Cloning by cuttings in Nordmann fir, Abies nordmanniana: hormonal characteristics in relation crown position, rooting competence, and orthotropism as ramets

Abstract

Conifer tree species belonging to Abies are notoriously difficult to propagate vegetatively due to aging of material, slow rooting, and persistent plagiotropism in rooted cuttings. We produced orthotropic shoots by reiteration from strongly pruned trees (5–6 years and 12–14 years, respectively), and harvested cuttings in summer. By HPLC–MS we analyzed the stem base of each cutting for initial hormonal status, and used state-of-the art techniques for a lengthy rooting procedure. Rooting efficiency and orthotropism of the resulting ramets were recorded. Hormonal content varied significantly among cuttings types with differing positional origins on the mother tree. High rooting percentages were obtained in all types; a low original position on the main stem gave slightly better rooting but orthotropism in the ramets was slightly less frequent. Striking differences were found in cytokinin profiles between cuttings from young and mature trees. This might explain a generally lower rooting success in the latter; neither auxin levels nor the auxin: active cytokinin ratio showed any correlation with rooting capacity. Cuttings from mature trees were also less likely to remain orthotropic after rooting. Cuttings that eventually developed into orthotropic ramets were characterized by low ABA, and high levels in a range of cytokinins. The study suggests that active: conjugated cytokinins may be related to the maturation process in trees and that cytokinin content may also relate to shoot dimorphism. These results contribute to a protocol for propagation of orthotropic ramets in a Massart model tree species with strong plagiotropism.