Black and Hairy Nightshade, the First Weedy Hosts of Potato virus A in the United States.

Potato virus A (PVA; genus Potyvirus, family Potyviridae) occurs wherever potatoes are grown and may reduce tuber yields as much as 40%. Its host range consists of six experimental hosts (Lycopersicon pimpinellifolium (Jusl.) P. Mill., Nicandra physalodes (L.) Gaertn., Nicotiana tabacum L., Solanum demissum Lindl., S. demissum × S. tuberosum, and Nicotiana debneyi Domin.) and two natural hosts (S. tuberosum L. and S. betaceae (Cav.) Sendt.) (1). N. physalodes and Nicotiana tabacum sometimes grow in nature in the eastern and southern United States (2) but have not been reported to be PVA sources in nature. PVA is known to survive winter in temperate climates only in tubers used for potato propagation and potato volunteers. We detected PVA in all six Black Nightshade (S. nigrum L.) and all six Hairy Nightshade (S. sarrachoides Sendt.) weeds expressing mild mosaic symptoms and growing in PVA-infected potato fields near Prosser, WA in September of 2002. PVA was not detected in any of the 24 Cutleaf Nightshade (S. trifolium) plants selected from the same fields. The virus was detected using double antibody sandwich enzyme-linked immunosorbent assay with a test kit obtained from Agdia, Inc. (Elkhart, IN) and by reverse transcription-polymerase chain reaction using primers designated 3 (gta-ctg-aac-tgg-aaa-agt-act) and 4 (ccc-tga-cag-ttg-aaa-cat-aag) (3). One positive control for these assays was a PVA virus isolate from the "Shultz Collection" provided by Robert Goth (USDA, ARS, Beltsville, MD) in 1986. The Agdia, Inc. test kit also provided a positive control. We also transmitted PVA from one of the Black Nightshade and one of the Hairy Nightshade weeds to greenhouse-produced Nicotiana megalosiphon Van Heurck & Mull. Agr., Nicotiana tabacum cv. Samsum NN, S. tuberosum cv. Russet Burbank, S. sarrachoides, and S. nigrum plants by Myzus persicae Sulzer in a stylet-borne manner. The virus was transmitted from the greenhouse test plants back to S. sarrachoides and S. nigrum plants where it produced mild mosaic symptoms identical to virus from the original sources. PVA was not transmitted from weedy sources to Datura tatula L., Physalis floridana Rydb., or S. trifolium. M. persicae readily colonized S. sarrachoides, S. nigrum, and S. trifolium in the field and greenhouse. Since black and hairy nightshade are frequently found in potato fields (4) and our findings show these weeds to be hosts of PVA, their role in the epidemiology of this disease should be more fully evaluated. References: (1) A. Brunt. Potyviruses. Pages 77-86 in: Virus and Virus-Like Diseases of Potatoes and Production of Seed Potatoes. G. Loebenstein et al., eds. Kluwer Academic Publishers, Boston, 2001 (2) A. Ogg and B. S. Rogers. Rev. Weed Sci. 4:25, 1989. (3) M. Rajamaki et al. Virology 88:311, 1998. (4) USDA, NTPD, National Plant Data Center, Version 3.5 On-line Publication, 2004.