Published online 20 May 2008
Published in Crop Sci 48:1187-1192 (2008)
© 2008 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
Salinity Tolerance of 33 Greens-Type Poa annua Experimental Lines
Jing Dai,
Maxim J. Schlossberg and
David R. Huff*
Dep. of Crop and Soil Sciences, The Pennsylvania State Univ., University Park, PA 16802. Mention of trade names or commercial products in this article is solely for the purpose of providing information and does not imply recommendation or endorsement by The Pennsylvania State University
* Corresponding author (drh15{at}psu.edu).
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ABSTRACT
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Current literature suggests Poa annua L. (annual bluegrass) is intolerant to salinity stress. Response of greens-type Poa annua to chronic salinity stress (12 wk at 8.0 dS m–1) was evaluated over two greenhouse experiments. Vegetative samples of 33 greens-type P. annua experimental lines were maintained at a 6.4-mm mowing height and irrigated daily with modified Hoagland's solutions possessing salinity levels of 0.7 dS m–1 (nonsaline control) or 8.0 dS m–1 (NaCl treatment, approaching 0.25 strength sea water, approx. 13.5 dS m–1). Clipping yield dry weight (CYD) and leaf water content (LWC) were measured weekly. Digital images were collected at the end of weeks 1, 4, 8, and 12 to determine percentage cover (PC) and dark green color index (DGCI). Across all lines, all sample dates, and both experiments, salinity stress significantly reduced PC (30.8%), DGCI (9.3%), CYD (33.9%), and LWC (3.3%) compared with nonsaline controls (
= 0.05), suggesting chronic salinity stress is detrimental to greens-type P. annua quality. However, significant differences in relative PC and relative CYD were observed among lines, indicating that substantial variation in salinity tolerance exists in greens-type P. annua. Numerous greens-types P. annua experimental lines, such as PSU 99-9-21, PSU 01-1-46, and PSU 05-1-14, possess moderate-to-good salinity tolerance and are potentially suitable for use on golf courses with moderate salt problems.
Abbreviations: CYD, clipping yield dry weight • CYF, clipping yield fresh weight • DGCI, dark green color index • LWC, leaf water content • PAR, photosynthetically active radiation • PC, percentage cover
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INTRODUCTION
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SALT PROBLEMS ON GOLF courses are becoming more pronounced. One of the reasons is that turfgrasses are increasingly being irrigated with salt-rich water as the availability of freshwater resources decreases (Carrow and Duncan, 1998; Carrow et al., 2001). Local water conservation plans and potable water use restrictions can exacerbate existing soil salinity by limiting opportunities to leach salts (Fu et al., 2005; Qian et al., 2004). Therefore, selection and use of relatively salt tolerant cultivars have become important in many regions.
Poa annua L. (annual bluegrass), found across climatic regions of six continents (Beard et al., 1978; Gibeault, 1970), is one of the most widespread species maintained on golf courses. Although many turfgrass managers consider it a weed, P. annua is often a dominant and sometimes a substantial component of golf course putting greens (Beard et al., 1978; Huff, 1999). Among different biotypes identified in this species, greens-type P. annua possesses a competitive edge against creeping bentgrass (Agrostis stolonifera L.) in terms of shoot density, verdure biomass, and tolerance to close mowing, especially in shady, temperate environments (Huff, 1999). Some turfgrass professionals are considering use of greens-type P. annua on putting greens, particularly in regions and climates where creeping bentgrass performs poorly. Greens-type P. annua genotypes have been collected and tested on experimental greens for the purpose of developing improved cultivars (Huff, 1998). One of the limiting obstacles thus far is P. annua's general susceptibility to abiotic stresses such as salinity as described by Carrow and Duncan (1998).
