Although the general concept of growth is understood by most as an increase in size, before describing the growth patterns and how they are measured, it is useful to define what "growth" means scientifically. The strict biological concept of growth is an irreversible increase in dry weight (weight after all water is removed). Dry weight growth is important to consider in physiological studies of tree growth and development, as it relates to the energy required for growth. However, in commerce, tree fruit are normally sold on the basis of fruit diameter or fruit fresh weight, so growth measurements in diameter and fresh weight are common also.
The apparent pattern of growth of a fruit may vary depending on whether fresh weight, dry weight, or diameter is considered. Volume and weight represent all three dimensions of the fruit, while diameter represents only one dimension. So, interpretations of growth are affected by the measurement used. For example, if an apple fruit near harvest grows in diameter from 75 to 80 millimeters, that represents about a 7 percent increase in diameter, but a 20 percent increase in fresh weight growth. Consequently, growth curves of fruit size over a season will be presented in all three expressions of diameter, fresh weight, and dry weight.
Another consideration that is important to understanding fruit growth is the "growth rate," which is the amount of growth per time (day, week, etc.). If developing fruit are given no or few limitations (no competition from other fruit, healthy tree, etc.), they will grow near their maximum rates. Such growth rate patterns probably represent the inherent genetically controlled pattern of "demand" of the fruit for support from the tree. Variations from a maximum growth rate can help identify competition among organs within a tree (shoots, roots, fruit, wood) for resources that may reduce fruit growth. In practice, fruit growers try to balance the competition within trees to allow good yields and fruit quality while still maintaining good vegetative growth and annual flowering.
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