Apple Fruit Growth and Cell Division in Relation to Embryo and Endosperm Development in Two Climates, New York State and Washington State

In 2002 in New York State, we collected king fruit of `Gala' and `Red Delicious' on fruiting spurs from 0 to 66 days after full bloom (DAB). In 2003 in Washington State, we collected king fruit of these cultivars from 14 to 62 DAB. At each collection we determined radial cell number across the fruit cortex and developmental stage of the embryo and endosperm in seeds. Fruit diameter was slightly greater in Washington fruit than in New York fruit until about 40 DAB; thereafter, New York `Delicious' outgrew Washington `Delicious', while `Gala' in the two climates (and two different years) grew identically. The New York fruits had a much earlier rise in fruit growth rate and maintained a slightly higher rate throughout the period. The cortex thickness of Washington fruit was greater than that of New York fruit for both cultivars. Most rapid cell division in the cortex occurred between 10 and 28 DAB and, by 40 DAB, most cell proliferation had ceased. The Washington fruit formed more cells across the radius than did New York fruit. Cortex thickness increased with respect to increase in cortex cell number about 30% to 40% faster in Washington fruit than in New York fruit. Developmental stages of embryos and endosperm followed a sigmoid time pattern for both cultivars in both states. By 60 DAB, embryos and endosperm reached their maximum stage of development. In both cultivars and states, cell divisions were nearly completed by the time the embryo and endosperm approached stage 3: for embryos this is the heart-shaped stage, for endosperm it is near completion of cell wall formation. The completion of wall formation in the endosperm, the near completion of cortex cell division, and the generation of the cotyledons and apical meristems in the embryo are highly correlated processes. We saw no evidence that endosperm development precedes embryo development.