Olive mild mosaic virus transmission by Olpidium virulentus

The ability of Olpidium virulentus to vector Olive latent virus 1 (OLV-1), Olive mild mosaic virus (OMMV) and Tobacco necrosis virus D (TNV-D) was evaluated. Transmission assays involved zoospore acquisition of each virus, inoculation onto cabbage plant roots followed by viral detection. Assays revealed that these viruses are transmitted in the absence of the fungus, but the transmission rates of OMMV are much higher when OMMV is incubated with O. virulentus zoospores prior to inoculation, while the transmission rates of each OLV-1 and TNV-D do not change when they are incubated with the fungus. Our data shows that O. virulentus is an efficient vector of OMMV, greatly enhancing virus transmissibility, but not that of OLV-1 nor TNV-D. Prior studies have shown that another fungus, O. brassicae, also enhances OMMV transmission. To our knowledge, this is the first report of a plant virus, OMMV, being efficiently transmitted by two different species of fungi.