Characterization and Evaluation of Two Indigenous Bacillus thuringiensis Isolates against Helicoverpa armigera Hubner

Two isolates of Bacillus thuringiensis isolated from dead lepidopteran larvae from a tea garden in Jorhat, Assam and one isolated from soil sample from Rajasthan, obtained in a nationwide screening program showed bipyramidal crystal morphology. These two isolates named as NBAII-BTAS and NBAII-BTG4 were characterized by their high level of toxicity against diamond back moth ( Plutella xylostella ). The PCR amplification of these two isolates revealed the expected size of the PCR product for cry 1Aa, cry 1Ab, cry 1Ac, cry 1E, cry 1G, cry 1I, and cry 2 of 390 bps, 1111bps, 238 bps, 540 bps, 300 bps, 468 bps, and 1170 bps respectively. Purified cry proteins from each of these two cultures were subjected to SDS-PAGE analysis, where, two distinct bands of 130–140 Kda and 65 Kda corresponding to cry 1 and cry 2 proteins were observed. Toxicity studies was carried out using trypsin activated purified proteins against Helicoverpa armigera , where NBAII-BTG4 derived crystal proteins displayed more toxicity (0.93µg\ml) than NBAII-BTAS.