Screening for salinity stress in turfgrass species is becoming increasingly important (Marcum, 2001; Qian et al., 2000; Rose-Fricker and Wipff, 2001; Suplick-Ploense et al., 2002; Torello and Symington, 1984). However, little published information regarding the salinity tolerance of greens-type P. annua exists. Thus, it seems that current knowledge on salinity tolerance of P. annua is mostly based on empirical observations. Previous research shows that under a 6.4-mm mowing height, greens-type P. annua was more tolerant to salt stress than turf-type P. annua, indicating that the greens-type is potentially suitable for use on golf course putting greens afflicted with salinity problems (Dai, 2006). The objective of the present study is to determine (i) if chronic salinity stress has an adverse effect on greens-type P. annua and (ii) if variation in salinity tolerance exists in greens-type P. annua by measuring color, growth, and leaf water content responses of 33 experimental lines following 12 wk of exposure to moderate salinity stress (8.0 dS m–1). Since no large-scale screening has been conducted for this purpose, this study may provide useful information about the salinity tolerance of greens-type P. annua, facilitate screening of sensitive lines from the breeding program, and accelerate P. annua cultivar development.
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MATERIALS AND METHODS
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Greenhouse studies were conducted from November 2005 to April 2006 (Exp. 1) or from December 2005 to May 2006 (Exp. 2) at The Pennsylvania State University, University Park, PA. Six plugs (11 cm i.d.) for each of 33 greens-type P. annua experimental lines were collected from an experimental putting green at the Valentine Turfgrass Research Center, University Park. Sandy soil (60:20:20% vol. coarse sands:soil:Sphagnum peat moss) from the experimental putting green, approximately 2 cm in depth, was left at the bottom of each plug to protect fine roots. Plugs were transplanted into plastic pots (11 cm i.d., 8 cm depth) containing a sand mix (80:20% vol. coarse sands:Sphagnum peat moss). Plants were maintained at a 6.4-mm mowing height and irrigated daily (5.3 mm) with diluted Hoagland's no. 1 solutions (Hoagland and Arnon, 1939) containing a measured salinity level of 0.7 dS m–1. The solutions were supplemented with 1.1 kg ha–1 foliar applications of Fe, as FeCl3, once every 2 wk. Mean canopy temperatures ranged from 15.6 to 35.6°C in both experiments. Mean photosynthetically active radiation (PAR) under natural sunlight conditions in the greenhouse ranged from 70.3 to 295.4 µmol m–2 s–1 in Exp. 1 and from 70.3 to 300.6 µmol m–2 s–1 in Exp. 2 (Table 1
). Experimental lines in the highest statistical grouping, PSU 99-9-21 and PSU 97-1-25, maintained more than 80% PC relative to the nonsaline controls.
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Table 1. Mean minimum and maximum canopy temperatures and mean photosynthetically active radiation (PAR) under natural sunlight conditions in the greenhouse during Exp. 1 and Exp. 2 in 2005 and 2006.
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Soil salinity on golf courses demonstrates wide temporal and spatial variability (Devitt et al., 2007). Differences in topography, parent material, and soil texture can cause substantial variation in spatial distribution of salts. In regions predominated by xeric soil moisture regimes, effluent or reclaimed water may serve as the sole water source to irrigate turfgrass systems through the dry season. Increased use of low-quality irrigation water, necessary to satisfy evapotranspirational demands over the dry season, often has compounding effects on salinity levels of turfgrass root zones. Fortunately, winter precipitation levels dependably purge accumulated salts and facilitate the return of these soils to an optimal salinity status. To a certain extent, this influence of both spatial and seasonal soil salinity variability is taken into account in the measure of mean turfgrass quality (i.e., soils that are 50% saline and 50% nonsaline over time and/or space). That is why both mean and relative turfgrass quality measures are important cultivar screening criteria. Experimental lines PSU 99-9-21, PSU 97-1-25, PSU 01-1-46, PSU 99-2-5, and PSU 98-5-30 comprised the top statistical group for mean PC (Table 3). The natural daylength was extended by 2 h during early morning and late afternoon (November 2005–March 2006) with high-pressure sodium lamps (400 W; P.L. Light Systems, Beamsville, ON, Canada). The light bank, suspended 1.5 m above the canopy, provided supplemental PAR averaging 250 µmol m–2 s–1. To ensure adaptation, the plugs were maintained in the greenhouse 8 wk before the initiation of the salinity treatment.
