GENE-ACTION FOR ADULT-PLANT RESISTANCE TO POWDERY MILDEW IN WHEAT

Gene action for adult-plant resistance to powdery mildew was studied using generation mean analyses of parents and of F-1, F-2, and backcross populations derived from a diallel cross of one susceptible and three adult-plant resistant wheat cultivars. Joint scaling tests showed that an additive-dominance model was sufficient to explain the variability in the expression of adult-plant resistance in one cross, while digenic epistasis was involved in the other five crosses. Additive gene effects were predominant; however, dominance was significant in four crosses, additive X additive interaction was significant in three crosses, additive X dominance interaction was significant in three crosses, and dominance X dominance interaction was significant in one cross. Therefore, selection for adult-plant resistance would likely be most effective in advanced generations derived from crosses among the adult-plant resistant cultivars Redcoat, Houser, and Massey.