Volatile organic compounds of Enterobacter asburiae SA-9 suppress Meloidogyne graminicola in Rice via multiple...

The rice root-knot nematode Meloidogyne graminicola causes severe yield losses in rice production, requiring eco-friendly control measures. Here, we isolated Enterobacter asburiae SA-9 from rice rhizosphere soil and evaluated the biocontrol potential of its volatile organic compounds (VOCs) against M. graminicola. In vitro, SA-9 VOCs exhibited potent fumigant activity, causing high mortality of second-stage juveniles (J2s) and significant inhibition of egg hatching. Chemotaxis assays showed that SA-9 disrupted nematode chemotaxis through repellent activity. Further investigations revealed that exposure to SA-9 VOCs significantly downregulated key chemosensory genes (Mg-odr-1, Mg-odr-3, Mg-osm-9, Mg-tax-4) in J2s, impairing their host-seeking and infection abilities. In double-layered pot, SA-9 VOCs effectively reduced root gall index and nematode populations, while concurrently promoting rice growth, accompanied by upregulation of auxin (OsAUX1, OsYUCCA1) and gibberellin (OsGID1) biosynthesis-related genes. Furthermore, SA-9 VOCs induced genes related to systemic resistance in rice, as evidenced by the increased expression of defense-related genes in the salicylic acid (OsPR1a, OsWRKY45) and jasmonic acid (OsAOS2, OsMYC2) signaling pathways. SPME-GC-MS profiling identified 11 VOCs produced by SA-9, with 2-phenylethanol, 2-methylbutyric acid, isobutyric acid and propanoic acid exhibiting significant contact and fumigation nematicidal activities against J2s. These findings demonstrate that SA-9 VOCs suppress M. graminicola through multiple mechanisms, highlighting their potential as sustainable biocontrol agents for managing root-knot nematodes in rice agroecosystems.