POWDERY MILDEW RESISTANCE IN WINTER-WHEAT .1. GENE NUMBER AND MODE OF INHERITANCE

Few widely effective sources of resistance to powdery mildew, caused by Blumeria graminis (DC) E. O. Speer f. sp. tritici Em. Marchal, have been identified in wheat (Triticum aestivum L.), and the identity of resistance genes in many cultivars is unknown. Ten winter wheat lines selected from the 1982 International Winter Wheat Mildew and Rust Nurseries were studied to characterize gene number and mode of inheritance of resistance to powdery mildew. Each of the lines were crossed to the susceptible cultivar Chancellor. Seedlings of the parental lines, F-1, F-2, BC1 (Chancellor x F-1), and F-3 populations were inoculated with isolate 127 of B. graminis in the greenhouse and evaluated for powdery mildew reaction. Ad parents were resistant, except for ST1-25, which had an intermediate reaction type. Genetic analyses revealed that resistance in C39 and SI5 is conferred by three dominant genes, and resistance in A55-2, R107, GO4779, OK75R3645, and Bulk PV63-6 is governed by single partially dominant genes. Data from F-2, F-3, and BC1 populations, derived from crosses between 'Armada' and Chancellor, were inconsistent but indicated that Armada has at least one dominant gene for resistance, which likely is Pm4b as previously postulated. Resistance in VPM1 and ST1-25 is governed by one recessive gene in each line. Three to 11 different resistance genes are represented among the 10 parents.