Biocontrol capability of Metschnikowia pulcherrima against Botrytis postharvest rot of apple

The biocontrol capability of two isolates of the yeast Metschnikowia pulcherrima against Botrytis postharvest rot of apple was studied in vitro and on apples under different storage conditions. The biocontrol activity of M. pulcherrima 2.33 or 4.4 can be reduced or totally suppressed by the addition of several nitrates. The addition of 100 g l(-1) fructose inhibited the pathogen per se, while leaving unaltered the antagonistic capability of M. pulcherrima. These results support the hypothesis that competition for nutrients plays a major role in the biocontrol capability of M. pulcherrima against Botrytis postharvest rot of apple. However, both yeasts strongly inhibited the growth and spore germination of B. cinerea in vitro even under non-restrictive nutrient conditions. There was no evidence for the involvement of diffusible toxic metabolites in the biocontrol efficacy. The antagonistic activity of M. pulcherrima was dependent on the concentration of the antagonist. At 10(7)-10(8) cells ml(-1), 2.33 was most effective when applied at least 6 h before the pathogen, while 4.4 provided consistent results when co-inoculated with B. cinerea or applied 1 h later. Rapid colonisation of fresh apple fruit wounds was observed at room temperature during the first 24-48 h, and then the populations stabilised for the remaining storage period. On apple wounds kept at 4 degrees C, the increase in population density of M. pulcherrima was lower, but continued over 96-128 h after application of the antagonists until it reached the same saturation level observed on apples stored at room temperature. (C) 1997 Elsevier Science B.V.