Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

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A second explanation is that disruptive selection may reduce the fitness of pathogen populations that cycle between host genotypes in mixtures. The disruptive selection hypothesis is supported by the reduced fitness of M. graminicola populations derived from the variety mixtures as compared to the pure stands. It should be noted that the mean 27% fitness reduction of populations from mixtures that was found in our study is likely an underestimation, as disease severity in a monocyclic test accounts for only infection efficiency and lesion expansion, but not other fitness components such as sporulation rate or latent period. Additional support for the disruptive selection hypothesis is that variety mixtures suppressed epidemic development under conditions of natural inoculation, but not when artificially inoculated with a limited number of isolates. This result would be expected under the disruptive selection hypothesis, as there would be insufficient pathogen variation within the artificially inoculated plots for disruptive selection to occur. Such disruptive selection was earlier suggested to increase the efficacy of barley variety mixtures for control of powdery mildew (caused by Erysiphe graminis) (Wolfe et al., 1981) and to reduce the fitness of mildew genotypes that were able to overcome more than one major resistance gene in the mixtures (Chin and Wolfe, 1984). The levels of disease suppression contributed by our variety mixtures may not be sufficient as the sole control practice, but would certainly be useful in an integrated management program. In addition, we are currently more interested in the potential for varietal diversification to slow pathogen evolution towards increased virulence and/or aggressiveness (sensu Vanderplank, 1968) than we are for the immediate effects on epidemic progression. This is crucial in the Willamette Valley of Oregon, as there is evidence that even quantitative resistance to M. graminicola may erode in our environment (Mundt et al., 1999). Though not addressed in the research reported here, major genes for resistance may contribute substantially to control of septoria diseases in wheat variety mixtures. Our earlier studies showed that mixtures containing both a susceptible and a highly resistant variety provided greater disease control than other types of mixtures (Mundt et al. 1995). The subsequent “breakdown” of the high-level resistance in the variety Gene (Cowger et al., this volume) might be seen to increase the overall level of disease in such mixtures. On the other hand, mixtures of a virulent and avirulent pathogen isolate have been shown to reduce pycnidial production of M. graminicola very substantially (Halperin et al., 1996), which could greatly increase the value of “defeated” major genes in variety mixtures. Disease Management Using Varietal Mixtures 115 In summary, there appears to be some potential for variety mixtures to suppress septoria blotch epidemics and to slow pathogen evolution. Currently available data are very scant, however, and substantially greater field evaluation is required to determine the short- and long-term value of the diversity approach for control of Septoria/Stagonospora diseases. References Ahmed, H.U., Mundt, C.C., and Coakley, S.M. 1995. Host-pathogen relationship of geographically diverse isolates of Septoria tritici and wheat cultivars. Plant Pathol. 44:838-847. Ahmed, H.U., Mundt, C.C., Hoffer, M.E., and Coakley, S.M. 1996. Selective influence of wheat cultivars on pathogenicity of Mycosphaerella graminicola (anamorph Septoria tritici). Phytopathology 86:454-458. Chin, K.M., and Wolfe, M.S. 1984. Selection on Erysiphe graminis in pure and mixed stands of barley. Plant Pathol. 33:535-546. DiLeone, J.A., Karow, R.S., Coakley, S.M., and Mundt, C.C. 1997. Biology and Control of Septoria Diseases of Winter Wheat in Western Oregon. Oregon State Univ. Ext. Serv. Crop Sci. Bull. 109. 17 pp. Fitt, B.D.L., and McCartney, H.A. 1986. Spore dispersal in relation to epidemic models. Pages 311-345 in: Plant Disease Epidemiology, Vol. 1. K.J. Leonard and W.E. Fry, eds. McGraw-Hill, New York. Garrett, K.A., and Mundt, C.C. 1999. Epidemiology in mixed host populations (mini-review). Phytopathology 89:accepted pending revisions. Halperin, T., Schuster, S., Pnini- Cohen, S., Zilberstein, A., and Eyal, Z. 1996. The suppression of pycnidial production on wheat seedlings following sequential inoculation by isolates of Septoria tritici. Phytopathology 86:728-732.
