Geographical distribution of genes for resistance to formae speciales of Erysiphe graminis in common wheat.

The geographical distribution of Pm10, Pm11, Pm14, and Pm15 wheat genes for resistance to inappropriate formae speciales of Erysiphe graminis was investigated using gene-for-gene relationships. Pm10 and Pm15 were very common among many indigenous accessions of common wheat collected from various areas in the world. The diversity of genotypes, which consisted of allelic combination at those loci, was high near the center of origin of common wheat and decreased with increasing distance from the center. In Europe, an apparent contrast of predominant genotypes occurred between the south and the north, suggesting that these genes are useful markers for revealing the routes by which common wheat spread in Europe. On a whole, the genes for resistance to inappropriate formae speciales were observed to be widely distributed throughout the world. We suggest that the difference between these genes and the genes for resistance to races of an appropriate forma specialis may only be in their distribution and that of their corresponding avirulence genes.