Race identification in powdery mildew (Sphaerotheca fuliginea) on melon (Cucumis melo) in Japan

Powdery mildew fungi isolated from single lesions on leaves of susceptible melon genotypes during semi‐forcing and late‐raising cultivation in Japan were tested. All 80 of the isolated strains were identified as Sphaerotheca fuliginea. The dominant fungus races found during semiforcing cultivation were race 5 in March (100%) and race 1 in May (100%), and race 1 (80%) during late‐raising cultivation. Although the frequencies were quite low (13% in late August, but no isolation earlier in the season), two new races of S. fuliginea , which could not be identified by the differential genotypes, appeared during late‐raising cultivation. These results suggest that the resistance gene to races 1 and 5 of S. fuliginea should be introduced into the breeding materials in Japan.