Beyond contact toxicity: Volatile and systemic nematode suppression by 'Candidatus Pseudomonas auctus' JDE115 in soybean.

Plant-parasitic nematodes such as soybean cyst nematodes (SCNs) (Heterodera glycines) and root-knot nematodes (Meloidogyne spp.) pose a significant threat to global soybean productivity. This study evaluated the multimodal biocontrol potential of 'Candidatus Pseudomonas auctus' JDE115, a soybean nodule-derived bacterium known for its plant growth-promoting properties. Greenhouse-based pot and split-root assays showed that JDE115 not only significantly improved soybean growth and nodulation but also suppressed SCN reproduction by over 90% locally and 85% systemically, indicating both direct antagonism and possibly induced systemic resistance. Volatile profiling using solid-phase microextraction gas chromatography-mass spectrometry identified dimethyl disulfide and 1-undecene as distinctive volatile organic compounds produced by JDE115. Bioassays with free-living nematodes demonstrated that 1-undecene elicits strong avoidance behavior and causes rapid mortality in nematodes in the absence of direct contact. Furthermore, a colorimetric picrate assay confirmed substantial hydrogen cyanide production by the bacterium. Additional tests revealed that JDE115 inhibits egg hatching and causes juvenile mortality through a combination of chemical toxicity and enzymatic degradation. Collectively, these findings establish JDE115 as a multifunctional plant growth-promoting rhizobacterium with potential nematicidal activity and broad biocontrol potential, underscoring its value as a next-generation microbial tool for integrated nematode management in soybean cultivation. To our knowledge, this is the first report demonstrating combined volatile-mediated and systemic suppression of SCN by a nodule-derived Pseudomonas.