Enhancing the efficacy of yeast biocontrol agents against postharvest pathogens through nutrient profiling and the use of other additives

Vishniacozyma victoriae and Pichia membranifaciens were selected in a previous work for their biocontrol effectiveness against Penicillium expansum and Botrytis cinerea, the causal agents of blue and grey mold of pear fruits. The objective of this study was to determine the effects of different nutrient or additives on the growth of the two antagonist yeasts and of the two fungal pathogens in order to develop a rational selection based on nutritional profiles to be used in biocontrol enhancement of decay in pear fruits. Twenty-six different nutrient sources including 18 amino acids, five sugars, three inorganic nitrogen and one iron source were tested in vitro for their effect on the growth of the two yeasts and the two pathogens. Nutrients that promoted the growth of the yeasts and inhibited the growth of pathogens were applied with the antagonist to wounded fruits to evaluate their effect on enhancing biocontrol in cold storage. In general, the effect of each additive was specific to the yeasts and pathogens used in the in situ assays. The combination of the yeast and some additives resulted in a significantly higher activity with respect to the single treatments applied separately, producing synergistic effects. The effect of the exogenous application of CaCl2 and chitosan together with the antagonist yeasts was also evaluated against the two pathogens. The most effective mixtures were the CaCl2 with the two antagonist yeasts. Our research demonstrates that manipulating the chemical environment by adding several amino acid and/or Cl2Ca results in improved antagonistic activity of Vishniacozyma victoriae and Pichia membranifaciens against two postharvest diseases of pear fruits.