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Published online 21 November 2006
Published in Crop Sci 46:2571-2574 (2006)
© 2006 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TURFGRASS SCIENCE

Salinity Tolerance and Salt Gland Excretion Efficiency of Bermudagrass Turf Cultivars

K. B. Marcuma,* and M. Pessaraklib

a Dep. of Applied Biological Sciences, Arizona State Univ., Mesa, AZ 85212
b Dep. of Plant Sciences, Univ. of Arizona, Tucson, AZ 85721

* Corresponding author (Kenneth.Marcum{at}asu.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Need for salt tolerant turfgrasses is increasing due to government mandates requiring use of low quality, secondary water sources for turfgrass irrigation. Objectives of this study were to determine the range in salinity tolerance among modern Cynodon spp. (bermudagrass) turf cultivars, determine if leaf salt gland excretion is an important salinity tolerance mechanism in bermudagrass, and if salinity tolerance is associated with the rate, or efficiency of leaf salt gland excretion. Salinity responses of thirty five bermudagrass turf cultivars [Cynodon dactylon (L.) Pers, and C. dactylon x Cynodon transvaalensis (Burtt-Davey)] were determined by exposing plants to five salinity levels (0, 15, 30, 45, and 60 dS m–1). Salinity tolerance among cultivars was determined by shoot dry weight reduction relative to control plants and by percent green leaf canopy area (GLCA). Salinity resulting in 50% reduction in shoot dry weight (SW50) ranged from 26 to 40 dS m–1, indicating a wide range in salinity tolerance within this genus. Salt glands were present on both abaxial and adaxial leaf surfaces of all cultivars. Salinity tolerance was negatively correlated with leaf tissue Na+ concentration and positively correlated with leaf salt gland Na+ excretion rate, indicating that salinity tolerance in bermudagrasses is associated with shoot saline ion exclusion and to leaf salt gland excretion efficiency.

Abbreviations: GLCA, green leaf canopy area • LSD, least significant difference • PAR, photosynthetically active radiation • SW50, 50% reduction shoot dry weight


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
INCREASING demands on limited potable water resources has resulted in widespread government-mandated water use restrictions, requiring use of reclaimed or other secondary water sources for irrigation of turfgrass landscapes (Arizona Department of Water Resources, 1999; California State Water Resources Control Board, 1994; Florida Department of Environmental Protection, 1999). Cynodon spp. (bermudagrasses), the most popularly-utilized turfgrasses in warm regions worldwide, are recognized as being both drought and salt tolerant (Harivandi et al., 1992; Carrow, 1996; Duble, 1996). Differences in salinity tolerance indicated by shoot dry weight reductions relative to control have been reported in studies examining a limited number of older bermudagrass cultivars (Dudeck et al., 1983; Francois, 1988; Marcum and Murdoch, 1990a). Recently, six modern cultivars were compared for salinity tolerance, using the same criteria (Peacock et al., 2004).

Numerous studies have compared relative salinity tolerance among turfgrass cultivars, however, only a few of them have attempted to elucidate tolerance mechanisms in turfgrasses. Though shoot sap osmotic adjustment under salt stress, relative to root media salinity, has been documented in C4 turfgrasses (Peacock and Dudeck, 1985; Marcum and Murdoch, 1990a), salinity tolerance has been associated with saline ion exclusion from shoots in C3 (Torello and Rice, 1986) and C4 (Marcum and Murdoch, 1994) turfgrasses, accompanied by minimal changes in shoot sap osmotic potential (Marcum, 1999). Turfgrasses may exclude saline ions in several ways: via compatible solute accumulation associated with ion compartmentation (Marcum, 1999), exclusion at the root cortex (Leonard, 1983), and excretion by salt glands (Marcum and Murdoch, 1990b).

