Control efficacy of fermentation extracts from Streptomyces violaceusniger 5–6 against postharvest mango anthracnose and associated host defense responses

Mango anthracnose caused by Colletotrichum gloeosporioides is a major postharvest disease. This study evaluated the control efficacy of fermentation extracts derived from Streptomyces violaceusniger 5–6 and investigated their associated antifungal and host-response mechanisms. At 8 days post-inoculation, the 3 ×EC₅₀ extract treatment reduced the disease index from 93.33% in the blank control to 40.00% and decreased the lesion area percentage by 88.99%, while maintaining postharvest fruit quality. The extracts were also associated with increased activities of defense-related enzymes, including PAL, POD, PPO, CAT, and SOD. Transcriptomic and WGCNA analyses identified responsive genes associated with plant–pathogen interaction, calcium signaling, and the plant MAPK signaling pathway, suggesting that these pathways may participate in extract-associated defense responses. Untargeted metabolomic analysis identified several putatively annotated co-culture-associated metabolites, and a commercially available Ansamitocin P-3 standard exhibited antifungal activity, supporting its consideration as a candidate bioactive metabolite. qRT-PCR analysis of representative DEGs showed expression patterns consistent with the RNA-seq results, supporting the reliability of the transcriptomic analysis. However, the functions of these candidate genes remain to be experimentally validated, and the metabolite identities were not comprehensively confirmed by targeted analytical methods. Further functional and chemical validation is therefore required. These findings indicate that the fermentation extracts have potential to reduce postharvest mango anthracnose through direct antifungal activity and defense-associated host responses.