Endophytic ability of indigenous Bacillus thuringiensis strain VKK-BB2: new horizons for the development of novel insect pest-resistant crops

Background Brinjal shoot and fruit borer (BSFB), Leucinodes orbonalis Guenee is the key pest of brinjal that causes a significant yield loss. Farmers spray wide range of insecticides right from vegetative stage till last harvesting stage to protect the crop from the notorious BSFB, which leads to pesticide residue and insecticide resistance problems. To overcome this, now focus has shifted to bio pesticides but their commercial application is limited due to their susceptibility to abiotic factors. To overcome these bottlenecks, a hidden ecological role played by entomopathogenic bacteria as endophytes was sought. The control of pests by establishment of potential entomopathogenic bacteria as an endophyte is an alternative method of pest management that may contribute to reduce or eliminate the use of pesticides. Results Present study describes the colonization of green fluorescent protein (GFP)-tagged potential native Bacillus thuringiensis strain VKK-BB2 (BtVKK-BB2) in brinjal plants. Seeds and seedlings of brinjal were inoculated with gfp -tagged BtVKK-BB2 cells through seed treatment, soil drenching and foliar spray. After inoculation gfp -tagged bacterium could be re-isolated from all parts of the plant. Presence of bacteria within the leaves was confirmed by amplification of gfp and cry gene in the re-isolated Bt colonies from brinjal leaves and shoot. Leaves taken from the BtVKK-BB2 colonized plants were able to cause mortality when fed to neonates of Leucinodes orbonalis . Conclusions Establishment of native Bt strain as endophytes in plants, accompanied by the production of Cry proteins opens new horizons for the development of a novel pest-resistant crops which could be an alternative to Bt transgenic crops. However, inoculation of Bt through seed and foliar spray has to be further explored against larval herbivores especially internal borers to enhance its biocontrol potential through endophytic mediation which may open a novel set of strategies to control the insect pests in a sustainable way. Graphical Abstract