Arboriculture & Urban Forestry 35(3): May 2009 Arboriculture & Urban Forestry 2009. 35(3): 129–134 129 Revisiting the Salinity Tolerance of Crapemyrtles (Lagerstroemia spp.) Raul I. Cabrera Abstract. The crapemyrtle (Lagerstroemia L.) is one of the most popular flowering trees in the U.S. and abroad. L. indica cultivars have dominated urban and landscape settings until their recent displacement by modern interspecific L. indica × L. fauriei Kohene hybrids. This study evaluated the salt tolerance of an older L. indica cultivar, ‘Pink Lace,’ and the hybrids ‘Natchez’ and ‘Basham’s Party Pink.’ While the growth of these three cultivars was significantly and negatively affected by in- creasing NaCl salinity (0 to 24 mM) in the irrigation water, the shoot to root ratio (S/R) and aesthetic parameters (chlorophyll content and salt burn ratings) of ‘Pink Lace’ was the most affected. This cultivar showed the most responsive relationships be- tween salt burn ratings and sodium (Na) and chloride (Cl) accumulation in leaf tissues. ‘Basham’s Party Pink’ was rated as the most salt tolerant, with relatively steady S/R, chlorophyll contents and salt burn rating across all salinities, and its leaf tissues had the lowest accumulation of Na and Cl. Results from this study also support the hypothesis that geographical and ecologi- cal origins of the parent Lagerstroemia species and selections largely influences the relative salinity tolerance of the cultivars. Key Words. Irrigation; Salinity Tolerance; Water Quality. The woody ornamental crapemyrtle (Lagerstroemia), native to Southeast Asia, has been a favorite landscape plant and a staple nursery crop for the southern U.S. since the late 1700s (Egolf and Andrick 1978; Byers 1997; Dirr 1998). Selections and cultivars of the common crapemyrtle (L. indica L.) have been the most widely used, favored for their colorful summer flow- ering and wide assortment of inflorescence colors and plant sizes (Egolf and Andrick 1978). The relatively recent introduc- tion of interspecific hybrids of L. indica, native of China (Egolf and Andrick 1978; Dirr 1998), and L. fauriei Kohene, endemic only to the Japanese island of Yakushima (Egolf and Andrick 1978; Byers, 1997), have significantly enhanced crapemyrtle versatility by enhancing its cold hardiness, variety of growth habits, exfoliating bark and resistance to powdery mildew and certain species of beetles (Egolf and Andrick 1978; Byers 1997; Cabrera 2004; Hagan et al. 1998; Cabrera et al. 2008). The common crapemyrtle (L. indica) has been recently named the official shrub for Texas (Cabrera 2004), a state in which water quantity and quality are serious and pervasive is- sues affecting its nursery and landscape industries. While the literature suggests that crapemyrtles are a salt-sensitive species (Francois 1982; Cabrera and Devereaux 1998), the only formal salinity study that included this genus did it only with a single L. indica selection (nonnamed cultivar) growing in a sandy loam soil (Francois 1982). The present study was conducted to obtain preliminary information regarding the tolerance of representative modern crapemyrtles cultivars, growing under production condi- tions, to increasing levels of salt stress in the irrigation water. MATERIALS AND METHODS Rooted cuttings, growing in 5 cm (2 in) square pots, of three crapemyrtle cultivars—L indica ‘Pink Lace’ and the L. indica × fauriei hybrids ‘Natchez’ and ‘Basham’s Party Pink’—were used in the present study. ‘Pink Lace’ is an old cultivar, selected in 1957 in North Texas, and has been used extensively as a pistillate parent in the crapemyrtle breeding program at the U.S. National Arboretum (Egolf and Andrick 1978). The white-flowered hybrid ‘Natchez,’ introduced by the U.S. National Arboretum in 1978, is known for its fast growth rate and outstanding exfoliating bark, and is considered the most widely planted hybrid cultivar (By- ers 1997; Dirr 1998). On the other hand, ‘Basham’s Party Pink’ has the distinction of being the first known L. indica × fauriei hybrid, originating as a chance seedling identified and selected in 1963 in Houston, TX (Byers 1997; Egolf and Andrick 1978). The cuttings were transplanted on June 7, into #4 [13 L (3.4 gal)] containers filled with a peat: pine bark: sand (2:1:1 v/v) medium amended with 3.0 kg/m3 mitic limestone and 0.6 kg/m3 (1 lb/yd3 (5 lbs/yd3 ) of dolo- ) of both the micronu- trient fertilizer Micromax® (Scotts Co., Marysville, OH) and the wetting agent Aquagro® 2000G (Aquatrols, Paulsboro, NJ). Following transplant, the containers were top-dressed with 5.0 kg/m3 (8.4 lbs/yd3 ) of the controlled-release fertilizer Woodace 20-4-11 (Vigoro Industries, Fairview Heights, IL). The containerized plants were placed in gravel beds lined with weed barrier fabric. There were a total of 6 replications (plants) per each treatment (cultivar × salt level) arranged in a completely randomized block design. The treatment plants were arranged in rows of three abreast, spaced at 30 cm (12 in) on centers, sur- rounded by rows of border (nontreatment) plants on the outsides. The plants were irrigated for 15-weeks (June 29–October 10) with tap water [pH = 7.4; electrical conductivity (E)] = 0.5 dS m-1 at concentrations of 0, 3, 6, 12, and 24 mM (equivalent to ir- rigation solution ECs of 0.5, 0.8, 1.1, 1.7, and 2.9 dS m-1 (mmhos/cm); 73 ppm alkalinity] salinized with NaCl salt , re- spectively—including the EC of the tap water). The plants were irrigated on average 2-4 times per week by pumping solutions from 100 L (26.4 gal) tanks, and delivered through individual ©2009 International Society of Arboriculture
May 2009
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