LIGHT AND FRUIT DISTRIBUTIONS WITHIN A CANOPY OF FUJI APPLE-TREES TRAINED TO A TRADITIONAL OPEN-CENTER SYSTEM IN JAPAN

Light and fruit distributions within foliar canopies were measured on three 27-year-old 'Fuji'/Marubakaido (Malus prunifolia Borkh. var. rin go Asami) apple trees trained to a traditional flat open-center system developed in Japan. The canopies extended more horizontally than in d epth and were interspersed with many open spaces. The percent instanta neous incident photosynthetic photon flux density (%INPPFD) was measur ed with quantum sensors on overcast days in mid-September and early No vember. Measurements were taken on four vertical plane grids placed th rough the center of each tree with an angle of 45 degrees made by two neighboring grids. Because of the canopy conformation, the imaginary l ines 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 l ess 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 t he zones receiving 20% or less INPPFD. Light measurements in early Nov ember revealed that the leaf removal practice to obtain better fruit c oloration significantly improved light environment within the canopy, almost eliminating the areas receiving 20% or less INPPFD.