Cytokinin level and flowering in Douglas-fir

Abstract

Clones of Douglas-fir [ Pseudotsuga menziesii (Mirb.) Franco] were propagated by cuttings and grown in pots. In 1982, when plants were about 1.5 m high (four years after propagation), they were subjected to a series of treatments known to induce flowering in this species. The apical and basal portions of growing shoots were sampled six weeks after budburst (time of bud differentiation) and analyzed for cytokinin content by immunoaffinity chromatography and radioimmunoassay. Production of male and female cones were recorded for each tree in the subsequent year. Trees with shoots having high concentrations of cytokinins had no female flowers and few male flowers. Female flowers occurred only on plants having low concentrations of cytokinins, although low cytokinin content did not guarantee flowering. Most striking was the polarity of cytokinins in shoots. Apical portions usually contained higher concentrations than basal portions of shoots. A subsequent experiment in which plants were treated with GA and flooding showed that both treatments induced flowering and that the effects were additive.