First report of Papaya ringspot virus – W in bottlegourd (Lagenaria siceraria) from India

Bottlegourd (Lagenaria siceraria) is an important vegetable crop of cucurbitaceae. In recent years, mosaic disease has been one of the major constraints to the cultivation of this crop in the Maharashtra State. Surveys indicated that bottlegourd mosaic disease is endemic in the Nasik, Ahmednagar and Pune regions of this State, where the incidence varies from 10 to 100%. A representative bottlegourd mosaic isolate (BgM-NW-3), collected from Wadner, Nasik was studied. The virus isolate produced characteristic symptoms of mosaic, mottling, interveinal chlorotic bands, leaf distortion, malformation of fruits and reduction in fruit size (Fig. 1, Fig. 2. In severe infections, blisters on the surface of fruit is a common occurrence (Fig. 2c).

The virus was transmitted by mechanical inoculation and also by the aphid vector Aphis gossypii. The virus isolate produced systemic mosaic mottling symptoms in 11 cucurbitaceous and three solanaceous hosts but failed to infect leguminous ones.

ELISA testing using sixteen antisera from five distinct virus groups (poty, cucumo, tobomo, tospo and ilarviruses) revealed that the virus isolate reacted strongly to Papaya ringspot virus (P and W strains), in addition to weaker reactions with 3 other potyvirus antisera: Tobacco etch virus, Chilli veinal mottle virus and Potato virus Y. It failed to react to Zucchini yellow mosaic virus (ZYMV) antiserum. Electron microscope examination of purified preparations of BgM-NW-3 revealed typical potyvirus-like flexuous particles of 750-780 nm long and 11-13 nm wide. The same preparations were decorated with PRSV-W antiserum after immunosorbent electron microscopy. Representative field isolates collected from Maharashtra, Andhra Pradesh, Karnataka and Chattisgarh tested positive for PRSV but negative for ZYMV by DAS-ELISA. Cross inoculation studies showed that a PRSV-P isolate from papaya infected bottlegourd but mosaic virus isolated from bottlegourd failed to infect Papaya; indicating that the virus isolate under study is a cucurbit isolate (W) and not a papaya isolate (P). In addition Beta vulgaris, a non-host for PRSV-W, failed to infect. These results indicate that the bottlegourd mosaic virus isolated from Nasik and other regions is a potyvirus closely related to PRSV-W and distinct from the virus previously reported by Verma et al. (2004).