Distribution of Bacillus thuringiensis in the Soils of Nepal and Their Bioassay
AbstractA study was carried out to isolate indigenous lepidopteran-toxic Bacillus thuringiensis strains from the soils collected from different regions of Nepa1.A total of 350 soil samples were collected from far western, mid western, western, central and eastern regions covering 33 districts in Nepal.Three thousand eight hundred colonies recovered after acetate selection, were screened for bipyramidal crystal morphology Eight strains of B. thuringiensis were isolated and bioassayed for their effectiveness against the cabbage butterfly, Pieris brassicae nepalensis Doubleday and the cotton bollworm, Helicoverpa armigera Hubner. Results showed the prevalence of B. thuringiensis from an altitude ranging from 72 to 5050 m. above sea level (masl) in the soils. Among the eight B, thuringiensis strains isolated, Chit-5 isolated from uncultivated land in Chitwan (400 masl) proved to be the most efective against the third instar larvae of both the above insects. The other isolates showed varying degrees of toxicity to both or one of the pest species. Preliminary qualitative bioassay demonstrated that the local strain Chit-5 was more toxic than the commercial strain of B. thuringiensis used in the study. Further investigation is needed in this area.
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