Loss of productive lands as a result of soil salinization is a growing worldwide problem that affects arid zone regions most acutely. This, coupled with a growing scarcity of fresh water and increased use of effluent or low-quality water for turfgrass irrigation, has prompted turfgrass researchers to develop and test salt-tolerant turfgrass varieties. Establishing turfgrass from seeds under saline conditions is becoming increasingly important, particularly in arid regions of the world. The first step in the process of screening for salinity tolerance in any plant species is to conduct a germination test. According to protocols outlined by the Association of Official Seed Analysts (AOSA, 2009), media considered acceptable for use in standard germination tests include blotter paper, creped cellulose paper, filter paper, sponge rock, vermiculite, sand, and paper toweling. However, it is not clear whether all of these substrata are adequate for screening purposes when the germination test is conducted under saline conditions or when coated seeds are used.
A wide variety of substrata have been used to investigate the effect of salinity on germination of turfgrasses. Dewey (1962) used salinized soil to test wheatgrass (Agropyron desertorum Fisch.) germination at 6,000, 12,000 and 18,000 ppm NaCl and CaCl2. Harivandi et al. (1982) studied germination of several cool-season grasses on washed sand and germination pads (blotter paper). The sand substrata can be easily used; however, it has little water-holding capacity, which may cause salts to concentrate over the course of the experiments (Dudeck et al., 1986). Others have used hydroponic culture systems to study the effect of salinity on germination and growth of a number of cool-season grasses (Brilman and Sardar, 2010; Horst and Beadle, 1984; Horst and Dunning, 1989; Horst and Taylor, 1983; Richardson and McCalla, 2008; Wu, 1981; Zhang et al., 2011). Although these studies reported differences in salt tolerance among the turfgrasses tested, the saline aqueous environment in which the seeds were exposed may not accurately simulate saline conditions occurring in soil. Moreover, hydroponic culture experiments are very labor-intensive (Dudeck et al., 1986). Agar gel was first used as a germination medium by Torello and Symington (1984) to test the effect of salinity (10,000 ppm) on germination of several kentucky bluegrass, alkaligrass [Puccinella distans (L.) Parl.], and red fescue varieties. Since then, other researchers have used agar to study the effects of various salinity levels on germination of a number of warm- and cool-season grasses (Dai et al., 2009; Dudeck and Peacock, 1985; McCarty and Dudeck, 1993; Peacock and Dudeck, 1989; Wang and Zhang, 2010; Zhang et al., 2011). However, with the exception of Wang and Zhang (2010) and Zhang et al. (2011), only low salinity levels were tested in the aforementioned studies. Blotter or filter paper has also been widely used as a germination medium to screen for salinity tolerance in turfgrasses (Camberato and Martin, 2004; Johnson et al., 2007; Lunt et al., 1961; Marcar, 1987; Qian and Suplick, 2001; Serena et al., 2010; Shahba et al., 2008; Zhang et al., 2011). As reported by Dudeck et al. (1986), blotter paper tends to lose more water than agar media and salinity levels surrounding the seed may be higher in blotter paper than in agar.
Seed coatings were first introduced in the late 1930s and early 1940s (Kaufman, 1991; Ross and Moore, 1975) to improve seeding and establishment of vegetables. More recently coatings have been used to improve the microenvironment of turfgrass seeds (Scott, 1989). Grass seeds have been coated with a number of materials, including limestone (Hathcock et al., 1984a), fertilizers (Bruneau et al., 1989; Hathcock et al., 1984b), diatomaceous earth and cytokinins (Greipson, 1999), fungicides (Hummel, 1991; Newell, 1997; Newell et al., 1999), and water adsorbents (Berdhal and Barker, 1980), resulting in increased germination and/or establishment of turf. Since its introduction in 2006, the corn starch coating by the name of ZEBA® has been promoted for use on warm- and cool-season turfgrass seeds (Ardens, 2007) for its water retention capabilities. The coating consists of a polymer [starch-g-poly (2-propenamide-co-propenoic acid) potassium salt], which, according to the manufacturer, absorbs water up to 400 times its weight (Absorbent Technologies, 2006; Ardens, 2007). Leinauer et al. (2010) documented that ZEBA® coating resulted in increased field emergence of ‘Bengal’ creeping bentgrass and in improved establishment of several cool-season blends and mixes. The authors also showed that increased moisture retention from seed coating could compensate for reduced seeding rates, reduced irrigation during establishment, and for a combination of both. However, it is not known if seed coating will have similar beneficial effects on germination under saline conditions.
To identify the optimal germination medium for salt tolerance screening of turfgrasses, more studies are needed that compare media, species, and seed treatments. Dudeck et al. (1986) compared germination of perennial ryegrass (Lolium perenne L.) on blotter paper vs. agar at salinity levels of up to 5000 ppm. Although the authors found no differences between the two media, only one species was tested, and moderate salinity levels were used. Zhang et al. (2011) compared germination of several varieties of four cool-season species using a maximum salt concentration of 20 g·L−1 NaCl and three different media. To date, no studies have compared germination of both warm- and cool-season grasses under highly saline conditions on more than one medium. In addition, studies are lacking on how seed coatings purported to increase moisture retention influence germination under a wide range of salinities. In this study, we compared germination of coated and uncoated cool- and warm-season grasses on two of the most widely used media under low [potable or electrical conductivity (EC) = 0.6 dS·m−1] to highly saline conditions (EC = 22.5 dS·m−1). The substrata chosen for the study were 1% agar gel and filter paper, and ZEBA® cornstarch material was used on the coated seeds. The objective of this study was to compare the performance of two commonly used media for germinating coated and uncoated turfgrass seed under saline conditions.
Absorbent Technologies 2006 Material safety data sheet ZEBA 20 Apr. 2011. <http://www.zeba.com/pdfs/linked/20147_MSDS-All_Products.pdf>.
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