AN EXPOLINEAR MODEL OF THE GROWTH-PATTERN OF THE APPLE FRUIT

The expolinear growth model of Goudriaan and Monteith (1990) is proposed as a new model for the inherent growth pattern of fruit of apple (Malus domestica Borkh.), defined as growth pattern under apparently non-limiting conditions This function has three parameters: maximum relative growth rate, maximum absolute growth rate, and ''lost time'' (x intercept of the linear growth phase). Apple fruit growth (weight basis) at very low crop loads and apparently optimum environmental conditions, displays an early positive curvilinear growth followed by linear growth to harvest, and is described well by the expolinear function. The model also fits growth patterns of 'Empire' and 'Golden Delicious' apple fruit differing in the rate of growth in the exponential phase due to differences in the crop load. Estimates of cortical cell numbers in 'Empire' fruit from related studies suggest that during the linear phase in mid-season, different growth rates among crop load treatments were apparently controlled by differences in numbers of cells in the fruit, since estimated growth rates per cortical cell were essentially constant over several treatments.