The biocontrol effect and mechanism of the marine-derived fungus Epicoccum nigrum against Alternaria alternata, the causal agent of tomato black spot disease.

Tomato black spot disease, caused by the fungus Alternaria alternata, leads to plant wilting and chlorosis and results in sunken, black lesions on harvested fruit, thereby causing significant economic losses in the tomato industry. To mitigate issues related to environmental contamination and the emergence of resistant pathogens, this study investigated a high-efficacy, low-toxicity biocontrol strategy. The marine-derived fungus Q8-1 inhibited the growth of A. alternata by up to 87.04 %. Based on morphological features and ITS rDNA sequencing, the strain was identified as Epicoccum nigrum. Genome-wide analysis revealed that its biocontrol activity was primarily mediated by secondary metabolites. Supporting this mechanism, the crude extract of Q8-1 exhibited an EC₅₀ of 0.78 mg/mL against hyphal growth, and in vivo assays demonstrated that it reduced disease incidence on tomato fruits and seedlings by 71.43 % and 82.96 %, respectively. Disruption of ergosterol biosynthesis by the extract confirmed its impact on membrane integrity, leading to leakage of intracellular components. Furthermore, the induction of redox imbalance and excessive accumulation of reactive oxygen species (ROS) suggested that the extract interfered with the metabolic processes of the pathogen, ultimately triggering programmed cell death. Genome sequencing identified 43 secondary metabolite biosynthetic gene clusters, while LC-MS/MS analysis detected putative antifungal compounds, including tolypyridone C, epipyrone A, and scytalone. Overall, these findings provide a theoretical basis for the development of a biopesticide of E. nigrum Q8-1 and offer a new, sustainable approach for controlling tomato black spot disease.