| Summary: | The yeast <i>Metschnikowia pulcherrima</i> is frequently isolated from environmental samples and has often been reported to exhibit strong antagonistic activity against plant pathogens. In order to assess the potential of this species for its development into a plant protection product, the survival during formulation and storage were quantified and field efficacy was assessed over a period of five years. Freeze dried and liquid <i>M. pulcherrima</i> formulations (i.e., with skim milk powder (SMP), sucrose, glycerol, xanthan, without additives) were prepared and the number of viable cells was quantified during storage at different temperatures. Field trials against apple postharvest diseases (<i>Neofabreae</i>) were performed with different dry formulations. <i>M. pulcherrima</i> proved exceptionally stable for many months and even years. Five years of field trials with the yeast revealed variable effects, but reduced <i>Neofabreae</i> infections of stored apples were observed in some years. <i>M. pulcherrima</i> applications after prior fungicide treatments repeatedly showed an additive effect as compared to the fungicide treatments alone. In summary, <i>M. pulcherrima</i> exhibited highly advantageous storage properties and encouraging activity against apple postharvest rots. Further studies to identify the factors responsible for antagonistic activity in the field and survival during storage are expected to lay the foundation for the future development of a plant protection product.
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