Selection, characterization and potency determination of a Bacillus thuringiensis kurstaki isolate toxic to major lepidopteran pests

Abstract

Screening 50 isolates of Bacillus thuringiensis (Bt) kurstaki from soil samples of Rajasthan and Telangana states, India led to identification of 10 isolates promising against the polyphagous pests Spodoptera litura (Fabricius) and Helicoverpa armigera (Hübner). rep-PCR revealed distinctness of one isolate DOR Bt-127 with cry1Ac, 1Ae, 1C, 1E, 2Aa, 2Ab genes coding for toxins effective against a wide range of insect pests. Spore-crystal mixture of Bt-127 had a high spore count of 9x1022/g and delta endotoxin content 18.28%, possessed bipyramidal crystals (0.64-2.12 µm) and ellipsoidal spores (1.92-2.2 µm). SDS-PAGE resulted in a 62 kDa band corresponding to the Cry1 toxin. Potencies against the less susceptible pests S. litura and S. exigua (Hübner) were 71309 and 46205 SU/mg respectively while potencies against the susceptible pests H. armigera, Plutella xylostella (Linnaeus) and Achaea janata (Linnaeus) were 35844, 26571 and 51667 IU/mg respectively. DOR Bt-127 holds great promise for management of these important pests overcoming the need for using different Bt varieties.