Abstract
Many plantation eucalypts are difficult to propagate from cuttings, and their rooted cuttings often possess very few adventitious roots. We microscopically examined the stem anatomy of cuttings from 12 species of eucalypts and we determined whether adventitious root formation in auxin-treated cuttings of four species was limited to particular positions around the vascular tissue. Most species contained a central pith that was arranged in a four-pointed stellate pattern. The surrounding vascular tissue was also arranged in a stellate pattern near the shoot apex but it developed a more rectangular shape at the outer phloem as the stems enlarged radially. Adventitious roots formed at, or slightly peripheral to, the vascular cambium, and they formed at both the corners and the sides of the rectangular-shaped vascular tissue. The study highlighted that auxin-treated eucalypt cuttings can produce roots at multiple positions around the vascular tissue and so propagation methods can aim to produce more than four adventitious roots per rooted cutting. Higher numbers of adventitious roots could improve the root system symmetry, stability, survival and growth rate of clonal eucalypt trees.
Highlights
The eucalypts, Angophora, Corymbia, and Eucalyptus, are the world’s most widely planted hardwood trees because of their diversity of species, adaptability to marginal production environments, and wide variety of commercial uses [1,2]
The anatomy of young shoots has not been studied across the taxonomic range of eucalypts, a rectangular arrangement of vascular tissue is evident from transverse sections of the shoots of C. ficifolia, C. torelliana × C. citriodora, E. benthamii, E. camaldulensis, E. grandis, E. preissiana, E. grandis × E. urophylla and E. pellita ×
We examined the anatomy of young stems of 12 species across the taxonomic range of eucalypts, and we observed whether adventitious root formation in four of these species was limited to particular positions such as corners or sides of the vascular tissue
Summary
The eucalypts, Angophora, Corymbia, and Eucalyptus, are the world’s most widely planted hardwood trees because of their diversity of species, adaptability to marginal production environments, and wide variety of commercial uses [1,2]. One of the main problems encountered during clonal propagation of eucalypts has been the low number of adventitious roots produced per cutting, which affects root system symmetry and tree stability [12]. Adventitious roots of some easy-to-propagate woody plants are formed in longitudinal rows along the stem, with the positions being related to the anatomy of the underlying vascular tissue [26]. We hypothesized that the number of adventitious roots produced by auxin-treated eucalypt shoots is related to the arrangement of vascular tissue in the stem. We examined the anatomy of young stems of 12 species across the taxonomic range of eucalypts, and we observed whether adventitious root formation in four of these species was limited to particular positions such as corners or sides of the vascular tissue
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