Abstract
Alnus sieboldiana is the pioneer species and produce a large amounts of pollens. Recently, the pollen of A. sieboldiana was found to cause serious pollen allergies to the people living near the Rokko Mountains where many A. sieboldiana were planted. Therefore, the effects of gibberellin (GA3) and uniconazole-P, an inhibitor of the biosynthesis of gibberellin, treatments on the flower-bud formation of A. sieboldiana were studied in order to reduce the pollen scattering. Field-grown trees of A. sieboldiana between six and eight years-old were treated with foliar spray and stem injection of gibberellin and uniconazole-P in June, 1994 and 1995. The number of male and female inflorescences was counted in the following spring. Male flower-bud formation was strongly inhibited by both foliar spray and stem injection of gibberellin of small quantity. On the other hand, male flower-bud formation tended to increase with uniconazole-P treatment. Furthermore, gibberellin application reduced the size of axillary buds and promoted the elongation growth of shoots. It is assumed that flower-bud formation of A. sieboldiana is closely related with the level of endogenous gibberellins. Stem injection of gibberellin is an easy and effective treatment to inhibit the flower-bud formation of mature trees of A. sieboldiana.
