Isolation of Lepidopteran Active Native Bacillus thuringiensis Strains Through PCR Panning

Screening the environment for new and highly potent strains of Bacillus thuringiensis (B. thuringiensis) has become inevitable as one of the strategies for insect resistance management. By adopting the modified acetate selection method, ento - mocidally potent B. thuringiensis isolates were obtained from grain samples and soil samples from sericulture environment. PCR was performed to determine the insecticidal potential of the isolates. SDS-PAGE analysis of PCR positive isolates exhibited typical Cry1 protein profiles with 130 to 140 kDa protoxin. Preliminary larvicidal assays against Heliothis armigera with spore- crystal mixture, showed that all 30 B. thuringiensis isolates were toxic to this species. Two isolates, namely BTRX24 (B. thuringiensis RathinamXavier 24) and BTRX 28 (B. thuringiensis RathinamXavier 28) showed higher mortality compared to other isolates. A dose response efficacy study was conducted in Heliothis armigera, Plutella xylostella with BTRX24 and BTRX28. BTRX28 showed elevated larvicidal activity, which may be attributed to the presence of multiple cry genes and possible synergistic activity among the cry proteins. Periodical introduction of such new strains will play a key role in insect resistance management against