Effect of planting density on leaf growth of 'Starking Delicious' apple trees grafted on dwarfing and semi-dwarfing rootstocks

The effect of planting density on the leaf growth of 'Starking Delicious'apple trees (Malus domestica Borkh.), grafted on dwarfing (M.9 and M.26) and semi-dwarfing (M.7 and MM.106) rootstocks, was studied. 1. On all four rootstocks, the mean area per leaf and the mean dry weight per leaf tended to decrease, but the specific leaf area (SLA) increased, as the density increased. 2. On all rootstocks, the leaf dry weight per tree, the leaf area per tree, and the leaf number per tree decreased, but the leaf area index (LAI) increased, as the density increased. 3. The relationship between the planting density (rho) and the leaf area per tree (u), the leaf dry weight per tree (w) or the LAI (F) could be represented by the following reciprocal equations, 1/u = A(u)rho + B-u (4) 1/w = A(w)rho + B-w (5) 1/F = A(u)+ B-u/rho (7) where A(u), B-u, A(w) and B-w depend on the tree age and rootstocks. 4. The relationship between the trunk cross-sectional area ( theta) and the leaf area or the leaf dry weight per tree could be prescribed by the following equations, u = H' theta(h) (8) w = H" theta(h-) (9) where H', h',H" and h" depend on the tree age and rootstocks. 5. When the LAI at the optimum planting density (rho(opt)) is defined as optimum LAI (F-opt), the F-opt can be expressed by the following equation, F-opt = p(opt)/(A(u)p(opt) + B-u). (10) Based on A(u) and B-u obtained from Eqs. (4) and (8), and rho(opt) obtained from Eq. (3), the F-opt estimated by Eq. (10) had values of 3 similar to 4, regardless of tree age and rootstocks. 6. No relationship was found between the fruit yield per hectare and the LAI. However, a high correlation coefficient (r = +0.865**) exists between the fruit yield per hectare and the fruit production rate per unit leaf area, independent of tree age and rootstock, indicating that fruit yield per hectare depends on fruit production rate per unit leaf area.