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Theses

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2005 - 20102
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Subject: Plant Pathology × Author: Ayisha, R × Author: KAU × End date: 2019 ×
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    ThesisItemOpen Access
    Characterisation of a tospovirus causing necrosis disease of cowpea (vigna unguiculata (L.) walp.)
    (Department of Plant Pathology, College of Agriculture, Vellayani, 2005) Ayisha, R; KAU; Umamaheswaran, K
    Studies were conducted on the tospo virus causing necrosis disease of cowpea [Vigna unguiculata (L.) Walp.] in Kerala. This investigation was conducted to characterize the virus. The characteristic symptoms appeared as chlorotic spots, veinal and bud necrosis, distortion and reduction in leaf size. Host range studies were done and the virus was found to have its host range in the members of the families Chenopodiaceae, Solanaceae, Leguminosae, Amaranthaceae and Malvaceae. The virus was mechanically transmitted through sap extracted in 0.01M phosphate buffer (pH 7.2) containing 2mercapto ethanol. The virus could be efficiently transmitted by the aphid vector, Aphis craccivora and Thrips palmi. The virus could be transmitted through graft but not through seeds. Thermal inactivation point was 50-55oC, dilution end point, 10-2-10-3 and longevity in vitro for 4 h at room temperature (28±2oC) and 8 h under refrigerated conditions (8oC). The virus causing necrosis was identified as tospo virus by ELISA and DIBA. Virus was related to WSMV, a tospo isolate. Biochemical changes indicated a decrease in chlorophyll content in virus inoculated leaves compared to healthy control. There was no significant difference observed in carbohydrates. Increase in protein content was observed in inoculated cowpea plants. The phenol content was found more in inoculated leaves compared to healthy control. The level decreased during later stages. Peroxidase, polyphenol oxidase and phenyl alanine ammonialyase showed a decreasing trend with age in both inoculated and healthy plants. But it was comparatively high in inoculated plants. Native polyacrylamide gel electrophoresis performed for PPO and peroxidase revealed that there was four isoforms of PPO for both inoulated and uninoculated control. Only quantitative change in one of the isoform was observed in PPO. One isoform in peroxidase was observed in inoculated plant but no isoform was observed in healthy. PAGE analysis of proteins with samples extracted from diseased and healthy plants showed the presence of three novel proteins in diseased sample. One of the proteins molecular weight, 28 kDa co-relates with the N-Protein of TSWV reported earlier.
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    ThesisItemOpen Access
    Characterization and management of viral diseases of black pepper(Piper nigrum L.)
    (College of Agriculture, Vellayani, 2010) Ayisha, R; KAU; Joseph, P J
    A detailed survey was undertaken to study the occurrence and distribution of viral diseases in black pepper in Thiruvananthapuram and Kollam districts of Kerala. Disease incidence (DI) and per cent disease index (PDI) were determined during survey which showed that per cent DI varied between 0-57 and PDI between 0-18. The disease was prevalent in both the districts. Most of the local cultivars and improved varieties were susceptible to the disease. The characteristics symptoms of disease were chlorotic spots on emerging younger leaves, vein clearing, scattered chlorotic flecks followed by chlorotic mottling along veins leading to interveinal chlorosis and characteristic twisting and curling of leaves. The infected leaves were also observed to be small, crinkled, and brittle with reduced internodal length, leading to typical stunting of plants. Most of the diseased plants were found to be infected with both Cucumber mosaic virus (CMV) and Pepper yellow mottle virus (PYMo V). The presence of these viruses was confirmed through conducting enzyme linked immunosorbent assay (ELISA) on representative samples collected from different locations. The virus was not mechanically transmitted to healthy pepper seedlings. However the virus was found to be transmitted through grafting, insect vectors and also through seeds. The mealy bug, Ferrisia I virgata was found to be the efficient vector although aphid, Toxoptera aurantii, was also found to be transmitting the virus. Thermal inactivation point was recorded at a range of 40-450C and dilution end point between 10-3 and 10-4 for CMV. Host range studies revealed that virus could be readily transmitted to other species in Piperaceae family as well to some of the weed hosts. The virus was partially purified and antiserum was produced with a titre of 1:128. Identification and serological characterization of the virus was done using ELISA and DIBA. Molecular detection of the virus was also performed using PCR and a PCR product of amplicon size 500 bp and 300 bp were obtained for primers specific to CMV and banana streak virus (BSV) respectively. The pathophysiological studies revealed that virus infected plants showed increased phenol, carbohydrate and protein content. The chlorophyll content was found to be less in infected samples. The activity of defence related enzymes like peroxidase, polyphenol oxidase and phenylalanine ammonialyase were found to be more in infected plants. Electrophoretic analysis of virus infected samples through SOS-PAGE revealed the presence of two novel proteins in diseased samples. Analysis of isozymes through native gel revealed the production of an additional isoform of peroxidase and over expression of polyphenol oxidase in infected plants. In screening of varieties for the source of resistance Panniyur, 2, 3 and 4 were found moderately resistant and Karimunda was highly susceptible. Piper colubrinum showed resistance to the virus. Meristem culure attempted was unsuccessful and could not be used as a viable strategy for eliminating the virus infecting black pepper as the meristems were seen contaminated with the pepper badnavirus.