Seasonal changes in dry matter accumulation and partitioning in the shoots, roots, and leaves in 5-year-old 'Kousui' and 'Housui' Japanese pear (Pyrus pyrifolia Nakai) trees on 'Yamanasi' rootstocks grown in a restricted root beds (160 1/tree) under a transparent film were investigated. Scion top and total tree fresh and dry weights increased significantly in both cultivars as the growing season proceeded; the annual fresh and dry weights gains, respectively, per tree were 18kg (82 t/ha) and 3.37 kg (15 t/ha) for 'Kousui' and 21 kg (96 t/ha) and 3.75 kg (17 t/ha) for 'Housui'. 'Housui' trees consistently outyielded those of 'Kousui'. Likewise, the annual dry matter gains per unit leaf dry weight and per unit leaf area which increased significantly during the growing season, respectively, were 6.33 kg and 0.54 kg in 'Kousui' and 6.59 kg and 0.53 kg in 'Housui'; there are no significant differences in weights between the cultivars. In 'Kousui' and 'Housui', the percentages of assimilates partitioned into current shoot, leaf and fine root increased as the shoots elongated. Fruits assimilated dry matter fastest during their enlargement period. After harvest, the percentage of assimilates partitioned into old wood increased until autumnal leaf fall. In both cultivars, the percentages of assimilates partitioned into the fruit, current shoot, old wood, leaf, and roots were about 31, 18, 16, 15, and 19%, respectively. Dry matter gains per unit leaf dry weight per day were high from mid-April to early September in both cultivars; subsequently, they decreased until leaf fall. Dry matter accumulation was rapid during early June to early August after which the rate gradually decreased untill leaf fall. About 42 and 44 % of the dry matter produced during the year were gained in early July, whereas 79 and 85% were gained prior to early September in 'Kousui' and 'Housui', respectively.
