenetration of drops is undisturbed.Septoria triticiIn countries where M. graminicola hasnot been found, it is still assumed thatpycnidiospores of S. tritici serve as theprimary inoculum. It is probable,however, that M. graminicola will befound in other wheat-growing areas andcountries as more effort is devoted tosystematically searching for thepseudothecia and ascospores.The primary inoculum for initiatingepidemics of septoria tritici blotch in NewZealand, Australia, and the UnitedKingdom is wind-blown ascospores of M.graminicola. Early seedling infection byascospores was reported to have a greatereffect on yield in New Zealand than laterinfection by pycnidiospores on upperplant parts. This phenomenon is called atwo-staged epidemic cycle.Cultural practices in New Zealand leavethe wheat plants after harvest as standingstubble during wet periods, whereas inmany other places the wheat residue isleft as debris on the soil surface orincorporated into the soil (114). Thisdifference in wheat residue managementis considered the main factor for thedevelopment of the sexual fruiting bodieswhen the environmental conditions arefavorable (summer rains). Because thestanding stubble is predominantly dry andwhen wetted dries out rapidly, it is notsubjected to rapid breakdown bysaprophytic microorganisms. Standingstubble, therefore, is in a much betterphysical position to produce pseudotheciaand release ascospores. During milderautumn and winter conditions,pseudothecia and ascospores have beenfound in Australia, Europe, New Zealand,and the United States. Where the absenceof summer rains and high temperaturesmakes conditions unfavorable fordevelopment of the sexual state and leafdebris remains relatively untouched onthe soil surface for long periods, pycnidiaof the asexual state are most likely themain primary source of inoculum. Cropresidues that remain in direct contact withthe soil surface are, however, veryvulnerable to decay, as are incorporatedcrop residues.Soil management practices that leavelarge amounts of wheat stubble anddebris on the soil surface increase thechance of septoria epidemics underfavorable climatic conditions. Culturalpractices that reduce wheat residuethrough plowing, burning, removal forfeeding, crop rotation, etc., help removethe major source of primary inoculum.Crop rotation with wheat croppingintervals of 3-5 years has decreasedseptoria tritici blotch incidences in Israel.However, spores themselves may survivein soil up to 20 months and remainpathogenic (136).Unlike pycnidiospores, ascospores havethe potential to travel long distances byair currents from the source of origin andthreaten new crops, in addition to their

ability to introduce new virulencecombinations. The horizontal spread ofseptoria tritici blotch from an infectedcenter is associated with the upwardspread of the disease in infected plants.The vertical and horizontal spread is slowunder unfavorable conditions, such as lowtemperatures and lack of rainfall. Thespread is faster when the minimumtemperatures rise to 8-1OOC during thenights, provided that rainfall is adequate.The horizontal spread increases in lessdense fields because splashing raindropspenetrate better to infected lower plantparts.Long rainless intervals with hightemperatures often occur in Mediterraneanenvironments towards the end of thegrowing season. These intervals interruptseptoria tritici blotch progress from lowerinfected leaves to upper plant parts.Septoria nodorumSeptoria nodorum epidemics can startfrom infected seeds, especially in wetteryears (26). In the southeastem U.S.A.,seed infection by S. nodorum was chronicand varied from 40 to more than 50%(80). One infected seedling in 5,000 wasenough to initiate a septoria nodorumblotch epidemic in the field (53).Besides infected seed, crop debris is animportant source of primary inoculum.After 1 year, wheat straw still containspycnidia able to produce viable andinfective pycnidiospores (115). Croprotations out of wheat for 1 or 2 years didnot lead to lower disease levels in thesubsequent wheat crop if infected seedwas used for planting. Even inconjunction with fungicide treatment(benornyl) of the seed, a l-year rotationdid not reduce infection in the crop.However, when the seed was treated anda 2-year rotation was observed, then theamount of disease was greatly reduced,but nevertheless still present (81). Itappears therefore that infected crop debrison the soil may function as a source ofprimary inoculum for a number of years.A combination of seed treatment or theuse of clean, certified seed, plus at least 2years of rotation; seems desirable if highlevels of disease are to be avoided. Aconfounding factor may nevertheless bethe survival of S. nodorum as potentiallypathogenic spores in the soil up to 20months (136).Septoria nodorum spores are mostlydispersed over short distances withincrops causing localized disease spread.Although most spore-carrying rain dropletsare 200-400 p:m in diameter, some aresmaller and often become airborne inmoving air (13). Septoria nodorum sporesmay be carried in such small droplets,and can be dispersed over considerabledistances (44, 150). Most S. nodorumspores, however, are dispersed less than2 m in the large "ballistic" splashdroplets. Wind greatly increases thedispersal of smaller droplets and spores inthe downwind direction (12, 13).Tall cultivars often show lower levels ofinfection with S. nodorum than shortones. The dispersal of S. nodorum fromthe base to the top of the plant occursless readily when the distance to betravelled is greater (127). The canopy of ataller cultivar might generate amicroclimate that is less conducive to thedevelopment of S. nodorum than that of ashort cultivar, which may be denser andcloser to the soiI. Leaf wetness may beless and its duration may be shorter thanthat in some short cultivars that havedenser canopies.

