Combined biocontrol to tomato gray mold and inhibition via multi-mechanistic antifungal activity to Botrytis cinerea by Trichoderma harzianum T4.

Tomato gray mold, caused by Botrytis cinerea, causes severe global economic losses. This study evaluates the biocontrol efficacy and underlying mechanisms of Trichoderma harzianum T4 which has application potential. Results showed that T. harzianum T4 significantly promoted tomato seed germination and growth while enhancing systemic resistance. T4 exhibited high ecological fitness, maintaining growth and sporulation under salinity, acid, and nutrient stress. Notably, both volatile organic compounds and cell-free culture filtrates of T4 markedly inhibited B. cinerea by disrupting physiological homeostasis. These treatments triggered reactive oxygen species accumulation, impaired toxicant efflux transport, and induced apoptosis-like programmed cell death. Transcriptomic and RT-qPCR analyses confirmed that T4 treatments downregulated genes related to virulence, cellulolysis, and infection structure formation in B. cinerea. These findings demonstrate the multi-targeted antagonistic strategy of T. harzianum T4, providing a theoretical and technical foundation for its application as a sustainable antimicrobial agent in integrated management.