Anatomical Analysis of Fruit Development of Different-Sized 'Hongro' and 'Fuji' Apple Fruits

摘要

A Major issue in apple marketability is the determination of fruit size. In order to illustrate the mechanism underlying the construction of fruit size, the anatomical observation of mesocarp cells was conducted during fruit development on two apple genotypes that set different-sized fruits, mid season-'Hongro'/M.9 and late season-'Fuji'/M.9. It was observed that fruit size of 'Hongro' was larger than that of 'Fuji' at their respective maturity, although they were grown under the same condition. The microscopic observation of mesocarp cells showed that cell size of 'Hongro' and 'Fuji' gradually increased during fruit growth developmental stages, with 'Hongro' fruit showing 2.4-fold of 'Fuji' cell size at their respective maturities. 'Hongro' fruit expressed a more active cell proliferation than 'Fuji' fruit, Which resulted in a significantly larger cell number compared to 'Fuji' fruit. Thus, it was demonstrated that the difference in fruit size between the two apple genotypes was attributed to both cell size and cell number. Within the same genotype, large-sized 'Hongro' fruit exhibited larger cell size, whereas the large size of 'Fuji' fruit was resulted from the greater number of cells. These observations suggested that the two genotypes undergo different mechanisms of fruit construction: cell size is the critical factor for determining the final 'Hongro' fruit size, while cell number is dominant for 'Fuji' fruit.