Genetics of avirulence and interacting inhibitors in Puccinia striiformis f. sp. tritici.

The segregation of molecular markers and avirulence was investigated in three progeny populations of Puccinia striiformis f. sp. tritici (Pst), derived from selfing of the three European isolates DK09_11(PstS7), DK02d_12 (PstS8) and DK219_19 (PstS15). Progeny isolates were genotyped using 19 Single Sequence Repeat (SSR) markers and phenotyped for avirulence on a differential set of 34 wheat lines including at least two independent lines per Yr-gene considered. All three progeny populations were virulent to most of the tested Yr-genes and were largely homozygous for either virulence or avirulence. Segregation was observed for avirulence to Yr4, YrSp, Yr8 and a resistance specificity in Avocet S (AvS). In one population (DK219_19, PstS15), segregation ratios indicated that avirulence to Yr4 was a dominant trait controlled by a single gene. For YrSp, the observed ratios were consistent with both 13:3 and 3:1 (avirulence: virulence) suggesting that avirulence was a dominant trait, potentially controlled by either one or two interacting genes. In another population (DK02d_12, PstS8), most progeny isolates were virulent to Yr8 and AvS, and segregation ratios were consistent with both 1:3 and 3:13, suggesting the presence of dominant inhibition of avirulence or alternatively, avirulence being a recessive trait controlled by either one or two genes. The third population (DK09_11, PstS7) showed no segregation at known avirulence loci, indicating that these were homozygous either for avirulence or virulence to each Yr-gene tested.