microbial potency, characterization and effect of indigenously isolated ubiquitous bacterium bacillus thuringiensis (berliner) in biological subjugation of leaf folder cnaphalocrocis medinalis (guenee) in rice

Research Article
A.Ramamourti, P. Tholkappian and. S. Jayachandran
Bacillus thuringiensis, Leaf folder, Cnaphalocrocis medinalis, Bioassay, Indigenous isolate.

Ubiquitous bacterium Bacillus thuringiensis (Bt) (Berliner) has been indigenously isolated from the various crop canopies viz., Rhizosphere, Phyllosphere and Insect cadavers in Puducherry region and the promising isolate was identified based on cultural, molecular, biochemical characteristics and Bioassay studies. Among ten Bacillus isolates, the isolate 1, 9 and 12 derived from Rhizosphere and isolate 22 obtained from Insect cadaver had behaved in resemblance with Bacillus thuringiensis characteristic features but the isolate 9 had invariably showed its supremacy over other isolates by exhibiting the characteristic features of Bacillus thuringiensis like Colonial count, Total cell protein, Bipyramidal crystals, Crystalliferous protein and Bioassay using parasporal inclusions. Characterizing the potency of Bt bacterial biopesticide in skirmishing the rice leaf folder Cnaphalocrocis medinalis , it was estimated at 22,121 IU/ mg with the LC50 0.6 x 108. Thus, Bacillus isolate 9 was found to be considered as promising isolate and this was chosen for further studies. The microbial preparation of the promising indigenous Bt isolate 9 in various dosages viz., 0.5, 1.0, 1.5, 2.0 and 2.5 g per litre of water were applied over the foliage surface of rice using atomizer. The dosage 2.5 gram per litre of water was effective in causing the highest mean mortality of 61.30 % and the dosage 0.5 g / litre of water was found the least (26.16 %) in 72h. under laboratory conditions. The crystalliferous parasporal inclusions were rampant in Bt isolate 9 and they were the rule of thumb for killing the leaf folder larvae in Rice through septicemia.