Biocontrol potential of Bacillus velezensis against the postharvest pink mold rot in Citrus reticulata and investigations on some of the mechanisms of action

Trichothecium roseum , the causal agent of postharvest pink rot, causes significant economic losses in mandarin orange ( Citrus reticulata ) and other crops. However, limited information is available regarding biocontrol agents against this pathogen. In this study, we evaluated the biocontrol potential of Bacillus velezensis strain ZM202201 against T. roseum via in vivo and in vitro assays. Our results demonstrated that B. velezensis ZM202201 inhibited T. roseum colony growth by 78.69 % and significantly impaired spore germination and hyphal development in vitro . In vivo assays further revealed that the strain reduced disease incidence by up to 50 %, suppressed conidial germination and hyphal expansion of T. roseum , and enhanced antioxidant enzyme activities (POD, SOD, CAT) and defense-related enzyme activity (PPO) in mandarin fruit. Whole-genome sequencing of B. velezensis ZM202201 identified a 3929,794 bp circular chromosome harboring biosynthetic gene clusters for known antifungal compounds, including surfactin, fengycin, and bacillaene, which are likely key mediators of its biocontrol activity. These findings suggest that B. velezensis ZM202201 inhibited T. roseum through direct antifungal effects and host resistance induction. Collectively, our study highlights B. velezensis as a promising biocontrol agent for managing postharvest pink rot in mandarin oranges and provides new insights into a sustainable approach for postharvest disease control.