Effects of IBA and NAA treatments on rooting Douglas-fir stem cuttings

Abstract

The effectiveness of six IBA and fourNAA concentrations, four combinations of IBA and NAAconcentrations, and control were tested for theirability to enhance rooting frequency (%) ofDouglas-fir cuttings. Two IBA and one NAA treatmentswere also compared to the control for quality of rootsystem. Between 1984 and 1998, six independentstudies were conducted in mist or fog environmentswith the same 11 or 14 clones. Auxin concentrationstested ranged from 0 to 123 mM IBA and 0 to 10 mM NAA. Auxin, clone, and auxin by clone effects weresignificant in every study, although individual cloneanalyses showed only two clones to differsignificantly for auxin. All auxin treatments but the10 uM NAA treatment induced significantly greaterrooting percentage than the control, but no singleauxin, auxin concentration or combination of auxinswas clearly superior in every study. The 10 mM NAAconcentration was the only concentration tested thatreduced rooting percentage to less than the control. Both NAA and IBA appeared to have broad ranges ofroot-enhancing activity. However, within theeffective range of IBA evaluated, 24.6 mM produced thegreatest rooting percentage in four of five studiestesting IBA. NAA solutions with concentrationsbetween 2.5 and 7.4 mM NAA generally resulted insimilar rooting success. Rooting responses toincreased IBA and NAA were both nonlinear; rootingdecreased with both too little and too much auxin. Combinations of IBA and NAA in the same solution didnot increase rooting percentage above what wasachieved with one auxin. For root system quality,auxin treated cuttings in one study, had significantlybetter root systems than control, but there was nodifference in the other study in which root qualitywas estimated.