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International audience; Zoospores of 12 isolates O. bornovanus from geographically diverse sites and representing the three host specific cucurbit strains were tested as vectors for seven viruses using watermelon bait plants and the in vitro acquisition method. All isolates of the cucumber, melon, and squash strains transmitted melon necrotic spot carmovirus (MNSV) and cucumber necrosis tombusvirus (CNV) but none transmitted petunia asteroid mosaic tombusvirus (PAMV) or tobacco necrosis necrovirus (TNV). The isolates varied as vectors of three other carmoviruses: cucumber leaf spot virus (CLSV); cucumber soil borne virus (CSBV); and squash necrosis virus (SqNV). All cucumber isolates transmitted CLSV and SqNV but not CSBV. Some of the melon isolates transmitted CLSV and SqNV but none transmitted CSBV. Two squash isolates transmitted CSBV and SqNV but not CLSV. Two isolates of O. brassicae transmitted only TNV and a third did not transmit any of the viruses. The species of bait plant sometimes affected transmission. The most efficient vector strains of O. bornovanus, as determined by reducing zoospores and virus in the inoculum, were the cucumber strain for CLSV; the cucumber strain for CNV if cucumber was the bait plant or melon strain if watermelon was the bait plant; and the squash strain for SqNV. The plurivorous strain of O. brassicae was the most efficient vector of TNV. Olpidium bornovanus is the first vector reported for CSBV and is confirmed as a vector of SqNV. It is proposed that all carmoviruses may have fungal vectors. Ligniera sp. did not transmit any of the viruses in one attempt.

International audience

PI 525088-PMR is a watermelon (Citrullus lanatus var. lanatus) line having resistance to melon race one powdery mildew (PM) Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.). The line is derived from the U.S. Plant Introduction (PI) 525088 (Citrullus lanatus var. lanatus). PI 525088PMR does not have desirable fruit quality with fruit flesh color being white to light pink and an average Brix value of 6. However, it could be a useful parent for introducing race one powdery mildew (P. xanthii) resistance into adapted watermelon cultivars.

International audience; 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 cichor-acearum was only observed on two samples of watermelon showing mild symptoms. Ieeveillula 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.