EFFECTS OF HEAT-TREATMENT, TIMING OF HEAT-TREATMENT, AND GIBBERELLIN A(4 7) ON FLOWERING IN POTTED PICEA-ABIES GRAFTS/

Potted grafts, made from scions of more than 50-year-old Norway spruce trees (Picea abies (L.) Karst.), were induced to flower in several ex periments by heat- and gibberellin A(4/7) (GA) treatments in an acryli c greenhouse at Biri nursery in Norway. The grafts were treated when t hey were 1.5-3 m tall, 4-8 years after grafting. GA alone (spray and i njection) enhanced female flowering, especially in combination with he at. Heat alone was ineffective; few grafts formed seed cone buds. Low amounts of GA (0.5-2 mg per graft) could enhance female flowering in p reviously treated grafts (retreatment), but only a slight response to 2 mg GA was found among previously untreated grafts. Heat alone induce d profuse male flowering, GA + heat did not further enhance the male r esponse, and GA alone did not induce formation of pollen cone buds. Th e highest male scores were found for early and long heat treatments (L HT) which started when shoots were elongated to 25-60% of final length and ended at least one week after termination of shoot elongation. La te and short heat treatment (SHT), starting from 86-95% elongation and ending on the same date as LHT, gave significantly fewer pollen cone buds than LHT in each experiment. If heat treatments started early (20 -30% elongation), but terminated before or at time of shoot growth ces sation (95-100%), no pollen cones were formed. GA could be phytotoxic, especially after spraying, but also when high amounts of GA were inje cted (40 mg). Good female flowering and low levels of needle damage we re found when 2-10 mg GA was injected. The possibility of regulating s ex expression in Norway spruce is discussed.