Evaluation of native Bacillus thuringiensis strains possessing nematicidal specific cry genes against Meloidogyne incognita

Abstract

Plant-parasitic nematodes, including root-knot nematodes, are phyto-parasites that cause significant crop damage and economic losses. Bacillus thuringiensis (Bt), which produces nematicidal toxins, is extensively used to combat nematode infestations in agricultural and horticultural crops. This research assessed the efficacy of native Bt strains as a biocontrol agents against the root-knot nematode Meloidogyne incognita. Twenty native Bt strains were evaluated for the presence of nematicidal cry genes using PCR. Eight strains, namely Bt1, Bt5, Bt6, Bt7, Bt17, Bt19, Bt23, and Bt24, exhibited the presence of nematicidal cry genes, specifically cry5, app6, cry12, cry13, cry14, cry21, xpp55, cry31, cry73, and cry40, as determined by gene-specific primers. The in vitro effectiveness of the Bt strains was assessed against M. incognita using a cavity block test, revealing that the Bt strains, namely Bt7 and Bt19, impeded the hatching of M. incognita eggs and were deadly to nematode larvae (J2 stage). SEM analysis of spore-crystal mixtures of Bt isolates revealed different crystal shapes that confirmed the nematicidal activity. Pot experiments revealed that the Bt7 and Bt19 strains are the most efficacious biological agents, exhibiting superior nematicidal activity in Brinjal and Tomato. The molecular characterization of the most virulent Bt strains, namely Bt-7 and Bt-19, using 16S rDNA sequencing, validated their molecular identification as Bacillus thuringiensis.

Keywords: cry gene amplification; In vitro and in vivo study; Molecular characterization; Nematicidal Cry protein; Plant growth performance; SEM analysis.