Abstract
Fruit growers prefer apple trees that grow with moderate vigor, demand little labour and produce consistent and high quality yields. These requirements are best met by grafting plants on dwarfing apple rootstocks. The dwarfing rootstock M.9 holds the greatest promise for Italy's high density orchards. However, with some vigorous cultivars, this rootstock may not be dwarfing enough. Instead of choosing another rootstock type, an increase of the dwarfing effect can be achieved by modifying budding height and the planting depth of the rootstocks. The rootstock length exposed above the ground level was especially effective in influencing the dwarfing effect on the tree. Atrial was established in 2001 and continued until 2008 at the Research Centre for Agriculture and Forestry Laimburg, to find the optimal budding height and planting depth of 'Fuji' and 'Golden Delicious' apple trees, grafted on M.9 apple rootstocks. Trees with the longer exposed rootstock shanks (high planted budding units) were smaller in comparison to deep planted ones. A reduction in fruit size and trunk cross sectional area was shown in higher planted and higher grafted apple trees. Overall, we can state an optimal combination is given when trees are planted at low depth and rootstock shanks are covered after planting with soil. INTRODUCTION New training systems ('slender spindle' and 'superspindle') were introduced that gained increased acceptance in Italy's apple fruit production areas. However, problems rose, due to the increased impacts of those systems either on plant or soil. Of concern was the distribution of the photosynthetically active radiation within high planting density orchards, in order to obtain high quality fruits. This is primarily achieved by coordinated tree vigour reducing practices. Probably the best working strategy for managing tree vigour is based upon an accurate rootstock selection (Sosna, 1999). T337 is the most planted M.9 rootstock clone in Italy's apple orchards (Mantinger and Stainer, 1996), but with vigorous cultivars it is still not dwarfing enough. Weaker growing rootstocks have reduced yield and lower fruit quality. Tree vigour may be influenced by pomological practices (Toorenaar, 1955) such as, budding height (Liebster, 1968; Pollet and Bockstaele, 1973; Van Rooyen, 1975; van Oosten, 1978) and planting depth (Rogers and Parry, 1968; Quamme et al. 1997). According to Sosna (1999) high budded trees showed a lower vigour, expressed by the increment of trunk cross sectional area and yielded better than lower budded trees. The objective was to evaluate the effect of budding height and planting depth of two different apple cultivars ('Fuji' and 'Golden Delicious') on tree vigour, yield and final fruit quality parameters in a seven year study.