The Effect of Postinoculation Periods of Leaf Wetness on the Response of Wheat Cultivars to Infection by Septoria nodorum

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1 Ecology an Epiemiology The Effect of Postinoculation Perios of Leaf Wetness on the Response of Wheat Cultivars to Infection by Septoria noorum Z. Eyal, J. F. Brown, J. M. Krupinsky, an A. L. Scharen Former Postoctoral Research Fellows, Biological Research Technician, an Research Plant Pathologist, respectively, U.S. Department of Agriculture (USDA), Agriculture Research Service (ARS), Western Region, Department of Plant Pathology, Montana State University, Boeman, MT Present aress of authors: Department of Botany, Tel-Aviv University, Ramat-Aviv, Israel; Department of Botany, University of New Englan, Armiale, N.S.W. 2351, Australia; an Department of Plant Pathology, Montana State University, Boeman, MT 59715, respectively. Cooperative investigations of the ARS, USDA, an the Montana Agricultural Experiment Station. Journal Paper No This research was fune jointly by the Montana Wheat Research an Marketing Committee an the USDA, ARS. Accepte for publication 3 January ABSTRACT EYAL, Z., J. F. BROWN, J. M. KRUPINSKY, an A. L. SCHAREN The effect of postinoculation perios of leaf wetness on the response of wheat cultivars to infection by Septoria noorum. Phytopathology 67: The length of postinoculation wet perios ha varying effects on symptom expression in spring an winter wheat cultivars inoculate at the seeling stage of growth with pycniiospores of Septoria noorum. A progressive increase in the wetting perio ha a marke effect on the number of lesions an area of necrosis prouce per leaf of the spring wheat cultivars, with each cultivar responing in a characteristic - manner. Winter wheats showe more resistance to infection an less response to length of wet perio than spring wheats, but ifferences in response to infection by S. noorum also were observe among the winter wheat cultivars. The ifferences in isease amage among spring an winter wheat cultivars in response to prolonge postinoculation wet perios can be use to etect resistant germplasm an for screening segregating populations in breeing material. Aitional key wors: Triticum aestivum, glume blotch, environmental effects. Septoria glume blotch of wheat, cause by Septoria noorum (Berk.) Berk. (perfect state = Leptosphaeria noorum Mfiller) can become epiemic an reuce yiels susceptible spring wheat cultivar Fortuna, a 2-hr wet perio was reportely sufficient for a severe isease reaction (47.2% average yiel loss per hea) (2). Holmes significantly (1,2,13, 19). Alternate wet an ry cycles are necessary for the prouction of new pycniia on infecte straw, an for the replenishment of pycniiospores in oler fruiting boies (15). Rainfall, accompanie by win, moves pycniiospores about in water roplets an accomplishes vertical an horiontal sprea of the pathogen uner fiel conitions (5, 14, 2). High inciences of the isease are epenent upon timely rainfall for spore issemination, followe by high humiity to promote spore germination an leaf infection (1, 2, 13, 14, 17). There are conflicting reports as to the length of the ew perio neee for spore germination an leaf infection, an the subsequent perio of high humiity an/or free moisture necessary to support isease evelopment uner artificial as well as natural inoculation conitions (1, 2, 16, 19, 2). Thomas (19) reporte that for seelings of wheat cultivar Atlas 66 inoculate with S. noorum, exposure to a wet perio of 92 hr resulte in greater leaf amage than exposure to the same conitions for 24 or 48 hr. Shearer (16) showe that the egree of leaf injury was maximal after exposure to a 72-hr wet perio. On the very an Colhoun (6) inoculate the winter wheat cultivar Cappelle-Despre an the spring wheat cultivar Carinal with S. noorum, then provie perios of high humiity of various lengths after inoculation. Carinal showe a trace of infection 15 ays after inoculation when the postinoculation perio of high humiity ha been only 3 hr. However, in orer for as