Pathogenic SpecializationWheat cultivars reported to be resistant inone country may sometimes succumb toattack by septoria populations in anothercountry. Some sources of resistance wereovercome by the pathogens after theywere incorporated into agronomicallysuitable wheats and submitted to nationaltrials. Knowledge of the virulence spectraof the septoria pathogens would be usefulin establishing a reliable resistancebreeding program (88). Specific hostpathogeninteractions have been reportedfor both S. tritici and S. nodorum, buttheir generality remains unproven.Septoria triticiThere are conflicting reports on the issueof physiologic specialization in S. ttitici,Cultures of S. tritici isolated in Israel havebehaved as races in the conventionalconnotation on both Triticum aestivumand T. durum (36, 153). Their parasiticcharacters have remained stable throughsuccessive host passages and repeatedtransfers on nutrient media. Physiologicspecialization has been reported in theU.S.A. (94), Australia (6), and Uruguay(30). Isolates secured from T. aestivum arein general avirulent on T. durum withseveral exceptions (36). In Tunisia, thereappears to be a lack of resistance in mostdurum wheats while several bread wheatsare highly resistant to the local S. triticipopulation (31).Isolates and cultivars may differsignificantly with respect to the incubationperiod , percentage of leaf area infected,and the number of pycnidia produced(30). The interaction between cultivars xisolates may also be significant for theabove parameters. In that case, thissuggests the existence of races. Virulencepatterns were evaluated for 97 isolatesfrom 22 countries on seedlings of 35wheat and triticale cultivars (39).Significant cultivar x isolate interactionindicated the presence of specificvirulence genes among isolates. Thegeographical regions and countries variedconsiderably in their relative virulencefrequencies. The virulence frequencies ofS. tritici were the highest in LatinAmerica, with Uruguay and Mexicohaving the most virulent populations.The cultivar x isolate interaction wasminute when the reaction of 13 durumwheats to 34 isolates from seven countrieswas evaluated. Comparison of geneticeffects among these cultivars also suggeststhat the presence of classical races isunlikely (148, 149). It seems that certainS. tritici isolates are better able to infectbread wheats than durum wheats, andvice versa. Isolates may differ in theinfection levels they can cause within aspecies, either bread wheat or durumwheat. In the absence of differentialinteraction between cultivars and isolates,such differences are due to varying levelsof aggressiveness among the isolates (84,148, 149).Septoria occurring naturally in commonchickweed (Stellaria media) is pathogenicon wheat. Wheat was inoculated with thisisolate and spores were collected from theresulting pycnidia. Upon reinoculation ofnew wheat plants, the level of virulencehad increased. With repeated passagesthrough wheat, the virulence on this cropkept increasing (95).Inoculation with certain combinations ofS. tritici isolates grown together inmixtures or grown separately and mixedprior to inoculation may result in amarked reduction in the level ofsymptoms compared to the level onplants inoculated separately with theindividual components of the mixture.Symptom expression may be dependenton the ratio of each of the isolates in themixture (155).Septoria nodorumThe presence of classical races for S.nodorum also remains unclear.Researchers have found 282 isolates of S.nodorum from the principal wheatgrowingareas in northern Florida to havedistinct resistance patterns. Despitedifferential interactions, this did notpermit conventional race differentiation(1). Nine isolates of S. nodorum ofdiverse origin on four winter wheatcultivars were found to have significantcultivar x isolate interactions that indicatespecific resistance (107, 108).Cultivar x isolate interactions togetherwith continuous variation in host responsewere reported among 14 different culturesof S. nodorum on 10 winter and springwheats (119).Virulence frequencies of 33 isolates of S.nodorum from eight countries wereevaluated on 38 wheat and triticalecultivars. Assuming a gene-for-generelationship, 21 different genes weredetermined operative among the cultivars.Isolates from Brazil, Chile, and Ecuadorexpressed high relative virulence (120).It appears that, in S. nodorum , terms suchas "race," "cultivar," and "isolate" mightnot be meaningful outside a specificexperimental situation (54).Barley isolates of S. nodorum exhibitedincreased virulence to wheat after twopassages through wheat, but no changeoccurred during passage of wheat isolatesthrough barley (47). Isolates of S.nodorum from wheat werecharacteristically virulent to wheat andavirulent to barley. However, a biotype

pathogenic on barley has been recoveredfrom wheat isolates after various numbersof passages through barley. The biotype ofS. nodorum on barley which occurs inthe southern U.S.A. appears to be largelyrestricted to barley (25). Septaria nodorumisolates of barley and wheat were highlyvirulent to their original host butnevertheless weakly virulent to theopposite crop in reciprocal inoculations(27). Isolates from wheat and barley withdiffering characters might therefore beconsidered biotypes of S. nadorum.Septaria nodarum may infect severalforage grass species (74). Three of theisolates studied were still pathogenic onwheat after passage through the grasshosts.SummaryFor both Septaria spp., there are reportssupporting and arguing against thepresence of classical races operative inthe host-pathogen system. There is a needto evaluate the diversity of the twopathogens in relation to their hosts. Theimplications of differential interaction, ifshown to be widely applicable, would begreat for growers, breeders, andpathologists alike.Exact knowledge of the host-isolateresponses will aid in the identification ofdistinct resistance sources and in theselection of resistant germplasm.Consequently, it will enable the design ofmore effective breeding and diseasecontrol strategies.

