Arboriculture & Urban Forestry 43(5): September 2017 budding and graſting success can be explained by high production of IAA in early spring by young and actively growing leaves, which influences both callus production and differentiation (Aloni 2015) Large bark patch graſts could be an alterna- tive to bridge-graſting for spanning trunk wounds and pruning cuts. Girdling wounds can be bridged with bark implants or bridge graſts (Harris et al. 2004), so why not consider a bark patch graſting technique using bark patches cut from branches or other areas on the trunk of an affected tree? The patches should be cut with clean edges, positioned to ensure good cambial contact, and protected from desiccation (Priestly and Scott 1955; Fahn 1985; Hartmann et al. 2010), which can be achieved by covering the graſt with materials such as graſting clay, wax or tape, rubber latex, paraffin wax, waxed cloth, plastic strips, and raffia (McGarry 2001; Hart- mann et al. 2010). Proper orientation of the patch is important, as experiments have shown that tis- sues can be adversely affected if the orientation is changed from the original (Thair and Steeves 1976). In 1991, a bark patch was attached to an Ulmus procera growing in the gardens of Burnley College, Melbourne, Australia, following the removal of a large branch. Before the branch was removed, a large flap of bark on the underside of the limb was carefully removed from contact with the limb, and when the limb was cut, the flap was folded upward and used as a bark patch to cover the wound (Figure 1). The connection of the patch with the tissue below it remained intact and the patch remained in place and healthy until the removal of the tree in 2014. The wound had been included and had successfully compartmentalized. This successful bark patch graft precipitated this experiment which investigated whether bark patches could be removed and then successfully replaced on the same tree, whether there were dif- ferences between tree species in their responses, and whether the season when the damage and patch grafting was done had any effect of suc- cessful re-attachment. The bark patches used in the experiments were small and were done on seedling trees as a model system. However, the production of callus and its differentiation have been reported to be similar in studies on mature and embryonic tissues, callus-based research, and shoot organ development (Sawchuk and Scar- 189 Figure 1. A bark graft patch, attached to the trunk of an Ulmus procera growing in Burnley Gardens, Australia (approximately 240 mm in diameter), 10 years prior to the photograph. Note the uniform ring of callus forming at the branch bark ridge. pella 2013). Because plant responses to phyto- hormones occur at the cellular level, consistent tissue responses are to be expected (Nakamura et al. 2012; Koepke and Dhingra 2013). The experiments provided data that could inform the use of bark from damaged trees as a patch over parts of the trunk or branch stubs to facilitate rapid growing over and compartmentalization. MATERIALS AND METHODS Fiſty trees from each of six species commonly planted in Australia streets and gardens, com- prising both native and exotics—Acacia dealbata Link, Banksia integrifolia L.f., Eucalyptus viminalis Labill, Platanus × acerifolia (Air) Willd., Quercus robur L., and Pinus radiata D. Don.—were grown outdoors and maintained with regular irrigation and fortnightly liquid fertilizer applica- tions of Phostrogen® at 74 mg N/L. Seedlings of A. dealbata, B. integrifolia, and E. viminalis were purchased as tubestock and potted to standard, black 150 mm pots. P. × acerifolia and Q. robur were sourced as bare-rooted material, and the P. × acerifolia were potted to standard 150 mm pots, and the Q. robur, with larger root systems, were potted into larger 300 mm squat pots sprayed with Spin- out® to reduce the likelihood of the trees becom- ing pot bound. Pinus radiata trees were sourced as “treelings” from in-ground cutting beds and pot- ©2017 International Society of Arboriculture
September 2017
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