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Table 3. Effects of chronic salinity stress (12 wk at 8 dS m–1) on relative percentage cover (PC), mean PC, relative clipping yield dry weight (CYD), and mean CYD of 33 greens-type Poa annua experimental lines. Relative CYD and relative PC were obtained by dividing the treatment of each line by its nonsaline control. Mean CYD and mean PC were determined by averaging the treatment and nonsaline control of each line. Data pooled across all weeks are presented.
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The concentration of NaCl was increased in the treatment irrigation solutions by 1 dS m–1 daily while the salinity level of the nonsaline control solutions remained at 0.7 dS m–1. Data collection began when the ultimate salinity level of 8 dS m–1 was reached. Clippings were collected weekly for each experimental line for a period of 12 wk. Weekly clippings were weighed fresh, oven dried (72 h at 60°C), and reweighed. Leaf water content (LWC, mg g–1) was determined by (CYF – CYD)/CYF, where CYF is clipping yield fresh weight and CYD is clipping yield dry weight. Prepared solutions were monitored daily for salinity levels using a laboratory conductivity meter (model CDB-430, Omega Engineering, Stamford, CT).
Images were collected with a Canon PowerShot A95 digital camera (Canon U.S.A., NY) at the end of wk 1, 4, 8, and 12 to determine percentage cover (PC) (cm2 m–2) (Richardson et al., 2001) and dark green color index (DGCI) (Karcher and Richardson, 2003). Digital images were downloaded to a personal computer and cropped for each experimental unit. Cropped images were analyzed with SigmaScan Pro (v. 5.0, SPSS, Chicago, IL) assisted by a batch analysis macro (Karcher and Richardson, 2005) to determine PC and DGCI. To ensure actual turfgrass vegetation was represented, pots were kept free of moss by frequent hand removal.
The experiments were arranged in a split-plot design in three blocks, salinity levels being the whole plot factor and experimental lines the split-plot factor. Thus, the six plugs of each experimental line were randomly assigned to six experimental units comprised of three blocks x two salinity levels. Relative CYD, relative LWC, relative PC, and relative DGCI were obtained by comparing the treatment of each line to its nonsaline control. Mean CYD, mean LWC, mean PC, and mean DGCI were determined by averaging the treatment and nonsaline control of each line.
All data were subjected to analysis of variance using PROC GLM (SAS Institute, 2001). To meet the constant variance assumption of ANOVA, data for CYD and LWC were subjected to logarithm and square transformations, respectively. Mean separations were performed for mean PC, mean CYD, relative PC, and relative CYD using Fisher's LSD (SAS Institute, 2001).
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RESULTS AND DISCUSSION
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Percentage cover, DGCI, CYD, and LWC were significantly reduced under chronic salinity stress (12 wk at 8 dS m–1) compared with the nonsaline controls (all lines and all weeks pooled) (Table 2
). Significant interactions were detected between salinity levels and experimental lines for PC and CYD, but not for DGCI and LWC. No significant interaction was found between experiment and salinity level or between experiment and lines for any parameter, supporting presentation of simplified data pooled across both experiments.
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Table 2. Effects of chronic salinity stress (12 wk at 8 dS m–1) on percentage cover (PC), dark green color index (DGCI), clipping yield dry weight (CYD), and leaf water content (LWC). Data pooled across all weeks and all experimental lines are presented.
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Digital image analysis methods have recently been developed to quantify turfgrass PC and color (Karcher and Richardson, 2005; Richardson et al., 2001), enabling estimation at previously unobtainable degrees of resolution. In the present study, chronic salinity stress had a significant adverse effect on PC (30.8%) compared with the nonsaline controls (Table 2). Following 12 wk exposure to 8 dS m–1 salinity treatment, significant differences in relative PC among experimental lines were observed (Table 3
); however, lines such as PSU 99-11-19, PSU 99-3-19, and PSU 97-1-3 showed PC levels comparable to PSU 99-9-21 and should not be underestimated only because they had a significantly lower rel. PC than PSU 99-9-21.