Breeding forDisease ResistanceMost of the high-yielding wheat cultivarsgrown today are susceptible to septoriatritici blotch and septoria nodorum blotch.Therefore, resistance is a high-prioritybreeding goal. Host resistance is "themain pillar of defense against disease"(21, 122) . But not enough is known aboutthe types of resistance, their mode ofaction, inheritance, manipulation, andaccumulation. These aspects, togetherwith the possibil ity (35, 107, 108, 119)that 5. tritici and S. nodorum are able toadapt their virulence or aggressiveness,are difficulties faced by the programs thatbreed for resistance to these pathogens.Favorable environmental conditions, lackof resistant cultivars, chronic seedinfection (5. nodorum), and impropercultural practices are the major factorsthat contribute to severe septoriaoutbreaks in certain parts of the world. Ayield loss of 1% for each 1% incrementin severity on the flag leaf and a loss ofabout 0.6% for each 1% increment onthe leaf below the flag leaf has beenrecorded (71).Evaluating the relationship betweendisease severity and losses in yield oryield components (17, 43, 145) inadvanced cultivars of septoria-infected vs.fungicide-protected trials should provideinformation on the vulnerability of theselines to the pathogen. It should alsopermit agriculturists to design properprotective measures (chemical control,limited varietal distribution, improvedbreeding approaches, etc.), Resistance toseptoria can be evaluated in fieldnurseries, which are naturally orartificially infected. Low infection levelsare often associated with late maturity andtall plant stature. In countries where rainsstop early in the season and/ortemperatures increase rapidly, there is agreater chance of escaping infection.In order to evaluate host response to bothpathogens, disease epidemics of a uniformand quite high level should be establishedin the nurseries. Artificial inoculation ofthe nursery assures infection. Hostresponse can then be evaluated.Evaluation is restricted to thepathogenicity spectrum of the selectedisolates. Differences in aggressivenessamong isolates can shift the initialvirulence spectrum of the isolate mixture.This may result in an unbalancedvirulence spectrum. Artificial inoculationof screening nurseries should beperformed several times throughout theseason, ending when later-maturingwheats reach anthesis. Such methodsmight introduce difficulties in evaluation ifslow disease progress is sought or plantgrowth stage affects host receptivity (132).These difficulties might be partiallyovercome if early maturing wheats andlater maturing wheats are divided intoseparate subnurseries. In these nurseries,accessions could be compared with thesame check cultivars representing wheatsof various growth habits . One may alsoprefer to inoculate heavily only in thetillering stage and subsequently allownatural development of the epidemicfueled by autoinfection.Resistances to septaria tritici blotch andseptaria nodarum blotch appear to bemore widely distributed among breadwheat (Triticum aestivum) cultivars withwinter growth habit than among thosewith spring growth habit. Resistance hasalso been reported in several wildrelatives of wheat (14, 151, 152).Dominant, partially dominant, recessive,and additive gene actions were found tocondition resistance to both septoria triticiblotch and septoria nodorum blotch (20,31,72,73,75,76,89,90,98,100,104,106, 107, 110, 116, 122, 128, 139, 148,149, 152). The additional presence ofgenes that modify the expression ofdominant genes for resistance mightexplain in part the lack of success intransferring adequate protection from thecultivars in certain crosses.Resistance to both Septoria spp. did notoften reside in the same line when 43varieties resistant to S. tritici wereevaluated for their reaction to isolates of5. nodorum collected in Montana, U.S.A.(118). However, when a similar group ofcultivars was tested for resistance to alarge number of isolates of bothpathogens collected from eight differentcountries, a very high correlation wasfound between host responses to the twopathogens (120). This stresses the need tostudy the diversity in the two pathogensand their dissimilarities.Plant height and growth habit(photoperiod and vernal izationrequirements) interact with specificgenetic factors that control diseaseexpression. This interaction makesevaluation of germplasm to septoriadiseases difficult (29, 35, 125, 140).Tolerance to septoria pathogens (thatqual ity enabling a susceptible cultivar toendure severe attack by a pathogenwithout sustaining severe losses in yield)has been identified in certain highyieldingwheat cultivars (16, 156). Thetolerant cultivars yielded well andproduced heavy, unshrivelled kernelsunder severe septoria epidemics whencompared to fungicide-protected plots andnontolerant wheat cultivars. In the future,tolerance could be combined withresistance expressed by low diseaseseverity. This would provide theendurance together with a recognizableresistance.

