Management of pumpkin mosaic using selected medicinal plant extracts

Abstract

"Management of pumpkin mosaic using selected medicinal plant extracts" was undertaken in the College of Horticulture, Kerala Agricultural University, Vellanikkara, Thrissur during 1998-2002. Selection of suitable medicinal plant having antiviral property to pumpkin mosaic virus (PMV), isolation of the inhibitory principle present in the medicinal plant, management of pumpkin mosaic using the plant extract and partial purification and serological studies of PMV were the objectives of the study. Symptomatology, transmission, host range and electron microscopy of PM V were also studied. The symptomatology of pumpkin mosaic was studied by observing the development of symptoms in naturally infected as well as artificially inoculated pumpkin plants. The symptoms appeared as typical mosaic mottling with light and dark green patches in the leaf lamina. This was followed by blistering and malformation of leaves into filiform or some other shapes and resulted in reduction of leaf area. The infected plants were stunted, flowered very sparingly with less number of female flowers and reduced fruit setting. The fruits were often malformed . The virus could be transmitted mainly through sap and vector, Aphis gossypii. The virus found to be weakly transmitted also through seeds. The inoculation of PMV on host plants of four families viz., cucurbitaceae, solanaceae, fabaceae and caricaceae showed systemic infection in water melon, snake gourd, bitter gourd, winter squash,' wild ash gourd (cucurbitaceae) chilli, datura (solanaceae), soybean, cow pea (fabaceae) and papaya (caricaceae). Electron microscopic studies revealed the presence of flexuous virus particles (700-800 x 11 nm) in infected leaf sample. Antiserum was raised against the virus and used for serodiagnostic work. The antiserum showed serological relationship with poty viruses infecting snake gourd, bitter gourd, wild ash gourd, cowpea, soybean, chilli and papaya. DAC- ELISA procedure was standardized and used for detection of PM V from pumpkin.

The inhibitory property of extracts of five medicinal plants namely Basella alba, Glycyrrhiza glabra, Phyllanthus fraternus, Plumbago rosea 'and Thespesia populnea were studied-against PMV by pre-inoculation application on pumpkin seedlings. The medicinal plant extracts were prepared using different extraction media viz., chloroform, distilled water, ethyl acetate and petroleum ether at different dilutions. The inhibitory property varied with extraction media and dilution used. The PMV inhibitory property of different parts of Plumbago viz., tender leaf, mature leaf, tender stem, mature stem and root were studied at different temperatures and found that all parts showed inhibitory property which varied with temperature. The root extract which showed the maximum inhibitory property at 30°C (near to room temperature) was used for further studies. The effect of Plumbago on vector transmission was studied by applying the extract before acquisition feeding and inoculation feeding of Aphis gossypii, the vector of PMV. Application before inoculation feeding was found to be effective than acquisition feeding and the inhibitory effect decreased with time after application. Distilled water extract of Plumbago was separated through silica gel column to isolate the inhibitory fraction and found that individual fractions were not effective as plant extract as such against PMV. The inhibitory effect of Plumbago water extract one per cent, on artificially inoculated and healthy pumpkin seedlings was tested by weekly, fortnightly, monthly, bimonthly and single application. Weekly spray was effective to reduce disease severity of artificially inoculated and naturally infected pumpkin seedlings. Delayed incidence of the mosaic and enhanced yield of infected plants was also resulted due to weekly spray of the extract. Enzyme, protein, chlorophyll and phenolics estimation revealed that Plumbago extract spray favoured the resistance and thereby suppression of symptoms. The DAC-ELISA of field samples showed the lower concentration of the virus in Plumbago treated plants.