Relative abundance of soybean viruses in South Africa

A total of 695 soyabean plants were collected during the 1993/94 and 1994/95 seasons in the major soyabean production areas of South Africa to determine the relative abundance of viruses. Soybean mosaic potyvirus was detected in 19.3% of the samples, occurring in most fields throughout the production areas. It was prevalent in the experimental trials but had a low incidence on individual commercial farms, except for 2 fields where it was present in 10 and 12.5% of the plants. Peanut mottle potyvirus was identified in 1.9% of the samples and occurred in commercial fields and experimental trials. Cowpea aphid-borne mosaic potyvirus [cowpea Moroccan aphid-borne mosaic potyvirus] was only detected in 1993/94, occurring in 1.2% of the samples collected. Alfalfa mosaic alfamovirus was detected in 0.7% of samples. Soybean rhabdovirus-associated disease was prevalent (10-50% of symptomatic plants in a field) in all commercial fields and experimental trials in the Brits/Thabazimbi, Loskopdam Irrigation Scheme and Badplaas areas. The disease was diagnosed in 20.9% of samples collected, and virus particles were regularly detected in these plants by immuno-electron microscopy. Tospoviruses were identified in 2 samples from geographically distinct fields and an unidentified flexuous, rod-shaped virus was found in a single sample