Incidence, spatial patterns, and associations among viruses in snap bean and alfalfa in New York

Recent epidemics in snap bean (Phoseolus vulgaris) characterized by virus-like symptoms prompted a survey of commercial fields for Alfalfa mosaic virus (AMV). Cucumber mosaic virus (CMV), and the Bean yellow mosaic virus (BYMV)/Clover yellow vein virus (C1YVV) complex in 2002 and 2003. Snap bean fields were either remote from or adjacent to alfalfa (Medicago sativa), a putative source of these viruses. Bean fields were sampled at the bloom stage in both years. Model-adjusted mean incidences of infection by AMV, BYMV/C1YVV, and CMV were 41.96, 6.56, and 6.69%, respectively, in alfalfa, and 6.66, 6.38, and 17.20% in snap bean. In 2002, 25.9% of snap bean plants were infected by more than one virus; < 1% had more than one virus in 2003. Virus incidences did not differ between snap bean adjacent to or remote from alfalfa, but incidence of infection by AMV and BYMV/C1YVV was significantly higher in snap bean planted later in the season rather than earlier. In 2002, there was a positive association between AMV and CMV in the tendency to find both viruses in the same snap bean plant. In some years, infection by aphid-transmitted viruses can become widespread in snap bean in New York.