Biocontrol potential of Priestia megaterium YB-3 against Meloidogyne graminicola and its impact on the rhizosphere microbial community

Root-knot nematodes (Meloidogyne spp.) are highly destructive pests that cause enormous crop losses worldwide. With the increasing awareness of environmental protection, exploring the potential of biocontrol agents has become crucial for nematode management. Priestia megaterium YB-3 was originally isolated from rice rhizosphere soil. In vitro experiments with the fermentation supernatant of YB-3 exhibited up to 96.0% mortality of M. graminicola second-stage juveniles (J2) and 39.2% egg hatching inhibition rate at 48 h after treatment. In greenhouse and field experiments, the application of YB-3 significantly suppressed the gall index, final nematode and egg populations compared to the untreated control, while it promoted rice (Oryza sativa) growth. YB-3 showed consistently high biocontrol efficacy against M. graminicola. Moreover, YB-3 remarkably enhanced the expression of defence genes involved in salicylic acid (OsNPR1, OsWRKY45, OsPR1a), jasmonic acid (OsJaMYB, OsAOS2) and ethylene (OsACS1) signalling pathways at different levels. In addition, YB-3 steadily colonized rice rhizosphere soil at levels ranging from 3.54 × 10³ to 9.08 × 10⁴ cfu/g soil. High-throughput sequencing analysis showed that the application of YB-3 had no significant influence on the rice rhizosphere microbial community structure, and the taxa enriched in the YB-3 treatment were Acidobacteria, Bacteroidetes and Ascomycota. YB-3 effectively suppressed M. graminicola infection, possibly because it colonized the rice rhizosphere, induced plant resistance and increased the relative abundances of beneficial microorganisms. Priestia megaterium YB-3 could be a promising and safe biological component in the integrated management of M. graminicola.