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Incidence of Prunus Necrotic Ringspot Virus in Selected Peach Orchards of South Carolina. S. W. Scott, Department of Plant Pathology and Physiology, Clemson University, Sandhill Research and Education Center, Elgin, SC 29045-0280. O. W. Barnett, and P. M. Burrows. Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29634-0377; and Department of Experimental Statistics, Clemson University, Clemson, SC 29634-0367. Plant Dis. 73:913-916. Accepted for publication 1 March 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0913.

A survey was conducted in 1987 to determine the prevalence of Prunus necrotic ringspot virus (PNRSV) in peach orchards of South Carolina and to investigate variation in the incidence of the virus among the major cultivars and production areas. Virus detection was by ELISA of floral or juvenile tissues. The major peach cultivars grown in the state were sampled, with the design of the survey being based on the counts reported in a triennial statewide census of peach trees last completed in 1985. Samples were collected from trees 610 yr old. A bud stick was collected from each quadrant of a tree, and tissue from the four sticks was combined to form the sample extracted for ELISA. A total of 5,833 trees was sampled from seven cultivars in 114 orchards in the three peach-growing regions of the state. Observed incidence of PNRSV in individual orchards ranged from 0 to 100%. After adjustment for effects of regions, growers, and orchard age, the estimated incidences of PNRSV in the cultivars were 6.9% in Harvester, 10.6% in Junegold, 15.0% in Redglobe, 39.5% in Loring, 44.1% in Blake, 52.9% in Coronet, and 74.5% in Redhaven. Some young orchards were apparently 100% infected; these were inferred to have been established with trees propagated from sources of scionwood infected with PNRSV. At these levels of infection the potential yield losses caused by this virus are immense. As the virus was detected by ELISA, however, certain constraints on estimating losses based upon such data exist.