title: Characterization of Bacillus thuringiensis isolates and their differential toxicity against Helicoverpa armigera populations.
abstract: Bacillus thuringiensis isolates were characterized in rhizospheric cotton soils by using acetate selection process from eight different locations in South India. The fact that B. thuringiensis indices were higher in proportion in soil samples taken from Tamil Nadu and Karnataka than from Andhra Pradesh, indicates the abundance of B. thuringiensis populations in the cotton rhizosphere. Biochemical typing of the isolates designated eight local isolates (BtNg13, BtCo1, BtHyb7, BtAm2, BtRm5, BtWr3, BtPl 4, BtN 9), which belong to subspecies kurstaki, the most prevalent subspecies. Toxicity assays on American boll worm larval (F(1) ) populations collected from the Andhra Pradesh, Bangalore and Coimbatore regions, with a susceptible insect strain against different isolates of B. thuringiensis kurstaki spore-crystal mix, revealed distinct susceptibility patterns and specificity. The highest susceptibility was observed in the F(1) populations of Coimbatore, followed by Bangalore and Hyderabad populations, in comparison with the susceptible insect strain. Significant differences were observed (p < 0.0005 and CD = 5.3975) among Btk local isolates, H. armigera biotypes, Btk spore-crystal mix concentration and their interactions, through the Multifactorial ANOVA analysis. The toxicity of local B. thuringiensis isolates was higher than that of HD-1 (reference B.t.k strain). Indigenous Btk isolates have an enormous potential for the management of H. armigera in terms of development of resistance to HD-1. The present study would serve as a baseline data for future resistance monitoring of B. thuringiensis strains in H. armigera in Southern India.
authors.affiliation: Centre for Environmental Risk Assessment and Remediation CERAR, University of South Australia, Mawson Lakes campus, Mawson Lakes, South Australia.
authors.forename: Deepak
authors.initials: D
authors.lastname: Anitha
authors.forename: Nachimuthu Senthil
authors.initials: NS
authors.lastname: Kumar
authors.forename: Deepu
authors.initials: D
authors.lastname: Vijayan
authors.forename: Kunhikrishnan
authors.initials: K
authors.lastname: Ajithkumar
authors.forename: Guruswami
authors.initials: G
authors.lastname: Gurusubramanian
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000145:classification* / Q000302:isolation & purification; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000633:toxicity*; D015373:Bacterial Typing Techniques; D004731:Endotoxins / Q000633:toxicity*; D003368:Gossypium / Q000382:microbiology; D006460:Hemolysin Proteins / Q000633:toxicity*; D007814:Larva / Q000187:drug effects / Q000382:microbiology; D009036:Moths / Q000187:drug effects* / Q000254:growth & development; D010572:Pest Control, Biological; D058441:Rhizosphere; D012988:Soil Microbiology; D013171:Spores, Bacterial / Q000145:classification / Q000302:isolation & purification
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis