Impact of environmental factors on Streptomyces spp. metabolites against Botrytis cinerea

Botrytis cinerea is an economically important disease on numerous vegetables including tomato. From our previous studies, a spore suspension of Streptomyces philanthi RL‐1‐178 and RM‐1‐138 and Streptomyces mycarofaciens SS‐2‐243 showed strong inhibition against B. cinerea. In this study, the efficacy of their antifungal metabolites against B. cinerea was investigated after enhancing the production through the optimum culture medium and environmental conditions (temperature, light/dark cycle). In vitro studies indicated that glucose yeast‐malt (GYM) agar and incubation at 28°C were optimal for growth and mass spore production of all three Streptomyces strains. Moreover, light/dark conditions had a positive effect on the growth and spore production of S. philanthi RM‐1‐138 and RL‐1‐178 but not on S. mycarofaciens SS‐2‐243. Both strains of S. philanthi possessed an antifungal activity against B. cinerea (100% inhibition) while S. mycarofaciens showed different results on PDA (83% inhibition) and GYM (88% inhibition) at the optimum incubation temperature at 21°C. The antifungal compounds from S. philanthi RM‐1‐138 exhibited the highest protection efficacy against B. cinerea on tomato leaves (82.89% and 0.33 cm² lesion areas symptoms). The antifungal compounds RM‐1‐138, identified by GC‐MS, were greatly altered based on components concentration under various temperatures and light/dark conditions. The anti‐B. cinerea of S. philanthi RM‐1‐138 was established at a higher level in several metabolic compounds in the dark condition (11 and 32 antifungal compounds after incubation at 21°C and 28°C, respectively) than in the light condition (11 and 19 antifungal compounds after incubation at 21°C and 28°C, respectively). At 21°C, the dominant component was acetic acid (67.41% and 68.77% in light and dark conditions, respectively) while at 28°C, benzeneacetamide (43.58% in light) and propanamide (20.68% in the dark) were dominant. The results clearly demonstrated the significant influence of environmental factors on the production of antifungal metabolites of Streptomyces spp.