Browsing by Author "Ammu Asok, A"

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    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 J
    The 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.