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 A4 and A7 (GA4/7) 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 GA4/7, particularly for the poor-flowering families which did not respond well to GA4/7 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 GA4/7 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 +GA4/7 to be a most effective cone-bud enhancement treatment for use in young Douglas-fir breeding and seed production orchards.

Breeding Douglas‐Fir

“…Flower stimulation generally refers to the enhanced production of male and female strobili on trees that are already competent to flower. Flowering can be increased using stem injections of gibberellic acid (i.e., a mixture of GA 4 and GA 7 ), wounding the trees with stem girdles or root pruning, and/or fertilizing with calcium nitrate (Ebell 1972;Ross et al 1985;Woods 1989). These treatments are applied in the spring, and mature seeds are available two growing seasons later.…”

2. The role of plant growth regulators in promotion of flowering

“…However, good results have also been obtained on larger trees in more common outdoor seed orchards [78,98], generally after the combination of treatment with PGRs and a cultural treatment such as bark girdling or root pruning .…”

3. Control of sex expression in conifers

“…Development of patterns of sexual zonation within the tree crown is similar for most conifers (61,70,118,120,140) . As the tree matures and increases in size, female strobili are initiated/differentiated first on strong leading shoot in the upper crown.…”