With rapid increases in urban populations and industrial development, the availability of fresh water for landscape irrigation will be limited in the future. Therefore, alternative water sources such as reclaimed water are becoming commonly used to irrigate urban landscapes and agricultural crops (Niu and Rodriguez, 2008). Reclaimed water contains high levels of soluble salts, inducing salt stress to plants. High soil salinity is the result of low rainfall and high evapotranspiration in arid and semiarid regions, whereas it is the result of deicing salts in northern areas (Niu et al., 2013). Increasing soil salinity negatively affects plant physiological and biochemical mechanisms that are associated with plant growth and development. Thus, screening and identifying salt-tolerant plant species and cultivars is becoming increasingly important, which could permit the use of lower quality water and conserve higher quality water for other purposes.
Sodium (Na+) and chloride (Cl–) are usually the most prevalent ions in saline water, which may cause deleterious effects in plants such as necrosis and leaf edge burn (Wahome et al., 2001). Excessive Na+ and Cl– uptake competes with uptake of other nutrient ions such as potassium (K+), calcium (Ca2+), or nitrogen (N), resulting in nutritional disorders and reduced yield and plant quality (Grattan and Grieve, 1999). High soil salinity also causes reduction in soil water potential, inhibiting plants’ ability to extract water from the soil and maintain turgor. In addition, high ionic concentration can disturb membrane integrity and function, internal solute balance, and nutrient uptake, and it affects plant growth, water relations, and photosynthesis (Grattan and Grieve, 1999). Increased sodium chloride (NaCl) levels resulted in a reduction in shoot, root, and leaf biomass and an increase in root/shoot ratio, which were reported in cotton (Gossypium hirsutum L.), soybean [Glycine max (L.) Merr.], and alfalfa (Medicago sativa L.) (Berstein and Ogata, 1966; Kant et al., 1994; Meloni et al., 2001).
Plants have various salt tolerance mechanisms, including ion exclusion, maximizing Na+ efflux from roots and its recirculation out of shoots and intercellular compartments, maintaining high cytosolic K+/Na+ ratio, or accumulation of optimal amount of compatible solute (Tester and Davenport, 2003). Salt-tolerant plants usually have less adverse effects on foliar salt injury and growth and yield reduction at elevated salinity (Grieve et al., 2008). The relative salt tolerance among multiple cultivars based on their growth and physiological responses at elevated salinity levels has been studied in greenhouse and garden roses and rose rootstocks (Cabrera et al., 2009; Niu et al., 2008, 2013; Niu and Rodriguez, 2008). As irrigation salinity increased from 1.4 to 6.4 dS·m−1, there was no or little visual damage in salt-tolerant rose cultivars, Little Buckaroo, Sea Foam, and Rise N Shine, and shoot DW of these cultivars was unaffected by salt stress (Niu et al., 2013). In a study by Niu et al. (2008), R. ×fortuniana was relatively more salt-tolerant than the other two rootstocks, R. odorata and R. multiflora, with smaller growth reductions and higher visual quality at elevated salinities.
Garden roses (Rosa hybrida L.) are some of the most economically important flowering shrubs in the world. Generally, roses are salt-sensitive species with reduction in yield and quality at salinity levels that exceed EC of 3.0 dS·m−1 (Urban, 2003). Earth-Kind® is a special designation given to select rose cultivars by the Texas AgriLife Extension Service through the Earth-Kind® landscaping program (Aggie Horticulture, 2014). These roses are trialed in large outdoor field plots in a location with typical conditions (MacKay et al., 2008). During years of testing, no pesticides and chemical or organic were applied to the research and trial roses. Based on actual recorded field data, best rose cultivars are selected by conformational trials throughout the region in various soil types, ranging from acid sands to highly alkaline clays (MacKay et al., 2008). The Earth-Kind® Rose Trials help to serve the horticulture community by identifying the most adaptable landscape roses (Harp et al., 2009). These roses exhibit consistent and superior pest tolerance combined with outstanding landscape performance with minimum fertilizer, water, and pesticides (Aggie Horticulture, 2014). However, salt stress was not a factor considered during the evaluation process. There is little science-based knowledge about the responses of the Earth-Kind® roses to high salinity levels.
Using salt-tolerant garden roses is important in urban landscapes in areas where soil salinity is high or irrigation water quality is poor. Our objectives were to compare the relative salt tolerance in 18 Earth-Kind® rose cultivars (Belinda’s Dream, Cecile Brunner, Climbing Pinkie, Ducher, Duchesse de Brabant, Else Poulsen, Georgetown Tea, La Marne, Madame Antoine Mari, Marie Daly, Monsieur Tillier, Mrs. Dudley Cross, Mutabilis, Perle d’Or, Reve d’Or, Sea Foam, Souvenir de St. Anne’s, and Spice) in College Station, TX, and 10 of the same 18 Earth-Kind® rose cultivars replicated in El Paso, TX, and to determine the visual quality, shoot growth, flower number and DW, chlorophyll content, and gas exchange of these rose cultivars to elevated salinity.
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