Interaction between gibberellin A_4/7 and root-pruning on the reproductive and vegetative process in Douglas-fir. II. Effects on shoot elongation and its relationship to flowering

Abstract

Shoot elongation and female flowering response were assessed for gibberellin A4/7 (GA4/7) and root-pruning (RP) treatments in 9- and 10-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings of families with good- and poor-flowering histories. In families with a poor-flowering history, stem injections of GA4/7 significantly enhanced elongation of third-whorl terminal shoots but produced no flowering response. In families with a good-flowering history, GA4/7 treatment had no effect on shoot elongation but did result in a significant increase in seed-cone buds. In contrast, root-pruning significantly retarded shoot growth in families with both good- and poor-flowering histories and was also the single most effective treatment for enhancing flowering. Combined, GA4/7 plus RP had a synergistic effect on flowering and GA4/7 partially overcame the inhibition of shoot growth caused by RP alone. These results are consistent with a hypothesis that exogenous and endogenous gibberellins are used preferentially for vegetative growth processes, with increased flowering occurring only after a threshold concentration of effector gibberellins is reached.

Maturation in Larch

“…Although the log-linear response to increasing age mimics the dose-response to most plant growth regulators, there is little evidence that the latter play a primary role in controlling maturation. While gibberellin promotes flowering in many conifers, there is ample evidence that their application cannot offset a genetic indisposition of individual trees to flower (6,29). The control mechanisms for flowering, and possibly maturation as well, are probably the result of the products or regulatory activities of many different genes.…”

The occurrence of flowering and fruiting on individual trees over 3 years and their effects on subsequent crown condition

“…In Sitka spruce, the enhancement of flowering after girdling was only evident in cases where flowering would have been weak without treatment (Philipson 1987). Root pruning has also been used to enhance flowering Webber et al 1985), as has root flooding (Bonnet-Masimbert 1982). The relationship with stress is not applicable to nutrition: fertilisation of trees results in increased flowering and cone or cupule production (Le Tacon et al 1977;Mikola 1987;Wesoly et al 1987).…”

Quantitation of Gibberellins A1, A3, A4, A9 and a Putative A9-Conjugate in Grafts of Sitka Spruce (Picea sitchensis) during the Period of Shoot Elongation

“…This correlation might indicate that the GAs at this time are preferentially used for controlling shoot extension (33). If the conditions are favorable for vegetative growth or if the material is of a poor flowering clone, bud differentiation may be directed preferentially toward vegetative buds due to a more rapid conversion of the less polar GAs, GA9 and GA4, to the more polar GAs, GA, and GA3, the latter GAs being the known 'effectors' of vegetative growth in maize, and probably in many higher plants (23).…”

“…However, with increased maturity the effect on shoot growth decreased and the effect on flowering increased. Webber et al (33) found a positive effect of GA4/7 on shoot growth and no effect on flowering of Douglas-fir families with a poor flowering history. Conversely, families with a history of good flowering responded to GA4/7 with an increased flowering (29).…”