MULTIPLE TRANSMISSION OF PLANT-VIRUSES BY OLPIDIUM-BRASSICAE

Tobacco necrosis virus (TNV), tobacco stunt virus (TSV), and lettuce big-vein virus (LBVV) in various combinations were transmitted by zoospores of Olpidium brassicae. Zoospores, obtained by immersing washed roots of TSV-Olpidium (tobacco strain)infected tobacco (Nicotiana tabacum 'Bright Yellow') or of LBVV-Olpidium (lettuce strain)-infected lettuce (Lactuca sativa 'Great Lakes') in 0.01 M phosphate buffer pH 7.0, transmitted TNV when the partially purified virus was added to the zoospores prior to dip-inoculation of mung bean (Phaseolus aureus) seedlings, as did zoospores from virus-free tobacco or lettuce strains of O. brassicae. There were no significant differences in TNV acquisition and transmission between virus-free Olpidium and Olpidium from TSV- and LBVV-infected source plants regardless of the strain of Olpidium. When inoculum, prepared by crushing the roots of mung beans previously inoculated by dipping in suspensions containing TSV-Olpidium zoospores or LBVV-Olpidium zoospores, was poured into the soil around tobacco or lettuce seedlings, TSV symptoms were produced in tobacco and LEVV symptoms in lettuce. TNV became dominant when crushed root inoculum from mung beans previously inoculated with TNV + TSV-Olpidium zoospores or TNV + LBVV-Olpidium zoospores was poured into son in the same way. This is the first systematic demonstration of multiple transmission of plant viruses using different strains of O. brassicae.