Septoria triticiOf 22 T. monoeoeeum boeotieum lines(genome AA), only two were susceptibleto a wide virulence spectrum of S. triticiin Israel (153). Of 47 wild emmer(T. turgidum dieoeeoides) lines, 25 wereresistant to all seven S. tritici isolates usedin the experiment. A high level ofresistance to S. tritici has been detectedamong populations and accessions ofT. longissimum, T. speltoides, andT. tausehii lAegilops squarrosa) no. 33.Resistance to S. tritiei has been transferredto bread wheat from Agropyronelongatum (52).In many countries (31, 35, 118, 119),durum wheats and triticales have a higherfrequency of resistance to S. tritici thanspring bread wheats. However, in Tunisiaseveral bread wheat lines and cultivarswere highly resistant to S. tritici whereasvery few durum wheat cultivars showedgood resistance (31). This condition mightresult from the fact that durum wheats arewidely grown in Tunisia, thus producingdirected selection pressure on thepathogen to adapt to durum wheats ratherthan bread wheats, which are grown on amuch smaller scale.Resistance to septoria tritici blotch fromwinter wheat germplasm (Aurora,Bezostaya 1, Kavkaz, and others),available in agronomically suitable,resistant semidwarf cultivars developed bythe International Maize and WheatImprovement Center (C1MMYT) in Mexicoand released by national programs,although not universal, is effective againsta rather wide spectrum of pathogenicitypatterns. The inheritance of resistance ofBezostaya 1 and Bezostaya 1-derivedwinter wheats (Aurora, Kavkaz, andTrakia) to two distinct S. tritici isolatesunder controlled field trials indicated thatthe resistance of the four winter wheats tothe isolate ISR398 (ATCC 48507) iscontrolled by one or two dominant genes.There was no indication for maternaleffect on the expression of diseasecoverage. The two S. tritici isolates(ISR398 and ISR8036) possess at least twodifferent genes for virulence. Lowcorrelations were expressed betweenheading date and plant height andpycnidial coverage of septoria triticiblotch (28). A gene that modifies theexpression of the dominant effect ofBezostaya 1 to S. tritici has been reported(29). Additive effects in the inheritance ofresistance to S. tritici have been shown tobe of prime importance, althoughdominance effects have been also oftenpresent. Epistasis seemed negligible in thedurum wheat material studied (148, 149).The dwarfing gene Rht2 has only a slighteffect on resistance to S. tritici (125, 127).Therefore the relationship between heightand resistance appears to be determinedchiefly by genes other than Rht2.Resistance to S. tritici in some winterwheat cultivars is expressed by lowpycnidial density which has beensuccessfully transferred to early-maturing,short-statured wheats (29).Septoria nodorumResistance to S. nodorum was successfullytransferred from T. tausehii (Aegilopssquarrosa) no. 33 to winter wheat (144).In moderately resistant cultivars, resistancemay be controlled by additive action ofseveral genes, whereas in highly resistantcultivars, resistance may be governed bymajor resistance genes (119). There issome evidence that resistance at theseedling stage is conferred by one ormore dominant genes. Availableexperimental analyses indicate, however,that the resistance of wheat to S.nodorum is mainly under polygeniccontrol and involves several genes (79,87, 89, 90, 120). General combiningability (GCA) effects are highly significant,but specific combining ability (SCA)effects have been observed as well,indicating nonadditive gene action forsome specific crosses (89). In advancedgenerations, transgressive segregation mayoccur (117). One or more genes modifythe expression of resistance of thedominant gene of Atlas 66 to S. nodorum.Resistance in wheat to S. nodorum maybe of a nonrace-specific or "horizontal"type and, while reasonably durable, relieson several individual partial resistancecomponents (64). These components canbe subdivided into resistance to infection,resistance to colonization, and resistanceto reproduction (93). If all thecomponents are acting together, diseasewill be reduced and yield increased. Fourprincipal components of partial resistancehave been determined which mayrepresent genuine physiological processesunder genetic control that may possiblybe separable: 1) infection frequency; 2)latent period; 3) size, shape, and rate ofgrowth of lesions; and 4) sporeproduction and its mode of increase.Significant differences between linesunder severe attack by S. nodorum wereobserved in the incubation time and inthe rate of symptom expression, whichexplain the differences in epidemicdevelopment and the slowing down ofdisease progress (99). The durability ofpartial resistance to S. nodorum of thecultivars Razon and R82 can apparentlybe overcome only if a biotype with newaggressiveness is present in the pathogenpopulation at the beginning of theepidemic (101).

There appears to be a connectionbetween resistance to S. nodorum andplant height. This association wassuggested to be due to chance associationbetween shortness and susceptibility inparental lines, genetic linkage, orpleiotropy (128). Results indicate thatthese characters may not be associated bychance, but at least partly by pleiotropyor linkage (126). The same association isapparent, but less consistent, betweenresistance to S. nodorum and lateness.Resistance in the crosses studied is notdetermined by individually identifiablegenes of large effect. Resistance may bedetermined by certain genes of smalleffect, possibly many in number.Pleiotropy may be the most probablecause of the association between height,heading, and resistance to S. nodorum inthe material studied. The genetic variationin resistance to S. nodorum in thecultivars examined can be partitioned intoheight-dependent and height-independentcomponents (127). The height-dependentcomponent reflects at least, in part,pleiotropic inheritance of height andresistance. Microclimate effects of thecanopy structure may play an importantrole in accounting for the pleiotropicrelationship. The dwarfing gene Rht2 hadlittle effect on resistance to S. nodorum oryield. Other genes than Rht2 seem togovern the relationship between heightand resistance.Numerous genetic studies indicate thattolerance to septoria nodorum blotch isadditively and polygenically inheritedwith a relatively high heritability value(17). Most progress in breeding forseptoria tolerance may arrive through acombination of tolerance with the "slowseptoring" or slow disease developmenteffect.SummaryA uniform and moderately high level ofdisease is required in breeding nurseriesso that there is sufficient disease pressureon the material for selection. Artificialinoculation will assure this. Positiveselection will then be possible withoutthe risk of escapes. In both pathogens,dominant, partially dominant, andrecessive genes that condition resistancehave been found. Additive gene action,polygenically inherited, appears to be ofmajor importance. Resistance may also beavailable in wild relatives of wheat.Linkage between height and susceptibilitydoes not seem to be strong. Therelationship rather appears to be one ofpleiotropy for some genes, mainlyexpressed in an altered plant architectureaffecting disease spread and severity.Tolerance has been insufficientlyexplored.

