Production of seeds in Thujopsis dolabrata Sieb. et Zucc. var. hondai Makino bygibberellin applied

The flower promoting effect of gibberellin (GA) on Thujopsis dolabrata Sieb. et Zucc. var. hondai Makino was examined by varying the time when foliar spray was applied and the number of applications. In addition, the maturation and germination rates of seeds and the opening and color of cones harvested at different times were examined to clarify the effect of GA on the fertility and germinability of the seed, and the best time to harvest cones. GA applied on June 25, July 15, and August 5 markedly promoted flower-bud formation ; the GA application on August 5 was the most effective in inducing male and female flowers. However, the number of GA applications did not influence the effect. In practice, a few GA applications in August may be most appropriate. The maturation and germination rates of the seeds produced by GA treatment were 48 and 97%, respectively, showing that the GA induced flowers to produce normal seeds. The seeds harvested 45 days before seed dispersal had a high germination rate, similar to that after dispersion. 82.5% of the cones changed to greenish brown at this time. The best time to harvest cones is therefore thought to be when they change from green to greenish brown.