INHERITANCE OF RESISTANCE TO MYCOSPHAERELLA-GRAMINICOLA IN HEXAPLOID WHEAT

Septoria tritici blotch constitutes a major disease problem of wheat w orld-wide. To efficiently breed wheat for resistance to this disease, an understanding is required of the inheritance of resistance. Our obj ective was to study the quantitative inheritance of resistance under f ield conditions. A nine-parent diallel and a generation mean experimen ts were conducted at Toluca, Mexico in 1986 and 1987, respectively, to investigate gene effects. General combining ability effects accounted for most of the variation although specific combining ability effects were detected in some crosses. Ias205/H567.71, Thornbird, and RPB709 .71/Coc contributed the most to reduced disease severity. Reciprocal e ffects were detected in two of 36 crosses, where RPB709.71/Coc contrib uted additional reduced disease severity when used as female. The anal ysis of generation means confirmed results obtained from the diallel. Additive effects were also most important. Dominance effects and epist asis, mostly of the additive x additive type, were found in some cross es. Hence, substantial genetic progress for resistance can be expected among progeny from crosses with resistant parents. However, selection would be most effective if delayed to later generations because of do minance, and choice of the specific female parent may produce a higher level of resistance.