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Subject: Plant Pathology × Author: KAU × End date: 1996 × Start date: 1996 × Type: Thesis × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Vascular streak dieback of cocoa and its management
    (Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Ajay Kumar, K M; KAU; Koshy, Abraham
    Vascular streak dieback (VSD) is a destructive disease of cocoa. Corticium culture medium, Water agar, Potato dextrose agar gave promising results in isolation of the pathogen. Petiole and midrib gave maximum success in isolation. Potato dextrose agar and Corticium culture media supported the growth of the fungus. Fusarium sp. And Colletotrichum gloeosporioides were the major contaminants interfering in the isolation of VSD. The morphological characters of the pathogen were studied from the sporophores occurring on naturally infected cocoa plants. Based on these characters, the pathogen causing VSD was identified as Oncobasidium theobromae Talbot and Keane. The disease produced various typical symptoms on leaves and stems of infected plants like pale green colour of leaves and subsequent yellowing with green islets, defoliation, brown marks on the scars of fallen leaves, axillary bud growth of the infected stem, rusty discolouration of cambium, vascular streak, whitish sporophores on the leaf scar of fallen infected leaves and finally the death of the infected twig. Histopathological studies showed the presence of fungal mycelium in the xylem vessels. Transmission studies by grafting and budding revealed no establishment of buds or grafts. But there was vascular streaking. No seed transmission was observed. In general Kitazin and Bavistin as a seed treatment had an effect on the height of plant and leaf production. Evaluation of cocoa types planted at three seed gradens indicated that some of them possess resistance/tolerance against VSD. Variation in disease incidence and intensity of VSD was noted in germplasm VI. Calixin spraying had an effect in preventing the incidence of the disease in seedlings.
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    ThesisItemOpen Access
    Transmission, physical properties and host range of brinjal mosaic virus
    (Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Surendran, M; KAU; Rajagopalan, B
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    ThesisItemOpen Access
    Etiology and management of damping-off of solanaceous vegetables
    (Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Bindu, Menon; KAU; Sally, K Mathew
    The etiology and management studies of damping-off of chilli, brinjal and tomato were carried out at the College of Horticulture, Vellanikkara, Thrissur during 1994-95. Bacterial wilt resistant varieties like Ujwala of chilli, Surya of brinjal and Sakthi of tomato were used for the study. Fungi like Aspergillus niger, A. flavus, Penicillium sp. And Rhizopus stolonifer were found associated with the seeds of chilli, brinjal and tomato. In addition, Curvularia lunata, Drechstera rostrata and Alternaria sp. were isolated from chilli, brinjal and tomato respectively. The pathogens responsible for pre and post-emergence-off were Rhizoctonia solani in summer and Pythium aphanidermatum, Phytophthora parasitica and Drechslera rostrata in rainy season. In varietal reaction, none of the varieties/genotypes was found to be immune to the disease. However, certain genotypes like LCA-304 of chilli, BB-60-C of brinjal and LE-79-5 of tomato showed resistance in both seasons. In in vitro studies, Bordeaux mixture (1%) and copper oxychloride (0.3%) completely inhibited the growth of P. aphanidermatum and P. parasitica whereas all six fungicides tested were found equally effective against R. solani and D. rostrata. in vitro evalution of Trichoderma viride, against all the isolated organisms of damping-off resulted in die-back and disintegration of the pathogens. Among the fungicides, seed treatment with chlorothalonil and thiram @ 2 g/kg seed gave maximum germination and minimum incidence of emergence damping-off both seasons. Bordeaux mixture (1%) and potassium phosphate (0.3%) have affected the germination of seeds especially in tomato. In rainy season, compared to all other treatments, maximum germination, and minimum pre-emergence damping-off was observed in solarized plots. Carbendazim (0.1%) and Bordeaux mixture (1%) treatments were found to be most effective in controlling post-emergence damping-off during summer and rainy season respectively. Solarization followed by application of antagonist was also equally effective as Bordeaux mixture treatment in rainy season.
