Promotion of Flowering in the Pinaceae by Gibberellins

Abstract

Abstract Flowering was significantly promoted in 4‐year‐old grafts of mature coastal Douglas‐fir ( Pseudotsuga menziesii (Mirb.) Franco) clones by exogenous gibberellins (GAs) A 4 and A 7 (as a mixture) applied alone and in combination with A 5 and A 9 . Biweekly applications of 400 μg GA 4/7 per branch between late March and late June gave a 5‐fold increase in ovulate and 3‐fold increase in staminate strobilus production over untreated controls. 6 N‐benzyladenine and 2,3,5‐triiodobenzoic acid applied in combination with GAs had no consistent effect on strobilus production. Non‐destructive branch girdling, ineffective by itself as a cultural treatment, enhanced the GA benefit to flowering. Exogenous application of GA 4/7 is effective and appears to be a practical method for promotion of early and enhanced flowering in grafted Douglas‐fir seed orchards.