Biocontrol potential of rhizosphere Streptomyces LWT20 against postharvest decay on grape caused by Botrytis cinerea

Gray mold ( Botrytis cinerea ) is a major postharvest disease of grapes, and alternatives to chemical fungicides are urgently needed. In this study, an actinomycete strain, LWT20, exhibiting potent antifungal activity against B. cinerea was isolated from the rhizosphere of common reed ( Phragmites australis ). Morphological and 16S rRNA analysis identified LWT20 as Streptomyces sp. In vitro , its extracts suppressed hyphal development and spore germination. When applied at 0.06g/L, 2 h post-inoculation on grape berries (23 °C), LWT20 extracts reduced both disease incidence and severity by more than 60 %. The treatment maintained critical fruit quality during storage, including chromatic characteristics, textural firmness, soluble solids content, ascorbic acid (Vc) retention, reducing sugar levels, and total phenolic/flavonoid content. Additionally, the application of the extracts led to a notable upregulation of key defense enzymes in grapes. A total of 16 compounds were identified through GC-MS, with 2,3-butanediol and dibutyl phthalate dominating the composition. Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) profiling revealed 24 chemically distinct inhibitory compounds with activity in the extract. These findings demonstrate that LWT20 may effectively suppress gray mold progression in postharvest grapes, preserve fruit quality, activate plant defenses, and provide a promising biocontrol approach to extend shelf life.