Light and Fruit Distributions within a Canopy of 'Fuji' Apple Trees Trained to a Traditional Open-Center System in Japan

Abstract

Light and fruit distributions within foliar canopies were measured on three 27-year-old 'Fuji'/Marubakaido (Malus prunifolia Borkh. var. ringo Asami) apple trees trained to a traditional flat open-center system developed in Japan. The canopies extended more horizontally than in depth and were interspersed with many open spaces. The percent instantaneous incident photosynthetic photon flux density (%INPPFD) was measured with quantum sensors on overcast days in mid-September and early November. Measurements were taken on four vertical plane grids placed through the center of each tree with an angle of 45 degrees made by two neighboring grids. Because of the canopy conformation, the imaginary lines connecting points of equal %INPPFD (contour lines) extended along the horizontal plane, suggesting a prevailing influence of the light from above on the within-tree environment. The canopy area receiving less than 20% INPPFD was fairly limited in depth. The depth of the main cropping zone was estimated from the contour maps at a mean height of 1.7m. More than 50% of the fruits were distributed in the canopy area receiving 40% or less INPPFD. Relatively large fruits were found in the zones receiving 20% or less INPPFD. Light measurements in early November revealed that the leaf removal practice to obtain better fruit coloration significantly improved light environment within the canopy, almost eliminating the areas receiving 20% or less INPPFD.