John Fosu-Nyarko

The most economically important virus infecting subterranean clover within pastures in Australia is subterranean clover mottle virus (SCMoV) which is transmitted by trampling and grazing of stock, on mower blades, on the wheels of vehicles and through seed. SCMoV was originally discovered in 1979 in plots of subterranean clover at Karridale in south-west Australia. Subsequently, infection was shown to be common in high rainfall pastures in Western Australia, Tasmania, South Australia, New South Wales and Victoria. It was also found naturally infecting some other cultivated annual clovers, and wild annual clovers, such as cluster clover. Diseased clover plants show obvious symptoms consisting of leaf mottling, leaf distortion, decreased leaf size and plant stunting. The incidence of infection often reaches high levels within old pastures. Infection decreases herbage and seed production, diminishing feed for stock and ability of pastures to regenerate annually from seed. The virus contributes to the decline of the subterranean clover component within pastures. Although the reactions of subterranean clover and annual medics to infection with SCMoV are known, there is incomplete information on whether infection with SCMoV might pose a threat to the productivity of pastures sown with the alternative annual pasture and forage legumes currently under evaluation for their commercial potential or already being sown commercially.