Powdery mildew fungi isolated from single lesions on leaves of susceptible
melon genotypes during semi-forcing and late-raising cultivation in Japan w
ere tested. All 80 of the isolated strains were identified as Sphaerotheca
fuliginca. The dominant fungus races found during semiforcing cultivation w
ere race 5 in March (100%) and race 1 in May (100%), and race 1 (80%) durin
g 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, app
eared during late-raising cultivation. These results suggest that the resis
tance gene to races 1 and 5 of S. fuliginea should be introduced into the b
reeding materials in Japan.