EFFECT OF SPUR AGE ON THE TRANSLOCATION OF ASSIMILATES FROM SPURS OF NIJISSEIKI PEAR (PYRUS-PYRIFOLIA NAKAI)

The influence of spur age on C-13 partitioning of spur complex in 'Nij isseiki' pear (Pyrus pyrifolia Nakai) was investigated under field con ditions. Leaves on 1-, 3-, 5-, and 7-year-old fruiting spurs were expo sed to (CO2)-C-13 at 6, 12, 18, and 21 weeks after anthesis (WAA). At each treatment time, half the spurs of the same age were girdled at th e base of the spurs to measure the total amount of C-13 absorbed. Six WAA, spurs of all ages exported C-13-assimilates; the amount exported increased with increasing spur age. Twelve WAA, only spurs over 3 year s old exported labeled photosynthates, but the rate was half that at s ix WAA. At Is and 21 WAA, no C-13-labelled substance was exported from any spurs. At 18 WAA, about 60% of the C-13 was partitioned to the fr uit on spurs of all ages within 72 hr of labeling. However, the absolu te amount of C-13 translocated to fruit was largest in 5-year-old spur s. The partitioning rate of C-13 to shoots differed significantly amon g spurs of different ages, ranging from about 2% in 1-year-old spurs t o more than 8% in 7-year-old spurs.