Sclerotinia sclerotiorum (Lib) de Bary, a destructive fungal pathogen with an extensive host range, causes various diseases with the potential to cause huge economic losses to crops worldwide. Streptomyces species produce secondary metabolites with variable structures and biological activities that offer possible control methods for crop diseases. Herein, we evaluated the inhibitory effects of Wuyiencin, a secondary metabolite of Streptomyces albulus CK-15, against S. sclerotiorum. The results showed that Wuyiencin markedly inhibited mycelial growth and germination, and the formation of sclerotia. It also increased cell membrane permeability, resulting in leakage of intracellular substances in pathogen mycelia. Wuyiencin markedly decreased oxalic acid (OA) content and the activities of polygalacturonase (PG) and pectin methyl-galacturonic (PMG) enzymes. Moreover, it downregulated Nox1, ITL, pph1, Caf1 and sca1, all genes related to growth and infection. Lesions were smaller and less pronounced on soybean (Glycine max (Linn.) Merr.) leaves pretreated with Wuyiencin in vitro, and the inhibition rate reached 78.36%. The results suggest that Wuyiencin holds promise for the management of diseases caused by S. sclerotiorum, and the findings provide clues on the mechanism of action.

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Aims: Wuyiencin is a nucleoside antibiotic produced by Streptomyces albulus CK-15. The aim of this study was to determine whether wuyiencin can be used, as a suitable alternative to chemical pesticides, to protect cucumbers (Cucumis sativus L.) from powdery mildew caused by Sphaerotheca fuliginea. Further, the mechanisms underlying the control of cucumber powdery mildew by S. albulus CK-15 were preliminarily elucidated. Methods and Results: Wuyiencin solutions of different concentrations were used to treat infected cucumber plants under greenhouse conditions. The results indicated that wuyiencin could significantly reduce powdery mildew disease incidence, with a maximum prevention efficacy of 94Á38%. Further, scanning electron micrographs and enzyme assays showed that wuyiencin inhibited S. fuliginea spore growth and elicited the activity of plant systemic resistance-related enzymes. Additionally, real-time quantitative reverse transcription PCR suggested that wuyiencin can activate a salicylic aciddependent plant defence response. Conclusions: Wuyiencin produced by S. albulus CK-15 possessed antifungal effects and was able to mitigate cucumber powdery mildew disease via antagonistic action. Wuyiencin also induced defence responses in the plants. Significance and Impact of the Study: These results reinforce the biotechnological potential of wuyiencin as both an antagonistic agent and an inducer of plant systemic resistance.