GENETIC-STUDY OF NATURAL INTROGRESSION SUPPORTS DELIMITATION OF BIOLOGICAL SPECIES IN THE SACCHAROMYCES-SENSU-STRICTO COMPLEX

Wine Saccharomyces cerevisiae strains having high nDNA/nDNA homology w ith sibling species S. paradoxus or S. bayanus (RODRIGUES DE SOUSA et al. Syst. Appl. Microbiol. 18, 44-51 (1995) have been studied by genet ic and karyotypic analyses. Despite the natural introgression the stra ins had the S. cerevisiae-S. paradoxus specific karyotype and belonged to the biological species S. cerevisiae. Their intraspecific hybrids were fertile having 28-99% ascospore viability and normal meiotic segr egation of control markers while interspecific hybrids were sterile. T he results demonstrate that molecular karyotyping is a reliable tool f or delimiting strains of S. bayanus from S. cerevisiae and S. paradoxu s. The latter two species, having nearly identical karyotypes, can be distinguished by genetic analysis. Several Saccharomyces sensu stricto strains monitored earlier by different molecular methods [GUILLAMON e t al. Int. J. Syst. Bacteriol. 44, 708-714 (1994); MOLNAR et al. Syste m Appl. Microbiol. 18, 136-145 (1995)] have been reidentified genetica lly as S. bayanus and S. paradoxus.