Nematicidal activity of native Bacillus thuringiensis against the root knot nematode, Meloidogyne incognita (Kofoid and White)

Abstract In this study, potential of the native Bacillus thuringiensis Berliner was investigated against the root knot nematode, Meloidogyne incognita (Kofoid and White) under laboratory and greenhouse conditions. Fourteen out of 50 Bt isolates obtained from root zone of vegetable crops of north western zone of Tamil Nadu, India, were found to be encoded with nematicidal cry genes, confirmed by gene-specific PCR. Nine different Cry protein profiles were obtained from native Bt. Spore-crystal mixtures of 6 isolates out of 14 (at 0.5%) showed 100% inhibition to J2 juveniles emergence from egg masses of M. incognita within 72 h of treatment. Analysis by SEM revealed that fluffy egg masses were observed in untreated samples due to hatching, whereas egg masses were covered by gelatinous matrix, when treated with spore-crystal mixture of nematicidal Bt. Two (BC and BD) of the 6 isolates were selected based on their highest nematicidal activity against J2 of M. incognita with LC50 values of 0.12 and 0.23 μg/ml of protein. The spore-crystal mixtures of isolates BC and BD when applied to tomato plants under greenhouse conditions exhibited the enhanced biocontrol potential by suppressing number of egg masses, reduction of female population and decreased root gall index, when compared to control and chemical treatments.