Antifungal capacity and field validation of native Bacillus subtilis strains for sustainable potato disease control

Increasing demand for sustainable crop protection has intensified the search for effective biological alternatives to chemical fungicides. The present study evaluated native Bacillus subtilis strains isolated from Iranian soils for their biocontrol potential against major potato pathogens ( Fusarium , Alternaria , Phytophthora , and Sclerotinia ). Among 45 bacterial isolates, two strains (BS1-Kaolin and BS2-Maharloo) were molecularly identified as B. subtilis and selected for their superior antifungal activity. In vitro assays demonstrated that BS1 strongly inhibited fungal growth (48% suppression of F. oxysporum ), whereas field trials revealed its dual functionality: increasing tuber weight by 30–45% and tuber proliferation by 18–27% compared to those of the controls ( P < 0.05). Although chemical fungicides resulted in greater weight enhancement (55–60% increase), bacterial treatments resulted in higher total tuber yields (BS1: 640.1 g; BS2: 528.8 g) and improved postharvest quality, including higher mean tuber weight per plant, a favorable tuber to plant biomass ratio, and greater dry matter accumulation in aerial parts. Industrial potential was confirmed through optimized biomass production (43.1 g/l wet weight in TSB medium) and efficient sporulation (95% by day 10). The present studyaddresses important gaps in native bacterial biocontrol agents with antifungal activity by demonstrating the strong in vitro antagonistic activity of indigenous bacterial strains against the target pathogen and their positive effects in potato yield under field conditions. The study also indicates the potential for large-scale production of these native Bacillus subtilis strains without the use of synthetic antibiotics or antifungal agents, providing a practical and costeffective approach for integrated potato disease management. These findings support the potential use of these ecofriendly strains as alternatives for sustainable and organic potato production systems.