Bacillus velezensis A-27 as a potential biocontrol agent against Meloidogyne incognita and effects on rhizosphere communities of celery in field

Meloidogyne incognita, a highly destructive plant-parasitic nematode, poses a significant threat to crop production. The reliance on chemical nematicides for nematode control has been crucial; however, the banning of many effective nematicides due to their adverse effects has necessitated the exploration of alternative solutions. Rhizosphere biocontrol bacteria, particularly strains of Bacillus, have demonstrated promising results in managing plant-parasitic nematodes. In this study, strain A-27 was identified as Bacillus velezensis based on its morphological, physiological, and molecular characteristics, including 16 S rRNA and gyrA sequencing. Strain A-27 exhibited high larvicidal and ovicidal efficacy in vitro, with estimated LC50 values of 4.0570 x 108 CFU/mL for larvicidal efficacy and 3.6464 x 108 CFU/mL for ovicidal efficacy. In a pot experiment, B. velezensis A-27 significantly reduced the root gall index, achieving a control efficacy of 85.36%. Field experiments further indicated that A-27 reduced the root gall index with a control efficacy of 67.31%, while also decreasing the J2 population density of M. incognita and significantly enhancing the growth of celery plants. Additionally, high-throughput sequencing analysis revealed that B. velezensis A-27 significantly increased the relative abundances of Bacillus and Sphingomonas, while markedly reducing the relative abundances of Fusarium, Mortierella, and Cephaliophora in the celery rhizosphere. These findings suggest that B. velezensis A-27 has potential as an effective biocontrol agent against M. incognita, offering a promising alternative to chemical nematicides in sustainable agriculture.