Carbohydrate Reserves of Non-fruiting Young Kiwifruit Vines as Affected by Early Artificial Defoliation Yong-Bum Kwack 1 , Hong Lim Kim 1 , Won-Byoung Chae 2 , Seung Heui Kim 3 , Yong-Bok Lee 4 , and Jin Gook Kim 4,5* 1 Namhae Sub-Station, National Institute of Horticultural & Herbal Science, Rural Development Administration, Namhae 668-812, Korea 2 Vegetable Research Division, National Institute of Horticultural & Herbal Science, Rural Development Administration, Suwon 440-706, Korea 3 Department of Korea Project on International Agriculture Group, Rural Development Administration, Jeonju 560-500, Korea 4 Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 660-701, Korea 5 Department of Horticulture, College of Agriculture and Life Sciences, Gyeongsang National University, Jinju 660-701, Korea *Corresponding author: jgkim119@gnu.ac.kr Received April 13, 2014 / Revised August 5, 2014 / Accepted August 7, 2014 Ⓒ Korean Society for Horticultural Science and Springer 2014 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’. Additional key words: dry weight, Goldrush, soluble sugars, starch Hort. Environ. Biotechnol. 55(6):462-470. 2014. DOI 10.1007/s13580-014-0042-5 ISSN (p rin t) : 2211-3452 ISSN (online) : 2211-3460 Research Report Introduction The accumulation of nutrient reserves is important for various functions of deciduous fruit trees, including budbreak, shoot growth, and floral development during spring when trees do not have leaves yet, which are required for photo- synthesis, or when young leaves are not yet fully functional (Cheng and Fuchigami, 2002; Loescher et al., 1990; Oliveira and Priestly, 1988; Titus and Kang, 1982; Tromp, 1983). Nutrient reserves are mainly accumulated in roots at the end of the growing season (i.e., autumn) in the proximity of leaves abscission. Most of the accumulated nutrients are carbohydrates, such as starch, which is the primary non- structural storage carbohydrate (Loescher et al., 1990; Oliveira and Priestly, 1988). In apples (Faby and Naumann, 1986a; Kandiah, 1979), sweet cherries (Keller and Loescher, 1989), and pecans (Smith et al., 1986), starch is accumulated in the roots when the fruit is almost ripe. However, in mulberries, starch accumulation begins shortly after leaf expansion, and reaches a plateau at the end of shoot growth (Yamashita, 1984, 1986). Therefore, the pattern of starch accumulation in the vines of kiwifruit may differ to that of apple, peach, and grape, which have longer periods between fruit ripening and leaf abscission.