Gentisaldehyde Suppresses Phytophthora sojae by Combined Damage to Membrane Integrity and Energy Metabolism.

The soil-borne oomycete Phytophthora sojae causes severe Phytophthora root and stem rot (PRR) in soybean. Rhizosphere metabolites, integral to plant defense, represent an underexplored resource for novel control strategies. A metabolomic comparison of rhizospheres from resistant (Williams82) and susceptible (Williams) soybeans identified gentisaldehyde as a key differential metabolite. In vitro, gentisaldehyde demonstrated broad, concentration-dependent inhibition of P. sojae, suppressing mycelial growth, oospore formation, oospore survival, zoosporangium formation, zoospore encystment, and cyst germination. Integrating physiological and transcriptomic analyses revealed that gentisaldehyde exerts its anti-oomycete activity through a multi-target mechanism, disrupting plasma membrane integrity, inhibiting energy metabolism, and inducing oxidative stress. Importantly, soil application of gentisaldehyde at 0.4 μmol g-1 soil significantly reduced the PRR disease index in natural soil and also provided significant protection in sterilized soil, indicating direct pathogen inhibition. These results suggest that gentisaldehyde plays a role in rhizosphere defense and may be a lead compound for PRR management.