Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2001
Publication Date: N/A
Interpretive Summary: Losses from fruit decay caused by molds after harvest can be significant at the producer and consumer levels. Fungicides have been used to reduce fruit decays, but development of resistance in molds, lack of effective replacement fungicides, and public demand to reduce pesticides necessitate development of alternative control methods. During the last decade, biological control of postharvest decays emerged as the most effective alternative. We found that yeast Metschnikowia pulcherrima, that naturally occurs on apple, can reduce blue-mold decay of apples very efficiently and has excellent commercial potential because it grows rapidly at low storage temperatures and is compatible with postharvest practices, especially those in the Central and Eastern United States. This beneficial yeast is a common inhabitant of apple and many other fruits. It is also an integral part in wine making, which will make it easily acceptable for treating consumable products and further increase its chances of development into a commercial product.
Technical Abstract: Eight strains of yeast Metschnikowia pulcherrima isolated over a 4-year period from an unmanaged orchard and selected for their biocontrol activity against blue mold (caused by Penicillium expansum) of apples were characterized phenotypically, genetically, and for their biocontrol potential against blue mold on apples. All strains grew well and differ slightly in their growth in NYDB medium at 1 deg C, but large differences occurred at O deg c with strain T5-A2 outgrowing other strains. This strain was also one of the most resistant to diphenylamine, an antioxidant used to dip apples after harvest. All strains required biotin for growth in minimum salt medium (MS). None of the strains produced killer toxins. Analysis of a Biolog data from YT plates for all eight strains using MLCLUST program resulted in separation of the strain to one major cluster containing four strains and four scattered strains from which strain ST1-D10 was most distant from all other strains. Genetic differentiation of the eight strains using maximum parsimony analysis of partial sequences of D1/D2 domain of nuclear large subunit (26S) ribosomal DNA resulted in two major branches separated by 5 nucleotide changes. Strain ST1-D10 grouped with the type strain of M. pulcherrima but remaining seven strains grouped separately, which suggest that they may comprise a new species. This separation was confirmed by bootstrap analysis with frequency of 77% & 68% for the two branches, respectively. All strains significantly reduced blue mold on very susceptible, mature Golden Delicious apple during 1 month storage at 1 deg C followed by 7 days at room temperature, but strains T5- A2 & T4-A2 were distinctly more effective. Strain T5-A2 was also most effective in tests on harvest-mature apples stored for 3 months at 1 deg C.