Seasonal changes of dry matter production and assimilate partitioning in Japanese pear trees (Pyrus pyrifolia Nakai) cv. Kousui and Housui grown under film.

摘要

This study was conducted on 5-year-old P. pyrifolia trees of the cultivars Kousui and Housui, on Yamanasi rootstocks, grown in restricted root beds (160 litres/tree) under a transparent film. Scion top and total tree fresh and dry weights increasedsignificantly in both cultivars as the growing season proceeded; the annual fresh and dry weight gains, respectively, per tree were 18 kg (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 inHousui; there were no significant differences in weights between the cultivars. In Kousui and Housui, the percentages of assimilates partitioned into current shoots, leaves and fine roots 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 fruits, current shoots, old wood, leaves 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 drop. Dry matter accumulation was rapid during early June to early August after which the rate gradually decreased until leaf fall. About 42 and 44% of the dry matter produced during the year was gained in early July, whereas 79 and 85% were gained prior to early September in Kousui and Housui, respectively.