Inhibition of Streptomyces lydicus K2 on Botrytis cinerea and identification of its inhibitory substances

Abstract:

Gray mold is a common disease in the production process of a variety of cash crops, and in the storage and transportation of fruits and vegetables. Streptomyces spp. can produce many secondary metabolites with strong inhibition effects on Botrytis cinerea. [Objective] The present study focused on screening Streptomyces sp. with more efficient functions and provides excellent strains for the research and development of biocontrol agents for gray mold. [Methods] Tube dish method was applied for the selecting culture media and for determining bioactivities of culture broth of strain K2. The antifungal activity of volatile substances against B. cinerea was determined by double dish confrontation. 16S rRNA gene sequence analysis was used for identification of strain K2. High performance liquid chromatography and liquid chromatography-mass spectrometry methods were applied for qualitatively verification of the active components in the culture broth. Volatile components were determined using headspace solid phase micro-extraction gas chromatography-mass spectrometry. [Results] The secondary metabolites produced by strain K2 in culture medium A had strong inhibitory effects on a variety of plant pathogenic fungi such as Valsa mali, Physalospora piricola, Sclerotinia sclerotiorum, Botryosphaeria dothidea and Alternaria alternata. The inhibition rate of volatile substances produced by K2 on B. cinerea reached 100%, and the inhibition effect was correlated with the amount of volatile substances in the culture broth. K2 was identified as Streptomyces lydicus through the 16S rRNA gene sequence (maximum identity of 99%), glutamicin, fengamycin and natamycin were detected in the culture broth with high performance liquid chromatography. A total of 30 volatile substances including olefins, alcohols, esters and alkenes were detected using headspace solid phase micro-extraction gas chromatography and mass spectroscopy, in which 2-methylisoborneol, 1-undecene, p-menth-8-ene and 3-methylene were the major biochemicals. Two substances with fungicidal activity, benzothiazole and β-pinene, were detected as well. [Conclusion] The strain K2 was identified as Streptomyces lydicus and its culture broth had a broad spectrum of bioactivities against different plant pathogens, and its volatile substances also had good inhibitory effects on B. cinerea. As a result, K2 can be used as a high-quality biocontrol agent to develop bio-fungicides for controlling gray mold on some fruit and vegetable crops.