Genotypic characterization of strains of commercial wine yeasts by tetrad analysis.

The objective of this work was to use tetrad analysis to define the genotypes of a number of commercially available wine yeasts for a range of characteristics related to wine making. The levels of sporulation and spore viability of 13 wine yeasts were determined. Sporulation was very low in one strain and varied from low to high in the other 12 strains. Spore viability of these 12 strains varied from 0-95% and this range was comparable to a large sample of naturally-occurring wine strains. Colonies from viable spores, predominantly from 4-spored asci, from 11 strains were characterized for the ten traits: homothallism/heterothallism, fermentation of sucrose, galactose, maltose; growth on glycerol (nonfermentable); slow growth on glucose and glycerol; level of sulfide production; copper resistance; putative presence of a recessive lethal mutation (inviability of at least two spores/tetrad); yellow pigment (in colonies) on sugar media. The number of heterozygosities for these ten characteristics varied from zero to seven in 11 strains, and eight strains were genetically distinct. Another three strains, distinct from these eight strains, were identical for the ten characteristics and also equivalent for the levels of sporulation and spore viability. Although these three strains are marketed under different designations, there is a strong probability that they were derived from a common ancestral strain. The genotypic characterization of these 11 strains constitutes an important foundation for their identification and their use in breeding programs.