A mixture of four volatile organic compounds identified from Aureobasidium pullulans, suppresses the growth of Botrytis cinerea and Alternaria alternata

The use of microbial volatile organic compounds as natural products with antimicrobial properties has become extremely popular in different host-pathogen interactions because of their biodegradability, toxicity at low concentrations and bioactivity regardless of a physical contact with the targeted host . The volatilome of Aureobasidium pullulans was investigated in the current study as a potential biocontrol agent against a wide range of fungal phytopathogens . Initial experiments demonstrated that the growth of Botrytis cinerea and Alternaria alternata was suppressed after exposure to A. pullulans volatile organic compounds (VOCs). A solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) approach was employed for the quantitative identification of A. pullulans VOCs. A novel setup was devised to grow both antagonist and pathogen without a physical interaction and to add an internal standard prior to the GC-MS analysis. Multivariate curve resolution-alternating least squares deconvolution of SPME-GC-MS spectra and subsequent analysis, revealed thirteen VOCs from A. pullulans culture headspace. Acetone, 2-heptanone, ethyl butyrate, 3-methylbutyl acetate and 2-methylpropyl acetate were identified as new A. pullulans VOCs. A partial least squares discriminant analysis model was applied to the volatilome of cultures and variable importance in projection scores and selectivity ratios used to identify four VOCs; ethanol, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethanol with high explanatory power to discriminate the headspace of A. pullulans inoculated samples from pathogens. Those four compounds were quantified and ethanol was the VOC with the highest abundance in A. pullulans culture headspace. A Box-Behnken design with response surface modelling approach determined the main effects and interactions among those four VOCs to suppress the growth of targeted pathogens in vitro. The four compounds showed different inhibitory levels. Ethanol and 2-phenylethanol were identified with significant (p<0.05) inhibitory effects against both B. cinerea and A. alternata. Our findings give insights into the potential use of A. pullulans VOCs to control B. cinerea and A. alternata.