TREE GROWTH AND PHYSIOLOGICAL FRUIT DROP OF 'HACHIYA' PERSIMMON ON D. KAKI AND D. LOTUS ROOTSTOCKS

‘Hachiya’ persimmons, characterized by vigorous shoot growth and severe fruit-drop in the southern part of Korea, were grafted on D. kaki and D. lotus seedlings in 1996 and transplanted in 1997. Annual tree growth and percent fruit drop were monitored until 2005 when the trees were nine years old. Trunk cross-sectional area (TCSA) and the height of the trees were greater on D. lotus than on D. kaki. The differences between the two rootstocks increased with increasing tree age. TCSA measured from 9-year-old trees in 2005 was 2-fold larger on D. lotus than on D. kaki. The trees grafted on D. lotus showed 1.5-fold longer terminal shoots and 7.1-fold increase in water sprout numbers in 2005 compared with those on D. kaki. Fruit drop of the trees on D. lotus was higher by 15% in 2002 and 13% in 2003. In February, 2006, the difference of the root growth in 0.25 m³ soil and its reserve accumulation were measured. Results showed that the root dry weight of D. lotus was far more than that of D. kaki, but concentrations of carbohydrates and inorganic elements were not different between the rootstocks. This difference in root growth resulted in the difference in shoot growth of the two rootstocks, which could in turn have played a role for the increased fruit drop of ‘Hachiya’ trees grafted on D. lotus.