Occurrence of alfalfa mosaic, clover yellow vein, subterranean clover red leaf, and white clover mosaic viruses in white clover throughout Australia

Abstract

The levels of infection with 4 viruses in young white clover (Trifolium repens L.) plots sown in 1991 or 1992 were monitored at a total of 17 sites across the 6 States of Australia. Tests were undertaken for alfalfa mosaic (AMV), clover yellow vein (ClYVV), subterranean clover red leaf (SCRLV) (syn. soybean dwarf), and white clover mosaic (WClMV) viruses on field samples of 17 different cultivars, plus a local naturalised ecotype at each location, twice yearly over 3 years. The tests were undertaken using double antibody sandwich enzyme-linked immunosorbent assay (DASELISA). AMV and WClMV were the most common and widespread viruses. They infected plants atmany sites soon after establishment and then rapidly increased to high levels, occasionally exceeding 90% of plants. In contrast, at some sites, no infection with these viruses was detected. Analysis of the infection data at 4 sites, where significant spread of AMV occurred, indicated that the epidemics developed like compound interest models. Tests for SCRLV were done only in 1994 when moderate levels of infection were found at most southern, winter-rainfall dominant sites. The occurrence o fClYVV was sporadic and infection levels were always low.