Studies on beet western yellows virus in oilseed rape (Brassica napus ssp. oleifera) and sugar beet (Beta vulgaris)

Abstract

SUMMARYOilseed rape (Brassica napus L. ssp. oleifera) was studied as a potential overwintering host for the sugar‐beet yellowing viruses, beet yellows virus (BYV) and beet mild yellowing virus (BMYV), and their principal vector, Myzus persicae. In spring 1982, plants infected with a virus which reacted positively in enzyme‐linked immunosorbent assay (ELISA) with BMYV antibody globulin were found in oilseed‐rape crops; none of the plants contained virus which reacted with BYV antibody globulin. This virus was subsequently identified as beet western yellows virus (BWYV). No leaf symptoms could be consistently associated with infection of oilseed rape, but the virus was reliably detected by sampling any leaf on an infected oilseed‐rape plant. Some isolates from oilseed rape did infect sugar beet in glasshouse tests, but the proportions of inoculated plants which became infected were low. Apparently there is therefore little danger of much direct transmission of BWYV by M. persicae from oilseed rape to sugar beet in spring.BWYV was introduced to and spread within oilseed‐rape crops in autumn by M. persicae, and autumn‐sown oilseed rape proved to be a potentially important overwintering host for M. persicae. In a survey of 80 autumn‐sown crops of oilseed rape in East Anglia, northern England and Scotland in spring 1983, 78 were shown to be extensively infected with BWYV.Experimental plots of oilseed rape with 100% BWYV‐infection yielded approximately 13.4% less oil than plots with 18% virus infection, the result of a decrease in both seed yield and oil content.