Toxicity Analysis and cry Gene Profiling of Bacillus thuringiensis Isolated from Western Ghats of Tamil Nadu State, India
Initial identification of novel cry genes from new isolates of Bacillus thuringiensis (Bt) is mainly based on the insect bioassays and screening by PCR with specific primers. In the present study, 70 new isolates of Bt from Western Ghats were analysed for toxicity against Helicoverpa armigera (Hubner) and screened by PCR for the presence of cry genes. The isolates showing 90 to 100, 50 to 89 and less than
50 per cent mortality in H. armigera were categorised into group I, II and III, respectively. Eight and fourteen new isolates of Bt were coming under the group of I and II, respectively. Whereas 48 new isolates of Bt were clustered under the group of III. The eight Bt isolates of group I gave amplification for one or more of the following cry genes viz., cry1, cry2 and cry9. The five different cry genes viz., cry1, cry2, cry3, cry4 and cry9 were found in 14 new isolates of Bt which is coming under group II. All the 48 isolates coming under group III did not show presence of cry3 gene. Among the 48 isolates, 20 isolates failed to give amplification for all the five cry genes tested. The remaining 28 isolates had one or more of the following cry genes viz., cry1, cry2, cry4 and cry9. The cry1, cry2, cry4 and cry9. Of the 70 new isolates, cry1, cry2, cry4 and cry9 genes were observed in 41.4 and 35.7, 12.8 and 15.7 per cent of the isolates, respectively.
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