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In agricultural sciences, breeding strategies have historically been used to select new, optimized plant varieties or animal breeds. Similar strategies are possible for genetic improvement of wine yeasts. We optimized 11 relevant enological traits in a single clone using successive hybridization and segregation steps. A hybrid obtained by crossing two parent strains derived from commercial wine yeasts showed that some of the traits were readily optimized. Dominance/recessivity, heterosis and transgression were observed among 51 segregating progeny. On the basis of this information, all the optimal characters from both parents were combined in a single strain following two targeted sexual crosses. This article presents a powerful methodology for obtaining a single wine strain with numerous fermentative qualities that does not produce off-flavors.

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The yeast Lachancea thermotolerans (previously Kluyveromyces thermotolerans) is a species of large, yet underexplored, oenological potential. This study delivers comprehensive oenological phenomes of 94 L. thermotolerans strains obtained from diverse ecological niches worldwide, classified in nine genetic groups based on their pre-determined microsatellite genotypes. The strains and the genetic groups were compared for their alcoholic fermentation performance, production of primary and secondary metabolites and pH modulation in Chardonnay grape juice fermentations. The common oenological features of L. thermotolerans strains were their glucophilic character, relatively extensive fermentation ability, low production of acetic acid and the formation of lactic acid, which significantly affected the pH of the wines. An untargeted analysis of volatile compounds, used for the first time in a population-scale phenotyping of a non-Saccharomyces yeast, revealed that 58 out of 90 volatiles were affected at an L. thermotolerans strain level. Besides the remarkable extent of intra-specific diversity, our results confirmed the distinct phenotypic performance of L. thermotolerans genetic groups. Together, these observations provide further support for the occurrence of domestication events and allopatric differentiation in L. thermotolerans population.

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Wine yeast strains exhibit a wide variability in their technological properties. The large number of allelic variants and the high degree of heterozygosity explain this genetic variability found among the yeast flora. Furthermore, most enological traits are controlled by polygenic systems presenting complex interactions between the alleles. Taking this into account, we hypothesized that the meiotic segregation of such alleles from a given strain might generate a progeny population with very different technological properties. In this work, a population of 50 progeny clones derived from four industrial wine strains of Saccharomyces cerevisiae was characterized for three major enological traits: ethanol tolerance, volatile-acidity production and hydrogen sulphide production. For this purpose, reliable laboratory fermentation tests were developed in accordance with enological practice. A wide variability in the values of the various parameters was found among spore clones obtained after sporulation. Many clones presenting better aptitudes than the parental strains were obtained. Moreover, analysis of the progeny demonstrated that: (1) traits are in part inheritable; (2) traits are clearly polygenic; (3) broad relations of dominance/recessivity can be established. All these findings constitute an initial step for establishing breeding strategies for wine yeast improvement.