Antifungal activity of l‐azetidine‐2‐carboxylic acid isolated from Disporopsis aspera rhizomes against Podosphaera xanthii

Powdery mildew is one of the fungal diseases commonly occurring in the process of cucurbits protected and open cultivation. Cucumbers, melons and pumpkins are extremely susceptible. The secondary metabolites produced by plants are important sources of fungicides with low toxicity and environment-friendly characteristics. The aim of this study was to reveal the main active ingredient in the crude extracts of Disporopsis aspera rhizomes that inhibit cucurbits powdery mildew and evaluate its activities.In this study, the crude extracts of Disporopsis aspera rhizomes were found to exhibit excellent antifungal activity aganist Podosphaera xanthii, a causal agent of cucurbits powdery mildew. Based on the bioassay-guided method, l-azetidine-2-carboxylic acid (l-Aze) was isolated from this genus for the first time. l-Aze showed unique curative and eradicative activity against Podosphaera xanthii in vivo, which has never been reported before. Microscopic observation revealed that the curative spraying of l-Aze could effectively inhibit the mycelial growth, resulting in hollow parts of the mycelia, not forming conidiophores, and interrupting the life cycle of powdery mildew. The eradicative spraying of l-Aze caused the fracture of mycelia and deformity of conidiophores, which could not continue to produce conidia.l-Aze was the main active ingredient of D. aspera against Podosphaera xanthii, which had both curative and eradicative effects. The results provided a strong possibility of using the crude extracts of D. aspera rhizomes and its main effective component, l-Aze as biocontrol agents to control cucurbits powdery mildew.