Abstract
Light intensity and fruit distribution within foliar canopies were measured on 'Fuji'/Marubakaido (M. prunifolia Borkh. var. ringo Asami) trees trained to "HU (Hirosaki University) central leader training system" planted at distances of 5 in×3.5 m. The percent instantaneous incident photosynthetic photon flux density (%INPPFD) was measured on overcast days with quantam sensors. Measurements were taken on four vertical plane grids (grid section : 0.5 m×0.5 m) placed through the center of each tree, one directed along the tree row (NE-SW), one at 90 degrees (NW-SE) and two at 45 degrees (S-N, W-E) with the tree row. The number of fruits within the grids were also counted.
About 7080% of fruits were found on the cross sections of canopy directed at 45 degrees with the tree row; they were well-distributed throughout the sections. The contour lines of INPPFD which extended horizontally with a broad top indicate that light from above as well as from sides of the trees penetrated the canopy.
The favorable within-canopy light condition was brought about by the characteristic framework of HU central leader trees : the four bottom limbs are directed at 45 degrees with the tree row and slanted at an angle of 45 degrees above the horizontal; the other branches arising from the central leader are kept much shorter than the bottom limbs. The mean depth of leaf canopy favorable for fruit production was estimated to be 1.7 m, which is the same as that we estimated for open-center trees.
