GENETICS OF AVIRULENCES IN ERYSIPHE-GRAMINIS F SP HORDEI

The genetics of avirulences towards barley mildew resistances were ana lysed in crosses of the Erysiphe graminis f.sp. hordei isolate DH14 wi th 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 a s single genes in one or other cross. However, F-1 segregation data we re consistent with avirulence matching the Mla7 resistance gene being controlled by two genes, designated Avr(a7)1 and Avr(a7)2. Infection t ypes of avirulent isolates differed on varieties in which Mla7 had bee n derived from each of the four known sources of that resistance. Link age 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) an d the triadimenol response gene Tdl2 in CC138 x DH14.