Characterisation of Bacillus thuringiensis kurstaki strains by toxicity, plasmid profiles and numerical analysis of their cryIA genes

In the present comparative study, four Bacillus thuringiensis kurstaki strains (HD1, dipel, HD73, HD1dipel) were characterized by investigating their total plasmid profiling; cryIA genes profiling andtoxicity towards local isolates of agricultural insects Helicoverpa armigera and Spodoptera litura. Result showed that LC50 for S. litura were 0.11 g of HD73, 0.027 g of HD1, 0.20 g of dipel and 0.018g of HD1 dipel, while LC50 for H. armigera insect were 0.04 g of HD73, 0.031 g of HD1, 0.011 g of dipel and 0.008 g of HD1dipel. The native plasmid number and type varied from 4 - 8 among these strains and HindIII restriction showed 0.4 to 8.0 kb size fragments. The numerical classification of the cryIA gene profiles showed two distinct clusters at 48% similarity level. Cluster one of 80% similarity comprises of two strains HD73 and dipel, while cluster two of 65% consisted of HD1 and HD1dipel strains. Southern analysis of restricted plasmid combined with cryIA profile can provide an effective approach for investigation of taxonomic relationship within Bacillus thuringiensis kurstaki strains