Stem incorporation of gibberellins to promote sexual development of white spruce, Norway spruce, and jack pine

Abstract

Stem incorporation of gibberellins (GA4/7 60:40) by injecting a liquid formulation or implanting a solid formulation was evaluated for promoting sexual reproductive development and for effects on vegetative development and foliage chlorosis in seedling and grafted white spruce, Piceaglauca (Moench) Voss; seedling Norway spruce, Piceaabies (L.) Karst.; and jack pine, Pinusbanksiana Lamb., seed trees. Spruces were treated with a single application of 0.76 or 1.53 mg GA4/7 per square centimetre of stem cross-sectional area at breast height during the late stage of shoot elongation (June 9 for white spruce and June 19 and 20 for Norway spruce). Jack pine was treated with a single early (July 5) or late (August 15) application of 1.53 mg GA4/7/cm2 or a split early–late application of 0.76 mg GA4/7/cm2. Results were evaluated in the subsequent season (i) by counting seed and pollen strobili, developing vegetative shoots, latent vegetative buds, and dead buds and (ii) by assessing foliage chlorosis and mortality. The numbers of seed strobili were increased by injections of GA4/7 at low and high application rates on seedling white spruce and Norway spruce and by the high application rate on grafted white spruce; implants were effective on seedling white and Norway spruce at the high application rate. In jack pine, the number of seed strobili was not increased by GA4/7. The numbers of pollen strobili were not significantly increased by GA4/7 treatments to white spruce or Norway spruce but were increased on jack pine by a single early injection at the high rate and split injections at the low rate. The number of developing vegetative shoots was reduced by GA4/7 injections at both rates on white spruce grafted trees and Norway spruce; the implants reduced them only on the grafted white spruce given the low rate. For the spruces, treatments with GA4/7 did not influence bud mortality. Foliage chlorosis and mortality, evident on jack pine but not on white or Norway spruce trees, was more severe with injections than with implants.