VIRUS TRANSMISSION BY HOST-SPECIFIC STRAINS OF OLPIDIUM-BORNOVANUS AND OLPIDIUM-BRASSICAE

Zoospores of 12 isolates O. bornovanus from geographically diverse sit es and representing the three host specific cucurbit strains were test ed as vectors for seven viruses using watermelon bait plants and the i n vitro acquisition method. All isolates of the cucumber, melon, and s quash strains transmitted melon necrotic spot carmovirus (MNSV) and cu cumber necrosis tombusvirus (CNV) but none transmitted petunia asteroi d 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 necros is virus (SqNV). All cucumber isolates transmitted CLSV and SqNV but n ot CSBV. Some of the melon isolates transmitted CLSV and SqNV but none transmitted CSBV. Two squash isolates transmitted CSBV and SqNV but n ot CLSV. Two isolates of O. brassicae transmitted only TNV and a third did not transmit any of the viruses. The species of bait plant someti mes affected transmission. The most efficient vector strains of O. bor novanus, as determined by reducing zoospores and virus in the inoculum , were the cucumber strain for CLSV; the cucumber strain for CNV if cu cumber was the bait plant or melon strain if watermelon was the bait p lant; and the squash strain for SqNV. The plurivorous strain of O. bra ssicae was the most efficient vector of TNV. Olpidium bornovanus is th e first vector reported for CSBV and is confirmed as a vector of SqNV. It is proposed that all carmoviruses may have fungal vectors. Lignier a sp. did not transmit any of the viruses in one attempt.