Incidence of six viruses was tested in white clover from 28 rotationally grazed pastures of Pennsylvania (PA), New York (NY), and Vermont (VT). Each of 17 PA pastures was sampled fall 1994, spring 1995, fall 1995, and spring 1996, and 10 pastures were sampled fall 1996. Each of five NY and six VT pastures was sampled spring and fall 1995 and 1996. Enzyme-linked immunosorbent assays (ELISA) were conducted for red clover vein mosaic virus (RCVMV), white clover mosaic virus (WCMV), alfalfa mosaic virus (AlMV), peanut stunt virus (PSV), clover yellow mosaic virus (CYMV), and the potyvirus group (POTY). RCVMV, WCMV, AlMV, and POTY were detected in 28, 28, 27, and 25 of the 28 pastures and in 67, 32, 30, and 7% of the 3,065 samples tested, respectively. PSV occurred at low to moderate levels in 11 PA pastures. PSV was rare in NY and was not detected in VT. CYMV was never found. Incidence of each virus varied significantly among pastures. For any given virus, there was not a significant variation in incidence among sampling dates within the NY-VT samples. RCVMV, WCMV, and POTY varied among dates within PA.
Polar Assembly of Clover Yellow Mosaic Virus
