Seasonal Changes in Auxin Effect on Rooting of Douglas‐Fir Stem Cuttings as Related to Bud Activity

Abstract

AbstractThe relation of seasonal bud activity to the periodicity of rooting in Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, stem cuttings was studied in combination with auxin and cold storage treatments. Cuttings were collected in all months except April and May, for 3 years.Rooting was least in September and October when bud dormancy was most pronounced, greatest in December and January if exogenous auxin was applied, or in February and March if no auxin was used. The buds contributed significantly to rooting from January to April, and were responsible for differences in rooting of terminal and lateral cuttings during this period. Auxin did not enhance rooting in September and October, but at other times it replaced or supplemented the role of vegetative buds in promoting rooting. Auxin also removed the differences in rooting between lateral and terminal cuttings. Cold treatment in October and November removed bud dormancy and enhanced rooting. After November the need for auxin or cold treatment diminished and rooting without either treatment reached a maximum in February and March. Auxin did not change the seasonal pattern of rooting but broadened and enhanced the rooting response in favor of earliness.These results are discussed in relation to the effect of bud activity on auxin response and root initiation. The hypotheses are proposed that cambial dormancy or auxin deficiency is not the limiting factor during bud dormancy, and that cold treatments have the effect of bringing inhibitors and promoters into proper balance for optimum rooting response.