Investigations on mosaic disease of bitter gourd

Abstract

Bitter gourd mosaic virus disease commonly occurring in Kerala was investigated. The symptoms appeared as typical mosaic mottling with dark green and light green patches. Diseased plants were severely stunted and produced only a few flowers and fruits. Transmission studies showed that the virus could be transmitted through mechanical means, grafting and by aphid vectors. The virus was found to be transmitted by the aphids aphis gossypii Glov., Aphis malvae Koch., Myzus persicae Sclz. And aphis craccivora Koch. Among the four species of aphids, A. gossypii and A. malvae were found to be the most efficient vectors. Investigations on the physical properties of the virus revealed that the virus had a thermal inactivation point between 50 and 600C, dilution end point between 1:1000 and 1:10000, longevity in vitro between 12 and 24 h at room temperature (28 - 300C) and 48 and 72 h at 100c. The minimum acquisition feeding and inoculation feeding period of the vector A. malvae were found to be 30s and I min respectively. But the percentage of transmission was maximum when an acquisition feeding period of 30 min and inoculation feeding period of 2 h were given. Influence of starvation before acquisition and inoculation feeding period proved that pre – acquisition starvation for 2 h produced maximum infection but post- acquisition starvation decreased the per cent infection. The vector could retain the virus for I h only. A single aphid could transmit the virus to healthy test plants, but maximum percentage of transmission was obtained with 10 aphids. Host range studies showed that the virus was restricted to the members of the family Araceae, Chenopodiaceae, Cucurbitaceae, Musaceae, Polygonaceae and Solanaceae. Datura metal acted as a symptomless carrier of bitter gourd mosaic virus. Serological studies showed that bitter gourd mosaic virus is related to cucumber mosaic virus, pumpkin mosaic virus and snake gourd mosaic virus. Varietal screening showed that all the varieties and collections were susceptible to biter gourd mosaic virus infection, but the variety Arka Harit and the collections 87 green long 1 C 68234, 61 white medium 1C 45358 and 177 green medium 1C 68324 were least susceptible. Studies on estimation of loss revealed that early infection of bitter gourd plants by the virus significantly reduced the number of leaves, leaf area, intermodal length, thickness of vines, length of vines, number of branches, number of flowers, number of fruits and other fruit characters viz., length of fruits, girth of fruits, weight of fruits and total yield of fruits.