The yields and fruit quality of 'Fuji' apple trees on 'Marubakaido' rootstock with the M. 26 interstock trained to a Y-trellis system were compared with those trained to a central leader. The experiment continued until the trees were 9-yr-old.
1. The trees in the Y-trellis system consistently yielded more fruits annually than did those trained to a central leader, the former yielded 6.200a, 1.3 times more than did the latter in the final season.
2. No significant difference in fruit weight was observed between two training systems, but the fruit color was superior and soluble solids content (brix) was higher in fruits harvested from the Y-trellis system than they were in fruits from the central leader trees. 3. The crown density of 8- to 9-yr-old trees trained to the Y-trellis reached 96%, whereas that of central leader trees attained only 75% ; the maximum leaf area indices (LAI/land area) were almost the same, about 3 in both training systems, and the maximum LAI/tree crown area were 3.8 and 3.2 respectively.
4. Maximum yields were attained when the crown density attained the ultimate levels in both training systems, and reached to each maximum level at the LAI of 3 in the Y-trellis and at that of 2.3 in the central leader.
5. From above results, it seems possible to assume that the superior yield and fruit quality obtained in Y-trellis is due to its higher crown density as well as its larger LAI.