EFFECT OF DEPTH OF PLANTING/BUDDING HEIGHT AND SOLAR RADIATION EXPOSURE OF M.26, MM.106 ROOTSTOCKS AND B.9/MM.111 INTERSTEMS ON THE GROWTH AND YIELD OF 'IDARED' APPLE TREES

Trees that are high budded and planted on dwarfing apple rootstocks are widely used in high-density orchards. The greater dwarfing effect of such trees is caused by the longer rootstock part (shank) exposed above ground level, where the auxin transport loss and decomposition in the rootstock bark is believed to be more intense. On medium vigour apple rootstocks like MM.106, this phenomenon has however not been reported. In the trial reported here, ‘Idared’ trees were produced on M.26 and MM.106 rootstocks, budded uniformly at 30 cm height but planted in the orchard at different depths, in order to obtain trees with rootstock shanks having 10 cm or 20 cm solar radiation exposure. Similarly, trees on MM.111 rootstocks with B.9 interstems were planted with 10 cm, 20 cm and 30 cm above soil exposed interstem parts. The trees with the longer exposed shanks of MM.106 rootstocks (high-planted budding units), similarly to M.26, reduced the tree size in comparison to deep-planted trees. The high-planted (20 cm exposure) budding unit also reduced the anchorage of trees on MM.106, thus they needed support. Based on our results, it can be concluded that solar radiation exposure influences the expression of dwarfing; the more exposed the rootstock part is the more effective the dwarfing. Inversely, the dwarfing effect of the rootstock part covered by soil is diminished. The trees on M.26 with 30 cm rootstock stem covered by soil (deep planted) were similar in size to MM.106. The longer the solar radiation-exposed part the greater the dwarfing effect. Associated with the greater dwarfing effect, the precocity and the yield efficiency increased on M.26 and MM.106. Considering the yield and fruit quality, under our climatic conditions, 10-15 cm height for planting of budding unit can be recommended for M.26 and MM.106. Interstem trees with B.9 on MM.111 rootstocks produced the highest yield efficiency when planted deep (5 cm exposure of interstem part). On interstem trees, increased suckering was observed.