Volatile organic compounds produced by Streptomyces sp. SA51 mitigate Fusarium oxysporum f.sp. lactucae infection and stimulate lettuce seedling growth

Abstract Microorganisms can produce volatile organic compounds (VOCs). Bacterial VOCs may be involved in a wide range of processes, such as plant growth promotion, the control of plant pathogens and pests, and the induction of resistance in plants. For these reasons, they are currently attracting more and more interest as a sustainable alternative to the use of synthetic plant protection products in agriculture. Fusarium oxysporum f.sp. lactucae (FOL) is a soil-borne pathogenic fungus that infects all types of lettuce causing crop losses. This study aims to investigate the biocontrol activity of VOCs produced by a strain of Streptomyces sp. against FOL race 1, both in vitro and in planta . VOCs produced by a culture of Streptomyces sp. showed an inhibitory effect on mycelial growth in vitro (−8%). In planta , the McKinney index, used for assessing disease severity, decreased by 25%, when infected lettuce seedlings were grown in the presence of bacterial VOCs. To identify the VOCs produced by the beneficial streptomycete, a headspace solid phase micro extraction, coupled to gas chromatography with mass-spectrometry detection was used. Results revealed a complex VOCs profile that included compounds with antagonistic properties, such as Germacrene D and Phenylethyl alcohol. The VOCs-producing Streptomyces sp. strain demonstrated a good potential as biocontrol agent against FOL race 1 and as plant biostimulant for the growth of lettuce seedlings.