Carbohydrate Reserves of Non-fruiting Young Kiwifruit Vines as Affected by Early Artificial Defoliation

Abstract

Accumulated nutrient reserves provide an important energy source for deciduous fruit trees in their initial growth and development the following spring. This study investigated the effect of mid-season defoliation on the growth and accumulation of carbohydrate reserves of kiwifruit vines in Korea. The 'Goldrush' (Actinidia chinensis) vine was used for this experiment, following de-blossoming in spring. The vines were artificially defoliated to varying degrees at 1 month intervals from Jul. 15 to Oct. 14. The degree of defoliation was 0 (control), 25, 50, 75, and 100%. From Jul. 15 to Sep. 15, the dry weight of kiwifruit vines with 50% or more defoliation was reduced as compared to the control. In particular, 75 and 100% defoliation on Aug. 16 resulted in decrease of 79.2 and 83.1 g from the control vines (145.6 g), respectively. Defoliation on Aug. 16 decreased both the aboveground and underground dry weight of the vines. Most carbohydrate reserve of the young vines (which did not have fruit) accumulated in the roots. Defoliation on Aug. 16 and Sep. 15 reduced the accumulation of carbohydrate reserves, which was correlated with a decline in vine dry weight. For vines with 75% or more defoliation on Aug. 16 and Sep. 15, about less than half amount of starch accumulated in the roots as compared to the control (4.3 g per vine). In contrast, the accumulation of soluble sugars was not significantly influenced by defoliation, except for vines with 75% or more defoliation on Aug. 16. In conclusion, 75% or more defoliation on Aug. 16 and Sep. 15 has a negative impact on the growth and carbohydrate reserve of a new cultivar, 'Goldrush'.