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Galinsoga mosaic virus (GMV) was isolated from Galinsoga parviflora plants growing near Gympie in south-eastern Queensland. Although the virus was always recovered from the roots of naturally infected G. parviflora plants, the tops sometimes contained no detectable virus. When soil collected near naturally infected plilnts was kept moist in a glasshouse for 15 months and periodically planted with seed or seedlings of G. parviflora, the plants continued to become infected. Addition of captafol or ethazol fungicides to the soil had no effect on transmission of GMV in a glasshouse. Air-drying the soil for 20 days abolished its infectivity to G. parvi/lora plants and also decreased the amount of virus directly extractable from it. Pasteurized or autoclaved potting mix became infective to G. pariJif/ora when mixed with GMVcontaining plant roots, tops, leaf extracts or drainage water of infected G. parvif/ora. When leafinoculated and healthy G. parviflora plants were grown together in the same autoclaved potting mix with their tops separated by a glass partition, transmission between roots occurred. When there was foliage but not root contact, transmission was also obtained. The virus was transmitted neither by seed of infected G. parviftora plants, nor by the fungus OIpidium brassicae which, with tobacco necrosis virus, usually coexisted with GMV in the field.

During an investigation of stipple streak disease of French beans near Nambour in south-eastern Queensland (Behncken 1968), the roots of a number of weed species were indexed for tobacco necrosis virus (TNV). A virus was regularly isolated from the roots of Galinsoga parvijlora Cav., an annual commonly called potato weed. It was distinguished from TNV on the basis of differences in host reactions, absence of any serological reaction with TNV antisera, and its failure to be transmitted to the roots of seedlings of mung bean (Phaseolu8 aureU8 Roxb.) by zoospores of the fungus Olpidium bra88icae (Wor.) Dang.