Abstract
Earlier flowering in one-year-old seedling plants, one-year-old seedlings grown up from cuttings, and eight-year-old seedling trees of Cryptomeria japonica was induced by repeated foliar sprays of gibberellin at various concentrations from 10 to 200 ppm.
The effect of gibberellin on flower formation was larger at high concentrations than at low ones; spraying with gibberellin of high concentrations above 50 ppm promoted flower formation remarkably. In one-year-old seedlings, the formation of female flowers was promoted by sprays with gibberellin of high concentrations, but the number of seedlings which bore only male flowers was more at low concentrations.
Generally speaking, the flower formation induced by spray with gibberellin was more promotive in old trees than in young seedling, especially the formation of female flowers seems to be increased in old trees by spray of gibberellin at low concentrations.
The most effective season for foliar spraying with gibberellin to induce the flower formation seems to be from the end of June to the latter part of July. Spraying with gibberellin after the middle part of August inhibited the formation of male flowers in comparison with female ones.
Spraying with potassium indoleacetate, sodium alpha-naphthaleneacetate, 2, 4-dichlorophenoxyacetate, and maleic hydrazide did not induce flowering.
The pollen grains collected from male flowers borne by spray with gibberellin were morphologically normal, and their germination showed as good percentage as that of un-treated control. Therefore, forest geneticists will definitely be able to use such pollens for artificial pollination.
