The promotion of flowering in large field-grown Sitka spruce by girdling and stem injections of gibberellin A4/7

Abstract

Mature 14-year-old grafted Piceasitchensis (Bong.) Carr. which were field grown and 6 m tall were given stem injections of gibberellin A_4/7 (GA_4/7) alone and in combination with girdling. The GA_4/7 was applied twice, at 100 or 250 mg per application. GA_4/7 alone produced a large and significant stimulation of the numbers of both pollen and seed cones, with means of about 200 pollen and 90 seed cones per tree, and 90% of the clones flowering; both levels of GA_4/7 application stimulated flowering to approximately the same extent. The girdling treatment enhanced flowering when environmental conditions facilitated light flowering of the controls, and also increased the response to 100 mg GA_4/7. The stimulation of flowering was carried over into the 2nd year after treatment, but only when both girdling and GA_4/7 had been applied together.