Development of sweet melon (Cucumis melo) genotypes combining high sucrose and organic acid content

The sweet cultivars of Cucumis melo are characterized by high sucrose levels, together with low acid levels in the mature fruit flesh. The trait of high sugar accumulation in C. melo fruit is determined by a single recessive gene, suc. High acid content, conferred by a single dominant gene, So, is found only in C. melo varieties that do not accumulate high levels of sugar and are used for nondessert purposes. We combined the genetic traits of high acid content (low pH) and high sugar levels by crossing the nonsweet, high acid C. melo var. flexuosus, 'Faqqous' (So/So, Suc/Suc), with high sugar, low acid C. melo genotypes (so/so, suc/suc) and generating the recombinant genotype Sol-, suc/suc. Segregating F₂ populations derived from the cross between 'Faqqous' and a standard high sugar, low acid line showed that the traits of high sugar and low pH were inherited independently of each other. The accumulation of acid and sugar in the developing fruit of a recombinant high acid, high sugar breeding line, A6, were also temporally independent, with acid accumulation preceding the rise in sucrose levels. The low pH of A6 was correlated with the developmental increase in titratable acidity and particularly of citric acid levels. The combination of increased acidity and high sugar provides the melons with a unique taste due to a sugar to acid ratio not present in sweet C. melo cultivars. These results are discussed in terms of the evolution under domestication of C. melo.