Manipulation of Whole-vine Carbon Allocation Using Girdling, Pruning, and Fruit Thinning Affects Fruit Numbers and Quality in Kiwifruit

We compared the long-term effects of whole-vine source-sink manipulation on yield, composition, and quality of fruit from mature field-grown kiwifruit (Actinidia chinensis Planch. var. chinensis) ‘Hort16A’ vines. Four contrasting source/sink-modifying treatments were applied to vines each year from Spring 2003 to 2007: 1) control-standard canopy management techniques, no trunk girdle; 2) extended trunk girdle (ETG)-girdle was opened in late summer, kept open over winter, and allowed to heal the next spring; 3) "feast"-cropload was kept low and leaf numbers kept high, no trunk girdle; and 4) "famine"-fruit numbers were kept high and vines were heavily pruned to stimulate regrowth, no trunk girdle. Fruit from the famine vines were smaller with lower dry matter concentration (DMC; dry weight as a percentage of fresh weight) and had delayed maturity relative to fruit from the control vines. Return bloom was reduced in the famine vines, resulting in 42% less fruit in the famine vines compared with the feast vines, and this difference remained consistent across all three seasons. Fruit from the feast treatment were larger with advanced maturity relative to fruit from control vines; there were no differences in fruit numbers in subsequent seasons. Fruit DMC was higher and maturity was advanced in the ETG vines relative to the control vines. Fruit numbers in the ETG vines consistently increased relative to the control vines each season. There were no consistent treatment effects on fruit mineral concentrations, except that fruit from the feast vines had higher nitrogen concentrations than fruit from the famine vines. Seasonal variation in the incidence of storage disorders was large; in years when disorders were present, physiological pitting incidence was higher in fruit from the treatments that advanced maturity and the incidence of low temperature breakdown was highest in treatments that delayed maturity. Although the treatments affected vine productivity, fruit DMC, and storage performance, there was no evidence of a gradual decline in quality and productivity after 4 years of treatment application.