INDUCTION OF REPRODUCTIVE STRUCTURES IN Pseudotsuga menziesii

摘要

Pseudotsuga menziesii is a conifer widely used in Christmas tree plantations in Mexico, which increases the need for an efficient supply of quality germoplasm. In order to reduce the time required for seed production in this species, the effect of gibberelic acid (GA(4/7)) and trunk girdling on the formation of reproductive structures was evaluated in two field trials with juvenile trees. Four dosages of GA(4/7) (0, 1.27, 2.55 and 5.10 mg cm(-2)) injected into the tree trunk were used, and one year later, the percentage of trees with a response and the number and position of reproductive structures were evaluated. The treatments were more effective on formation of female cones, with a response that varied from 37.5 % in site 1, to 62.5 % in site 2, whereas less than 20 % of the trees formed male cones in both sites. The phenological stage of the tree at the time of applying the treatments influenced (p <= 0.01) the number of male and female cones formed. Also, the effect of GA(4/7) on the number of cones varied with each trial; in site 1 the lowest dose (1.27 mg cm(-2)) was the most effective for the induction of female cones, whereas in site 2, the high dose (5.10 mg cm(-2)) was the most effective. Trunk girdling increased (p <= 0.01) the number of cones when combined with low doses of GA(4/7), but had no positive effect when high doses were used. The analysis of the results indicates that the application of GA(4/7) combined with trunk girdling is effective in inducing flowering in sexually immature P menziesii trees, which helps accelerate the production of seed in this species.