Pseudarthrobacter oxydans RH60-mediated rhizobacterial interactions bidirectionally regulate cucumber root-knot disease.

Intensive cucumber continuous cropping disrupts rhizosphere balance and triggers severe Meloidogyne incognita infestation. Cucumber-pepper rotation alleviates this via recruiting the rhizobacteria Pseudarthrobacter oxydans RH60. However, the mediating role of rhizobacterial interaction networks remains unclear. Here, we clarified the bidirectional regulatory mechanism of this nematode disease via RH60-centered rhizobacterial interactions. Rhizobacteria from the rhizospheres of continuously cropped cucumber and rotated pepper were firstly isolated. Their effects on RH60 growth were screened via fermentation filtrate and filter disc assays. Target strains were identified by 16S rRNA gene sequencing and phenotypic characterization. Myroides odoratus P69 (from pepper rhizosphere) was identified as an RH60-synergistic strain and Bacillus toyonensis RH119 (from cucumber rhizosphere) as an RH60-antagonistic strain. Data from growth promotion and biofilm formation assays showed that pepper root exudates specifically recruited P69, while cucumber root exudates specifically enriched RH119. Two-compartment petri dish co-culture and gas chromatography-mass spectrometry (GC-MS) assays were performed. The results indicated that RH119 inhibited RH60 growth by releasing volatile organic compounds (VOCs) (predominantly isoamyl isovalerate and isopropyl 2-methylbutyrate). Quantitative real-time PCR (qPCR) was used to quantify RH60 rhizosphere colonization, and pot experiments were conducted to verify disease control efficacy. P69 enhanced RH60 colonization capacity and disease-suppressive effect, thereby promoting cucumber root growth. In contrast, RH119 reduced RH60 colonization and exacerbated the nematode disease. These results demonstrate the root exudates and microbe-derived VOCs jointly mediate RH60-centered interactions. These interactions drive bidirectional nematode disease regulation under continuous cropping and rotation, providing insights for sustainable cucumber production.