Role of bacterial antagonists of fungal pathogens, Bacillus thuringiensis KYC and Bacillus velezensis CE 100 in control of root-knot nematode, Meloidogyne incognita and subsequent growth promotion of tomato

In this study, the biocontrol ability of bacterial antagonists of fungal pathogens, B. thuringiensis KYC and B. velezensis CE 100 was investigated for the inhibition of root-knot nematode, Meloidogyne incognita, and subsequent growth promotion of tomato. Based on the results of dual-culture assay, both Bacillus strains showed antagonistic activities against six different phytopathogenic fungi. The bacterial culture filtrates (BCF) of two Bacillus strains had a strong toxic effect on egg hatching and second-stage juvenile (J2) survival of M. incognita. With increasing concentration of BCF and incubation period, the hatching rate of the nematode egg was significantly inhibited and J2 mortality was remarkably increased. Moreover, the crude enzymes which were extracted from culture supernatants of two Bacillus strains caused structural damage to nematode eggs and J2 at 1, 3 and 5 days after inoculation. The pot experiment revealed that B. thuringiensis KYC and B. velezensis CE 100 significantly promoted tomato shoot growth compared to fertiliser treatment. However, root fresh weight was significantly increased in fertiliser treatment due to numerous masses in roots. The number of egg masses and root gall index in the treatment group with both Bacillus strains were significantly decreased compared to those in fertiliser treatment. Higher populations of B. thuringiensis KYC and B. velezensis CE 100 (4.12 and 6.52 × 106 CFU g−1of soil) were detected in the tomato rhizosphere. These results demonstrated the potential of B. thuringiensis KYC and B. velezensis CE 100 as biocontrol agents to control plant-pathogenic fungi and root-knot nematode and as biofertilisers to promote plant growth.