Virus diseases of subterranean clover

SUMMARY Subterranean clover (Trifolium subterraneum) is grown as a pasture legume in several temperate regions of the world where the soils are acidic and infertile, and the rainfall is winter dominant and less than 600 mm annually. It is particularly important in southern Australia where more than 16 million ha have been sown with this species as the pasture legume component. Nine viruses have been recorded infecting subterranean clover in the field. These are alfalfa mosaic, bean yellow mosaic (pea mosaic), beet western yellows, clover yellow vein, cucumber mosaic, pea enation mosaic, soybean dwarf (subterranean clover red leaf), subterranean clover mottle and white clover mosaic. In addition there is an important problem referred to as subterranean clover stunt that was assumed to be caused by a virus but whose aetiology is still unknown. The importance of these diseases is reviewed and details on their epidemiologies are outlined together with details on progress towards their control and some comments on matters worthy of attention in the future. Reference is also made to several exotic viruses known to infect subterranean clover experimentally that could possible cause problems if introduced into Australia.