Pepper (Capsicum annuum) is an important spice crops consumed worldly as both a vegetable and seasoning. The pepper fruit is rich in phytochemicals and vitamins, including A, C, and B complex (Nee, 1985). In 2021, the yields of fresh and dried peppers were approximately 36.29 million tons and 4.84 million tons, respectively (FAOSTAT; http://faostat.fao.org/). During both growth and postharvest storage periods, pepper fruits are prone to infection by a variety of plant pathogens (Liotti et al., 2019). Anthracnose, caused by various species of Colletotrichum, is one of the most devastating diseases affecting pepper (Ali et al., 2016). Colletotrichum scovillei is considered as a major pathogen responsible for pepper anthracnose, resulting in substantial losses in pepper production (Mongkolporn and Taylor, 2018; de Silva et al., 2019). Therefore, controlling anthracnose in peppers is essential to ensure the safety of pepper production and to maintain its commercial value. Traditionally, the use of chemical fungicides has been the primary strategy for the management of anthracnose (Miller-Butler et al., 2018). However, the continued use of chemical pesticides can lead to the emergence of fungicide-resistant pathogen populations and environmental pollution (Marian et al., 2020). Thus, it is essential to identify environmentally friendly alternatives to prevent and manage pepper anthracnose.

Biocontrol agents, including beneficial microbial agents, are considered a promising alternative for controlling various phytopathogens that affect postharvest fruits and vegetables (Dukare et al., 2019; Lastochkina et al., 2019). These agents provide several advantages that help mitigate the drawbacks associated with chemical fungicides. Many antagonistic microorganisms have proven to have strong antimicrobial activities, exhibiting promising potential for combating postharvest diseases, such as anthracnose (Feliziani et al., 2016). For example, Staphylococcus sciuri MarR44 was showed to has an antifungal activity against C. nymphaeae, the causal agent of strawberry anthracnose (Alijani et al., 2019). Bacillus atrophaeus B5, B. velezensis S26, GX0002980, and HG-8-2 were reported to be effective biocontrol agents against anthracnose on soursop and avocado caused by C. scovillei, (Guardado-Valdivia et al., 2018), on strawberry caused by Colletotrichum spp. (Russi et al., 2024), on mango caused by C. gloesporioides (Wang et al., 2025), and on pepper caused by C. scovillei (Zhong et al., 2024), respectively.

Moreover, the application of actinobacteria has become a research focus that has attracted intensive attention for the biocontrol of postharvest diseases (Kim et al., 2020). Several Streptomyces species, belonging to actinobacteria, and their secondary metabolites have been reported to exhibit antifungal activities and are used for the control of anthracnose in fruits and vegetables (Marian et al., 2020; Li et al., 2021; Li et al., 2024; Liotti et al., 2019; Boukaew et al., 2018, Boukaew et al., 2021). For instance, Li et al. (2024) found that S. corchorusii CG-G2 exhibited an inhibitory effect on the development of anthracnose caused by C. gloeosporioides in strawberries. Metabolites from Streptomyces sp. H4 demonstrated antagonistic activity against C. fragariae, which is responsible for anthracnose in strawberries (Li et al., 2021). Moreover, S. griseocarneus R132 was reported to be effective in inhibiting C. gloeosporioides, the causal agent of anthracnose in pepper fruits (Liotti et al., 2019). Although numerous Streptomyces species have been reported for the control of postharvest anthracnose, studies specifically focusing on those antagonistic to pepper anthracnose caused by C. scovillei remain relatively rare.

In our previous study, a S. olivoreticuli ZZ-21 has been reported to show significant inhibitory effects on Rhizoctonia solani, effectively controlling tobacco target spot disease (Zhong et al., 2023). To identify natural biocontrol agents for managing pepper anthracnose caused by C. scovillei, this study assessed the antifungal activity of S. olivoreticuli ZZ-21 against C. scovillei in vivo and evaluated its control efficiency. Additionally, the potential mechanisms underlying the biocontrol efficacy of strain ZZ-21 were investigated.