Bicellular leaf salt glands have been reported in a number of grass species of the tribes Chlorideae, Eragrosteae, Aeluropodeae, and Pappophoreae, belonging to the subfamily Chloridoideae (Amarasinghe and Watson, 1989). Salt gland excretion rates can be significant, representing an important saline ion exclusion mechanism in salt tolerant grasses (Naidoo and Naidoo, 1998; Marcum, 2006). Salt gland excretion rate effectively predicted salinity tolerance among divergent genera of Chloridoid grasses (Marcum, 1999), and also among divergent genotypes within a single genera, Zoysia (Marcum et al., 1998). The goals of this study were to determine relative salinity tolerance among a broad selection of modern bermudagrass turf cultivars, and to determine if leaf salt gland excretion rate can effectively predict salinity tolerance among bermudagrasses.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
To minimize environmental interactions, research was conducted in a controlled environment glasshouse using a solution culture protocol (Marcum et al., 2005). Temperatures were maintained at 30–34°C day, and above 22°C night, with daily maximum photosynthetically active radiation (PAR) levels ranging from 1000 to 1325 µmol m–2 s–1, provided by sunlight. Experiments were conducted from March through August, with daylengths ranging from 12 to 14.3 h. Bermudagrass cultivars were either seeded (seeded cultivars) at 15 g m–2 hulled seed or vegetatively propagated (clonal cultivars) with uniform, bleach-sanitized rhizomes, into 7-cm-diameter x 8-cm-deep pots filled with coarse, acid-washed silica sand. Grasses were established under mist, then transferred to culture tanks containing 32 L of half-strength, constantly aerated Hoagland's no. 2 solution (Hoagland and Arnon, 1950), modified with Fe-sodium ferric diethylenetriamine pentaacetate (DTPA) chelate to provide 3 mg L–1 elemental Fe. Shoots were clipped 2X per wk at 2 cm (ultradwarf cultivars were clipped at 1 cm). Cultivars, including species and growth type, are listed in Table 1.


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  		Table 1. Bermudagrass cultivar entries, species, and growth type.

 
Turfgrasses were established for 2 mo under this mowing regime before initiation of salinity treatments. Salinity treatment protocol followed that of Marcum et al. (2005). Salinity levels were increased by 5 dS m–1 (1.463 g L–1) daily in treatment tanks (control tanks received no salt), using a 3:1 ratio by weight of NaCl:CaCl2 salts, until 15 dS m–1 total salinity was reached. Treatment grasses were held at 15 dS m–1 for 1 wk, then pots were visually rated for percent green leaf canopy area (GLCA), followed by clipping at 2 cm (ultradwarf cultivars were clipped at 1 cm). Following clipping, salinity ramping was resumed until 30 dS m–1 salinity was reached. Salinity was again held at this level for 1 wk, followed by rating for GLCA and clipping. The cycle was repeated at 15 dS m–1 intervals (15, 30, 45, and 60 dS m–1) until 60 dS m–1 salinity was reached. Salinity was again held for 1 wk, followed by final GLCA rating and clipping. Data collection began one wk after reaching each treatment salinity level, thereby continuing over a 5 wk period. Individual plant shoot growth responses to salinity were determined, and salinity level resulting in 50% shoot dry weight relative to control (SW50) calculated by linear regression (Der and Everitt, 2001).

Solutions were monitored daily for salinity level using a conductivity meter with platinum dip cell (model 2052; VWR Scientific, Chicago), adjusted when necessary, and changed every 14 d to ensure minimal changes in nutrient ion concentrations.

Leaf salt gland Na+ excretion rates and leaf tissue Na+ concentrations were determined in grasses exposed to 30 dS m–1 (Marcum, 1999). To determine salt gland Na+ excretion rates, immediately following clipping at 30 dS m–1, shoots were rinsed with deionized water, then plants were held at 30 dS m–1 for 1 wk. Four mature leaves per pot were then carefully excised and placed in vials containing 10 mL distilled water, sealed, and shaken for 5 s, sufficient to dissolve all external secreted salt crystals. Leaves were then removed, dried at 60°C overnight, and weighed. Vials were resealed and subsequently analyzed for Na+. To determine leaf tissue Na+ concentrations, grasses held at 30 dS m–1 for 1 wk were then thoroughly rinsed to remove external salt, and allowed to air dry before clipping. Four fully mature leaves per pot were then excised and immediately sealed in a microcentrifuge tube and frozen. Tubes were later thawed, and leaf sap expressed. Sap was then diluted with distilled water and filtered before Na+ analysis. Sodium analyses were done by inductively coupled plasma emission spectrophotometry (Leeman Labs PS1000, Hudson NH).

Experimental design was a randomized complete block, with 35 cultivars (sub-plots) included in each solution culture tank (main-plots). There were four replications. The experiment was repeated once. Results were similar and consistent between experiments, means of like variables being significantly correlated (average r = 0.76), so data were combined for final analysis and presentation. All data were statistically analyzed by analysis of variance, utilizing least significant difference (LSD) separation of treatment means (Der and Everitt, 2001). GLCA data were transformed by arcsin before analysis (Steel and Torrie, 1980), but are presented as percentages. Pearson product moment correlation coefficients were used to compare variables.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Relative Salinity Tolerance
Shoot dry weight of all cultivars decreased linearly with increasing salinity. Rather than comparing absolute growth under stress, salinity tolerance is better expressed as relative (to control) growth reduction, an indication of plant vigor under stress (Maas and Hoffman, 1977). A tolerance criteria commonly used in salinity studies is the salinity level resulting in 50% shoot dry weight relative to control (SW50) (Maas, 1986). SW50 ranged from 26 to 40 dS m–1, indicating a broad range in salinity tolerance within the Cynodon genus (Table 2, Fig. 1 ). Cultivars in the top statistical group for SW50 were FloraTex, Cheyenne, MS-Supreme, and Blue-muda.