much as 2% of the inoculate leaf area to show lesions after 25 ays, a postinoculation perio of high relative humiity of 5-7 hr was neee. Cappelle-Despre showe no lesions 25 ays after inoculation if the postinoculation perio of high humiity was less than 2 hr. Fifty hr of postinoculation high humiity resulte in lesions covering 2% of the inoculate leaf area 25 ays after the inoculation. Rapilly et al. (11, 12) reporte that infective S. noorum became ormant, but i not ie, if bright sunshine an low humiity followe a short perio of rain uring which spore issemination an infection took place. When such conitions were known to have occurre, plants were transplate from the fiel to a mist chamber where lesions evelope in about 2 wk; plants in the fiel remaine free of lesions, although they were known to have ormant infections (F. Rapilly, personal communication). After infection was establishe, further Copyright 1977 The American Phytopathological Society, 334 Pilot Knob Roa, St. Paul, MN All rights reserve, 874 evelopment of S. noorum within the host plant

2 July 1977] EYAL ET AL.: SEPTORIA/WHEAT LEAF WETNESS 875 remaine epenent upon external environmental 1 3 ergs/cm 2 /sec). Pycniiospore suspensions washe conitions, especially humiity. from the surface of several agar plates an ajuste with The objective of this stuy was to etermine the effects sterile water to a concentration of 17 spores/ml were of wet perios of various urations on the evelopment of use for seeling inoculations (9). lesions an necrosis in several spring an winter wheat See of spring an winter wheat cultivars (ientifie in cultivars quantitatively inoculate with pycniiospores of Tables 1 an 2) were sown in straight lines an at equal S. noorum. spacing on the periphery of square plastic containers fille with steame composte soil without ae MATERIALS AND METHODS nutrients. The plastic containers were 2 X 2 X 6.5 cm an 3-4 sees per cultivar were plante. One container The isolates of S. noorum use in this stuy were was plante per wet perio per trial. The spore originally collecte from wheat fiels in Montana, an all suspension was spraye (15 cc/ container) onto the wheat were selecte for high virulence. Cultures were grown on seelings (1 ays after sowing) as they were revolving on yeast-malt agar for 7 ays at 2 C uner constant light of a phonograph turntable at 45 rpm (4). Immeiately 2w cool-white fluorescent lamps (6.6 X following inoculation, the containers were move into a TABLE 1. Relationship of postinoculation wet perio to number of lesions an area of necrosis incite by Septoria noorum on several wheat lines Lesions/cm 2 (no.)w Necrosis/ cm 2 (%)w Wheat C. I. or P. I.v Regression Correlation Regression Correlation cultivar number coefficientsx coefficients coefficientsx coefficients DeKalb's SB-8.56 aby.97**.72 ab.97** Fletcher ab.98**.78 ab.99** Fortuna a.98**.85 a.98** Manitou b.95**.63 b.97** Norana b.88**.66 b.96** Shortana b.88**.63 b.98** Worl See ab.97**.72 ab.85** vcereal Introuction (C. I.) or Plant Introuction (P. I.) numbers. wdata were from three replicate experiments. xstatistical analysis conucte on the regression coefficients (b) of the linear (log-log) regression, where X = log wet perios; Y = log number of lesions/im 2, or log % necrosis/cm 2 - 'Values followe by the same letter are not significantly ifferent at P =.5, by the simultaneous test proceure (18). 'Double asterisks (**) inicate significant positive correlation (r) at P = Fortuna (-) r =,98 * A r=,98 ** B 2 N SManitou (- -)r=o, 95 r=,97 N 1.6- Norana (-.)r=o,88** 1.6 r=o.96** _ W U 2 LL.8- " -..4 _ I4 o -J -J W I _ I _I I I I I LOG POST- INOCULATION WET PERIODS (HOURS) Fig. 1-(A, B). The response of three spring wheat cultivars, Fortuna, Monitou, an Norana, to ifferent postinoculation wet perios, expresse in the function log Y = a + b log X, where Y = log of symptoms, an X = log of wet perios (hr). Correlation coefficients (r) (wet perios with lesions or necrosis) are given for each wheat cultivar. Graph A) represents lesions (no.)/ cm 2 ; an B) necrosis (%)/cm2.

