BREEDING OF BAKERS' YEAST-DETERMINATION OF THE PLOIDY AND AN ATTEMPT TO IMPROVE PRACTICAL PROPERTIES

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Abstract
The appearance of tetraploidy in bakers'' yeasts was demonstrated by analysis of mating type alleles and by determination of cell-size and cell-weight. The growing behavior of cells, e.g., the cluster-formation, may be related to heterozygosity or homozygosity of mating type alles rather than to the ploidy. The rate of fermentation of given yeasts in dough ain in flour free of medium was under the control of a heterozygous genetic constitution, in view of the variation in characters among segregants and among hybrids. In crossing experiments, the characters of hybrids and their segregants were statistically parallel to those of component maters prior to crossing, although accompanied by the unexplainable phenomenon that the rates of fermentation of component maters in dough containing a high concentration of sucrose were reduced when combined in hybrids. Selection and crossing are useful methods for improvement of the practical characters of yeast. By such methods, the rate of osmo-resistant fermentation was considerably increased over the value of the parents. The respiration-deficient yeasts were extremely low in osmo-resistant fermentation.

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