Plant growth-promoting rhizobacteria - Bacillus cereus KMT-5 and B. megaterium KMT-8 effectively suppressed Meloidogyne javanica infection

Root-knot nematodes are the most ecologically and economically damaging pests, causing significant crop losses worldwide. The management of root-knot nematodes via biological means is an effective and ecofriendly strategy being followed nowadays. This study aimed to isolate, identify, characterize plant growth-promoting rhizospheric bacteria (PGPR) KMT-5 and KMT-8 and evaluate against root-knot nematode Meloidogyne javanica under laboratory, greenhouse as well as field conditions. The bacterial strains KMT-5 and KMT-8 were identified based on 16S rRNA gene sequence analysis as Bacillus cereus (accession no. MT626659) and B. megaterium (accession no. MT626661), respectively. Both the strains showed various plant growth promoting attributes such as phytohormone production, ammonia excretion, and hydrogen cyanide production. In vitro experiments on culture filtrates of both the strains against M. javanica eggs and juveniles (J2)1 resulted in up to 96% hatching inhibition and nearly 85–89% mortality of juveniles. The nematode populations were significantly suppressed (up to 93%) in greenhouse experiments (2018 and 2021). A massive decline in the number of eggs and galls was observed compared to control. Both the strains significantly improved the plant growth and yield of brinjal and tomato crops compared to control as well as carbofuran treatment. A similar trend was followed during field trials on brinjal and cucumber in nematode-infected farmer's fields. Field nematode population went down up to 56% in KMT-5 and 68% in KMT-8 treated plots. A notable enhancement in brinjal and cucumber yield was also observed. The results were again significantly better than the carbofuran treatment. Therefore, the plant growth-promoting bacterial isolates KMT-5 and KMT-8 can act as potential biological control agents against root-knot nematodes and could be considered eco-friendly substitutes to synthetic nematicides.