Nursery growers and homeowners in arid and semiarid regions are facing ever-increasing pressure of limited supply of potable water for irrigating plants. This forces them to use alternative water sources such as municipal reclaimed water to irrigate nursery crops and landscapes (Wu et al., 2009). Reclaimed water contains beneficial nutrients for plant growth, but also contains relatively high levels of soluble salts, which adversely impact plant growth and development (Haering et al., 2009). Use of reclaimed water is not a widely acceptable practice for irrigating nursery and landscape plants because of potential salt damage to sensitive plant species and lack of information on their salt tolerance. To enhance sustainable development and expand the usage of reclaimed water, salt-tolerant ornamental plants should be identified for nursery production and landscapes in areas where alternative waters may be used for irrigation.
Salinity decreases soil water potential and thereby makes water less available to plants. Typical plant responses to salinity include slower plant growth, smaller size of whole plants, and foliar injury such as leaf burn, scorch, necrosis, and premature defoliation (Munns, 2002). Salinity may also induce a series of metabolic dysfunctions in plants including absorption of excessive minerals, nutrient imbalance, and inhibition of plant photosynthesis and stomatal conductance (gS) (Munns and Tester, 2008). The magnitude of the negative effects of salinity on plant growth and physiological processes often depends on salinity level and length of exposure. The actual response of a plant to salinity is highly variable depending on plant species or even cultivars. Ratibida columnaris is more salt tolerant than Oenothera elata and S. farinacea, followed by Berlandiera lyrata and Monarda citriodora in descending order (Niu et al., 2012a). Villarino and Mattson (2011) reported that Euphorbia hybrida ‘White Manaus’, Impatiens walleriana ‘Super Elfin XP White’, Salvia splendens ‘Vista Red’, Zinnia angustifolia ‘Star Gold’, and Viola tricolor ‘Delta Blue Blotch’ were sensitive to salinity. They also found that Tagetes patula ‘Crested Bonanza Bolero’ and Verbena ×hybrida were moderately tolerant to salinity. Niu and Rodriguez (2006a) found that Delosperma cooperi and Gazania rigen had a relatively high tolerance to salinity; Teucrium chamaedrys and Ceratostigma plumbaginoides were moderately tolerant; and Penstemon eatonii, P. strictus, P. pseudospectabilis, and Lavandula angustifolia were the least tolerant to salinity. Niu and Rodriguez (2006b) also reported that Achillea millefolium, Gaillardia aristata, and Salvia coccinea had relatively high salt tolerance, while Agastache cana and Echinacea purpurea were not salt tolerant.
The Texas Superstar® is a special designation given to plants that show superb performance in the Texas landscape based on observations made at replicated demonstration trials across the state (Mackay et al., 2001; Texas AgriLife Research and Extension Service, 2015). During the field trials, plants receive minimal soil preparation, reasonable levels of water, and no pesticides. After several years of extensive field trails, those plants demonstrating superior pest tolerance combined with outstanding landscape performance are awarded the Texas Superstar® designation. However, salt tolerance is not one of the factors considered during the evaluation process.
By 2015, Texas AgriLife Research and Extension Service listed 16 perennial plants as Texas Superstar® plants. Among them, Lantana ×hybrida ‘New Gold’ (‘New Gold’ lantana), Lantana montevidensis (purple lantana) and Plumbago auriculata (plumbago) are moderately tolerant to salt (Niu et al., 2007, 2010). Salt tolerance of M. arboreus var. drummondii (Turk’s cap), P. paniculata ‘John Fanick’ (‘John Fanick’ phlox), P. paniculata ‘Texas Pink’ (‘Texas Pink’ phlox), R. brittoniana ‘Katie Blue’ (‘Katie Blue’ ruellia), S. farinacea ‘Henry Duelberg’ (‘Henry Duelberg’ salvia), S. leucantha (mexican bush sage), and Verbena ×hybrida ‘Blue Princess’ (‘Blue Princess’ verbena) remains unknown. Turk’s cap is a drought-tolerant, rapidly growing, and a coarse-textured plant native to south Texas and produces a profusion of “turban-like” bright red, pink, or white flowers. ‘John Fanick’ phlox is a hardy perennial with compact growth habit, dark green foliage, and showy clusters of light pink blossoms with darker pink throats. This plant tolerates heat, drought, and powdery mildew. ‘Texas Pink’ phlox is a very hardy and disease-resistant phlox that forms clumps with upright multiple stems and provides fragrant blooms during hot summers. ‘Katie Blue’ ruellia is a perennial with a low, spreading mounds of narrow, dark green foliage and profusion of violet, light pink, or white flowers and is heat tolerant and highly pest resistant. ‘Henry Duelberg’ salvia is a native perennial with masses of showy blue flowers and is heat tolerant. Mexican bush sage is a drought-tolerant and a highly pest-resistant plant with showy spikes of purple and white, or solid purple blossoms. ‘Blue Princess’ verbena is a perennial with beautiful lavender blue flowers and has resistance to powdery mildew. The objective of this study was to evaluate salt tolerance of seven Texas Superstar® perennials described above in a greenhouse experiment based on their growth and physiological responses to different levels of salinity and the ion accumulation in their leaf tissue.
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