Session 6A / Session 6B — C.C. Mundt, C. Cowger, and M.E. Hoffer 116 Jeger, M.J., Griffiths, E., and Jones, D.G. 1981a. Disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars. I. Models. Ann. Appl. Biol. 98:187-198. Jeger, M.J., Jones, D.G., and Griffiths, E. 1981b. Disease progress of nonspecialised fungal pathogens in intraspecific mixed stands of cereal cultivars. II. Field experiments. Ann. Appl. Biol. 98:199-210. Kema, G.H.J., Sayoud, R., and van Silfhout, C.H. 1996. Genetic variation for virulence and resistance in the wheat- Mycosphaerella graminicola pathosystem. II. Analysis of interactions between pathogen isolates and host cultivars. Phytopathology 86:213-220. Kema, G.H.J., and van Silfhout, C.H. 1997. Genetic variation for virulence and resistance in the wheat-Mycosphaerella graminicola pathosystem. III. Comparative seedling and adult plant experiments. Phytopathology 86:213-220. McDonald, B.A., Mundt, C.C., and Chen, R.S. 1996. The role of selection on the genetic structure of pathogen populations: Evidence from field experiments with Mycosphaerella graminicola. Euphytica 92:73-80. Mundt, C.C. 1994. Use of host genetic diversity to control cereal diseases: Implications for rice blast. Pages 293-307 in: Rice Blast Disease. S.A. Leong, R.S. Zeigler, and P.S. Teng, eds. CAB International, Cambridge, and the International Rice Research Institute, Manila. Mundt, C.C., and Leonard, K.J. 1986. Analysis of factors affecting disease increase and spread in mixtures of immune and susceptible plants in computersimulated epidemics. Phytopathology 76:832-840. Mundt, C.C., Hoffer, M.E., Ahmed, H.U., Coakley, S.M., DiLeone, J.A., and Cowger, C. 1999. Population genetics and host resistance. Pages 115-130 in: Septoria in Cereals: a Study of Pathosystems. Lucas, J.A., Bowyer, P., Anderson, H.M., eds. CABI Publishing, Wallingford, UK. Mundt, C.C., Brophy, L.S., and Schmitt, M.E. 1995. Choosing crop cultivars and mixtures under high versus low disease pressure: A case study with wheat. Crop Prot. 14:509-515. Vanderplank, J.E. 1968. Disease Resistance in Plants. Academic Press, New York. 206 pp. Wolfe, M.S. 1985. The current status and prospects of multiline cultivars and variety mixtures for disease resistance. Annu. Rev. Phytopathol. 23:251-273. Wolfe, M.S., Barrett, J.A., and Jenkins, J.E.E. 1981. The use of cultivar mixtures for disease control. Pages 73-80 in: J.F. Jenkyn and R.T. Plumb, eds. Strategies for the Control of Cereal Disease. Blackwell, Oxford. Zhan, J., Mundt, C.C., and McDonald, B.A. 1998. Measuring immigration and sexual reproduction in field populations of Mycosphaerella graminicola. Phytopathology 88:1330-1337.
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Septoria and Stagonospora Diseases
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ii The Organizing Committee express
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iv 87 Genetic Variability in a Coll
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vi Foreword In the mid-1970s the id
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2 Opening Remarks — S. Rajaram ar
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4 Opening Remarks — S. Rajaram Ta
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6 Opening Remarks — S. Rajaram cu
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8 Opening Remarks — S. Rajaram br
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10 Opening Remarks — S. Rajaram T
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12 Opening Remarks — S. Rajaram t
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14 Opening Remarks — S. Rajaram C
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16 Opening Remarks — S. Rajaram r
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Session 1: Pathogen Biology Biology
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Table 2. The Septoria tritici/Stago
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Molecular Analysis of a DNA Fingerp
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histidine kinase in yeast, although
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According to the previous observati
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cultivars. The presence of pycnidia
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Provided that S. nodorum fungal gen
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;; yy ;; yy 6 28% 1 32% ;y; ; y y ;
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Table 1. Sources of isolates or DNA
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Septoria/Stagonospora Leaf Spot Dis
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Interrelations among Septoria triti
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42 Session 2 — B.M. Cunfer disper
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44 Session 2 — B.M. Cunfer beyond
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46 Aggressiveness of Phaeosphaeria
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48 Session 2 — P. Halama, F. Lala
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50 Growth of Stagonospora nodorum L
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52 Session 3A — G.H.J. Kema and E
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54 A Possible Gene-for-Gene Relatio
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56 Diallel Analysis of Septoria Tri
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58 Session 3A — X. Zhang, S.D. Ha
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60 Session 3A — L. Gilchrist, C.
