Genetic analysis was performed on 45 commercial yeasts which are used in winemaking because of their superior fermentation properties. Genome sizes were estimated by propidium iodide fluorescence and flow cytometry. Forty strains had genome sizes consistent with their being diploid, while five had a range of aneuploid genome sizes that ranged from 1.2 to 1.8 times larger. The diploid strains are all Saccharomyces cerevisiae, based on genetic analysis of microsatellite and minisatellite markers and on DNA sequence analysis of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA of four strains. Four of the five aneuploid strains appeared to be interspecific hybrids between Saccharomyces kudriavzevii and Saccharomyces cerevisiae, with the fifth a hybrid between two S. cerevisiae strains. An identification fingerprint was constructed for the commercial yeast strains using 17 molecular markers. These included six published trinucleotide microsatellites, seven new dinucleotide microsatellites, and four published minisatellite markers. The markers provided unambiguous identification of the majority of strains; however, several had identical or similar patterns, and likely represent the same strain or mutants derived from it. The combined use of all 17 polymorphic loci allowed us to identify a set of eleven commercial wine yeast strains that appear to be genetically homozygous. These strains are presumed to have undergone inbreeding to maintain their homozygosity, a process referred to previously as 'genome renewal'.

Background and Aims:The yeast flora from a range of New Zealand commercial wineries was surveyed to estimate the incidence of yeast species in grape juice. Methods and Results: Molecular analysis of the internal transcribed spacer region was performed for 1279 yeast colonies isolated from 17 different fresh grape juices sampled in eight New Zealand wineries between 2003 and 2009. The 17 juices contained at least 25 different species of yeast from nine genera. Microsatellite fingerprinting of Saccharomyces cerevisiae showed that some strains were identical to known commercial yeast varieties, but we also found evidence for local populations of S. cerevisiae common to individual wineries or regions. Five genotypes from Central Otago, New Zealand, were very closely related to a single sequenced strain derived from Chile, which in turn is related to European wine isolates. Conclusions: The yeast flora found in New Zealand grape juices is broadly similar to that found in wineries elsewhere around the world. Genotyping of S. cerevisiae suggests recent dispersal of both commercial and non-commercial yeast strains from Europe to New Zealand. Significance of the Study: These data are consistent with two human-mediated modes for the international dispersal of S. cerevisiae: one via the escape of strains traded commercially, and another via long distance dispersal of non-commercial strains.