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Rubus ellipticus, a Perennial Weed Host of Prunus Necrotic Ring Spot Virus in India

Rubus ellipticus is a perennial shrub occurring in natural vegetation of the temperate and subtropical Himalayas. For several years, plants of R. ellipticus in and around the Institute of Himalayan Bioresource Technology in Palampur were seen with mild mosaic and chlorotic symptoms on leaves followed by necrotic ring spots. Infected plants often recovered from the symptoms. The causal agent was mechanically transmissible to several herbaceous hosts including Cucumis sativus, Chenopodium album, C. quinoa, Cucurbita maxima, C. pepo, Melilotus alba, Trifolium repens, and Zinnia elegans. The virus incited chlorotic local lesions followed by systemic necrotic lesions or ring spots and severe stunting on C. sativus. Several aphid species (Myzus persicae, Aphis gossypii, A.fabae-solanella, Brevicoryne brassicae, and Macrosiphoniella sanbornii) were tried as viral vectors, but all failed to transmit the virus. Virus has been detected in pollen and fruit of infected plants. Ilarvirus-like particles, 27 nm in diameter, were observed in partially purified extracts of symptomatic plants of R. ellipticus and in experimentally infected C. sativus plants, but not in healthy plants. The isolate was distantly serologically related to apple mosaic virus and unrelated to tobacco streak virus. Presence of Prunus necrotic ring spot virus (PNRSV) in symptomatic plants was also confirmed by enzyme-linked immunosorbent assay with antiserum from American Type Culture Collection and Agdia, Inc. (Elkhart, IN). This is the first report of a viral disease in R. ellipticus. The presence of PNRSV in a new weed host may become an important constraint to production of susceptible agronomic crops around Palampur.