An Endophytic Pseudomonas nitroreducens ZPN-25 Strain with Antagonistic Activity Against Verticillium dahliae and Growth-Promoting Effects on Cotton

Beneficial endophytes are a promising resource for plant disease management. Here, an antagonistic bacterial strain, ZPN-25, was isolated from a Verticillium wilt-resistant cotton cultivar (Zhongzhimian No. 2) and identified as Pseudomonas nitroreducens. ZPN-25 exhibited an in vitro inhibition rate of 66.67% against V. dahliae Vd991. ZPN-25 co-inoculation induced the defence genes GhAOC4, GhPR1 and GhEIN2 relative to Vd991 alone. Co-inoculation also altered phytohormone levels and enhanced antioxidant enzyme activities, raising jasmonic acid (JA) and salicylic acid (SA) concentrations and catalase (CAT) and peroxidase (POD) activities while lowering abscisic acid (ABA) and malondialdehyde (MDA) levels. ZPN-25 concurrently enhanced cotton growth (root length increased by 29.76%) and restructured both the rhizosphere and phyllosphere microbiota, enriching putative beneficial taxa such as Sediminibacterium and Simplicillium below ground and Bacteroides and Epichloë above ground relative to water-only controls. ZPN-25 raised soil available phosphorus (AP), alkali-hydrolyzable nitrogen (AN), total phosphorus (TP), and soil organic matter (SOM) and suppressed cotton Verticillium wilt with a biocontrol efficacy of 79.21%, halving root biomass of Vd991. ZPN-25 therefore suppresses Verticillium wilt of cotton by combining direct inhibition of V. dahliae with activation of host defence and with microbiome restructuring in both the rhizosphere and the phyllosphere.