Six lines representing high, intermediate, and low salinity tolerance detected among 33 experimental lines were selected based on relative PC data. Relative PC generally decreased with increasing exposure time to salinity stress; yet significant interactions between experimental line and time were detected in both experiments (Fig. 1
). Separation among experimental lines became pronounced with prolonged exposure. Generally, PSU 96-1-9 declined most rapidly and PSU 98–3-30 most severely among the six representative experimental lines, while PSU 99-9-21 declined mildly and slowly. Intermediate lines such as PSU 97-1-25, PSU 99-11–6, and PSU 98-5-8 maintained good relative PC in the first 4 wk but experienced dramatic decline in relative PC in the later 8 wk. At the end of Week 1, six representative experimental lines were clustered into a narrow interval of 85 to 100% in relative PC. Greater separation of experimental lines was observed between Week 4 and 8. At the end of Week 12, PSU 99-9-21 experienced approximately 40% reduction in relative PC when compared with the end of Week 1, while PSU 98-3-30 experienced almost 80% reduction.
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Figure 1. Decline in relative percentage cover (PC) of six representative greens-type Poa annua experimental lines with increasing exposure time to 8 dS m–1 salinity treatment. Six lines were selected based on relative PC data to represent high (PSU 97-1-25, PSU 99-9-21), intermediate (PSU 99-11-6, PSU 98-5-8), and low (PSU 96-1-9, PSU 98-3-30) salinity tolerance detected among 33 experimental lines. Relative PC was obtained by dividing the treatment of each line by its nonsaline control. Vertical bars denote LSD values at 0.05 probability level (NS = nonsignificant).
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Clipping Yield
In this study, chronic salinity stress had a significant effect on clipping yield, resulting in an experiment-wide reduction of 33.9% in CYD compared with the nonsaline controls (Table 2). Substantial variation among experimental lines was also observed for relative CYD. Following 12 wk exposure to 8 dS m–1 salinity treatment, PSU 99-9-21, PSU 98-3-19, PSU 05-1-14, PSU 01-1-46, PSU 05-3-11, and PSU 98-2-26 showed the highest relative CYD and maintained greater than 70% CYD relative to the nonsaline controls (Table 3).
Similar to PC, both mean CYD and relative CYD should be considered when practically selecting for salt-tolerant greens-type P. annua experimental lines because lines with higher mean CYD may have more potential for use under field salinity conditions that are spatially and temporally variable. Experimental lines PSU 98-2-26, PSU 05-3-11, and PSU 05-1-14 had top performances for relative CYD (Table 3) but not for mean CYD. Lines such as PSU 97-1-25, although experiencing more reduction in relative CYD, performed significantly better for mean CYD and thus might deserve more attention than PSU 98-2-26, PSU 05-3-11, and PSU 05-1-14 for variable salinity sites.
Six experimental lines were chosen according to data on relative CYD to represent high, intermediate, and low salinity tolerance detected among 33 experimental lines. As exposure time to salinity stress increased, relative CYD generally decreased and the differences among experimental lines became evident (Fig. 2
). Generally, PSU 98-3-30 and PSU 96-1-9 were observed to have declined the most among the six representative experimental lines while PSU 99-9-21 declined the least. Experimental line PSU 98-3-30 showed good tolerance in the first 6 wk but declined dramatically in the later 6 wk. The six representative experimental lines were not significantly different from each other in relative CYD in the first 2 wk. Separation of experimental lines started from the end of Week 3 and became more evident between Week 7 and 12. At the end of Week 12, PSU 99-9-21 experienced approximately 35% reduction in relative PC when compared with the end of Week 1, while PSU 96-1-9 showed almost 70% and PSU 98-3-30 almost 85% reduction.
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Figure 2. Decline in relative clipping yield dry weight (CYD) of six representative greens-type Poa annua experimental lines with increasing exposure time to 8 dS m–1 salinity treatment. Six lines were selected based on relative CYD data to represent high (PSU 01-1-46, PSU 99-9-21), intermediate (PSU 99-3-19, PSU 98-4-21), and low (PSU 96-1-9, PSU 98-3-30) salinity tolerance detected among 33 experimental lines. Relative CYD was obtained by dividing the treatment of each line by its nonsaline control. Vertical bars denote LSD values at 0.05 probability level (NS = nonsignificant).
