Much of semiarid western North America is salt affected (Szabolcs, 1989) due to alkaline water and insufficient leaching that would otherwise remove salts from weathering of minerals and groundwater (Pitman and Lauchli, 2002). Irrigation contributes to increased soil salinity in semiarid climates at times of high evapotranspiration coupled with inadequate leaching, low-quality irrigation water, or rising water tables that receive salts leached from the plant root zone (Carrow and Duncan, 1998). Other sources of landscape salinity include salts used for roadside deicing (Hutchinson, 1970) and recycled wastewater for landscape irrigation (Lockett et al., 2008; Marcum, 2006).
Kentucky bluegrass is a widely used cool-season species in cool, semiarid climates; however, it has relatively poor salt tolerance (Alshammary, 2013; Marcum, 2008). Many studies have attempted to assess the potential for salt tolerance among kentucky bluegrass cultivars through many varying methods (Alshammary et al., 2004; Horst and Taylor, 1983; Koch and Bonos, 2010; Koch et al., 2011; Liu et al., 2011; Poss et al., 2010; Qian et al., 2001; Robins et al., 2009; Rose-Fricker and Wipff, 2001; Suplick-Ploense et al., 2002; Torello and Rice, 1986). Most studies found that TQ, a measure of turf color, density, and texture, showed significant variation among cultivars under salt stress. Although various mechanisms have been suggested for the variation in salt tolerance, it was found that kentucky bluegrass did not have the ability to exclude salt outside of the leaves, nor was it effective in excluding ions in the root zones (Alshammary, 2013; Alshammary et al., 2004; Xu and Fujiyama, 2013). Compartmentalization or sequestration of Na ions into the vacuole or apoplast was presented as a potential mechanism by which the species could tolerate higher levels of salt (Alshammary, 2013; Marcum, 2008). This sequestration is hypothesized to be accompanied by antioxidant mechanisms to prevent cell damage (Hasegawa et al., 2000; Munns, 2005; Puyang et al., 2015), and physiological mechanisms to maintain turgor and water potential. Consistent with these findings, Bushman et al. (2016) identified genes involved in cellular ion and water transport [tonoplast intrinsic protein (TIP4-1), V-type ATPase subunit b, and H-type ATPase] and genes involved in maintenance of cellular redox state [thioredoxin h-type, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and glutathione S-transferase (GST)] in a transcriptome survey between a salt-tolerant and susceptible kentucky bluegrass accession.
Although substantial variation has been detected in assessments of kentucky bluegrass salt tolerance, cultivars often show changes of rank in relative salt tolerance, depending on the study methods. The cultivars Midnight and Baron, ubiquitous kentucky bluegrass cultivars often included in studies as checks, have shown a range of responses to salt stress (Koch and Bonos, 2010; Koch et al., 2011; Puyang et al., 2015); such that their relative salt tolerance is unclear. Robins et al. (2009) used a different approach to find kentucky bluegrass entries with putative salt tolerance. Although previous quantitative measures were intensive, which thereby limited the entry numbers, Robins et al. (2009) submersed multiple plants from many cultivars in increasingly concentrated saline solutions over time and measured the concentration of salts and number of days treated when a lethal dose, whereupon 50% of the plants were dead (LD50), was reached for each entry. Rather than a mechanistic approach on relatively few entries, that method focused on turf color of multiple genotypes per entry and a higher number of entries. Although that method included the cultivar Midnight as a susceptible control, whether tolerant entries detected by Robins et al. (2009) would be tolerant under mechanistic approaches is unknown.
One of the purposes of this study was to confirm the salt tolerance of two putatively tolerant kentucky bluegrass accessions reported in Robins et al. (2009), and to investigate mechanisms by which those accessions respond to salt stress. The two accessions, PI 371768 and PI 440603, and the cultivars Baron and Midnight are measured in multiple greenhouse trials for TQ, gS, ψLEAF, EL, and the accumulation of inorganic ions on control and salt treatments. In addition, the expression profiles of genes involved in cellular ion sequestration and antioxidant activities previously reported in Bushman et al. (2016) are characterized for variation between the tolerant accessions and susceptible cultivars. These results identify new germplasm sources of salt tolerance in kentucky bluegrass and pinpoint mechanisms by which those lines tolerate salt stress that may be useful for selection of other salt-tolerant kentucky bluegrass germplasm.
