温州ミカンの樹体生長および開花•結実に及ぼす葉齢と摘葉処理の影響

Abstract

1. To observe the effects of spring leaves (spring cycle leaves of the current year) or old leaves on flowering and fruit set, experiments were conducted with secondary scaffold branches of Satsuma mandarin (Citrus unshiu MARC.) trees grown under field conditions. Treatments were as follows; (1) all spring and old leaves were removed from the shoot (no-leaf plot); (2) all old leaves were removed and enlarging spring leaves were retained (new-leaf plot); (3) developing spring leaves were removed and old leaves were retained (old-leaf plot); (4) both spring and old leaves were kept intact (control plot).When the above treatments were applied from early spring to the end of July, old-leaf plot gave the best development of floral organs at full bloom. These development of floral parts was reduced in the following order, no-leaf, control and new-leaf plot. Fruit set and fruit growth for the first month after blooming were also greatest in old-leaf plot. The ranking for these criteria was: control>no-leaf> new-leaf plots. Not only was the development of floral organs in new-leaf plot the poorest among the four plots, most of the fruits abscised in this plot immediately after bloom. In the remaining three treatments marked fruit drop was observed in early July, particularly, in old-leaf plot. This observation suggests that old leaves play an important role for fruit set and growth during the first month after blooming, but that new leaves are required for sustained fruit growth.When treatments were started two weeks after bloom, fruit set was best in control plot followed in order by new-leaf and old-leaf plots; almost all fruits were shed in the no-leaf plot. Fruit growth in control and new-leaf plots was superior than that in old-leaf and no-leaf plots.When treatments were made in August, fruits remaining on the trees in no-leaf and old-leaf plots decreased to 48.9% and 63.6%, respectively, but fruit sets in both new-leaf and control plots remained unchanged (100%). Treatments initiated during September resulted in no fruit abscission in any plots.2. With 3-year-old Satsuma mandarin trees grown in the pots, the effects of leaf age, temperature and light intensity on the development of floral organs were investigated. Leaf removal was done as described in the above experiments, while the temperature was kept at 23°C and 30°C in the conditioned growth chamber and the light intensity was varied from 10 to 100% of full sunlight. Flowering was accelerated at 30°C, but floral organs developed better at 23°C. At both temperatures, fresh weight of floral organs in the first inflorescence was smallest in new-leaf plot compared to the other treatments. Light intensity was no significant effect on the development of floral organs. At three light intensities, fresh weight of floral organs was smallest in new-leaf plot compared to the other treatments. Tree growth was suppressed proportionately with decreasing light intensity in all treatments. As the light intensities decreased from 100% to 10%, the percentage of old leaves abscised increased; that of the control plot being greater than in the old-leaf plot.