SEGREGATION OF AVIRULENCES AND GENETIC-BASIS OF INFECTION TYPES IN ERYSIPHE-GRAMINIS F SP HORDEI

The genetics of avirulence were studied in crosses of the barley powde ry mildew fungus Erysiphe graminis f. sp. hordei (synamorph Blumeria g raminis f. sp. hordei). The number of genes controlling avirulence on 10 near-isogenic lines of Pallas carrying different resistance genes w ere determined, as were the incompatible infection types (ITs) they co nferred. 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 giv ing 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 ge ne, Mla(Ru3), in addition to Mla13, and each resistance gene matches o ne avirulence gene; or (ii) P11 carries the single resistance gene Mla 13, which matches the two avirulence genes. Avirulences on P01 (Mla1), P08B (Mla9), P09 (Mla10), P10 (Mla12), P12 (Mla22), P16 (Mlk1), and P 21 (Mlg) were controlled by one gene in all crosses in which phenotype s segregated. It could not be concluded whether avirulence on P04B (Ml a7) and P23 (MlLa) was controlled by one or two genes. One linkage gro up, including Avr(a9), Avr(a10), Avr(a22), Avr(k1), and probably Avr(a 13)1, was detected.