Arboriculture & Urban Forestry 38(5): September 2012 planting than did the more northern Kentucky and Tennessee provenances (Arnold et al. 1998), suggesting the potential impor- tance of initial root regeneration responses in differential estab- lishment and growth among provenances. This would also sug- gest the possibility of selecting among provenances and clones within provenances for improved landscape establishment traits, such as rapid root regeneration potential, to produce landscape trees that generate a new root system more quickly, minimizing transplant losses. Ware (1980) suggested that native bottomland species may contain genotypes tolerant of current urban soil challenges, such as more poorly drained clays. Assessing root regeneration potentials, either in the field or in controlled en- vironments, can be tedious and time consuming (Bohm 1979). Thus, since many of the same hormonal factors control adven- titious root regeneration from both root and shoot tissues, it could be advantageous if adventitious root regeneration capacities that are important in transplant establishment followed similar pat- terns among genotypes as more easily assessed traits, such as ad- ventitious rooting of shoot tip cuttings. To that end, the rooting of shoot tips at various stages of maturation from five seedlings of a provenance shown (Shoemake et al. 2004) to have a high level of root regeneration capacity (Texas 1) and shoot tip cuttings from five seedlings of a provenance with a lower level of root regenera- tion capacity (Tennessee) were compared. Adventitious rooting from shoot cuttings in terms of rooting quantity measures, such as percent of cuttings that rooted, was greatest for both provenances with semi-hardwood cuttings (Figure 2A). Shoots from Texas 1 seedlings rooted similarly at the softwood and semi-hardwood stages, while softwood shoots from some of the Tennessee ramets did not root as well as those from semi-hardwood cuttings (Figure 2A). Shoots from all seedlings of both provenances, except Ten- nessee clone 5, rooted in much fewer numbers from hardwood cuttings (Figure 2A). This is in contrast to reports by Vlachov (1988), who reported winter rooting (hardwood cuttings) to yield optimal rooting percentages on three species of Platanus L. Root system quality measures, including the number of roots regener- ated per cutting (Figure 2B) or the elongation of those roots after initiation (Figure 2C), were greatest on semi-hardwood cuttings, intermediate on softwood cuttings, and typically lower on hard- wood cuttings. Neither the quantity of shoots that rooted (Figure 2A), nor the root system quality measures (Figure 2B; Figure 2C) followed the same pattern of responses with regard to prov- enances as was observed with root regeneration from root tissues (Shoemake et al. 2004). Thus, these data would not support the use of this trait as a predictor of rapid determination of new root growth potential from root tissue. However, this study used only a small sample of five seedlings from each of the two provenances and a larger sample size would be needed to provide more con- clusive evidence. What this study did confirm was the importance that the range in ability of seedlings within a provenance to ad- ventitiously produce roots from shoot cuttings would play in any effort to capture gains in broad sense heritability via vegetative propagation of superior clones within seedlings from a given provenance. Substantial variability in rooting measures was pres- ent at each developmental stage of shoot maturation among the clones of each provenance (Figure 2). The greatest degree of vari- ation was present with the hardwood cuttings, in which as large as ten-fold differences in adventitious rooting potential were present among clones of the same provenance at the same stage of shoot maturation (Figure 2). This is consistent with reports of a high 209 Figure 2. Variation in (A) adventitious rooting percentages, (B) adventitious root number per shoot tip cutting, and (C) the length of the five longest regenerated roots of selected clones (ramets) within seedling populations of Platanus occidentalis provenanc- es Texas 1 and Tennessee; columns represent means (± standard errors) from four replicate blocks of ten cuttings in each replicate block taken at softwood, semi-hardwood, and hardwood devel- opmental stages. Within a developmental stage, Texas 1 cuttings are indicated on the left with clear columns 1 through 5, respec- tively, for each clone (left to right), and Tennessee cuttings are indicated on the right side with shaded columns 1 through 5, respectively, for each clone (left to right). ©2012 International Society of Arboriculture
September 2012
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