M.Sc. (Agri.) dissertation

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Date
2005
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Publisher
AAU, Anand
Abstract
Investigations on various media for establishing their suitability for favourable growth and efficacy of agrochemicals and bio-pesticides including phytoextracts for their inhibitory action against Cercospora nicotianae, the cause of frogeye spot disease of bidi tobacco under in vitro conditions were carried out at Bidi Tobacco Research Station, Anand Agricultural University, Anand during 2003-04. In subsequent study, effective fungicides, insecticides, readymade bio-pesticides and acqueous leaf extracts of plant species were tested against the disease under nursery conditions. Reaction of bidi tobacco varieties/genotypes against the disease under nursery conditions was also studied Out of 7 media evaluated, carrot leaf decoction agar, fennel leaf decoction agar, coriander leaf decoction agar and sava leaf decoction agar were found to be highly favourable for good growth of C. nicotianae (52.40 to 60.80 mm colony diameter). Among these, fennel leaf decoction agar, coriander leaf decoction agar and sava leaf decoction agar were established for the first time as suitable media for the growth of the fungus (52.40 to 54.80 mm colony diameter) under laboratory condition. Carbendazim, thiophanate methyl, benomyl, mancozeb and Cosco (Carboxin 37.5 % + Thirum 37.5 %) 75 WP were most effective and completely suppressed the growth of the fungus on carrot leaf decoction agar under in vitro condition. Out of 16 insecticides, carbaryl and dichlorovos were effective and inhibitated the growth to the extent of 85.9 and 82.6 %, respectively. Among 29 plant species evaluated, acqueous leaf extract of Tecoma stans @ 25 % was most effective (76.0 % inhibition); this was followed by E. citriodora (49.0 % inhibition). Six readymade bio-pesticides viz., Econeem, Biosoft, Halt, Vanguard, Monitor-WP and Biolep were found highly effective in inhibiting the growth of C. nicotianae in vitro; the per cent inhibition ranged between 75.3 and 92.4. Results of evaluation of effective fungicides, viz., carbendazim @ 0.025 %, thiophanate methyl @ 0.07 %, mancozeb @ 0.2 %, Cosco @ 0.3 % and benomyl @ 0.025 %, leaf extracts of plant species viz., Tecoma stans and Eucalyptus citriodora, both at 25 %, insecticides carbaryl @ 0.2 % and dichlorovos @ 0.05 % and readymade biopesticides viz., Econeem @ 0.075 % and Biosoft @ 0.4 % under nursery conditions revealed that among fungicides, carbendazim and thiophanate methyl were most effective in the management of the disease giving better yield of transplants; these fungicides gave 100 and 96.6 % control, respectively. Between two plant species, acqueous leaf extract of T. stans gave 85.0 % control of the disease and significantly more number of transplants than control. Taking into account two most important attributes in the nursery viz., per cent disease intensity and transplants, two insecticides and two readymade bio-pesticides tested were not considered as effective against the disease. Among 10 different varieties/genotypes screened none was found free from the disease under nursery conditions. The variety GTH1, however, had minimum per cent disease intensity (45.60) and the variety Anand 119 had maximum per cent disease intensity (73.67). The results of the present investigations, thus, indicated that in addition to carrot leaf decoction agar, three more media viz., fennel leaf decoction agar, coriander leaf decoction agar and sava leaf decoction agar were established as favourable for the growth of C. nicotianae under laboratory condition. Two fungicides, carbendazim and thiophanate methyl, were most effective in the management of the disease in nursery. Efficacy of acqueous leaf extract of T. stans against frog-eye spot disease in nursery was established for the first time; it was found to yield significantly more number of transplants when compared with control. Leaf extract of T. stans could be used individually as botanical pesticide in minimizing losses due to the disease in question or it could be integrated with chemical fungicide/s. If integrated, it could help in minimizing frequency of applications of chemical fungicide/s, thus reducing the cost of seedlings production. Under these circumstances, it would also minimize the danger of resistance development in C. nicotianae under nursery conditions. However, detailed integrated schedule would need to be worked out before it can be advocated to the growers. Since none of the ten varieties/genotypes of bidi tobacco was resistant, it ultimately suggested that more extensive work involving very large number of genotypes is needed in order to locate resistance or tolerance to frog-eye spot disease.
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agriculture, plant pathology, study
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