Effect of Spur Age on the Translocation of Assimilates from Spurs of 'Nijisseiki' Pear (Pyrus pyrifolia Nakai)

Abstract

The influence of spur age on ¹³C partitioning of spur complex in 'Nijisseiki' pear (Pyrus pyrifolia Nakai) was investigated under field conditions. Leaves on 1-, 3-, 5-, and 7-year-old fruiting spurs were exposed to ¹³CO₂ at 6, 12, 18, and 21 weeks after anthesis (WAA). At each treatment time, half the spurs of the same age were girdled at the base of the spurs to measure the total amount of ¹³C absorbed. Six WAA, spurs of all ages exported ¹³C-assimilates ; the amount exported increased with increasing spur age. Twelve WAA, only spurs over 3 years old exported labeled photosynthates, but the rate was half that at six WAA. At 18 and 21 WAA, no ¹³C-labelled substance was exported from any spurs. At 18 WAA, about 60% of the ¹³C was partitioned to the fruit on spurs of all ages within 72 hr of labeling. However, the absolute amount of ¹³C translocated to fruit was largest in 5-year-old spurs. The partitioning rate of ¹³C to shoots differed significantly among spurs of different ages, ranging from about 2% in 1-year-old spurs to more than 8% in 7-year-old spurs.