EFFECTS OF GIBBERELLIN A(4 7) STEM INJECTION ON SEED CONE PRODUCTION IN MATURE BLACK SPRUCE/

Two injections of 50 mg of gibberellin A(4/7) (GA(4/7)) into the trunk base of 27-year-old black spruce, Picea mariana (Mill.) BSP, during r apid vegetative shoot elongation gave a fourfold significant increase of seed cone production in the following year compared with controls. Treated trees produced a mean number of 309 +/- 28 SE cones versus 57 +/- 7 and 83 +/- 10 produced by untreated trees and by control trees i njected with 95% ethanol (the solvent used), respectively. A similar i ncrease was reflected in the mean total weight per tree of nearly matu re cones. It is shown that GA(4/7) was able to induce additional cone buds during a very heavy cone crop. Potential effects of gibberellin t reatments on phytophagous insects are discussed.