Characterisation and management of bitter gourd distortion mosaic virus

Abstract

Studies on ‘Characterisation and management of bitter gourd distortion mosaic virus (BGDMV)’ conducted at College of Horticulture, Vellanikkara and Sugarcane Research Station, Thiruvalla during 1999-2004 dealt with various aspects especially on transmission, etiology, characterisation, identification of virus and management.

Transmission studies proved that BGDMV was not transmitted through sap and seed. Germination percentage of seeds from infected plants was 45 per cent whereas seeds from healthy plants showed 85 per cent germination. The seedlings raised from infected seeds were pale, lanky and non vigorous.

Studies on insect transmission revealed that whitefly, Bemisia tabaci Genn. was the vector of BGDMV. Minimum acquisition and inoculation feeding period for B. tabaci for transmission of BGDMV were found to be 15 min.

Under natural conditions, common symptoms observed were light green and dark green mosaic patterns, curling, crinkling and distortion of leaves, reduction in number of flowers and fruits and reduction in size of fruits. Under artificial inoculation, symptoms initiated as light green and dark green mosaic patches in inoculated leaves, which later spread to young leaves and resulted in brittleness, pointed leaf lobes and crinkling. Average incubation period of BGDMV in bitter gourd plant was 14 days and the incubation period was found to decrease with increase in acquisition feeding period, inoculation feeding period and increase in number of viruliferous insects. A single viruliferous whitefly was capable of transmission upto 33 per cent and cent per cent transmission was obtained with increase in number of whiteflies to 10.

Host range studies revealed that ash gourd, bottle gourd, coccinia, cucumber, pumpkin, snake gourd and water melon were not collateral hosts for the perpetuation of the virus.

Purified preparations of BGDMV gave a characteristic ultraviolet absorption spectra of nucleoprotein with a peak at 241 nm. Average A260/A280 value of purified preparation of BGDMV was 1.62 and average concentration of the virus was 0.132 mg ml-1/100 g plant tissue.

Characterisation of nucleic acid and viral proteins did not show any specific band of virus particles due to low concentration of particles in the purified preparation. Hence nucleic acid and protein coat could not be characterized. However SDS-PAGE of BGDMV infected field sample gave two additional bands at 16,419 and 24,970 D which could be proteins induced in host plant by virus infection.

Electron microscopic observation of purified preparation of BGDMV gave monomers of size 18 nm diameter and geminate particles of size 18-20 x 30 nm. Infected samples from the field showed flexuous rod shaped particles of 750 nm resembling poty virus, in addition to geminate particles of size 18-20 x 30 nm, indicating a mixed infection of gemini and poty viruses.

Immunosorbent electron microscopic observations using Indian cassava mosaic virus antiserum did not give a positive reaction, thus ruled out the relationship between BGDMV and Indian cassava mosaic virus.

Serological tests using DAC-ELISA with 10-1 dilution of BGDMV showed that the virus was closely related to squash leaf curl virus.

Based on transmission, electron microscopy and serological studies it was proved that the causal agent of bitter gourd distortion mosaic disease is a virus belonging to genus Begomo virus of family Geminiviridae.

In the management studies, it was found that none of the treatments was found effective in preventing BGDMV infection. Disease incidence and severity and coefficient of infection showed a progressive trend with growth of the plant. Considering the overall performance of various treatments during the two seasons, it was found that treatment of imidacloprid 0.025 per cent was very effective in reducing disease incidence, disease severity and coefficient of infection.

In the present study, application of coconut vinegar one per cent was also found to be effective in reducing disease incidence and severity of BGDMV.

In the present study also treatment with Apis melliphica 30 potency and Arsenicum album 30 potency showed reduction in BGDMV and also increase in yield.

During the second season, all the treatments were effective in reducing whitefly population than control.

Studies on weather parameters showed that influence of mean maximum temperature, mean relative humidity on disease incidence varied with two seasons. Relative humidity in the forenoon showed positive correlation with disease incidence and disease severity in both seasons, and hence found to be the most influencing weather parameter in BGDMV infection.