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  		Table 2. Predicted salinity resulting in 50% relative shoot growth (SW50), and percent green leaf canopy area (GLCA) of bermudagrasses under salinity stress.

 

Figure 1
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  		Fig. 1. Linear regressions of mean shoot clipping dry weight vs. salinity, and predicted 50% shoot dry weight growth reduction, for cvs. FloraTex and Mirage. Data means for each salinity level are indicated as points.

 
Percent green leaf canopy area (GLCA), a primary factor of turfgrass quality, was also used as an indicator of salinity tolerance. In cultivars exposed to 60 dS m–1, GLCA ranged from 9 to 36%, with FloraTex, Cheyenne, MS-Supreme, Blue-muda, Santa Ana and Midlawn most salt tolerant (Table 2). GLCA was positively correlated with SW50 (r = 0.62; Table 4), indicating that these variables predicted relative salinity tolerance similarly, though not exactly the same. This might be expected, as SW50 is a physiological, and GLCA a qualitative factor. In an earlier study, salinity tolerance decreased in the order: Tifdwarf, Tifgreen, Tifway, and VNS (AZ Common) (Dudeck et al., 1983). Recently, Tifsport was reported more salt tolerant than Tifway (Peacock et al., 2004). Results of these authors agree with this study. In addition, VNS (AZ Common) was in the lowest statistical group for both SW50 and GLCA.


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  		Table 4. Correlation coefficients (r) among predicted 50% relative shoot weight (SW50), percent canopy green leaf area (GLCA), leaf salt gland Na+ excretion rate, and leaf Na+ concentration for 35 bermudagrass cultivars.

 
Leaf Na+ and Salt Gland Activity
Leaf Na+ ranged from 4.1 to 18.7 mg g–1 leaf dry weight in bermudagrass cultivars exposed to 30 dS m–1 (Table 3). This is representative of the range in leaf tissue Na+ levels previously reported for Chloridoid turfgrasses, and for bermudagrass in particular (Marcum and Murdoch, 1990a; Grieve et al., 2004). Salinity tolerance, indicated by SW50 and GLCA, was negatively correlated with shoot Na+ concentrations among 35 bermudagrass turf cultivars (Table 4; Fig. 2 ). Results support previous reports that saline ion exclusion from shoots is associated with salinity tolerance in C3 and C4 turfgrasses (Torello and Rice, 1986; Marcum and Murdoch, 1994; Qian et al., 2001).


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  		Table 3. Leaf salt gland Na+ excretion rate, and leaf Na+ concentration of bermudagrasses exposed to 30 dS m–1.

 

Figure 2
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  		Fig. 2. Leaf salt gland Na+ excretion rate, and leaf sap Na+ concentration vs. relative salinity tolerance of 35 bermudagrass cultivars.

 
The appearance of salt crystals on leaves of plants growing under saline conditions is indicative of active salt excretion by salt glands or bladders (Fahn, 1988). Salt crystals were observed on both abaxial and adaxial leaves of all bermudagrass cultivars exposed to salinity. Bicellular leaf salt glands on bermudagrass have previously been observed via electron microscopy (Oross and Thomson, 1982; Amarasinghe and Watson, 1989; Marcum, 1999).

Leaf salt gland Na+ excretion rate was positively correlated with SW50 and GLCA, indicating the importance of salt gland activity in bermudagrass salinity tolerance. Salt gland excretion rate effectively predicted salinity tolerance among divergent genera of Chloridoid grasses (Marcum, 1999), as well as among genotypes within a single genera, Zoysia (Marcum et al., 1998). Leaf salt gland activity was found to be heritable, not environmentally induced, among Zoysia genotypes (Marcum et al., 2003). Salt gland excretion efficiency, being an easily-measured physiological trait, might therefore prove an effective selection tool in breeding improved, salinity-tolerant bermudagrass cultivars.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
This research was funded in part by the Arizona Dep. of Water Resources.

Received for publication January 13, 2006.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 





This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
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Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
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Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Marcum, K. B.
Right arrow Articles by Pessarakli, M.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Marcum, K. B.
Right arrow Articles by Pessarakli, M.
Agricola
Right arrow Articles by Marcum, K. B.
Right arrow Articles by Pessarakli, M.
Related Collections
Right arrow Turfgrass
Right arrow Plant and Environment Interactions

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