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    ThesisItemOpen Access
    Development of inoculant cultures of azospirillum for rice (Oryza sativa L.) in Kuttanad
    (Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Sasikumar, S; KAU; Sivaprasad, P
    Azospirillum was isolated from the rice roots of twenty five different locations of Kuttanad, Kerala in order to develop acid and salt tolerant inoculant cultures suited for the locality. The isolates were identified as A lipoferum and A brasilense. All the isolates showed good salt tolerance up to 2% NaCl concentration and good acid tolerance up to pH 5.0 and some isolates tolerated up to pH 4.0. The nitrogen fixing capacity in vitro by the isolates ranged between 11.20 and 2.28 mg/g malate and 1AA production between 24 µg 1-1 and 55 µg 1-1. Four isolates of them were selected for pot culture trials based on efficiency of nitrogen fixation, 1AA production, root elongation and acid and salt tolerance. The inoculated plants showed increased height, number of productive tillers and beneficial influence on root parameters. All these reflected in the final grain yield and AZR 15 gave highest yield followed by AZR 37. A saving of 25% nitrogen can be made by inoculation with these cultures in rice. The acridine orange curing of plasmids conducted to know the genetic basis of salt tolerance showed that the character is plasmid borne.
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    ThesisItemOpen Access
    Varietal screening host range and control of downy mildew of Bittergourd caused by Rostow
    (Department of Plant Pathology, College of Horticulture, Vellanikkara, 1996) Mini, SImon; KAU; Sally K, Mathew
    A study was conducted at the College of Horticulture, Vellanikkara, during 1993-95, on varietal screening, host range and control of downy mildew of bittergourd (Pseudoperonospora cubensis (Berk. & Curt.) Rostow). Varieties obtained from the Department of Olericulture were screened for disease resistance and it was found that all the varieties tested were moderately susceptible to the disease. A preliminary screening of 174 genotypes of bittergourd available at NBPGR was conducted during August 1994 and all the genotypes were found to be infected. Only 32 genotypes were moderately resistant to the disease. Host range studies revealed that P. cubensis from bittergourd can infect other cucurbitaceous crops, such as bottlegourd, pumpkin, cucumber, snakegourd, ashgourd, watermelon and ivygourd. Four fungicides and four plant extracts were tested in in vitro, pot culture and field conditions to find out their effectiveness in reducing downy mildew infection. Among the fungicides, chlorothalonil (0.2%) was found to be the most effective as it gave maximum disease control, maximum yield and highest cost: benefit ratio. Among the botanicals, Ocimum leaf extract (10%) gave maximum reduction of the disease. In crop loss assessment, it was found that the highest CODEX of 60.22 per cent could cause an yield loss of 45.7 per cent under natural condition.
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    ThesisItemOpen Access
    Mycoflora associated with leaf litter decomposition in homesteads
    (Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Jannet, Daniel; KAU; Gokulapalan, C
    Fungi play an inevitable role in the biodegradion of leaf litter. The present investigation was carried out to assess the role of mycoflora in the degradation of jack and mango in the identified homestead. Many litter decomposing fungi were isolated from both jack and mango leaf litter. The period of study was during September 1993 to March 1995. Nine genera of fungi were frequently isolated from mango leaf litter of which eight belonged to Deuteromycotina, and one to Zygomycotina. Thirteen genera of fungi were frequently isolated from jack leaf litter at different stages of decomposition, of which twelve belonged to Deuteromycotina and one to Zygomycotina. The common primary colonizers isolated were Aspergillus niger, A. flavus, Penicillium citrinum, P. oxalicum, P. islandicum, Pestalotia palmarum, Colletotrichum gloeosporioides, Trichoderma viride and T. harzianum. The common fungi isolated from decomposing leaf litter of both trees were Mucor hiemalis. Members of Basidiomycotina were also isolated from decomposing leaf litter. At higher temperature the fungal counts were lower in the fresh litter but higher in decomposed leaf litter of both trees. At higher rainfall the fungal count was more in surface litter but the same was lower in decomposed leaf litter. Identification and description of 30 fungal species were carried out following slide culture technique. The weight loss was more at 450C, when compared with weight loss at 350C and 250C of both mango and jack leaf litter. The weight loss was more pronounced in the field condition as against laboratory conditions. Higher temperature and higher rainfall led to an increased rate of litter decomposition. The decay process was faster in jack indicating the higher efficiency of decomposition in the case of jack litter as compared with mango. The decomposition constant (K) for jack was 1.52 as against a lower K value of 1.03 for mango. This indicates the faster decomposition of jack leaf liter when compared with mango litter. Trichoderma viride, Trichoderma harzianum, Chaetomium globosum, Verticillium theobromae, aspergillis niger, A. ochraceous, A. tamari, Penicillium oxalicum were found to be efficient in utilizing cellulose as their sole carbon source. There was an increase in nitrogen and ash content in the decomposing leaf litter when compared with fresh litter. The carbohydrate content was more in fresh litter and the same decreased with the progress of decomposition. Inoculation studies with common plant pathogens isolated from jack and mango leaf litter were done and Colletotrichum gloeosporioides was found to infect mango and jack leaf litter producing characteristic symptoms on mango and jack.