Abstract
Mobile nurseries were used to determine the virulence frequencies of wheat powdery mildew, Erysiphe graminis f. sp. tritici in fields. Test plants were exposed for 24hr in diseased wheat plots in Hokkaido, Tokyo and Okayama Prefectures in 1987-88. Nurseries consisted of eight lines with different resistance genes and a susceptible control line. Virulence was detected for all the eight genes tested: Pm1, Pm2, Pm3a, Pm3b, Pm4a, Pm5, a gene of Sapporo-haru-komugi (PmSh1) and Mli of cv, Ibis, but there were differences in frequency among regions. There was no clear relationship between previous use of a particular resistance gene and detected frequency of virulence to the gene. Mobile nursery method is a simple and efficient way to detect rare but dangerous races of virulent pathogens, and useful for finding important sources of resistance to powdery mildew. The method has considerable merit over conventional method in determining the variability and potential virulence of wheat powdery mildew. It should be helpful in similar studies with other air-borne plant pathogens.
