Relative antagonistic potential of some rhizosphere biocontrol agents for the management of rice root-knot nematode, Meloidogyne graminicola

Abstract

The relative effectiveness of twelve indigenous rhizosphere isolates of fungal and bacterial biocontrol agents (BCAs) was evaluated against rice root-knot nematode, Meloidogyne graminicola on rice cv. PS-5. The culture filtrates of BCAs significantly inhibited egg hatching and caused mortality to nematode juveniles. However, considerable variability was observed in the degree of virulence among different isolates/strains when tested in vitro. Six most efficient isolates/strains were selected to ascertain their effectiveness under pot condition. The BCAs were applied as soil application at 2 mL/pot (2–3.5 × 106 CFU/mL). Plants grown in the nematode inoculated soil developed terminal galls on roots and suffered 24–31% reduction in plant growth and yield. However, applications of BCA suppressed the negative impact of the nematode and subsequently increased plant growth and yield. Notably, application of Pseudomonas putida provided better control of root-knot disease, compared to rest of BCAs. The frequency of BCA colonization on eggs, juveniles and adult females of M. graminicola was highest with Trichoderma harzianum followed by Purpureocillium lilacinum. While these effects were minimal with Bacillus subtilis. However, the greatest build-up in the rhizosphere population was recorded with P. putida followed by P. fluorescens and T. harzianum. Our study revealed for the first time the antagonistic effect of P. putida against M. graminicola. Interestingly, the relative effectiveness of P. putida was found to be higher than P. fluorescens and P. lilacinum. In addition to these, we also observed T. harzianum to effectively suppress the M. graminicola, as an endophyte. Field trials under naturally infested plots validated the efficacy of P. putida and T. harzianum, and satisfactorily controlled M. graminicola with 60–74% enhancement in the tillering and yield of rice.