The antagonistic mechanisms of Streptomyces sioyaensis on the growth and metabolism of poplar canker pathogen Valsa sordida

Abstract Poplar (Populus spp.) is a high-economic-value tree species around the world. However, poplar trees are damaged by canker disease caused by Valsa sordida. In our previous study, an antagonistic bacterial strain of Streptomyces sioyaensis (No. F57) against V. sordida was isolated, however the antifungal mechanisms by which S. sioyaensis (No. F57) suppress the poplar canker pathogen V. sordida remains unclear. In the present study, S. sioyaensis (No. F57) fermentation broth significantly inhibited mycelial growth. The inhibition rate for mycelial dry weight and colony growth after 3 days was 89.27% and 83.94%, respectively. Spore germination of the pathogen was greatest inhibited 78.30% at 6 h. In vivo biocontrol assays, the disease index of poplar canker treated with S. sioyaensis (No. F57) fermentation broth was significantly reduced compared with the control. At concentrations of 10-fold diluent of fermentation broth, the control effect was up to 78.08%. The fermentation broth also increased mycelia electrical conductivity and the accumulation of malondialdehyde (MDA). The enzyme activities of succinate dehydrogenase (SDH) and Ca2+-Mg2+-ATPase in the tricarboxylic acid cycle (TCA cycle), Hexokinase (HK), Phosphofructokinase (PFK) and pyruvate kinase (PK) in the glycolytic pathway, and Glutathione peroxidase(GSH-Px) were all disrupted in the pathogen mycelia treated with S. sioyaensis (No. F57) fermentation broth. These result revealed that S. sioyaensis (No. F57) inhibited V. sordida by increasing the cell permeability and disrupting the metabolic pathways of the pathogen. Thus, S. sioyaensis (No. F57) can be a potent biocontrol agent for poplar canker disease management in application.