Histological analysis of fruit development between two melon (Cucumis melo L. reticulatus) genotypes setting a different size of fruit

A major issue in plant development in higher plants is the determination of fruit size. In order to address the mechanism, the histological observation of cells during fruit development between two melon (Cucumis melo L. reticulatus) genotypes, Fuyu A and Natsu 4, was used. Although the two genotypes have nearly identical genetic backgrounds, the fruit of Fuyu A is larger than that of Natsu 4 when grown under the same conditions. The microscopic observation of pericarp cells in several developmental stages showed that there were clear differences in cell size between the two genotypes. In spite of its smaller fruit size, the cell size of Natsu 4 was somewhat larger than that of Fuyu A. The cell proliferation period of Fuyu A was longer than that of Natsu 4, which may account for the difference in the cell number between both genotypes. Surprisingly, the difference in fruit size could also be defined by the number of the cells when each genotype was cultivated in different temperatures. These results suggest that fruit size is determined by the amount of cell proliferation in the early stage of fruit development and that the factor which regulates the amount of cell proliferation is affected by temperature.