PG Thesis
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Item Etiology and immuno- molecular detection of the virus causing mosaic disease in snake gourd(Department of Plant Pathology, College of Agriculture,Vellayani, 2024-01-23) Ammu Asok, A; Krishnapriya, P JThe study entitled “Etiology and immuno-molecular detection of the virus causing mosaic disease in snake gourd” was carried out at College of Agriculture, Vellayani during 2021-2023 with the objectives of symptomatology, maintenance of virus in systemic and local lesion host, host range studies, seed transmission, aphid transmission, immunological diagnosis, molecular diagnosis and host pathogen interaction of the viruses causing mosaic disease in snake gourd (Trichosanthes anguina). Mosaic diseased snake gourd samples were collected from three taluks of Thiruvananthapuram district (Thiruvananthapuram, Neyyattinkara and Varkala) of Kerala during January-March and July-September of 2021-23. The characteristic symptoms of snake gourd mosaic disease were mosaic, mosaic mottling, vein banding, blistering, distortion, puckering on leaves and deformed fruits. The disease incidence in majority of the fields was found to be over 25.0 per cent and disease severity progressed with age of the crop. In the surveyed locations, the highest disease incidence of 94.0 to 100 per cent and vulnerability index of 72.9 to 82.7 were observed in commercial variety Kaumudi from fields of College of Agriculture, Vellayani. In snake gourd variety Baby, disease incidence of 28.5 per cent and vulnerability index of 46.6 were observed. Similar symptoms of mosaic were observed on weeds like Hemidesmus indicus (F: Apocynaceae) and Synedrella nodiflora (F: Asteraceae) in snake gourd field. The snake gourd mosaic viruses were sap transmissible and maintained in systemic host viz., snake gourd varieties Kaumudi and Baby and also in local lesion hosts viz., Chenopodium amaranticolor and Nicotiana tabacum var. Samsun. Local lesion assay revealed that viruses associated with snake gourd mosaic disease were Potyviruses and Cucumoviruses. Based on host range studies, virus was mechanically transmissible to plants of family Cucurbitaceae viz., pumpkin, bitter gourd, cucumber, ridge gourd, bottle gourd, water melon and family Solanaceae viz., Nicotiana glutinosa and Nicotiana tabacum var. Samsun. However, no symptoms were produced in tomato, chilli, brinjal and papaya. Host range studies identified viruses associated with the snake gourd mosaic disease as Papaya ring spot virus (PRSV) Type W and Cucumber mosaic virus (CMV). No seed transmission was recorded in snake gourd plants raised from seeds produced by snake gourd mosaic viruses infected plant. Aphid transmission of the virus of 30.0 per cent was observed with Aphis craccivora and 50.0 per cent was observed with A. gossypii. The viruses causing snake gourd mosaic disease were immunologically detected using Double antibody sandwich-Enzyme linked immunosorbent assay (DAS-ELISA) and Direct antigen coating-ELISA (DAC-ELISA) with polyclonal antibodies specific to PRSV and CMV respectively. Dot immunobinding assay (DIBA) detected CMV from snake gourd mosaic diseased samples. Reverse transcriptase-Polymerase chain reaction (RT-PCR) was carried out and amplicons of sizes 1200 bp and 400 bp were obtained with primers specific to coat protein of PRSV and 2a protein of CMV respectively. Comparative nucleotide sequence alignment of the isolates revealed an 86.5 and 93.8 per cent homology with PRSV and CMV isolates from Tamil Nadu respectively. Comparative amino acid sequence alignment of the isolates revealed an 88.9 and 97.8 per cent homology with coat protein of PRSV-W and 2a protein of CMV respectively. The sequences were deposited in NCBI GenBank with accession numbers viz., OR601008 and OR601007. Phylogenetic tree was constructed and PRSV isolate grouped in the same clade along with other reported PRSV type-W isolates, thus the isolate was identified as PRSV Type-W. CMV isolate from snake gourd grouped in the same clade along with other CMV isolates from snake gourd and Musa sp. Virus inoculated snake gourd plants showed a significant reduction in total chlorophyll content (0.61 mg g-1) and increase in protein content (13.79 mg g-1) at 5 weeks after transmission. The activities of defense related enzymes (peroxidase, polyphenol oxidase, phenylalanine ammonialyase, superoxide dismutase and catalase) were higher in inoculated plants compared to healthy plants. Thus, the present study revealed that snake gourd mosaic disease is caused by the combined infection of PRSV-W and CMV in the surveyed locations of Thiruvananthapuram district. Synedrella nodiflora was identified as the suitable weed host and viruses were transmitted through Aphis gossypii and Aphis craccivora.Item Integrated management of anthracnose of snake gourd (Trichosanthes cucumerina L.)(Department of Plant Pathology,College of Agriculture, Vellayani, 2016) Aswani Devi; Kamala NayarItem Eco-friendly pest management in snakegourd(Department of Agricultural Entomology, College of Agriculture, Vellayani, 2001) Sivakumar, T; Jiji, TA study was conducted to document farmers' practices for pest control, record the population of pests of snakegourd and their natural enemy complex in farmers' field, as well as to evolve an eco - friendly package of practices for pest management. The survey conducted in the farmers' field revealed that the farmers were resorting to indiscriminate use of pesticides. The recommended pesticide/ fertilizer dosage was not practised by the farmers. Quinalphos was the most widely used pesticide followed by carbaryl. The frequency of spraying was the highest at fruiting stage. The major pests observed in the field were B. cucurbitae, A.peponis, D. indica, E. septima, Aulacophora sp. A. gossypii and L. trifolii. A very low population of pests and their natural enemies were present in the farmers' fields compared to untreated plot maintained in the Instructional Farm, Vellayani. In the untreated plot there was ten fold population of natural enemies compared to farmers' field. Fruit flies were found to be serious pests causing 63.63 per cent loss in unprotected field and this emphasised the importance and necessity for fruit fly management in snakegourd fields. Three fruit fly traps viz., were tested to assess their efficacy in catching fruit flies. Among the three traps tested, banana traps consisting of palayamkodan fruit pieces and carbofuran were the best. Three snakegourd varieties viz., Kaumudi, T.A. -19 and Local, were tested against insect infestation. Kaumudi had the lowest infestation by pests like pumpkin beetle (Aulacophora sp.), leaf eating caterpillar (Diaphania indicas, snakegourd semilooper (Anadevidia peponis) and fruit fly (Bactrocera cucurbitae). Kaumudi recorded the minimum fruit fly damage and consequently, the highest yield. Field evaluation of fourteen treatments was carried out at the Instructional Farm, Vellayani during 1999-2000. Chemical insecticides were found to be very . effective in controlling the pests of snakegourd at vegetative and flowering period, but the pest population build up was the highest with them. Neem oil - garlic emulsion was the best in controlling the pest menace with the least impact on natural enemies. Population build up of pests was also low in case of neem oil - garlic emulsion. The practice of covering fruits was very effective in preventing the flies from attacking the fruits. Covering the fruits and setting up of banana traps at the rate of two traps for three plants gave the best protection against the fruit flies. The treatments involving neem oil - garlic 2.5 per cent spray at vegetative stages + covering the fruits and banana trap setting at flowering and fruiting stages gave the highest yield and benefit - cost ratio (1.938). Spraying neem oil -garlic emulsion 2.5 per cent, on need basis, at vegetative stages and setting up of banana fruit fly traps and covering the fruits with reusable polythene covers was found to be the best eco- friendly and economical package for the management of major pests affecting snakegourd.