First Report of Twenty-two New Hosts of Potato leafroll virus.

The known host range of Potato leafroll virus (PLRV, genus Polerovirus, family Luteoviridae) is narrow, consisting of 21 species in 5 families: 3 Amaranthaceae, 2 Cruciferae, 1 Nolanaceae, 1 Portulacaceae, and 14 Solanaceae. Over a period of years, we identified 22 additional host species of PLRV in 5 new families and 1 previously identified family: 1 Chenopodiaceae, 2 Compositae, 1 Cucurbitaceae, 1 Labiatae, 2 Malvaceae, and 15 Solanaceae. The 22 additional host species are Cucurbita pepo L., Datura fastuosa L., Hibiscus golfrosens L., H. moscheutos L., Hypercymus niger L., Lactuca sativa L., Lycopersicon pimpinefolium (Jusl.) Mill., L. peruvianun L., Nicotiana accuminata Grah., N. agustifolia Comes, N. rustica L., N. tabacum L., N. glutinosa L., Ocimum basilicum L., Physalis ixocarpa Brot., P. lanceifolia Michx., P. peruvianum L., Solanum rostratum Dund., S. sarrachoides Sendtner, S. demissum L. (P.I. 230579), Spinacia oleraceae L., and Zinnia elegans Jaeq. In light of these new hosts, reevaluation of the epidemiology of PLRV may be advisable in regions where new virus hosts also host aphid vectors and where a virus host may ensure perennial survival of PLRV. Two new hosts were found naturally infected in the Columbia Basin of the Pacific Northwest. The potential impact of one of these, S. sarrachoides, a predominant and widespread weed in potatoes and an excellent host of the major PLRV vector, Myzus persicae Sulzer, may be very important. The second naturally infected host, Z. elegans, is of doubtful importance since it is largely confined to cultivated gardens, is a summer annual, and rarely is colonized by M. persicae. The new hosts were initially discovered in various experiments over a period of years. In confirmatory tests, the hosts were inoculated with six different isolates of PLRV collected from different regions of the United States. A portion of leaflet from the virus source plant, P. floridana Rydb., containing approximately 25 M. persicae, was placed on each test plant. Virus infection was assessed based on visual symptoms and double-antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) and confirmed by aphid transmission from inoculated test plants to a diagnostic host (P. floridana). Infection of the diagnostic host was confirmed based on symptoms and enzyme-linked immunosorbent assay (ELISA). Symptom severity varied markedly among symptomatic host species. Asymptomatic hosts included C. pepo, N. rustica, S. demissum, and Z. elegans. Field collections of two nonhosts, Malva neglecta Wallr. and Cardaria draba, often produced false-positive ELISA assays, but PLRV could not be isolated from these plants by aphid transmission nor detected using a polymerase chain reaction (PCR) assay. Species infected by some virus isolates but not others included C. pepo, H. golfrosens, H. moscheutos, N. rustica, N. tabacum, Lactuca sativa, O. basilicum, S. demissum, S. oleraceae, and Z. elegans. The variability in symptoms and host range indicates a considerable degree of variability in PLRV and may provide a much needed basis for PLRV strain separation and characterization. This work more than doubles the known host range of PLRV.