Bressan, R.A., Bohnert, H.J. & Hasegawa, P.M. 2008 Genetic engineering for salinity stress tolerance, p. 347–384. In: H.J. Bohnert, H. Nguyen, and N.G. Lewis (eds.). Advances in plant biochemistry and molecular biology. Pergamon Press, Oxford, UK
Bushman, B.S., Amundsen, K.L., Warnke, S.E., Robins, J.G. & Johnson, P.G. 2016 Transcriptome profiling of kentucky bluegrass (Poa pratensis L.) accessions in response to salt stress BMC Genomics 17 1 12
Carrow, R.N. & Duncan, R.R. 1998 Salt-affected turfgrass sites: Assessment and management. Wiley, Hoboken, NJ
Hasegawa, P.M., Bressan, R.A., Zhu, J.K. & Bohnert, H.J. 2000 Plant cellular and molecular responses to high salinity Annu. Rev. Plant Physiol. Plant Mol. Biol. 51 463 499
Koch, M.J. & Bonos, S.A. 2010 An overhead irrigation screening technique for salinity tolerance in cool-season turfgrasses Crop Sci. 50 2613 2619
Koch, M.J., Huang, B.R. & Bonos, S.A. 2011 Salinity tolerance of kentucky bluegrass cultivars and selections using an overhead irrigated screening technique Crop Sci. 51 2846 2857
Leksungnoen, N., Kjelgren, R.K., Beeson, R.C., Johnson, P.G., Cardon, G.E. & Hawks, A. 2014 Salt tolerance of three tree species differing in native habitats and leaf traits HortScience 49 1194 1200
Lesch, S.M., Corwin, D.L. & Robinson, D.A. 2005 Apparent soil electrical conductivity mapping as an agricultural management tool in arid zone soils Comput. Electron. Agr. 46 351 378
Lesch, S.M. & Suarez, D.L. 2009 Technical note: A short note on calculating the adjusted SAR index Trans. Amer. Soc. Agr. Biol. Eng. 52 493 496
Liu, L.M., Du, H.M., Wang, K., Huang, B.R. & Wang, Z.L. 2011 Differential photosynthetic responses to salinity stress between two perennial grass species contrasting in salinity tolerance HortScience 46 311 316
Lockett, A.M., Devittz, D.A. & Morris, R.L. 2008 Impact of reuse water on golf course soil and turfgrass parameters monitored over a 4.5-year period HortScience 43 2210 2218
Marcum, K.B. 2006 Use of saline and non-potable water in the turfgrass industry: Constraints and developments Agr. Water Mgt. 80 132 146
Marcum, K.B. 2008 Physiological adaptations of turfgrasses to salinity stress, p. 407–417. In: M. Pessarakli (ed.). Turfgrass management and physiology. CRC Press, Boca Raton, FL
Miller, R.O. 1998 High-temperature oxidation: Dry ashing, p. 53–56. In: Y.P. Kalra (ed.). Handbook and reference methods for plant analysis. CRC Press, Boca Raton, FL
Pitman, M.G. & Lauchli, A. 2002 Global impact of salinity and agricultural ecosystems, p. 3–20. In: A. Lauchli and U. Luttge (eds.). Salinity: Environment—Plants—Molecules. Springer, Dordrecht, The Netherlands
Poss, J.A., Russell, W.B., Bonos, S.A. & Grieve, C.M. 2010 Salt tolerance and canopy reflectance of kentucky bluegrass cultivars HortScience 45 952 960
Puyang, X., An, M., Han, L. & Zhang, X. 2015 Protective effect of spermidine on salt stress induced oxidative damage in two kentucky bluegrass (Poa pratensis L.) cultivars Ecotoxicol. Environ. Saf. 117 96 106
Qian, Y.L., Wilhelm, S.J. & Marcum, K.B. 2001 Comparative responses of two kentucky bluegrass cultivars to salinity stress Crop Sci. 41 1895 1900
Robins, J.G., Bushman, B.S., Waldron, B.L. & Johnson, P.G. 2009 Variation within Poa germplasm for salinity tolerance HortScience 44 1517 1521
Suplick-Ploense, M.R., Qian, Y.L. & Read, J.C. 2002 Relative NaCl tolerance of kentucky bluegrass, texas bluegrass, and their hybrids Crop Sci. 42 2025 2030
Szabolcs, I. 1989 Salt affected soils. CRC Press, Boca Raton, FL
Torello, W.A. & Rice, L.A. 1986 Effects of NaCl stress on proline and cation accumulation in salt sensitive and tolerant turfgrasses Plant Soil 93 241 247
Xu, R. & Fujiyama, H. 2013 Comparison of ionic concentration, organic solute accumulation and osmotic adaptation in kentucky bluegrass and tall fescue under NaCl stress Soil Sci. Plant Nutr. 59 168 179
Zhang, C-J., Zhao, B-C., Ge, W-N., Zhang, Y-F., Song, Y., Sun, D-Y. & Guo, Y. 2011 An apoplastic h-type thioredoxin is involved in the stress response through regulation of the apoplastic reactive oxygen species in rice Plant Physiol. 157 1884 1899
Primer sequences used for quantitative real-time reverse-transcription PCR of transport and antioxidant genes in kentucky bluegrass.