Reclamation of rhizobacteria newly isolated from black pepper plant roots as potential biocontrol agents of root-knot nematodes

Abstract

Rhizobacteria have been of great interest due to their promising use in biocontrol and promotion of plant growth. The aim of this study was to select active anti-nematode rhizobacteria, enhance their nematicidal activity by optimizing fermentation conditions, and then determine the active components of the fermented product. Among more than 100 isolates, 20 strains showed potent inhibition (81.67–99%) against root-knot nematodes from the genus Meiloidogyne. Almost all of these belong to the genus Bacillus (14 of 20 strains). The six most active strains (with max inhibition of 96.13–98.33%) were RB.DS.05, RB.DL.28, RB.DS.29, RB.DL.31, H11, and CC01; these strains were further investigated for their effect on nematode egg hatching. Of these, Bacillus subtilis RB.DL.28 demonstrated the greatest inhibition (82%). Chitinase and protease were closely associated with the inhibition of egg hatching, while it was newly discovered that natural compounds with thermal stability play a key role in killing J2 nematodes. Based on LC–MS analysis, two major constituents, sulfacetamide and metronidazole-OH, were identified from the filtrates of B. subtilis RB.DL.28. The results from this study suggest that the most active strain, B. subtilis RB.DL.28, and other newly identified rhizobacteria may be good candidates for biocontrol of Meiloidogyne spp. These results expand the catalogue of novel active anti-nematode rhizobacteria communities recently recorded in Vietnam.