DETERMINATION OF THE RELATIVE PLOIDY IN DIFFERENT SACCHAROMYCES-CEREVISIAE STRAINS USED FOR FERMENTATION AND FLOR FILM AGING OF DRY SHERRY-TYPE WINES

The full chromosomal karyotype of six enological Saccharomyces cerevis iae strains used for fermentation and biological ageing of sherry-type wines was studied. A genetic method based on the analysis of segregat ion frequencies of auxotrophic markers, among random spore progeny of hybrids, constructed between laboratory and industrial wine strains (B akalinsky and Snow, 1990) was used. This method was combined with the analysis of strains by pulsed-field gel electrophoresis. The results o btained clearly indicate the presence of two, three or four copies of a chromosome in the industrial strains examined, and thus confirm that aneuploidy/polyploidy is not uncommon in these strains. In all strain s examined, chromosome XIII polysomy is observed. This chromosome cont ains the ADH2 and ADH3 loci, that code for the ADHII and ADHIII isoenz ymes of alcohol dehydrogenase, which are involved in ethanol oxidative utilization during biological ageing of wines. Tetrad analysis for th e 'flor formation' character suggests two possibilities: this characte r is either regulated by at least a digenic system, or by only one gen e present on a chromosome which is, at least, disomic.