Influences of crown size and maturation on flower production and sex expression in Picea glauca treated with gibberellin A(4/7).

We evaluated the effects of exogenous gibberellin A(4/7) (GA(4/7)) on the production of seed and pollen cones in four stock types of Picea glauca (Moench) Voss. From 1987 to 1991, a combined treatment that included GA(4/7), root pruning and heat stress was applied to 5- to 10-year-old container-grown grafts, representing over 90 clones and originating from 17- to 27-year-old ortets. Hormonal treatments were applied to pruned field-grown grafts in 1991 and 1992, and to unpruned field-grown grafts from the same set of clones in 1990, 1991 and 1992. In 1992, 26-year-old mature trees in a progeny test were treated with GA(4/7). The GA(4/7) treatment was effective in promoting seed-cone production in all four stock types, whereas it promoted pollen-cone production only in unpruned field-grown grafts and mature trees. The older and taller a tree, the less the response to the GA(4/7) treatment was influenced by the climatic conditions prevailing during the differentiation phase.