diversity of bacillus thuringiensis isolates in various ecosystems of mazandaran province

bacillus thuringiensis (bt) is the most important microbial agent for biological control of insect pests of agricultural crops and forest plant. effective control of these pests mostly relies on finding and practical application of native bt isolates. in this study, 160 soil samples belong to various ecological area of mazandaran province (forest, orchard, urban, agricultural and non-vegetative regions) were screened through selective sodium acetate methods and 635 isolates were acquired. the soil samples were cultured on lba, t3 and ccy media and primary and final colony selection were conducted based on appearance of bt colonies on the media and microscopic determination, respectively. as consequence of microscopic description; 375 (59.05%), 100 (15.74%) and 160 (25.19%) isolates were produced spore, spore+cap and spore+cap+crystal, respectively. the most crystal producing isolates, based on geographical and ecological categories, were observed in the isolates of sari (40.9%) and juybar (40.54%) geographical regions and forest (32.63%) ecosystem. the results showed that the forest soil samples are an appropriate source for detecting the effective bt strains.