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Subject: Plant Pathology × Author: KAU × End date: 1993 × Start date: 1993 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Leaf blight of banana and its control
    (Department of Plant Pathology, College of Agriculture, Vellayani, 1993) Saj, KV; KAU; Sulochana, K K
    Survey conducted to study the fungal pathogens causing leaf blight disease in banana in the three agricultural subdivisions of Thiruvananthapuram district, yielded seven fungal pathogens viz., colletotrichum musae, Curvularia sp, Guignardia musae, khuskia oryzae, Nodulisporium gregarium, Pestalotiopsis versicolor and Phaeoseptoria sp. Among these, Curvularia sp, Khuskia oryzae and Nodulisporium gregarium are new reports. Morphological characters and pathogenicity tests of all the seven isolated cultures were studied and described. Detailed studies were conducted on five fungal pathogens viz., C. musae, G. musae, K. oryzae, N. gregarium and Phaeoseptoria sp., since severe infections could be noticed by these fungi. Studies conducted on the growth and sporulation of pathogens on different, media indicated that Richard’s medium was the best for C. musae and G. musae, potato dextrose medium for K. oryzae and Phaeoseptoria sp. In the case of N. gregarium, potato dextrose agar and Czapek (Dox) broth were found to be the best solid and liquid media respectively for its growth. Best growth of C. musae, N. gregarium and Phaeoseptoria sp was obtained with maltose as the carbon source, whereas G. musae and K. oryzae utilized maximum starch and sucrose for their growth. Maximum mycelial weight of C. musae was obtained with sodium nitrate as nitrogen source, G. musae and K. oryzae with potassium nitrate, N. gregarium with glutamine and Phaeoseptoria sp. with asparagine. Potato dextrose broth and Richard’s solution were found to be best media for the toxin production by C. musae K. oryzae , G. musae and Phaeoseptoria sp. produced maximum toxin in Richard’s solution and N. gregarium in potato dextrose broth. Host range studies of the pathogen (s) conducted indicated that they can infect a number of economically important plants like, clove, cocoa, colocasia, nutmeg and tapioca, but none of the pathogens could infect clerodendron. Dithane M-45, calixin and Bavistin were able to inhibit the growth of the leaf blighting pathogens under laboratory conditions and under field conditions Dithane M-45 (0.2%) was found to be the best. Varietal screening trials showed that variety Rasakadali was moderately resistant/tolerant among the four popular varieties screened, whereas Nendran was the most susceptible variety.
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    ThesisItemOpen Access
    Control of collar rot and root-knot of cowpea with VA mycorrhizae
    (Department of Plant Pathology, College of Agriculture, Vellayani, 1993) Deepti, N Varadan; KAU; Sivaprasad, P
    The objective of the present study was to evaluate VA mycorrhizae as a biocontrol agent against collar rot caused by Rhizoctonia solani and root-knot nematode Meloidogyneincognita in cowpea. Three different pot culture experiments were conducted. The first two were conducted to assess the effectiveness of VA mycorrhizal fungi viz. Glomus fasciculatum, G. mosseae and Acaulospora morroweae to suppress the pathogen R. solani and the nematode M. incognita. The results of the first two experiments revealed that G. fasciculatum is the best VA mycorrhizal fungus in terms of reducing the disease intensity (collar rot) and nematode population. Artificial inoculation with VA mycorrhizae significantly increased mycorrhizal colonization, nodulation, fresh weight, dry weight, plant height and leaf number of plants. A. morroweae was found to be a comparatively weaker symbiont in terms of increasing growth and suppressing the pathogens. Based on these results G. fasciculatum was used for further studies. Analysis of total phenols was done under conditions of interaction of G. fasciculatum, R. solani and M. incognita. Plants inoculated with VA mycorrhiza always showed a higher phenol content compared with the plants not inoculated with mycorrhiza. There was a significant positive correlation between mycorrhizal colonization and phenol content of plant tissue. Hence, the VA mycorrhizal mediated disease tolerance could be attributed to the enhanced phenol accumulation. The present investigation reveals that VA mycorrhizal technology has much potential as a biological tool for the management of root pathogens of cowpea. However, for practical application, the appropriate organism, for the host/environment should be chosen.