© 2003 Heron Publishing—Victoria, Canada
Timing of GA4/7 application and the flowering of Pinus sylvestris grafts in the greenhouse
Curt Almqvist
1. The Forestry Research Institute of Sweden (SkogForsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden (curt.almqvist@skogforsk.se) / Received January 11, 2002; accepted September 20, 2002; published online March 17, 2003
Summary
Effects of varying the time of stem injection of gibberellin A4/7 (GA4/7) on male and female flowering in potted grafts of Pinus sylvestris L. in a greenhouse were monitored in two consecutive years. Flowering results for each application time were correlated with
phenological characteristics and abiotic factors in an attempt to find reproducible indicators of the most effective time
of GA4/7 treatment. The GA4/7 treatment had a significant effect on female flowering, but no effect on male flowering. In both years, the largest effect
on female flowering was obtained with the latest application. Percent shoot and needle elongation (relative to final length)
were poor indicators of the optimal time of GA4/7 application. Three heat sum accumulation models gave equally accurate predictions of the optimal time for GA4/7 application; therefore, the simplest model, i.e., the sum of degree-days, is recommended. The timing window for stimulation
of female flowering with GA4/7 had a lower limit of about 500 degree-days (threshold +5 °C), and the optimal time of GA4/7 application was after about 700 degree-days.
Keywords:
flower stimulation, gibberellin A4/7, heat sum, phenology, Scots pine, tree breeding.
