BIOCONTROL CAPABILITY OF METSCHNIKOWIA-PULCHERRIMA AGAINST BOTRYTIS POSTHARVEST ROT OF APPLE

The biocontrol capability of two isolates of the yeast Metschnikowia p ulcherrima against Botrytis postharvest rot of apple was studied in vi tro and on apples under different storage conditions. The biocontrol a ctivity of M. pulcherrima 2.33 or 4.4 can be reduced or totally suppre ssed by the addition of several nitrates. The addition of 100 g l(-1) fructose inhibited the pathogen per se, while leaving unaltered the an tagonistic capability of M. pulcherrima. These results support the hyp othesis that competition for nutrients plays a major role in the bioco ntrol capability of M. pulcherrima against Botrytis postharvest rot of apple. However, both yeasts strongly inhibited the growth and spore g ermination of B. cinerea in vitro even under non-restrictive nutrient conditions. There was no evidence for the involvement of diffusible to xic 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 colonis ation of fresh apple fruit wounds was observed at room temperature dur ing the first 24-48 h, and then the populations stabilised for the rem aining storage period. On apple wounds kept at 4 degrees C, the increa se in population density of M. pulcherrima was lower, but continued ov er 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.