Salt Tolerance of Sego SupremeTM Plants

Abstract

Sego Supreme is a designated plant breeding and introduction program at the Utah State University Botanical Center and the Center for Water Efficient Landscaping. This plant selection program introduces native and adapted plants to the aridWest for aesthetic landscaping and water conservation. The plants are evaluated for characteristics such as color, flowering, ease of propagation, market demand, disease/ pest resistance, and drought tolerance. However, salt tolerance has not been considered during the evaluation processes. Four Sego Supreme plants [Aquilegia barnebyi (oil shale columbine), Clematis fruticosa (Mongolian gold clematis), Epilobium septentrionale (northern willowherb), and Tetraneuris acaulis var. arizonica (Arizona four-nerve daisy)] were evaluated for salt tolerance in a greenhouse. Uniform plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 1.25 dS·m as control or a saline solution at an EC of 2.5, 5.0, 7.5, or 10.0 dS·m for 8 weeks. After 8 weeks of irrigation, A. barnebyi irrigated with saline solution at an EC of 5.0 dS·m had slight foliar salt damage with an average visual score of 3.7 (0 = dead; 5 = excellent), and more than 50% of the plants were dead when irrigated with saline solutions at an EC of 7.5 and 10.0 dS·m. However, C. fruticosa, E. septentrionale, and T. acaulis had no or minimal foliar salt damage with visual scores of 4.2, 4.1, and 4.3, respectively, when irrigated with saline solution at an EC of 10.0 dS·m. As the salinity levels of treatment solutions increased, plant height, leaf area, and shoot dry weight of C. fruticosa and T. acaulis decreased linearly; plant height of A. barnebyi and E. septentrionale also declined linearly, but their leaf area and shoot dry weight decreased quadratically. Compared with the control, the shoot dry weights of A. barnebyi, C. fruticosa, E. septentrionale, and T. acaulis decreased by 71.3%, 56.3%, 69.7%, and 48.1%, respectively, when irrigated with saline solution at an EC of 10.0 dS·m. Aquilegia barnebyi and C. fruticosa did not bloom during the experiment at all treatments. Elevated salinity reduced the number of flowers in E. septentrionale and T. acaulis. Elevated salinity also reduced the number of shoots in all four species. Among the four species, sodium (Na) and chloride (Cl) concentration increased the most in A. barnebyi by 53 and 48 times, respectively, when irrigated with saline solution at an EC of 10.0 dS·m. In this study, C. fruticosa and T. acaulis had minimal foliar salt damage and less reduction in shoot dry weight, indicating that they are more tolerant to salinity. Epilobium septentrionale was moderately tolerant to saline solution irrigation with less foliar damage, although it had more reduction in shoot dry weight. On the other hand, A. barnebyi was the least tolerant with severe foliar damage, more reduction in shoot dry weight, and a greater concentration of Na and Cl. Field trials are used to successfully identify suitable plants with outstanding landscape performance for various plant selection and evaluation programs. Superior plants are selected mostly on the basis of their appearance, environmental adaptability, drought tolerance, and disease/pest tolerance. For example, Earth-Kind is one of the special plant selection programs of the Texas A&M Agrilife Extension Service (Aggie Horticulture, 2019). A total of 21 garden roses (Rosa ·hybrida) with superior stress tolerance and outstanding landscape performance were categorized as Earth-Kind Roses. Similarly, Texas Superstar program promotes superior plants that can grow well at various locations in Texas with minimal soil preparation and irrigation and no pesticides (Mackay et al., 2001). Sixteen perennial ornamental plants have been designated as Texas Superstar perennials. Colorado State University has collaborated with the Denver Botanic Gardens to establish the Plant Select program to promote plants annually which are waterwise and adapted to the Rocky Mountains (Colorado Gardening, 2019). Native plants from arid and semiarid environments, introduced by Plant Select program, are excellent candidates for water-efficient landscaping. Sales of native plants have grown from $1.46 million in 2007 to $1.68 million in 2012 through Plant Select program (National Information Management and Support System, 2019). However, these programs have overlooked the salinity tolerance of the plants during the selection and evaluation processes. Sego Supreme is a plant breeding and introduction program developed by Utah State University (USU) Botanical Center and the USU Center for Water-Efficient Landscaping with the intention of introducing native and adaptable plants into arid west landscapes to conserve water without compromising the aesthetic value of the landscapes (Anderson et al., 2014). Sego Supreme plants are evaluated for characteristics such as color, flowering, ease of propagation, market demand, disease/pest