The Role of Gibberellin A4/7, Heat and Drought in the Induction of Flowering in Sitka Spruce

Publisher Website
Google Scholar
Abstract
Mature five years grafted Sitka spruce plants were treated with gibberellin A4/7 in conjunction with cultural treatments of heat and/or drought by placing the grafts inside or outside a polythene house and regulating the water supply. Three main stem injections each of 2.0 mg GA4/7 in ethanol were applied in May, June and July. The degree of stress applied was monitored by measuring leaf water potential (ψ ), transpiration and vegetative growth. Heat and drought each stimulated the production of male cones. Drought appeared to be the more effective cultural treatment, and a decrease in ψ of only about 0.5 MPa enhanced flowering. By contrast, the GA4/7 application failed to induce flowering unless applied together with a cultural stress treatment, when the numbers of cones of both sexes were increased. In the most inductive treatments all clones responded even though there was no flowering in the controls, and the mean number of cones per treated plant rose to 8.8 females and 16.2 males.