YEASTS AS ANTAGONISTS AGAINST ERWINIA AMYLOVORA

Abstract

Epiphytic yeasts are potential antagonists to fire blight in apple blossoms. They showed effects against Erwinia amylovora in field experiments and reduced symptoms on detached apple blossoms. In this study, strains of Aureobasidium pullulans and Metschnikowia pulcherrima were investigated using the immature pear fruit assay and agar diffusion assay. Population studies were performed during the flowering period to examine which parts of the blossom were colonized by the antagonists. Coculture experiments in liquid basal media with synthetic nectar resulted in suppression of E. amylovora by yeast strains. A drop of pH in the medium is partially responsible for the decrease of the E. amylovora population. The production of an antimicrobial compound might be involved. Field, greenhouse and laboratory experiments indicated that yeasts have antagonistic properties against fire blight. The mode of action could possibly be a combination of effects resulting in suppression of E. amylovora.