Epidemiology of ryegrass mosaic virus in South Africa

Abstract

The distribution and seasonal occurrence of ryegrass mosaic virus (RMV) in South Africa was determined. Italian ryegrass plants were collected from eight different research stations twice during the growing season in 1990 and 1991. Samples were tested for the presence of RMV by means of symptomology, electron microscopy, transmission and serology. The virus was found in only three of the tested sites, namely, Nooitgedacht (Ermelo), Cedara (Pietermaritzburg) and Glen (Bloemfontein). At Nooitgedacht and Cedara, the number of infected plants increased from mid‐season to late season, while at Glen, the number of infected plants was low at mid‐season and decreased even further by late season. It is suggested that the distribution and intensity of RMV may depend on regional temperature differences.