Interaction between gibberellin A_4/7 and root-pruning on the reproductive and vegetative process in Douglas-fir. I. Effects on flowering

Abstract

In two seed orchard trials, profuse female flowering was induced in young, but ontogenetieally mature grafts of inherently poor-flowering clones (1979) and in 9-year-old seedling-origin trees of both good- and poor-flowering families (1981) of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) by the cultural treatment of root-pruning in conjunction with stem injections of the gibberellin A 4 and A 7 (GA 4/7 ) mixture. Promotion of male flowering, however, was confined to the more sexually mature grafts. As an individual treatment in the 1981 study, root-pruning was more effective than GA 4/7 , particularly for the poor-flowering families which did not respond well to GA 4/7 alone. The two treatments combined had a highly synergistic effect on both male and female flowering, the synergism being relatively greater for the poor-flowering than for the good-flowering families. Although GA 4/7 was not tested alone on grafted propagules, its use with root-pruning enhanced an already significant increase in seed- and pollen-cone buds from root-pruning alone by 540 and 92%, respectively. These and subsequent trials have shown root-pruning +GA 4/7 to be a most effective cone-bud enhancement treatment for use in young Douglas-fir breeding and seed production orchards.