Antagonistic effect of volatile and non-volatile compounds from Streptomyces strains on cultures of several phytopathogenic fungi

Fungi and oomycetes are important plant pathogens that constantly attacked plants, thus compromising the production of foods worldwide. Streptomyces strains might be useful to control fungal pathogens by different mechanism. The in vitro antagonistic activity of non-volatile and volatile metabolites from four Streptomyces strains was evaluated over cultures of phytopathogenic fungi and oomycetes. The non-volatile compounds from Streptomyces strains significantly reduced (44.2 to 92.1%) the growth of aerial mycelium of pathogens. The volatile compounds (VOCs) from Streptomyces strains reduced both aerial mycelium (22.5 to 96.7%) and mycelium growing inside of culture medium (0.0 - 9.4%). The pathogens maintained their capacity to grow normally in fresh culture medium without antagonists after confrontations with antagonist VOCs. The analysis of VOCs by gas chromatography coupled to mass spectrometry revealed different kinds of VOCs included alcohols, aldehydes, ketones, esters, terpenes, terpenoids, thioethers, among others. The most abundant VOCs were trans-1,10-dimethyl-trans-9-decalol (geosmin), 2-methylisoborneol, 2-methyl-2-bornene, 1,4-dimethyladamantane, and 4-penten-1-ol, trifluoroacetate. The antipathogenic activity of nine pure VOCs that had been identified in cultures of the Streptomyces strains alone was evaluated in vitro against phytopathogenic fungi and oomycetes. Trans-2-hexenal was the most effective of these VOCs, inhibiting completely the growth of tested phytopathogens. The volatile and non-volatile compounds from Streptomyces strains effectively reduced the in vitro growth of phytopathogens and they might be used as biological control. Further studies are required to demonstrate this activity on open field conditions.