Water shortages and poor water quality are critical challenges to gardening and landscaping in many regions of the world and will continue to be a serious issue due to climate changes (Cai et al., 2014a). Urban landscape irrigation with alternative water sources such as municipal reclaimed water is common in arid and semiarid regions (Grieve, 2011). A potential problem of using reclaimed water is elevated salt levels, which adversely affects plant growth, development, and causes foliar salt injury on sensitive plants (Cai et al., 2014b; Niu et al., 2012a; Veatch-Blohm et al., 2014). Unlike fruits and vegetables where maximizing yield is the ultimate goal, the maintenance of good aesthetic appearance and blemish-free foliar tissue are important for ornamental plants (Niu and Cabrera, 2010). Therefore, it is important to identify salt-tolerant plants for areas where poor quality water may be used for irrigation to conserve high-quality potable water, while maintaining an aesthetically appealing landscape (Niu and Rodriguez, 2006).
Asteraceae is an exceedingly large family of flowering plants widespread in the wild and landscape. Many aster species have been studied for salt tolerance, and their responses to salinity are highly dependent on the species. Plains zinnia (Zinnia grandiflora) plants all died at an EC of 7.3 dS·m−1, and chocolate daisy (Berlandiera lyrata) had low survival percentages and low foliar ratings at EC of 5.5 and 7.3 dS·m−1 (Niu et al., 2012a). Treasure flower (Gazania rigen), known as coastal gazania and naturalized on coastal dunes and roadsides in Australia, had 52.5% greater reduction of shoot DW at EC of 12 dS·m−1 compared with nonsalinized controls (EC of 0.8 dS·m−1), but had no other signs of stress or injury (Niu and Rodriguez, 2006). Seven cultivars of Zinnia marylandica all died when irrigated with EC at 6.0 and 8.2 dS·m−1 for 4 weeks (Niu et al., 2012b). Xeriscaping with native plants is promoted to conserve water, concurrent with use of reclaimed water (Meyer et al., 2009).
We investigated the relative salt tolerance of nine aster species and one hybrid, among which damianita (C. mexicana), gregg’s mistflower (E. greggii), blackfoot daisy (M. leucanthum), aromatic aster (S. oblongifolium), four-nerve daisy (T. scaposa), skeleton-leaf goldeneye (V. stenoloba), and zexmenia (W. texana) are native to Texas. Copper canyon daisy (T. lemmonii) is distributed in the mountains of southern Arizona and adjacent northern Mexico. Like many perennials native to southwestern United States, especially in New Mexico or Texas, most of the species aforementioned are considered drought tolerant (Lady Bird Johnson Wildflower Center, 2015); however, their salt tolerance is unknown. Shasta daisy (Leucanthemum ×superbum ‘Becky’) is perhaps the most popular shasta daisy in the United States because of its sturdy habit and garden dependability (Hawke, 2007). Lavender cotton (S. chamaecyparissus) is also a drought-tolerant border, foundation, rock garden, and seashore material; however, little is known on its response to salinity. There is little research-based knowledge about the responses of the aforementioned aster perennials to salinity. The purposes of this study were to determine the relative salt tolerance by quantifying and comparing the responses of shoot growth, number of flowers, DW, visual quality, chlorophyll content, and mineral concentration of these widely used aster perennials to elevated salinity in a greenhouse experiment.
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