Partitioning pattern of C-13-assimilates in young 'Nijisseiki' pear trees during the initial period of fruit growth

Using C-13 as a tracer, the partitioning patterns of current photosynthates in three-year-old 'Nijisseiki' pear trees were investigated during the ini tial period of fruit growth. One week after anthesis (WAA), unfolded leaves were found to export the labeled photosynthates to fruitlets. Whether labe led 1 or 2 WAA, most of the C-13 remained in source leaves; of that exporte d from leaves, the majority was translocated to the new growth of aerial pa rts within a week after labeling. Small amounts of C-13 were recovered in o lder tissues. No substantial amounts were recovered in new roots. When labe led two WAA, the highest concentration of C-13 was recovered from fruitlets . Thus, in 'Nijisseiki' pear, new growth of aerial parts commences to assim ilate current photosynthates within 1 WAA and new roots import less than th e new aerial parts.