resistance, and drought tolerance. However, salinity tolerance has not been considered during the evaluation processes. Soil salinity is one of the major obstacles for horticultural production all over the world. Soil is defined as a saline soil when the salinity level in a plant root zone exceeds 4 dS·m, which affects plant growth and may not be suitable to grow plants (Chinnusamy et al., 2005). Inmany parts of the world, poorquality water (such as reclaimed water that contains high concentrations of soluble ions) is used to irrigate ornamental plants to conserve potable water (Cassaniti et al., 2013; Niu and Cabrera, 2010). Both saline soil and irrigation water can have adverse effects on plant performance by affecting nutrient availability and competitive uptake, transport, and partitioning within the plant (Grattan and Grieve, 1999). Plant species or cultivars have different responses to salinity (Munns and Tester, 2008; Niu and Cabrera, 2010). Therefore, selection and identification of salt-tolerant ornamental plants are crucial for nursery production and landscape use. Plants selected from the Earth-Kind and Texas Superstar programs have been studied for salinity tolerance by independent researchers. The salt tolerance of 18 EarthKind Rose cultivars was investigated, and it was concluded that ‘Belinda’s Dream’, ‘Climbing Pinkie’, ‘Mrs. Dudley Cross’, ‘Reve d’Or’, and ‘Sea Foam’ roses were salt-tolerant when irrigated with saline water at an EC of 10.0 dS·m (Cai et al., 2014). Sun et al. (2015) reported that Texas Superstar perennials such asMalvaviscus arboreus var. drummondii (Turk’s cap), Ruellia brittoniana ‘Katie Blue’ (‘Katie Blue’ ruellia), Salvia farinacea ‘Henry Duelberg’ (‘Henry Duelberg’ salvia), and Verbena ·hybrida ‘Blue princess’ (‘Blue Princess’ verbena) were tolerant to salinity levels at ECs of 5.0 and 10.0 dS·m, whereas Phlox paniculata ‘John Fanick’ (‘John Fanick’ phlox), Phlox paniculata ‘Texas Pink’ (‘Texas Pink’ phlox), 2056 HORTSCIENCE VOL. 54(11) NOVEMBER 2019 and Salvia leucantha (Mexican bush sage) were sensitive to salinity levels at ECs of 5.0 and 10.0 dS·m. Aquilegia barnebyi, Clematis fruticosa, Epilobium septentrionale, and Tetraneuris acaulis var. arizonica are categorized as Sego Supreme selections. Aquilegia barnebyi is a perennial plant that usually occurs on oil shale substrates and is native to northeastern Utah and adjacent parts of Colorado (U.S. Department of Agriculture, 2019). It is a drought-tolerant species and suitable for xeriscaping (Dave’s Garden, 2019). Clematis fruticosa is an erect, woody shrub with insect and disease tolerance (Missouri Botanical Garden, 2019). It grows in medium moisture, well-drained soil and has some drought tolerance. Epilobium septentrionale, a droughttolerant perennial plant native to California, can grow in thin patches of soil between rocks (California Flora Nursery, 2019). Tetraneuris acaulis var. arizonica is a perennial plant that can tolerate many soil types and does not need much water once established in the landscape (Moosa Creek Nursery, 2019). It is native to western United States from Idaho to New Mexico (U.S. Department of Agriculture, 2019). These plants have potential for adoption by the landscape industry, but their salinity tolerance is unclear. In this study, the four Sego Supreme plant species were irrigated with saline solution at different salinity levels in a greenhouse to determine their salinity tolerance through measuring their growth responses and mineral nutrient status. Materials and Methods Plant materials and culture. The study was conducted in a research greenhouse at USU in Logan, UT (lat. 41 45#28$N, long. 111 48#48$W, elevation 1409 m). On 24 Aug. 2018, 1-year-old Sego Supreme plants produced from cuttings were received in a square pot (10.5 · 10.5 · 12.3 cm) from the USU Botanical Center (Kaysville, UT). On 27 Aug. 2018, plants were transplanted into 3.8-L injection-molded, polypropylene container (PC1D-4; Nursery Supplies, Orange, CA) filled with a soilless growing substrate consisting of 75% peatmoss (Canadian sphagnum peatmoss; SunGro Horticulture, Agawam, MA), 25% vermiculite (Therm-O-Rock West, Chandler, AZ), and 24.3 g·ft white athletic field marking gypsum (92% calcium sulfate dihydrate, 21% calcium, 17% sulfur; Western Mining and Minerals, Bakersfield, CA). All plants were watered with tap water (EC = 0.344 dS·m; pH = 7.65). During the experiment, aphids (Aphidoidea) and whiteflies (Aleyrodidae) were observed on C. fruticosa. To control aphids and whiteflies, all plants were sprayed with abamectin (Avid 0.15 EC; Syngenta Crop Protection, Greensboro, NC) at a rate of 0.1 mL per gallon as needed. During the experimental period, the average air temperature in the greenhouse was 24.9 ± 1.2 C during the day and 22.0 ± 2.4 C at night. The average daily light integral in the greenhouse was 24.8 ± 12.5 mol·m·d. Supplemental light at 160.4 mmol·m·s was provided using 1000-W high-pressure sodium lamps (Hyd