Volatile organic compounds from Streptomyces philanthi RM-1-138: Biocontrol of Sclerotium rolfsii and their impact on chili pepper seed germination

Streptomyces species have been recognized in agriculture both as biological control agents and as plant growth-promoting bacteria. In the present study, we aimed to investigate volatile organic compounds (VOCs) produced in wheat seed culture (WSC) of S. philanthi RM-1-138 (RM-1-138 VOCs) and its major component L-linalool against Sclerotium rolfsii and their effects on seed germination in chili pepper. Our in vitro sealed plate bioassay demonstrated that 30 g per air space of WSC of RM-1-138 and L-linalool at 20 μL per air space effectively killed S. rolfsii mycelia and sclerotia. In vitro bioprotection assays using chili pepper as a model revealed that RM-1-138 VOCs (30 g per air space) and L-linalool (40 μL per air space) achieved 100 % survival of chili pepper seedlings infected by S. rolfsii , a significantly higher survival rate compared to the pot bioassay experiments, which achieved only 60 % and 55 % survival, respectively. However, our seed germination experiments found that RM-1-138 VOCs and L-linalool were detrimental to chili pepper seed germination and growth. Specifically, seeds with radicles approximately 1 mm in size exposed to these VOCs exhibited a strong negative impact on stem length, root length, and fresh weight compared to the control. Microscopy images confirmed that both VOCs were highly toxic to cotyledon production, causing hypocotyls and radicles to turn dark brown and subsequently rot. While RM-1-138 VOCs and L-linalool demonstrate significant potential for controlling S. rolfsii growth, further studies are needed to explore strategies, such as combining these VOCs with plant growth-promoting bacteria or chemical elicitors, to mitigate their toxicity and enhance seed germination and root development in chili peppers. • RM-1-138 VOCs and L-linalool displayed significant antifungal biocontrol activity. • RM-1-138 VOCs and L-linalool successfully killed S. rolfsii mycelia and sclerotia. • Applications of RM-1-138 VOCs and L-linalool protected chili pepper seedlings from S. rolfsii infection. • RM-1-138 VOCs and L-linalool inhibited the germination of chili pepper seeds. • RM-1-138 VOCs and L-linalool inhibited the development of cotyledons, hypocotyls, and radicles in chili pepper seedlings.