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Inheritance of Triadimenol Resistance in Pyrenophora teres. Tobin L. Peever, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Michael G. Milgroom, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 82:821-828. Accepted for publication 20 April 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-821.

Progeny from crosses between isolates of Pyrenophora teres sensitive and resistant to the sterol demethylation-inhibiting fungicide (DMI) triadimenol revealed that resistance segregates at a single, major genetic locus. Crosses between isolates from different geographic regions (Canada, New Zealand, and the United States) indicated a lack of fertility barriers between isolates from these regions and indicated that resistance to triadimenol is conferred by alleles at the same genetic locus. When the ascospore progeny from the same crosses were grown on media containing propiconazole, a closely related DMI, resistance appeared to segregate in a quantitative manner. These different segregation patterns for resistance to two very closely related DMIs (both in the triazole class of DMIs) may be attributable to how the parents were selected for the crosses or to different phenotypic effects associated with DMI resistance genes. The results presented here indicate that the inheritance of DMI resistance may not be the same for different pathogens and DMIs; therefore, it is unlikely that any one model regarding the inheritance of resistance to DMIs would be appropriate.

Additional keywords: fungicide resistance.