Biocontrol potential of Streptomyces lateritius ZY37 against Phytophthora root rot in soybean and optimization of fermentation conditions

AIMS: Phytophthora root rot (PRR), caused by Phytophthora sojae Kaufm. & Gerd., is a devastating soil-borne disease. Chemical control risks pathogen resistance and environmental contamination, necessitating eco-friendly biocontrol agents. METHODS AND RESULTS: In this study, strain ZY37 was isolated from the soybean rhizosphere and identified as Streptomyces lateritius Sveshnikova. The dual culture showed that ZY37 exhibited a 76.91% inhibition rate against the mycelial growth of P. sojae. It secretes proteases, siderophores, cellulases, and phosphatases, exhibiting multifaceted biocontrol activities. Fermentation conditions were optimized using single-factor experiments, Plackett-Burman design, steepest ascent design, and central composite design. Under the optimal fermentation conditions (fermentation time: 133 h, rotational speed: 160 rpm, temperature: 36.1°C, inoculum size: 3%, pH: 7.0), the fermentation filtrate of ZY37 increased the inhibition rate of P. sojae from 54.88% to 66.46%. Pot experiments revealed ZY37 fermentation broth significantly reduced disease severity, comparable to chemical controls, while enhancing plant growth and root defense enzyme activities. CONCLUSIONS: This work provides a novel biocontrol strain and a theoretical foundation for sustainable PRR management.