Topophysis in Corymbia torelliana × C. citriodora seedlings: adventitious rooting capacity, stem anatomy, and auxin and abscisic acid concentrations

Abstract

Low amenability of the eucalypt, Corymbia torelliana 9 C. citriodora, to vegetative propagation has limited its establishment in plantations. This study determined whether rooting capacity and cutting vigour varied along the central shoot of Corymbia seedlings, and whether these differences are related to stem development and hormone concentrations. Dual-node cuttings were harvested from five positions (nodes 1/2, 3/4, 5/6, 7/8 and 9/10) along the seedling shoot (S1), and cuttings were treated with one of four levels of indole-3-butyric acid (IBA). Root formation, root and shoot growth, stem anatomy, and the concentrations of indole-3-acetic (IAA) and abscisic acid (ABA) were assessed at each shoot position. The central node of the rooted cuttings was harvested for fresh cuttings to observe whether maturation emerged in ramets (S2) from the different ortet positions. Rooting and vigour were highest from the most-apical seedling nodes (7/8 and 9/10 in S1), which had less lignification and sclerenchyma development than morebasal nodes (1/2, 3/4 and 5/6). IAA and ABA concentrations differed little between the seedling nodes. In contrast, cuttings from the ramets (in S2) had similar rooting, vigour, lignification and sclerification to each other, but there were large differences in IAA and ABA concentrations depending on their previous point-of-origin in the seedling. High doses of IBA reduced rooting. Rooting and vigour were related to lignification and sclerenchyma development rather than IAA or ABA concentrations. Mass vegetative propagation of C. torelliana 9 C. citriodora is achievable because mean rooting percentages in S1 and S2 were 61 and 68 %, respectively, using cuttings from small seedling ortets and their ramets.

The Use of Auxin Quantification for Understanding Clonal Tree Propagation

“…Chromatographic methods can provide excellent hormone separation and, when coupled with mass spectrometry (MS), allow quantification of compounds from multiple hormone classes in the same sample [69,106]. These methods have greatly improved endogenous auxin identification in forestry species [107][108][109][110].…”

“…GC-MS has also been used to quantify free IAA levels in vascular tissues of Populus × tomentosa Carrière [126], to show that the highest IAA oxidase activity in Ginkgo biloba L. leaves occurs in environments with high CO 2 and C concentrations [127], and to demonstrate that IAA contents are correlated with IAA oxidase activity in Pinus tabuliformis Carrière needles exposed previously to high CO 2 concentrations [128]. Recently, GC-MS has been used to measure IAA concentrations and identify their relationships with rooting capacity in Corymbia torelliana [110,129].…”

Tissue Culture of Corymbia and Eucalyptus

“…The proliferation capacity of shoot tips, nodes, or axillary buds and the subsequent growth of their plantlets may also be influenced strongly by the position of the tree from which the explant was harvested. Maturation effects such as reduced rooting capacity, shorter internode length, and decreased stem growth [54,55,[59][60][61][62] can become evident from very early stages (i.e., from relatively low explant positions) during the development of eucalypt trees [44,[63][64][65][66][67].…”

“…Callus can be induced from eucalypt hypocotyls, cotyledons, nodes, internodes, shoot apices, leaves, immature flowers, and stamens (Table A1). Explants from the base of the seedling such as the hypocotyls and cotyledons are typically the most responsive because these organs contain juvenile cells that have undergone minimal ageing [44,54,55,67]. However, eucalypt shoots regenerating from the hypocotyls are often easier to proliferate subsequently than shoots regenerating from the cotyledons.…”

“…Plantation trees generally display higher adventitious rooting capacity, stem growth, internode length, and developmental commitment to vegetative growth when they are propagated from juvenile, rather than mature, explants or cuttings [54,55,61,62,183,184]. However, many eucalypt species progress through some of these juvenile-to-mature phase transitions at a very young age and low canopy height [11,39,40,44,63,64,67,185]. This may be the one of the reasons why seeds (or in vitro seedlings) have been the initial explant source in 54% of the eucalypt tissue-culture techniques in which an explant source has been stated (Table A1).…”