Improvement of biocontrol yeast activity by integration with natural compounds

Inorganic and organic salts, organic acids and natural gums, mainly consisting of natural compounds used as additives in the food industry, were assayed in vitro and in vivo in order to improve the activity of Cryptococcus laurentii (Cl) and Aureobasidium pullulans (Ap), two antagonist yeasts of postharvest pathogens. In in vitro tests, based on their combined effects on the two yeasts and on the postharvest fungal pathogens Botrytis cinerea and Penicillium expansum, the compounds were ranked as follows: (i) products increasing or not affecting the growth of one or both the antagonists but inhibiting the pathogens; (ii) products inhibiting one or both antagonists but increasing pathogen growth; (iii) products inhibiting both antagonists and pathogens; (iv) products either increasing or not the growth of both antagonists and pathogens. Generally, the radial growth of B. cinerea in comparison with that of P. expansum was more consistently inhibited by the same substance. In in vitro tests, the selected substances, alone or combined with the yeasts, were applied on wounded apples inoculated with P. expansum. Different compounds significantly increased the antagonistic activity of the yeasts and showed additive or synergistic effects. The results of this investigation demonstrated that some substances can potentially be used as additives to improve the efficacy of yeast-based biofungicides.