Characterization of Indigenous Bacillus thuringiensis Isolates and Toxicity Analysis Against Brinjal Shoot and Fruit Borer, Leucinodes orbonalis (Guenee)

Abstract

The toxins derived from Bacillus thuringiensis (Bt) exhibit significant promise in managing specific orders of harmful insects without the drawbacks in using of chemical insecticides. This study examines 20 indigenous Bt isolates, with a focus on their colony and crystal morphology, gene content, protein profiles, and toxicity against the larvae of Leucinodes orbonalis. The results revealed that all colonies were creamy white in colour with fried egg type appearance, flat surface, and undulated margin with spherical shaped crystals. PCR screening detected the existence of cry1, cry2, and vip3A genes with varying gene combinations among the isolates. Protein profiles exhibited the presence of multiple proteins with molecular weights ranging from 20 to 135 kDa, particularly ~135 and ~65 kDa represents Cry1 and Cry2 protein. In vitro bioassays against L. orbonalis revealed that four isolates T193, T339, T374, and T380 having substantial toxicity (93.33 to 100% mortality), suggesting the potential for their utilization in sustainable pest management strategies.