3 [Vol. 67 PHYTOPATHOLOGY 876 RESULTS mist chamber, an miste by two cool-water humiifiers for 6, 12, 18, 24, 48, 72, an 96 hr with air temperature at 22 ± 2 C. Upon removal from the chamber, each inoculate container an noninoculate check was rie for about 5 min with a fan an returne to the controlleenvironment conition in which they were grown originally (15 C night/23 C ay, a 12-hr ay, an light intensity of 1.7 X 14ergs/cm 2 /sec). Eight ays after inoculation, each leaf to be consiere was marke at its base with a nonphytotoxic felt tip pen to elimit the area to be consiere in subsequent measurements. The number of lesions on each leaf was counte an the length an with of the leaf was measure. Fifteen ays after inoculation, the amount of necrotic tissue on infecte leaves was estimate by measuring the length of the necrotic region an relating it to the length an with of leaf previously recore. Lesion counts an estimates of necrotic tissue were recore separately for each centimeter of leaf length. The number of lesions per square centimeter an percentage of necrosis per square centimeter then were calculate for each entire leaf. Two experimental series were conucte to evaluate the effect of wet perio uration on isease amage to wheat seelings inoculate with S. noorum: a spring wheat cultivar series, an a group of resistant spring an winter wheat lines selecte in screening experiments. Each series of experiments was repeate three times, an the results were subjecte to statistical analysis (18). After several statistical transformations were attempte, the logarithm an square-root transformations were selecte as best fitting the ata (Fig. I an 2). Regression coefficients (b) an correlation coefficients (r) were calculate an are presente in tabular form rather than as aitional figures (Tables 1 an 2). Several spring an winter wheat cultivars iffere in number of lesions an areas of necrosis when infecte by S. noorum. The ifferences were accentuate by extening perios of leaf wetness after inoculation. The relationships between perios of leaf wetness an increase symptoms (manifestations of isease amage) followe linear functions. A log-log linear regression of length of wet perio on number of lesions an area of necrosis best fitte the ata from the spring wheats. All of the spring wheats suffere increasing amounts of isease amage as the postinoculation wet perio was extene (Fig. 1). The increases in isease amage (lesions an necrosis) were not ientical for all cultivars, an extening the wet perio increase the ifferences between cultivars. Linear regressions of lesions or necrosis on length of postinoculation wet perio were calculate, then a statistical analysis of the slopes (b) of the regression lines was one. The analysis showe that the cultivar Fortuna ha significantly more lesions an necrosis than i Manitou, Norana, an Shortana (Table 1). Cultivars DeKalb's SB-8, Fletcher, an Worl Sees 1812 were intermeiate, but not significantly ifferent from Fortuna, in their response to infection by S. noorum. Correlations between length of postinoculation wet perio an symptoms (number of lesions an area of necrosis) were calculate. Coefficients (r) were highly significant for each cultivar (Table 1). The effects of progressively longer perios of leaf wetness after inoculation with S. noorum were stuie on selecte resistant spring an winter wheat cultivars. Extension of the wet perio resulte in only a few more lesions an a relatively small increase in the area of necrosis when the more resistant winter wheat cultivars Y1 21 " U) 8 Fortuna (--)r=,96**9 Manitou (--)r=,93 Recoat l)r=,899** Rehart (...)r=,89 **r=, r=,795b r87 r =.84* o_ A " ( 2,i.. I - A... 1,o,o A -1 4 POST I ' INOCULATION WET PERIODS (HOURS) Fig. 2-(A, B). The response of two spring wheat cultivars, Fortuna an Manitou, an two winter wheat cultivars, Recoat an Rehart, to ifferent postinoculation wet perios, expresse in the function square root Y = a + bx, where Y = square root of symptoms, an X = wet perios (hr). Correlation coefficients (r) (wet perios with lesions or necrosis) are given for each wheat cultivar. Graph A) represents lesions (no.)/cm'; an B) necrosis (%)/cm 2.

