'Jonathan' apple trees on M.26 rootstock which had been planted in 1975 with the graft union as high as app. 20 cm above ground level grew slowly and were not occupying their allotted planting space. In 1980, these trees were mounded with soil to just below the graft union to induce tree vigor. The dry matter production rates and growth of these trees were compared with non-mounded (control) trees in 1989. 1. Trunk girth and yield were increased by the soil mounding treatment. Dry weight of the soil-mounded trees measured after lifting in November, 1989 was app. 2 times heavier than that of control trees. Less current shoot growth occurred especially on the upper half of the control trees. The main root system, which developed on the former stem portion of rootstock after soil mounding, replaced the "old root system" app. 30 cm below the graft union. 2. Average leaf indices (LAIa) were 2.04 in the soil mounded trees and 0.90 in the control trees. The latter trees had not filled their allotted volume in the planting row even in 1989, the 15th season after planting. 3. Total dry matter increase (DM) of the trees in the growing season in the soil mounding treatment was about twice as much as that of the control. Dry matter increases in leaf, current shoot, older wood and roots per a tree were also significantly higher in the soil mounding treatment. 4. There was a highly positive correlation (r = 0.95) between dry matter production rate per unit leaf dry weight (DM/L) and fruit-leaf dry weight ratio (F/L), even when trees in both treatments were combined. There was also a highly negative correlation (r = -0.93) between DM/L and leaf area per fruit. These results indicate that the dry matter production rate (DM/L) did not differ between the soil-mounded and the control trees, whenever fruit load value shown as F/L or leaf area per fruit was similar. 5. There was a negative correlation (r = -0.95) between the percent partition of dry matter to the scion portion and F/L, whether the trees were soil-mounded or not. The result seems to indicate that tree vigor does not always change the dry matter partitioning rate of the scion in apple trees.