Chemical Control36 ",Fungicide protection has been used eitheras a stop-gap measure, or as an integralpart of the crop management system. Itspurpose has been to secure the highyields of susceptible cultivars (23), Thedesign of an economical chemical controlprogram for protection from the septoriapathogens of wheat depends upon severalcrop management cons iderations. Prior toapplying chemicals, wheat growers and/orresearchers must decide whether to resortto chemical control of the specific wheatfield if necessary. The considerations areas follows: 1) early assessment of yieldpotential and economics of the specificwheat field; 2) vulnerability of the wheatcultivar to septoria and/or other diseases;3) history of wheat cropping and septoriaepidemics in the specific field; 4) diseaselevels in the specific field; 5) culturalpractices before sowing (burying of refuse,deep plowing, etc.) that might reduce theamount of primary inoculum; 6) earlydetection of the diseases and assessmentof their progress; 7) weather conditions;8) cost of fungicide protection relative toother investments in the crop; and 9)projected yields and losses.An effective chemical control program forseptoria diseases should be accompaniedby an extensive disease surveying system.Some countries routinely condud diseasesurveys and disease forecasting and a fewothers incorporate computer-generatedrecommendations based on data collectedin the field. This system provides for theearly detection of diseases, evaluation ofdisease distribution, and evaluation ofdisease development. Success indecreasing the effect of these diseases onyield potential depends on the integrationof all components into a diseasemanagement scheme that is part of theregular crop management system. Thesecomponents include epidemiology,cultural practices, genetic protection,chemical control, biological control, andextension.Foliar Applic ation sProtectantsDithiocarbamates (maneb, manzate,mancozeb, zineb) have proved effectivein controlling septoria diseases (31, 41).However, these protectant fungicidesrequire repeated application at 10- to14-day intervals. A chemical controlprogram of 3-4 maneb applications,where the upper plant parts responsiblefor grain filling are protected, can beeffective in reducing the impact of thepathogens. It is also economically justifiedwhen yield potential is high .If the spray program begins before fullemergence of the flag leaf, the use ofmancozeb (Dithane M-45 or Manzate200) fungicide to control septorianodarum blotch on the flag leaf and headis profitable for wheat growers in Florida(77). When the spray program is begun atgrowth stage 32 (second node detectable)or growth stage 37 (flag leaf just visible),5. nodorum infection is reduced on thelower part of the plant. Because onlythree applications of mancozeb on wheatare legal in the U.S.A. and becauseresidues of this fungicide decline withtime, chemical control programs forseptoria nodorum blotch are notrecommended prior to growth stage 32.For the control of septoria nodorumblotch, especially in the wheat heads,captafol is the most widely used fungicidein Germany. It is usually applied atheading when 75% or more of the headshave emerged . Captafol, like otherprotectants, requires critical timing andhas not controlled attacks of the leaves bythe Septoris spp. (45). When captafol isapplied with triadimefon at threesuccessive stages, i.e., prior to flag leafemergence (growth stages 32-37), preboot(growth stages 37-39), and at heading(growth stages 51-59), it is quite effectivein controlling septoria nodorum blotch.SystemicsSystemic fungicides with curativeproperties and longer protective actionagainst several leaf organisms may bemore beneficial than protectants. This isespecially true when the action thresholdis misjudged or the chemical protectionprogram improperly executed. Thesystemic fungicides benomyl (Benlate),prochloraz (Sportak), triadimefon(Bayleton), and propiconazole (Tilt) haveproved effective in controlling septariatritici blotch and septaria nodorum blotchin several countries. Other new-generationsystemic fungicides, such as HWG 1608,fenpropimarph (Corbel), and myclobutanil(RH 3866), have also been found to beeffective. Combining protectant andsystemic fungicides to control septoriadisease might provide an alternative route,since tolerance to carbendazim wasreported in S. nodorum (61). The systemicfungicides can lengthen the protectioneffect, counterading outbreaks and timingdifficulties. The protectant fungicidereduces the selection pressure on thepathogen exerted by the systemicfungicides and expands the controlspectrum and longevity of the controlprogram.Methyl benzimidazole carbamate (MBC)group-Under the normal commercialsituation in New Zealand, fungicide isapplied toward the end of the winterwhen the plants are at the 4-5 leaf stage.At that time, the natural dispersal ofascospores has ceased, but no symptomsare yet visible. A single spray of benomylat 0.25 kg active ingredientlha is thenadequate to control septoria tritici blotch(112).When disease levels on the wheat headsdue to S. nodorum are moderate tosevere, chemical control with MBC-typefung icides has proven profitable inEurope. In West Germany, toxicologicalconsiderations have, however, led to thewithdrawal of the official use of MBC-typefungicides (45).

