Canopy light distribution and fruit quality in excessive tall spindle apple production system

The tall spindle planting system achieves the goals of high sustained yield and good quality fruit. However, some growers in Korea let apple trees grow vigorously up to 4 m or higher in high-density planting of 3.5×1-m spacing with M.9 rootstock. Such practices lead to very tall trees with low-quality fruit in the lower canopy. We measured light distribution, flower buds, fruit quality, and leaf characteristics at different parts of the canopy. Light penetration in the interior part of the lower canopy (0.5 and 1.5 m in height) was less than 15% of natural light intensity. Leaf area index (LAI) was higher than 2.0 at the lower and interior part of the tree canopies, and light distribution values decreased rapidly with the increased LAI. Fruit color and soluble solids content (SSC) correlated well with light penetration. Leaf photosynthesis (A) in interior parts of the canopy was much lower than in the middle and exterior parts of the canopy. Similarly, leaves in the interior parts of the canopy had lower specific leaf weight (SLW), chlorophyll content, and flower-bud size than those of exterior parts. Therefore, excessive tree height should be reduced in tall spindle apple trees for the production of better fruit quality and high yield.