4 July 1977] 877 EYAL ET AL.: SEPTORIA/ WHEAT LEAF WETNESS TABLE 2. Relationship of postinoculation wet perio to number of lesions an area of necrosis incite by Septoria noorum on several wheat lines Wheat cultivar Spring wheats: Era Fortuna Manitou Svenno C. I. or P. I.V number Lesions/cm (no.)w Correlation Regression coefficients coefficientsx by a b bc.93**.96**.93**.94** Necrosis/ cm2 (%)w Regression coefficientsx Correlation coefficients.58 b.93 a.57 b.58 b.93**.95**.87**.91** Winter wheats:.87**.15 f.84**.13 Coker ** **.22 ef Haen.94**.23.92** e Harvest Queen.91**.18 ef.86** Hybri 143,.88**.18.91**.22 e Moking.84**.36 c.89**.28 c 1317 Recoat.88**.16.89**.16 ef 1219 Re Chief.89**.16 f.87** Rehart.85**.25.89**.27 c Turkey Sel VCereal Introuction (C. I.) or Plant Introuction (P. I.) numbers. WData were from three replicate experiments. xstatistical analysis conucte on the regression coefficients (b) of the linear regression, where x = wet perios, y = square root of lesions/cm2, or square root of % necrosis/cm2. 'Values followe by the same letter are not significantly ifferent at P =.5, by the Simultaneous Test Proceure (18). Double asterisks (**) inicate significant positive correlation (r) at P =.1. were inoculate. Linear regressions were calculate an transformations were trie for best fit to the ata. In this case, a square root transformation gave the best fit (Fig. 2). Regression coefficients for each cultivar were calculate, an a statistical analysis of slopes of the regression line (b) is shown in Table 2. With the exception of one spring wheat (Svenno) an two winter wheats (Recoat an Turkey Sel), the spring wheats ha significantly more lesions per square centimeter than i the winter wheats. As a result of infection by S. noorum all spring wheats ha significantly more necrosis than the winter wheats (Table 2). Among the winter wheats, only Recoat ha significantly less necrosis than the others, but there was consierable variation in the number of lesions per unit area. Since the ifferences reporte were base upon the slope of the regression line, the actual ifferences between cultivars became greater with increase length of postinoculation wet perio. Again, in every case there was a significant positive correlation (r) between length of wet perio an symptoms. DISCUSSION Postinoculation leaf wetness is a critical factor affecting whether or not symptoms will evelop on wheat leaves inoculate with S. noorum (1, 3, 14). We have confirme the observations of Holmes an Colhoun (6) that wheat cultivars vary in the length of postinoculation wet perio require for any symptoms to appear at all. Aitionally, we have shown that longer postinoculation wet perios support the evelopment of some symptoms on resistant cultivars, an many symptoms (lesions an areas of necrosis) on susceptible cultivars. Hosfor has reporte similar results with other wheat leaf-spotting organisms (7, 8). We have shown that spring wheats generally are more heavily amage in an environment favorable for isease evelopment than are winter wheats. We conclue, therefore, that among the cultivars stuie, the winter wheats are more resistant to S. noorum than are the spring wheats. A similar conclusion was reache in Israel where higher levels of resistance to S. tritici were observe in vernalie winter wheats than in spring wheats grown in fiel nurseries (Eyal an Wahl, unpublishe). In all of our experiments, the expression of cultivar resistance to infection by S. noorum as measure by the evelopment of lesions an necrosis was relate to the uration of postinoculation wet perios. Resistance was not altere, nor was ranking of cultivars change by exposure to extene perios of leaf wetness; but, numbers of lesions an areas of necrosis increase at a greater rate in some cultivars than in others when they were subjecte to prolonge perios of leaf wetness. Thus, long perios of postinoculation wetness ha the effect of spreaing cultivar reactions further apart an making it easier to etermine which ones were more or less resistant to S. noorum. Differences in the response of cultivars an lines of wheat to various postinoculation wet perios, linke with high spore concentrations in inoculum, are being use to etect resistant germplasm an for screening breeing populations at the seeling stage of growth for resistance to S. noorum an S. tritici (Scharen an Krupinsky, unpublishe). Our stuy, an others we have cite, inicate that the effect of postinoculation wet perios on the evelopment of isease in wheat ue to infection by S. noorum is a multi-phase process. Fungal spore germination an penetration of the host leaves constitutes the first phase, whereas the establishment of the host-parasite