37n .Isolates of S. tritici resistant tobenzimidazole have been reported in theU.K. The minimum inhibitoryconcentration was 0.2-0.4 ppm farbenomyl-sensitive isolates and greaterthan 1,000 ppm for benomyl-resistantisolates. An S. tritici culture resistant to4,000 ppm benomyl was recovered inIsrael. The culture did not differ from thewild type in its virulence spectrum (155).The benomyl-resistant isolates secured inthe U.K. were resistant to carbendazim,thiabendazole, and thiophanate-methyl,but not to 11 other fungicides includingcaptafol, chlorothalonil, iprodione,maneb, prochloraz, propiconazole,triadimefon, and triadimenol (46). Poarcontrol of S. tritici following five sprays ofcarbendazim has been associated with ahigh proportion of benzimidazole-resistantstrains in the pathogen population (86).Fungicides of the MBC group (e.g.,benomyl) in combination withdithiocarbamates (e.g., maneb) are used insome countries in northwestern Europe tocontrol septoria nodorum blotch (91, 92).Ergosterol-biosynthesis inhibitors-Theintroduction of ergosterol-biosynthesisinhibitors such as prochloraz (Sportak),propiconazole (Tilt), and triadimefon(Bayleton) has, to a certain extent,overcome the deficiencies of theprotectants. The new fungicides offermore flexibility in time of application, andthey are broad-spectrum fungicides thatcontrol rusts and, in some cases, powderymildew (Erysiphe graminis), in addition tothe septaria diseases. The mean infectionfrequency of S. nodorum is greatlyreduced by three fungicides (captafol,prochloraz, and propiconazole) on certainspring wheat cultivars, but less on others(64). The latent period often becomeslonger following fungicide treatment.Propiconazole and prochloraz inhibitpycnidial production, while captafolmarkedly reduces pycnidial production insome cultivars.In Germany, two applications ofpropiconazole (Tilt) several days apartwere found to be mare suppressive onseptaria nodorum blotch developmentand more effective in increasing yieldthan a single treatment. Treatment at theearly boot (growth stages 33-40) or boot(growth stage 45) stages is most likely tobe economical if attack on the lowerleaves is heavy and moderate to slight onthe higher leaves (45).In a fungicide trial conducted in Israel tocontrol septoria tritici blotch, the mosteffective treatment was two earlysuccessive applications of eitherpropiconazole (Tilt) or benomyl. Thefungicides were applied at growth stages40 and 47 when infection had reached5% on the first or second leaf below theflag leaf (the action threshold). Thisresulted in slower disease progress, lowpycnidia coverage, and significantlyhigher yields and kernel weights than theuntreated, inoculated controls (22). Asingle application of propiconazole at theaction threshold just mentioned was moreeffective in controlling the pathogen andsecuring high yields, than when appliedat a later date, but less effective than thetwo successive early applications. Underhigh disease levels, the curative effect ofpropiconazole was less obvious thanunder low to moderate disease levels.Repeated applications of the protectantmaneb were less effective than thesystemic fungicides, especially if theaction threshold was misjudged. Whenthe protectant was applied after thedisease severity was more than therecommended action threshold, anattempt to use propiconazole to correctthe earlier misjudgement was noteffective. A chemical control programmay require an earlier action threshold ifvery short, susceptible cultivars aregrown.Application of triadimefon (Bayleton) +Manzate 200 gave good control ofseptaria nodorum blotch, leaf rust(Puecinia recondite), and powdery mildewin Louisiana, U.S.A. (3). Comb inations ofsystemic + protectant fungicides(Bayleton + Dithane M45 , Tilt + DithaneM45, Bayleton + Difolatan, Prochloraz +Dithane M45) may cause significantreductions in foliar symptoms andincrease yields.When applied as leaf sprays, thefungicides triadimefon (Bayleton), RH2161, chlorothalonil (Bravo 500),carbendazim, and benomyl all reducedthe severity of S. tritiei in New Zealand .In addition, significant yield responseswere obtained in field plots (141). Asingle application of prochloraz 5 daysprior to artificial inoculation with S.nodorum was less effective than curativetreatments applied 1 week afterinoculation (45).Seed TreatmentsThe economic effectiveness of seeddressing in controlling septoria triticiblotch is questionable and supportiveinformation is lacking. Bimodal diseaseprogress curves are characteristic ofepidemics in Australia and New Zealand,in which M . graminieola ascospores are aprimary inoculum source for septoriatritici blotch for 2-3 months after seedlingemergence (19). As an alternative to foliarapplications, seed treatment has beeninvestigated. Seed treatment with systemicfungicides reduced pycnidiosporeproduction in Victoria, Australia, for up to3 months after sowing, though without ameasurable increase in yield. The mosteffective chemicals far seed treatmentwere: thiabendazole (1 .5 g/kg seed),triadimenol (0.3 glkg seed), and nuarimol(0.2 g/kg seed), which reduced thenumber of plants infected with S. tritici by62, 52, and 36%, respectively, butwithout improving yield .

