Genetics of avirulences in Erysiphe graminis f sp hordei

The genetics of avirulences towards barley mildew resistances were analysed in crosses of the Erysiphe graminis f.sp. hordei isolate DH14 with CC107 and with CC138. Nine avirulences, Avr(a9), Avr(a10), Avr(a11), Avr(a12), Avr(Ab), Avr(CP), Avr(h), Avr(k) and Avr(La), segregated as single genes in one or other cross. However, F-1 segregation data were consistent with avirulence matching the Mla7 resistance gene being controlled by two genes, designated Avr(a7)1 and Avr(a7)2. Infection types of avirulent isolates differed on varieties in which Mla7 had been derived from each of the four known sources of that resistance. Linkage was detected between Avr(a7)1 and Avr(h) in the cross CC107 x DH14, and between Avr(a10) and Avr(k), Avr(a11) and Avr(La), and Avr(h) and the triadimenol response gene Tdl2 in CC138 x DH14.