132 ingly, relative crapemyrtle dry weight yields showed increases with leaf tissue Cl concentrations up to 1.0 % (10,000 ppm) but were significantly depressed at higher concentrations (Figure 3b). The lattermost observation is remarkable in that it suggests the ‘optimum’ range for crapemyrtle leaf Cl concentration puts it ef- fectively in the macronutrient concentration range. While it has been reported that most salt sensitive woody species, like fruit trees, present toxicity symptoms when leaf Cl exceeds 0.35% (3500 ppm; Marschner 1995), some tree species, like kiwifruit (Actinidia deli- ciosa), have high Cl requirements with established leaf Cl critical concentrations of about 2.0% (20,000 ppm; Smith et al. 1987). Correlations of leaf Na and Cl with salt burn ratings re- vealed differential relationships between cultivars, with ‘Pink Lace’ plants showing the steeper and quickest responses (i.e., slopes). Leaf Na concentrations above 300 mg/kg-1 associated with rapidly increasing salt burn ratings in ‘Pink Lace’ but concentrations above 2,000 mg/kg-1 (ppm) were (ppm) were needed to produce unsatisfactory ratings in the hybrid cultivars (Figure 3c). On the other hand, and similar to plant dry weight response to tissue Cl accumulation, unsatisfactory salt burn rat- ings and plant appearance were observed when leaf Cl exceeded the 1.0 % (10,000 ppm) mark (Figure 3d). Once again, a steeper Cabrera: Salinity Tolerance of Crapemyrtles relationship between leaf Cl and salt burn was noted for ‘Pink Lace’ plants and was minimal in ‘Basham’s Party Pink’ plants. Overall result analysis indicates that while on the basis of plant biomass (growth) determinants, modern cultivars of the genus Lagestroemia could certainly retain a categoriza- tion of salt-sensitive; aesthetically they have a broader range of tolerance to salinity. While further evaluation is needed in a broader range of crapemyrtle cultivars, the data from the pres- ent study and that of Francois (1982), suggests that cultivars of the common crapemyrtle (L. indica) are less tolerant of salt stress than the modern interspecific hybrids (L. indica × fauriei) being widely used by the landscape industry today. From an ecophysiological perspective, it is contended the con- tinental origin of L. indica, attributed to mainland China (Egolf and Andrick 1978), would have evolutionarily provided less ex- posure of this species to the salinity stress experienced by an is- land species like the Japanese L. fauriei (Egolf and Andrick 1978; Byers 1997). Under the premise that natural selection has resulted in developing salt tolerant species, and ecotypes within species, researchers have logically expected best salinity tolerance results when using progeny of plants growing in increasingly saline en- vironments (Nicknam and McComb 2000). It is assumed the rela- tively higher salt tolerance of hybrids ‘Natchez’ and ‘Basham’s Party Pink’ observed in the present study was inherited from the Japanese parent. It should be noted that ‘Basham’s Party Pink’ was a chance seedling identified and selected in the coastal city of Houston, TX (Egolf and Andrick 1978). The results from the present study pointing ‘Basham’s Party Pink’ as effectively the most salt tolerant cultivar, with the more steady (less chang- ing) shoot to root ratios, leaf chlorophyll indices and salt burn ratings (Figure 2c, Figure 2e, Figure 2f) and lowest accumula- tion of Na and Cl in leaf tissues (Figure 3c, Figure 3d), sup- ports the contention that island and/or coastal regions would result in the selection of plant materials with higher salinity tolerance. While this selection strategy has been commonly used, the expectation however that these starting materials will show higher degrees of salinity tolerance has not always been met (Allen et al. 1994; Nicknam and McComb 2000). To effectively test this hypothesis in crapemyrtles, it will be necessary to comparatively evaluate the salin- ity tolerance of a larger number of cultivars represent- ing these and other Lagerstroemia species and their in- terspecific hybrids, an effort that is currently underway. LITERATURE CITED Adriano, D.C., and H.E. Doner. 1982. Bromine, chlorine, and flourine, pp. 460–461. In: A.L. Page, R.H. Miller, and D.R. Keeney (Eds). Methods of Soil Analysis, Part 2. American Society of Agronomy, Inc. and Soil Science Society of America, Inc. Madison, WI. Allen, J.A., J.L. Chambers, and D. McKinney. 1994. Intraspecific varia- tion in the response of Taxodium distichum seedlings to salinity. For- est Ecology and Management 70:203–214. Figure 2. Relative total (A) and root (B) dry weights, shoot to root ratio (C), relative growth index (D), leaf chlorophyll (SPAD) index (E) and foliage salt burn ratings (F) of three crapemyrtle (Lager- stroemia) cultivars irrigated with increasing levels of NaCl salin- ity. Data points are means ± standard errors of 6 plants. The pa- rameters for the fitted regression lines are shown in Table 2. Byers, D. 1997. Crapemyrtle: A Grower’s Thoughts. Owl Bay Publish- ers, Inc. Auburn, AL. Cabrera, R.I. 2004. Evaluating and promoting the cosmopolitan and mul- tipurpose Lagerstroemia. Acta Horticulturae 630:177–184. Cabrera, R.I., and D.R. Devereaux. 1998. Effects of nitrogen supply on growth and plant nutrient status of containerized crapemyrtle. Journal of Environmental Horticulture 16:98–104. ©2009 International Society of Arboriculture
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