When dealing with septoria nodorumblotch, seed dressing with suitablesystemic fungicides can be effective inreducing the primary infections fromseedborne inoculum. The frequency ofcurrent septoria nodorum blotchepidemics from infected seeds treatedwith seed-dressing fungicides is uncertain.Protecting the head with fungicides inseed production fields increases yield. Italso can reduce the percentage of infectedseed. Furthermore, seed treatment withfungicides can lessen the degree ofinfection by S. nodorum. Sanitarymeasures, such as decreasing seedborneinoculum, might also delay the start of anepidemic (26). Effective seed treatmentscombined with cultural practices thateliminate exposure to infested crop debriscan further reduce infection of seedlings.SummaryA comparison of different effectivechemical control programs againstseptoria tritici blotch and septorianodorum blotch is presented in Table5. Table 6 lists the fungicides currentlyused in the chemical control of S. triticiand S. nodorum.Table 5. Fungicides, rates, number of applications, thresholds, and application intervals of currently recommended chemicalcontrol programs against septoria tritici blotch (Septoria tritici; and septoria nodorum blotch (Septoria nodorum)Rate Threshold Application(g/ha) Number of growth intervalsFungicide (a.i.) applications stage1,2 (days) Countryfor S. triticiManeb 2000 3-4 37-40 10-14 IsraelMancozeb 1500 3 23 10-14 New ZealandChlorothalonil 166 3 23 10-14 New ZealandRH2161 250 3 23 10-14 New ZealandBenomyl 250 1-3 23 10-14 New ZealandBenomyl 400 2 37-40 14-18 IsraelBenomyl 250-300 2 32-39 The NetherlandsPropiconazole 125 1-2 37-40 14-18 IsraelPropiconazole 125 2 32-39 21-28 Fed. Rep. Germany+ 56-58Triadimefon 125 3 23 10-14 New ZealandTriadimefon 125 2 37-40 14-18 IsraelFor S. nodorumMancozeb 2250 3 32-39 10-14 U.s.A. (Florida)Captafol 1600 1 56-58 Fed. Rep. GermanyBenomyl + Maneb 1600 56-58 Belgium, France,Fed. Rep. GermanyPropiconazole 250 2 43-45 30 U.S.A. (Texas)Propiconazole 2 37-39 15 Fed. Rep. GermanyProchloraz 1 37-39 Fed. Rep. GermanyAction threshold combined growth stage and 5% pycnidial coverage of S. tritici on flag leaf minus 3 or flag leaf minus 2depending on cultivar height and vulnerability.2 Growth stages according to Zadoks et al (154). See Figure 10.

Table 6. Fungicides used in chemical control of septoria tritici blotch andseptoria nodorum blotch of wheat (chemical name, common name(s), andchemical composition)Foliar applicationsProtectantsMancozeb (Dithane M-45, Fore, Manzate 200, etc.)(coordination complex of 16% manganese, 2% zinc, and 62%ethylenebisdithiocarbamate)Maneb (GR5, GX-101, Manex 4F, RM5, WB5, etc.)(manganous ethylenebisdithiocarbamate)Chlorothalonil (Bravo, Daconil, etc.)(tetrachloroisophthalonitrile)CaptafoI (Difolatan, Ortho Difolatan SK, etc.)(N-(1,1,2,2,-tetrachloroethylthio)-4-cyclohexene-1,2-dicarboximide)SystemicsBenomyl (Benlate, Tersan 1991)(methyl-1-(butycarbamoyl)-2-benzimidazolecarbamate)Prochloraz (Sportak, BTS 40542, etc.)(N-propyl-N-(2-(2,4,6-trichlorophenoxy)ethyIHmidazole-1-carboxam ide)Propiconazole (Tilt, Banner, etc.)(1-(2-(2,4-dichlorophenyl)-4-propyl-1 ,3-dioxolan-2-ylmethyl)-1 H-1,2,4-triazole)Triadimefon (Bayleton, etc.)(1-(4-chlorophenoxy)-3,3-dimethyl-1-(1 H-1,2,4- triazole 1-yl)-2-butanone)New chemicalsFenpropimorph (Corbel, etc.)(4-(3-(4-(1,1-dimethyl-ethyl)phenyl)-2-methyl) propyl-2,6-cisdimethylmorpholine)HWG 1608Myclobutanil (RH3866)(butyl-4-ch lorophenyl-1 H-1,2,4-triazole-1- propanen itrile)Seed treatment of S. nodorumTriadimenol (Baytan, Summit, BAY KWG 0519, etc.)(fj-(4-chlorophenoxy)-Q( -(1,1-dimethylethyl)-1 H- 1,2,4-triazole-1-ethanol)Thiabendazole (Mertect, etc.)(2-(4-thiazolyl) benzimidazole)Nuarimol (Trimidal, EL-228, TF-3635, TF-3645, etc.)(0< -(2-chlorophenyl-0< -(4-fluorophenyl)-5-pyrimidinemethanol)Vitaflo 280 (carbathiin 14.9% + thiram 13.2%)

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GlossaryAgar-A gelatin-like material obtained fromseaweed and used to prepare culture mediaon which microorganisms are grown .Aggressiveness-A measure of the rate atwhich a virulent isolate produces a givenamount of disease.Apex-The tip or top .Ascomycetes-A group of fungi produ cingtheir sexual spores (ascospores) within asack-ascus.Ascospore-A sexually produced sporeborne in an ascus.Ascus-A sack-like hypha usually conta in ing8 ascospores (pI. asci).Asexual reproduction-Any type ofreproduction not involving the union ofgametes or meiosis.Attenuate-To decrease in pathogeni cactivity.Blotch-A di sease characterized by largeand irregularly shaped spots or blots onleaves, sheaths, stems, or glumes.Boot-Sheath or portion of leaves enclosin gthe inflorescence.Budding-A method of vegetativepropagation of conidia from the mother cellas with s. tritici grown in liquid shakeculture.Caryopsis-Seed.Chlorosis-Yellowing of normally greenti ssue due to chlorophyll destruction. Thefi rst type of symptoms prior to necrosis andpycnidial formation following infection withSeptaria spp.Cirrhus-A ribbon-like group of sporesdischarged through the ostiole .Coleoptile-Protective sheath surround ingthe primary leaves.Conidium-An asexual fungal spore formedwithin an asexual fruiting body or onartificial culture medium.Cultivar-Cultivated variety.Culture medium-The prepared foodmaterial on whi ch microorganisms arecultured.Desiccation-Drying up.Disease-Any disturbance of a plant thatinterferes with