Alternative water sources, such as reclaimed water, are being used to irrigate urban landscapes and agricultural crops due to the limited supply of fresh water, especially in arid and semiarid regions of the world. Reclaimed water contains relatively high levels of soluble salts compared with fresh water, and its salinity level depends on the source of water and treatment. For example, in California, the electrical conductivity (EC) of reclaimed water is typically two to three times that of fresh water (Wu et al., 2001). In addition to elevated salinity of irrigation water, soil salinization has occurred in more than 100 countries (Rengasamy, 2006). The soil salinity problem is even worse in arid and semiarid regions due to high evaporation rates, low rainfall, and irrigation with alternative water sources. Therefore, salt-tolerant plants are required in arid and semiarid regions to maintain aesthetically appealing landscapes.
The rose is one of the most economically important and widely grown ornamental crops worldwide. Information available on the salt tolerance of roses as cut flowers (Bernstein et al., 2006; Cabrera, 2001, 2002, 2003; de Vries, 2003; Fernández-Falcón et al., 1986; Hughes and Hanan, 1978; Raviv et al., 1998; Wahome et al., 2001) indicates that like other crops, salinity tolerance of rose plants depends on species, rootstock selection, substrate or soil type, and environmental conditions. However, little research has been conducted on garden roses under elevated salinity conditions.
Most garden roses are produced by grafting using the T-budding technique (Pemberton, 2003). Different rootstocks are recommended in various areas in the world based on regional differences in climate and soil conditions, in addition to the consideration of rootstock and scion compatibility. For example, R. multiflora is used in the south-central United States, Canada, and Japan, whereas ‘Dr. Huey’ is used in the western United States (Pemberton, 2003). R. ×fortuniana is used in areas with year-round temperate climate (Morrell, 1983). In the United States, R. ×fortuniana is mainly used in Florida and in the southwestern region (Martin, 2008). R. odorata is one of the most popular rose rootstocks for greenhouse cut flowers, but the species is also valued for garden roses (Cabrera, 2002; Singh and Chitkara, 1982, 1987).
Limited research compares the salt tolerance of various rose rootstocks. Wahome et al. (2001) compared the salt tolerance of two rose rootstocks and found that R. rubiginosa L. was more tolerant to NaCl stress than was R. chinensis Jacq. ‘Major’. Cabrera (2003) investigated the salt tolerance of ‘Bridal White’ grafted onto five rose rootstocks and found that its salt tolerance was higher when grafted onto Rosa ‘Manetti’ and ‘Natal Briar’ than R. odorata (syn. R. indica L. ‘Major’), R. multiflora ‘Rum 9’, and ‘Dr. Huey’. However, the relative salt tolerance of the five rootstocks alone (without grafting with scions) remains unknown. Comparison of the response of rose rootstocks alone to salinity will be helpful in understanding the mechanism of salt tolerance of major commercial rose rootstocks.
Most saline water and saline soils are dominated by chloride or sulfate salts (Manchanda and Sharma, 1989; Rogers et al., 1998). However, much of the research quantifying the salt tolerance of plant species has been based on experiments in which NaCl is the predominant salt. The degree of salt tolerance depends on the dominant salt type and species (Khan et al., 1995; Rogers et al., 1998). For example, sulfate salts were less deleterious than chloride salts to sweet pepper (Capsicum annuum L.) (Navarro et al., 2002), chickpea (Cicer arietinum L.) (Manchanda and Sharma, 1989), and siberian larch (Larix siberica L.) (Carter, 1980). Specific ions can affect mineral metabolism by promoting or inhibiting the uptake of other minerals (Carter, 1980). Salt type may also affect physiological parameters such as photosynthetic rates and transpiration rates (Meiri et al., 1971). Therefore, the objectives of this study were to compare the growth, ion uptake, and the daily evapotranspiration rate (ET) of four major rose rootstocks ‘Dr. Huey’, R. ×fortuniana, R. multiflora, and R. odorata in response to various salinity levels of irrigation solutions and to investigate if the dominant salt type affects the degree of salt tolerance of these rootstocks.
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