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62 Session 3A — L. Gilchrist, C.
Page 71 and 72: 64 Session 3B — E. Arseniuk and P
Page 75 and 76: 68 Cultivar variances Cultivar vari
Page 79 and 80: 72 Session 3B — N.E.A. Murphy, R.
Page 81 and 82: 74 Inheritance of Septoria Nodorum
Page 83 and 84: 76 Session 3B — N.E.A. Murphy, R.
Page 85 and 86: 78 Session 4 — B.A. McDonald, C.C
Page 91 and 92: 84 Session 4 — E. Arseniuk, H.S.
Page 93 and 94: 86 Session 4 — C. Cowger, C.C. Mu
Page 95 and 96: 88 each isolate. Two of the probes
Page 97 and 98: 90 Mating Type-Specific PCR Primers
Page 99 and 100: 92 Session 4 — Bennett, R.S., S.-
Page 101 and 102: 94 Session 5 — M.W. Shaw and the
Page 103 and 104: 96 Session 5 — M.W. Shaw The path
Page 105 and 106: 98 Spore Dispersal of Leaf Blotch P
Page 107 and 108: Session 5 — C.A. Cordo, M.R. Sim
Page 109 and 110: 102 Epidemiology of Seedborne Stago
Page 111 and 112: Session 5 — D.A. Shah and G.C. Be
Page 113 and 114: 106 Session 6A / Session 6B — J.M
Page 119 and 120: Session 6A / Session 6B — C.C. Mu
Page 121: Session 6A / Session 6B — C.C. Mu
Page 125 and 126: 118 Session 6C — M. van Ginkel an
Page 135 and 136: Session 6C — G. Shaner 128 An exa
Page 137 and 138: Session 6C — G. Shaner 130 Anothe
Page 139 and 140: Session 6C — M. Díaz de Ackerman
Page 141 and 142: 134 Septoria tritici Resistance Sou
Page 143 and 144: Session 6C — L. Gilchrist et al.
Page 145 and 146: Session 6C — L. Gilchrist et al.
Page 147 and 148: 140 Selecting Wheat for Resistance
Page 149 and 150: Session 6C — R.M. Gonzalez I., S.
Page 151 and 152: Session 6C — R.M. Gonzalez I., S.
Page 153 and 154: Session 6C — R. Loughman, R.E. Wi
Page 155 and 156: 148 Field Resistance of Wheat to Se
Page 157 and 158: 150 Using Precise Genetic Stocks to
Page 159 and 160: Session 6C — C.M. Ellerbrook, V.
Page 161 and 162: 154 Evaluating Triticum durum x Tri
Page 163 and 164: 156 Sources of Resistance to Septor
Page 165 and 166: Session 6C — H. Toubia-Rahme and
Page 167 and 168: 160 Partial Resistance to Stagonosp
Page 169 and 170: Session 6C — C.G. Du, L.R. Nelson
Page 171 and 172: Session 6C — D.E. Fraser, J.P. Mu
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Session 6C — C.G. Du, L.R. Nelson
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Session 6C — M. Mincu 168 Arcsin
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170 Comparison of Greenhouse and Fi
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Session 6C — S.L. Walker, S. Leat
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Session 6D — L.N. Jørgensen, K.E
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176
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Concluding Remarks — Z. Eyal 178
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184 Dr. Patrice Halama Professor In
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186 Dr. Hala Toubia-Rahme Research
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