Developmental Stage and Hormone Concentration Differentially Affect Vegetative Propagation of Select Baldcypress Clones

In previous studies baldcypress [Taxodium distichum (L.) L.C. Richard] clones were selected for improved field tolerance to alkaline soils, drought, or foliar or soil salinity exposure, and/or their ornamental traits.  Objectives of the current research were to 1) determine the clonal responses to K-IBA (potassium salts of indole-3-butyric acid) across seasonal developmental stages of cuttings, and 2) to determine if rooting rates (percentages) and rooted cutting quality (root number, length, and mass) would be sufficient for commercial production if the clones were released to industry.  Cuttings were taken from 24 clones at 3 developmental stages of stem growth (softwood, semi-hardwood and hardwood).  Three concentrations of K-IBA were tested (0, 7,500 and 15,000 mg∙L^-1) on each clone at each stage.  Rooting percentages ranged from approximately 94% (clone MX1MD33) at the softwood stage to 0% for several clones at the hardwood stage.  Some clones, such as MX5MD17 rooted at 88% and 83% in the softwood and semi-hardwood stages, respectively, while others such as 479-16 rooted at low levels (< 20%) in all stages.  In some cases, significant (P≤0.05) interactions occurred between growth stages and clones, such as that exhibited by clone 492-14 which rooted at 59% at the softwood stage but only 37% at the semi-hardwood stage.  Root number and length exhibited three way interactions (P≤0.05) among clones x developmental stages x K-IBA concentrations.  For example, mean total root length ranged from 2 cm per cutting on MX2MD31 at the semi-hardwood stage with no hormone to 81 cm per cutting on TX8DD38 at the softwood stage with 7500 mg∙L^-1  K-IBA.  Mean root length varied from 2 cm found in several clones at the semi-hardwood stage to 11 cm on MX2MD31 at the softwood stage treated with 15000 mg∙L^-1  K-IBA.  Most frequently, the greatest rooting percentages across K-IBA concentrations for clones were at the softwood stage and across rooting stages for most clones were at either 7500 or 15000 mg∙L^-1  K-IBA. None of the clones rooted well as hardwood cuttings and 15000 mg∙L^-1 sometimes induced basal stem damage.