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