Inheritance and selection of some fruit characters of apple. I. Inheritance of low and high acidity

Summary Fruit acidity as such appears to be gouverned by a single major gene, low acidity being a recessive character. The additional genetic variation is explainable by the additive gene action model. This mode of inheritance causes the pH distribution of seedlings in progenies to shift with a higher mid-parent pH towards more low-acid cum sweet (pH 3.8) and fewer high-acid cum sour (pH 2.9) seedlings or vice versa with a lower midparent pH. As a result, in crosses between heterozygotes (Mama) the total proportion of undesirable seedlings -low plus high-acid ones-, remains similar, irrespective of the mid-parent pH. This proportion constituted about one third of the seedlings. A same proportion, but of mainly sour plants, was found in crosses between relatively acid homozygotes (Mama) or between these and similar heterozygotes. It was less than one quarter if the heterozygous partner was medium-acid and a few percentages only when both the homozygous and heterozygous partner were medium-acid. Choosing parents in the absence of information, chances are that the very large majority of the medium-acid types are heterozygotes, that among the relatively acid ones one in two is homozygous and that the odds to find homozygotes among the sour types are probably best. Attention was drawn to the importance of a high sugar content — which is quantitatively inherited — in parents with a relatively low pH to increase the chances of selecting seedlings with a good sugar/acid ratio.