Streptomyces olivoreticuli ZZ-21 act as a potential biocontrol strain against pepper anthracnose caused by Colletotrichum scovillei

Colletotrichum scovillei is a pathogen that causes anthracnose, resulting in significant postharvest losses in pepper fruit. Biocontrol using antagonistic microbes is a promising solution for sustainable disease management. We previously identified Streptomyces olivoreticuli ZZ-21, which has broad-spectrum antifungal activity. In this study, we evaluated the antagonistic ability of ZZ-21 specifically against C. scovillei in both in vitro and pepper fruit assays, as well as the possible mechanisms involved. Dual culture assays revealed that strain ZZ-21 achieved 86.25 % mycelial inhibition rate against C. scovillei. Pepper fruit trials indicated that the culture filtrate of ZZ-21 significantly reduced both the incidence and lesion size of anthracnose caused by C. scovillei, while maintaining fruit quality. The efficacy of control was dependent on the concentrations of the ZZ-21 culture filtrate, with a 100 % control efficiency observed in the treatment utilizing 100 % culture filtrate. Moreover, the ZZ-21 culture filtrate obviously inhibited spore germination and damaged the cell membrane permeability of C. scovillei, while also inducing plant resistance by enhancing the activities of defense-related enzymes. The primary inhibitory substances were included in proteins and n-butyl alcohol crude extracts of the ZZ-21 culture filtrate, which exhibited EC₅₀ values of 56.88 ± 0.82 μg/mL and 65.37 ± 0.36 μg/mL, respectively. These substances were analyzed using LC-MS and were thought to contribute to the broad-spectrum antifungal activity of ZZ-21. Hence, strain ZZ-21 is a potent biocontrol agent for controlling anthracnose in pepper caused by C. scovillei.