Variation in sugar levels and invertase activity in mature fruit representing a broad spectrum of Cucumis melo genotypes

Sugar accumulation is a very important physiological process that determine s dessert-melon fruit quality. Considerable variation in the sugar content and composition in the mature flesh of Cucumis melo L. fruits was observed among 56 genotypes which represent the wide range of morphological and hort icultural types found in this species. Sucrose accumulation was observed no t only among 'dessert melons' of the inodorus and cantalupensis types, but also in representatives of other subgroups of C, melo, including some of th e accessions from agrestis and conomon groups. Among the genotypes that acc umulate sucrose, the levels of this sugar, and not of the hexoses, were cor related with the total sugar concentration. Hexose levels were correlated w ith total sugar levels only among low-sugar genotypes that did not accumula te sucrose. Activities of the sucrose hydrolyzing enzymes acid invertase (E C 3.2.1.26) and alkaline invertase (EC 3.2.1.27) were measured in the matur e fruit flesh and the results of this survey support the hypothesis that lo w acid invertase activity is a prerequisite for sucrose accumulation. The s ucrose accumulating, high sugar genotypes had less-acidic flesh pH values ( pH> 6) than the low-sugar genotypes. The latter were characterized by a bro ader range of pH values, including acidic (pH < 5.5) fruit flesh.