5 878 PHYTOPATHOLOGY [Vol. 67 relationship is the secon phase. But, even after plant age, air temperature, an relative humiity. Trans. establishment of the pathogen within host-tissue, the Br. Mycol. Soc. 63: progress of the isease an the eventual appearance of 7. HOSFORD, R. M., JR Varietal resistance an fungal symptoms remains epenent upon external environ- pathogenicity relate to wet perio. Proc. Am.. mental conitions, notably moisture an temperature (6, Phytopathol. Soc. 2:59 (Abstr.). 1, 11, 12). Disease progress an amage to the crop can 8. HOSFORD, R. M., JR Phoma glomerata, a new be arreste at any pathogen of wheat stage of evelopment by the onset of an triticales, cultivar resistance relate to wet perio. Phytopathology 65: warm, ry weather that is unfavorable to the isease. By 9. KRUPINSKY, J. M., A. L. SCHAREN, an J. A. exploiting the sources of resistance ientifie in this SCHILLINGER Pathogenic variation in Septoriastuy, an by using these methos to fin other resistance noorum (Berk.) Berk. in relation to organ specificity, sources, we expect that wheat cultivars may be evelope apparent photosynthetic rate an yiel of wheat. Physiol. that can withstan environmental conitions favoring Plant Pathol. 3: infection by S. noorum, an thus sustain less amage to 1. LEVITT, J Responses of plants to environmental yiel than is suffere by most presently grown cultivars. 1 stresses. Acaemic Press, New York. 697 p. 11. RAPILLY, F., B. FOUCAULT, an J. LACAZEDIEUX. We also encourage future investigations into the nature Etues sur l'inoculum e Septoria noorum Berk. of the effects of postinoculation leaf wetness upon isease (Leptosphaeria noorum Miller) agent e la Septoriose evelopment. The phenomenon of external u bl. I. Les ascospores. Ann. Phytopathol. 5: environmental influence on the spee an extent of 12. RAPILLY, F., an M. SKAJENNIKOFF Etues sur isease evelopment, especially in leaf-spot iseases l'inoculum e Septoria noorum Berk., agent e la cause by facultatively parasitic fungi, may be Septoriose u bl. II. Les pycniiospores. Ann. wiesprea. Some reevaluation of etiological concepts Phytopathol. 6: historically relate to leaf-spot iseases may be 13. SAARI, E. E., an R. D. WILCOXSON Plant isease ori yr ete. tsituation of high yieling warf wheats in Asia an Africa. Annu. Rev. Phytopathol. 12: LITERATURE CITED 14. SCHAREN, A. L Environmental influences on evelopment of glume blotch in wheat. Phytopathology 1. BECKER, C. J. K Glume blotch of wheat cause by 54:3-33. Leptosphaeria noorum Mfller. Tech. Ber. Sticht. Ne. 15. SCHAREN, A. L Cyclic prouction of pycniia an Graan-Cent p. spores in ea wheat tissue by Septoria noorum. 2. BRONNIMANN, A., B. K. SALLY, an E. L. SHARP. Phytopathology 56: Investigations on Septoria noorum in spring 16. SHEARER, B. L Epiemiology of Septoria noorum wheat in Montana. Plant Dis. Rep. 56: Berk. B.Sc. Honours Thesis, University of Western 3. COLHOUN, J Effects of environmental factors on Australia, Nelans, Australia. 142 p. plant isease. Annu. Rev. Phytopathol. 11: SHIPTON, W. A., W. R. J. BOYD, A. A. ROSIELLE, an 4. EYAL, Z., an A. L. SCHAREN A quantitative B. L. SHEARER The common Septoria iseases metho for the inoculation of wheat seelings with of wheat. Bot. Rev. 37: pycniiospores of Septoria noorum Berk. Phytopathology 67: SOKAL, R. R., an F. J. ROHLF Biometry. W. H. Freeman an Company, San Francisco. 776 p. 5. HOLMES, S. J. I., an J. COLHOUN Infection of wheat seelings by Septoria noorum in relation to 19. THOMAS, M. H Factors affecting glume blotch evelopment on wheat an variation in the causal environmental factors. Trans. Br. Mycol. Soc. 57:493- organism, Septoria noorum. Ph.D. Thesis, University of 5. North Carolina, Raleigh, North Carolina. 58 p. 6. HOLMES, S. J. I., an J. COLHOUN Infection of 2. WEBER, G. E II. Septoria iseases of wheat. wheat by Septoria noorum an S. tritici in relation to Phytopathology 12: