Assimilation and Translocation Patterns of Carbon-14 in the Shoot of Fruiting Pecan Trees Carya illinoensis Koch1,2

Assimilation and movement of 14 c followed 3 patterns in the shoot and 1-year-old branch of pecan. During pattern I (bud break and leaf expansion stages), photosynthates were assimilated but not translocated from the leaves. Patterns II and III were characterized by bidirectional and basipetal translocation, respectively. When a leaf matured, initial translocation from the leaf was basipetal to other parts of the tree and acropetal to immature leaves and pistillate flowers. Bidirectional translocation from the leaf shifted to basipetal once distal leaves began to export photosynthates. Successively, as distal leaves matured, this pattern was repeated until all leaves were exporting photosynthates. Through the fruit-enlargement and shell-hardening stages, basipetal and bidirectional translocation occurred from the lower and upper leaves, respectively. As the kernel developed, the sink capacity of the fruit intensified and translocation from the more basal leaves again became bidirectional. After fruit maturity, translocation of photosynthates was basipetal from all leaves. Relationship of translocation pattern to the irregular fruiting habit of the pecan is proposed.