Interactions between developing Citrus fruits and their supportive vascular system

The developing fruit is a strong sink, which demands large amounts of assimilates. A correlation between grapefruit (Citrus Paradisi Macf., var. Marsh seedless) fruit size and its pedicel cross sectional area (CSA) can be demonstrated, suggesting a close interaction between them. The presence of fruits seems to determine the developmental pattern of the vascular tissues within the branches on which the fruits are borne. The pedicel normally terminates its diametric growth prior to the linear phase of fruit growth. Fruit thinning (90%) and trunk girdling, performed in order to minimize carbohydrate limitations, result in dramatic increases in fruit growth rate and pedicel CSA. Partial girdling of the pedicel causes a transient decrease in fruit growth. An increase in specific mass transport (SMT) through the existing vascular routes is the immediate response, due to the instantaneous upsurge of carbohydrate supply to individual fruit. Nevertheless, the rapid development of new vascular tissues has been the major factor responsible for the long term enhancement, or recovery, of fruit growth, suggesting that limitation in transport capacity does occur. The cause and effect relationships between fruit and vascular development are discussed.