Biocontrol efficacy and possible mechanism of Streptomyces sp. H4 against postharvest anthracnose caused by Colletotrichum fragariae on strawberry fruit

Anthracnose is a fungal disease caused by Colletotrichum species, which is detrimental to numerous fruits, including strawberry. Use of fungicides to maintain fruit quality leads to potential environmental pollution and health risk. Biocontrol using beneficial microorganisms such as Streptomyces has been applied successfully for controlling postharvest diseases of fruit. In this study, strain H4 with a high antifungal activity against C. fragariae was isolated from Dichotella gemmacea in Xisha islands of South China Sea. Combining the morphological and biochemical characteristics with the 16S rRNA sequence analysis, this strain was assigned as Streptomyces sp. A preventive treatment using strain H4 extracts significantly reduced severity and incidence of anthracnose disease and maintained fruit hardness and color on harvested strawberry fruits. A minimum inhibitory concentration (MIC) and a minimum fungicidal concentration (MFC) were 1.563 × 10−3 g L-1 and 3.125 × 10−3 g L-1, respectively. Extracts could effectively inhibit mycelial growth and spore germination of C. fragariae in vitro. The mycelial structure of pathogenic fungi showed deformation, shrinkage, collapse and tortuosity. A significant decrease in sugar and protein contents was also observed in treated C. fragariae mycelia. Fourteen chemical compounds were identified by gas chromatography-mass spectrometer (GC–MS). Dibutyl phthalate was the major constituent. Notably, strain H4 and its extracts exhibited a broad-spectrum antifungal activity against seven selected plant pathogenic fungi. Hence, Streptomyces sp. H4 and its metabolites have a high efficiency of antagonistic roles against phytopathogenic fungi diseases. It provides a promising biological agent to control anthracnose of strawberry fruit.