CAUSAL AGENTS OF POWDERY MILDEW OF CUCURBITS IN SUDAN

In a survey of cucurbit crops in Sudan, 234 samples of melon, cucumber , and squash showing symptoms of powdery mildew were infected with Sph aerotheca fuliginea, while Erysiphe cichoracearum was only observed on two samples of watermelon showing mild symptoms, Leveillula taurica w as not observed on any sample. Field trials with differential lines of melon revealed the presence of race 1 of S. fuliginea in Gezira (Cent ral Sudan) in the summer of 1993, and race 2 in the following winter. Virulence tests in controlled conditions on a limited number of isolat es suggest that a shift in prevalence of those races may have occurred on that site over time. The geographic scale of this shift was probab ly limited as race 0 was observed in late autumn in northeast Sudan in the Gash Delta.