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

Abstract

Malus, apple, inheritance, fruit 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 lowacid cum sweet (pH 3 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 .

Genetic characterization of the Ma locus with pH and titratable acidity in apple

“…Apples with pH [ 3.8 are commonly considered to be low acid or sweet of the mama genotype (Nybom 1959;Visser and Verhaegh 1978;Maliepaard et al 1998). Consistent with these findings, the segregation ratio of the high/ medium-acid (pH \ 3.80) to the low-acid groups fits the 3:1 ratio in population GMAL 4595 and GMAL 4590, suggesting that the parental lines are all of the Mama genotype (Fig.…”

“…An early inheritance study conducted on fruit acidity (Nybom 1959), based on pH measurements, reported several important findings: (1) Apple varieties can be categorized into two groups-an acid/ sub-acid group with a fruit pH \ 3.8 and a sweet group of pH C 4.0; (2) the acid/sub-acid group is much more prevalent than the sweet group in cultivated apples; and (3) the sweet flavor is determined by one recessive gene present in 80-90% of apple varieties studied. These findings were independently confirmed in later studies based on fruit pH (Visser and Verhaegh 1978) as well as on malic acid concentration (Brown and Harvey 1971;Yao et al 2008). The major gene governing fruit acidity was designated Ma with the Ma allele representing the dominant high and medium acidity, and the ma allele for low acidity (Visser and Verhaegh 1978).…”

“…These findings were independently confirmed in later studies based on fruit pH (Visser and Verhaegh 1978) as well as on malic acid concentration (Brown and Harvey 1971;Yao et al 2008). The major gene governing fruit acidity was designated Ma with the Ma allele representing the dominant high and medium acidity, and the ma allele for low acidity (Visser and Verhaegh 1978). As there is a relatively wide acidity spectrum in highand medium-acid fruits, the dominance of high and medium acidity over low acidity was considered to be quantitative (Brown and Harvey 1971).…”

“…Based on these data, it appeared to be sufficient to simply evaluate fruit pH using pH papers to screen large populations in genetic studies of Ma that only need to discriminate the lowacidity genotypes (pH [ 3.8) from the high/medium group. Discovery and genetic mapping of the Ma locus were largely accomplished by estimation of fruit pH with pH indicators (Nybom 1959;Visser et al 1968;Visser and Verhaegh 1978;Maliepaard et al 1998). However, for selection and breeding purposes, TA also should be determined in order to more comprehensively evaluate acid and taste, including its derivative, the fruit sugar to acid ratio.…”

“…As there is a relatively wide acidity spectrum in highand medium-acid fruits, the dominance of high and medium acidity over low acidity was considered to be quantitative (Brown and Harvey 1971). This additional variation within the dominance class is proposed to be explained by the additive gene action model (Visser et al 1968;Visser and Verhaegh 1978).…”