Segregation of Avirulences and Genetic Basis of Infection Types inErysiphe graminisf. sp.hordei

The genetics of avirulence were studied in crosses of the barley powdery mildew fungus Erysiphe graminis f. sp. hordei (synamorph Blumeria graminis f. sp. hordei). The number of genes controlling avirulence on 10 near-isogenic lines of Pallas carrying different resistance genes were determined, as were the incompatible infection types (ITs) they conferred. Four crosses were made between isolates of different origins, and one cross, CC52 x DH14, was analyzed further with backcrosses and sibcrosses. Avirulence on P11 (Mla13) was controlled by two genes giving different ITs: Avr a13 1 with ITs 0 or 0-1 and Avr a13 2 with ITs 1-2 or 2. Two hypotheses can be suggested: (i) P11 carries a second gene, Mla(Ru3), in addition to Mla13, and each resistance gene matches one avirulence gene; or (ii) P11 carries the single resistance gene Mla13, which matches the two avirulence genes. Avirulences on P01 (Mlal), P08B (Mla9), P09 (Mla10), P10 (Mla12), P12 (Mla22), P16 (Mlkl), and P21 (Mlg) were controlled by one gene in all crosses in which phenotypes segregated. It could not be concluded whether avirulence on P04B (Mla7) and P23 (MlLa) was controlled by one or two genes. One linkage group, including Avr a9 , Avr a10 , Avr a22 , Avr k1 , and probably Avr a13 1, was detected.