자작나무류 開花誘導 處理 幼苗의 第2次 年度 生殖 生長 潛在力

Persistency of reproductive growth potential in the following year of forced flowering induction in seedlings of two birch species

Seedlings and grafts of Betula pendula and Betula platyphylla var. japonica were induced to flowering by one induction cycle(7 months~one year period) of forced flowering treatment under controlled environment in a plastic-greenhouse with sufficient mineral nutrients supply, CO₂ enrichment and 19-hour photoperiod. The persistency of induced state was evaluated by investigating the trees with fixed phase change from vegetative to reproductive one in the second growth period from the treatments. All the seedlings and 90% of the grafts of Betula pendula that induced to flowering during 1989~1990 induction period retained their state of reproductive phase in the second growth period in 1991. In case of Betula platyphylla, var. japonica all the seedlings and grafts that had induced to flowering during 1989~1990 induction period retained their induced state of flowering in the second growth period in 1991. Ninety four percent of the grafts of Betula platyphylla var. japonica that had induced to flowering during 1990~1991 induction period retained their induced state of flowering in the second growth period in 1992. It appeared from the result that most(at least 90% or more) of the seedlings and grafts of Betula pendula and Betula platyphylla var. Japonica that have induced to flowering just by one cycle of treatment retain their flowering capacity later on from the inducement. Thus the second cycle of treatments for flowering induction is unnecessary in practice.