Ecology and epidemiology of benyviruses and plasmodiophorid vectors

Beet necrotic yellow vein virus (BNYVV) and Beet soilborne mosaic virus (BSBMV) are members of the genus Benyvirus, and Burdock mottle virus (BdMV) is a tentative member. BNYVV and BSBMV are vectored by the plasmodiophorid Polymyxa betae, which has a worldwide distribution. Polymyxa betae is morphologically indistinguishable from P. graminis, but recent molecular studies support separation of the two species. The geographic distribution of BNYVV is also worldwide, but BSBMV has been identified only in the United States. In Europe and Japan, several genotypic strains of BNYVV have been identified, and those with a fifth RNA appear to be more aggressive. No thorough survey of genotypic variability of BNYVV or BSBMV has been conducted in the United States. However, both viruses are widespread and frequently found in the same field, infecting the same beet plant. The implications of this close proximity, with regard to disease incidence and severity, and for recombination, are uncertain. Recent technological advances that permit improved detection and quantification of these viruses and their vector offer tremendous research opportunities.