its normal structure, function,or economic value.Disease cycle-The chain of events involvedin disease development, including the stagesof development of the pathogen and theeffect of the disease on the host.Dispersal-The movement of fungal unitsfrom the place where they are formed to theplace where they may be active, e.g., raindispersed pycnidiospores and air-dispersedascospores.Epidemiology-The science of disease inpopulations, study of the development andspread of disease and of the factors affectingthese processes.Epistasis-Interaction between genes atdifferent loci.Exudate-Liquid or gel-like discharge fromdiseased or healthy plant tissue or the actualdischarging of this liquid.Fluorescence-Emission of light.Fruiting body-A complex fungal structur econtaining spores (pycnidium,pseudothecium).Fungicide-A compound toxic to fungi .Fungus-An undifferentiated plant lackin gchlorophyll and conductive tissues.Gene-A material substance in thechromosome wh ich determines orcond itions one or more hereditarycharacters. The smallest funct ioning unit ofthe genetic material.Genotype-The genetic constitution of anorganism especially as di stinguished from itsappearance or responses.Germination-The proc ess in which adispersal unit (pycnidiospore, ascospore),under specifi c environmental conditions,assumes increased metabol ic activity,resulting in the production of newstructures, most often the germ tube.Haploid-A cell or an organism whosenuclei have a single complete set ofchromosomes.Hemacytometer-Special glass slide used tocount spores (counting chamber).Host-A living organi sm on or in whi ch aparasite live s and from which the parasiteobtains its sustenance (e.g. wheat plant).Host range-The variou s kinds of hostplants that may be attacked by a parasite.Hypersensitivity-Excessive sensitivity ofplant tissues to certain pathogens or isolates.Affected cell s are killed quickly, blockingthe advance of obligate parasites.Imbibition-Absorption of water.Immune-Free from infection by a givenpathogen.Incubation period-Period of time betweenpenetration of a host by a pathogen and thefi rst appearance of symptoms on the host.Infect-To establish a pathogenicrelationship w ith a host plant.Infest-To introduce a pathogen into theenvironment.of a host.Inoculate-To introduce pathogenpropagules on or into a host for the purposeof producing infection for testingsusceptibili ty to infecti on.Inoculum-A collectio n of pathogenpropagul es capable of initiating di sease orintroduced for that purpose.Isolate-A single spore or pure culture andthe subcultures derived from it.

Latent period-The time elapsed fromarrival of pathogen propagules at asusceptible plant surface until the firstformation of the next generation of dispersalunits (spores).Lesion- A discoloration of the host tissuearound the point of invasion.Life cycle-The sequence of stages betweena spore form and its recurrence.Ligule-Thin outgrowth at junctio n of leafsheath and leaf blade.Linkage-Association of genes because theyare located on the same chromosome.Lyophilization-Freeze dryi ng.Micron (I!)-A unit of length equal to1/ 1000 of a mill imeterMillimicron (~m)-A unit of length equal to1/10 00 of a micron.Mesophyll-The leaf ti ssue cells betweenepidermal layers.M ycelium- The hypha or mass of hyphaethat make up the body of a fungus.Necrotic-Dead and disco lored.Ostiole-Op ening in pycnidiu m throughw hich pycnidiospores exudate from thefruiting body.. Parasite-An organism living on or inanother living organism (host) and obtainingits food from the latter.Pathogen- An organism able to causedisease.Pathogenicity- The relative capability of apathogen to cause disease.Perithecioid pseudothecium-The ascocarpof the Loculo ascomycetes, perithecioid inshape with an opening at the top.Phenotype-The physical makeup of anindividual resultin g from the interaction ofgenotypic characters and environment.Physiologic race-On e of a group of formsthat are ali ke in morp hology but unl ike incertain cultural, physio logical, biochemic al,pathologi cal, or other characteristic s.Pleiotropy- Mul tip le effects of a single geneinfluenci ng more than one character.Protectant- A substance that protects anorganism against infection by a pathogen.Pycnidiospore-Asexual spore borne in apycnidium .Pycnidium-An asexual, spherical, or flaskshapedfruiting body in whichpycnidiospores are produced.Resistance-The abiIity of a host toovercome, completely or in some degree,the effect of a pathogen or damaging factor.Resistant-Possessing qualities that hinderthe development of a given pathogen.Septum - A cross wall in a hypha or spore.Sexual state-The state of the life cycle inwhich sexual spores (ascospores) are formedafter nuclear fusion or by parthenogenesis.Surfact ant-Com pound which reducessurface tension of liquids.Susceptible-Lacking the inherent ability toresist disease or an attack by a givenpathogen.Symptom-The external and internalreactions or alterations of a plant as a resultof a disease.Systemic- A chemical substance absorbedinto the plant through roots or foliage.Tolerance-The ability of a plant to endure(sustain) the effect of a disease w ithoutshow ing severe reduction in econom icyield .Vernalization-Exposure to a period of coldto initiate flowe ring.Virulence-The degree or measure ofpathogenicity.Virulent-Capable of causing a severedisease; strongly pathogenic.

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