Relationship between Flower-bud Differentiation and Carbohydrate Contents in Spring Shoots of Very-early, Early and Late Maturing Cultivars of Satsuma Mandarin

Yahata Daijiro, Matsumoto Kazunori, Ushijima Kosaku

doi:10.2503/jjshs.73.405

Seasonal changes in the types of bud, vegetative, mixed or generative (reproductive), and carbohydrate contents in three satsuma mandarin (Citrus unshiu Marc.) cultivars, 'Yamakawa Wase', 'Okitsu Wase' and 'Aoshima Unshiu', were investigated. Shoots from these very-early, early and late maturing cultivars, respectively, were excised and examined for bud types from the pre-harvest period of the previous year to just before bud break in the spring (2001-2002). Tree growth of each cultivar in 2001 showed aspects of nearly the heaviest on-year of alternate bearing for the previous 10 years, so that a poor return bloom was expected in 2002. Shoots that sprouted in the spring of 2001 were sampled at monthly intervals from early-November to mid-March, 2002, defoliated, placed in a vase and sprayed with 100 ppm benzyladenine (BA) to force them into growth in a chamber kept at 28°C. After 8-14 days of incubation, developing buds were tallied whether they were vegetative, mixed or generative. In every cultivar, nearly all buds of shoots excised in early-November were vegetative; those with an inflorescence constantly increased up to mid-March. Shoots of 'Yamakawa Wase', whose trees were harvested in late-October, progressed from the vegetative to the generative phase most rapidly, followed by those of 'Okitsu Wase' and 'Aoshima Unshiu', whose trees were harvested in mid-November and mid-December, respectively. There was no significant difference in the bud types between 'Okitsu Wase' and 'Aoshima Unshiu' throughout the experimental period. From December to February, the starch concentrations in the spring shoots of 'Yamakawa Wase' were significantly higher than those of the other two cultivars. Spring shoots of 'Okitsu Wase' had the highest total sugar contents from December to January, but the least number of inflorescences. Higher total sugar accumulation in spring shoots after harvest seemed to have no promotive effect on flower-bud formation. Our data indicate that earlier harvest of satsuma mandarin induces rapid starch accumulation in spring shoots, resulting in a progressive differentiation of flower buds on inflorescences.

Relationship between Flower-bud Differentiation and Carbohydrate Contents in Spring Shoots of Very-early, Early and Late Maturing Cultivars of Satsuma Mandarin

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