Planting distance affects apple tree growth, fruit yield and quality

A study on the influence of planting distances on the growth, productivity and fruit quality of dwarf apple trees in a 15- to 18-year-old orchard was carried out at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry. Trees of the apple (Malus x domestica Borkh) cultivar 'Auksis' on rootstock P 60 were planted at distances of 3 x 1.5, 3 x 1.25, 3 x 1.00 m and 3 x 0.75 m. With increasing density of fruit trees, single-tree growth, generative development and yield were significantly reduced. The opposite results were obtained when these parameters were evaluated per unit area. Yield and fruit quality measurements were made at two canopy heights: 0-1.5 and 1.5-2.5 m. In the upper part of the fruit tree canopy, fruit average weight and diameter were higher, while the colour was more intense and less dependent on the planting density of fruit trees. In the lower part of the canopy, fruit quality was inferior and with increasing fruit tree density it further deteriorated. Planting distances had a significant effect on the accumulation of sugar, soluble solids and dry matter content: greater planting distances resulted in increased sugar content from 10.97% to 11.90%, soluble solids - from 12.30% to 13.17% and dry matter content - from 13.80% to 14.80%. Conversely, higher accumulation of phenolic and triterpenic compounds in apple fruits was found with decreasing planting distances. A significant increase of phenolic compounds from 2.91 up to 4.03 mg g(-1) DW (dry weight) was recorded at the upper part of the canopy, while an increase of triterpens from 12.9 up to 16.07 mg g(-1) DW - at the lower part of the canopy. The best productivity and fruit quality of 'Auksis' apple trees on P 60 rootstock at the full bearing stage were obtained, when fruit trees had been spaced at 3 x 1.25 m.