Abstract
To determine the optimum length of M.9 for ‘Fuji’ and ‘Hongro’ apples (Malus domestica Borkh.), the trees were planted in such a way that the exposed length of the rootstock to be 0, 10, 20, and 40 ㎝. Tree growth and fruit production were then evaluated for six years. The longer the exposure, the less the increase in TCSA of ‘Fuji’ and ‘Hongro’ by the sixth year after planting, at which time the 10-, 20- and 40-㎝ trees showed a 92, 72 and 49% in ‘Fuji’ and an 82, 57, and 34% of the TCSA with 0-㎝ trees in ‘Hongro,’ respectively. The swelling of the rootstock was obvious, but was less at the lower portion as the exposed length of M.9 increased. Shoot growth and leaf areas of 6-year-old trees were less with a longer M.9. Dry weight of both scion cultivars and the roots of 6-year-old trees declined more with a longer exposure of M.9. The top-to-root ratios were in 2.8 to 3.8 ranges in ‘Fuji’ and in 2.3 to 2.5 ranges in ‘Hongro’ depending on the length of M.9. The cumulative yield by the sixth year of ‘Fuji’ apples was not significantly different among 0-, 10- and 20-㎝ trees but was low in 40-㎝ trees. However, cumulative yield efficiency was higher in the trees with a longer exposure of M.9. Similar results were obtained with ‘Hongro,’ but the highest cumulative yield was from the 10-㎝ trees. The length of M.9 affected fruit quality little in both cultivars. Considering tree growth and productivity for the first six years after planting, it was concluded that the optimum length of M.9 exposure was 20 ㎝ for ‘Fuji’ and 10 to 20 ㎝ for ‘Hongro’ at the planting distance of 4 × 1.5 m.