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Dark Green Color Index and Leaf Water Content
Color is a vital component of turf quality and an effective indicator of water and nutrient status (Beard, 1973). Using DGCI to assess color differences caused by salinity stress has not yet been reported. The treatment DGCI (pooled across all lines and all weeks) was significantly reduced (9.3%) by chronic salinity stress (Table 2); however, the differences among experimental lines or the interactions between salinity level and experimental line were not significant for DGCI.
The treatment LWC (pooled across all lines and all weeks) was significantly reduced (3.3%) relative to the nonsaline controls (Table 2). Interactions between salinity level and experimental line or differences among lines were not significant for LWC. Although succulence in some halophytes can be promoted by salinity (Jennings, 1976; Munns et al., 1983), dehydration has been noted in less-tolerant species (Glenn, 1987; Glenn and O'Leary, 1984). In grass species, Ahmad et al. (1981) reported that exclusion of Na+ and accumulation of organic solutes are the mechanisms for osmotic adjustment and that water loss at high salinity levels is a symptom of internal osmotic imbalance resulting from uncontrolled Na+ uptake. However, Glenn (1987) argued that water loss and Na+ accumulation are coordinated processes that together account for the maintenance of a constant osmotic potential gradient between the internal and external solution. The relationship between water loss and Na+ uptake was not clear in the present study since no data were collected on Na+ contents in leaf tissues.
Over the 12-wk study, relative PC and relative DGCI measures were significantly correlated; relative CYD was also significantly correlated to both relative PC and relative DGCI. However, relative LWC showed no correlation with any other measured parameter (Table 4
). This suggests that LWC (mg g–1), as calculated, may not be an effective parameter to assess salinity tolerance in greens-type P. annua.
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Table 4. Pearson correlation coefficients and corresponding p-values for relative percentage cover (PC), relative dark green color index (DGCI), relative clipping yield dry weight (CYD), and relative leaf water content (LWC) in greens-type Poa annua. Relative CYD, relative LWC, relative PC, and relative DGCI were obtained by dividing the treatment of each line to its nonsaline control.
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Substantial variation in chronic salinity stress tolerance was detected among greens-type P. annua experimental lines. Exposure time is an important component of stress and a sensitive indicator of tolerance (Chen et al., 1982; Ingram et al., 1986; Levitt, 1972). The salinity treatment of 12 wk at 8 dS m–1 represented a moderate seasonal salinity stress. During summertime in some areas, drought may cause or exacerbate salt problems on golf courses (Devitt et al., 2007). Experimental lines such as PSU 98-3-30 may perform well for a limited amount of time but would not likely tolerate salinity stress as long as 12 wk. According to our results on PC and CYD, experimental lines PSU 99-9-21, PSU 01-1-46, PSU 99-2-5, and PSU 97-1-25 showed more tolerance to chronic salinity stress than others. Marcum (2001) studied chronic salinity tolerance (10 wk at 8 dS m–1) of 35 modern bentgrass cultivars using solution culture. On the basis of growth characteristics, ‘Mariner’, ‘Grand Prix’, ‘Seaside’, and ‘Seaside II’ were found to be the most salt tolerant while ‘Penn G-2’ was moderately salt tolerant. Neylan et al. (2005) compared the visual turfgrass quality and density of creeping bentgrass and P. annua irrigated with treated effluent water possessing a calculated salinity level up to 1700 mg L–1 for two irrigation seasons. Their data show that a blend of greens-type P. annua selections from The Pennsylvania State University, containing the experimental lines included in the present study, was as high in visual quality and density as Grand Prix and Penn G-2, and significantly higher than Mariner and Seaside II throughout the trial. Compared with Marcum's (2001) and Neylan et al.'s (2005) findings, our data suggest that specific experimental lines of greens-type P. annua may have potential for use on golf courses with moderate salt problems. However, future research is needed that direct compares salt tolerance of greens-type P. annua with that of other cool-season turfgrass species. Our research has demonstrated that developing salt-tolerant greens-type P. annua cultivars through breeding appears promising.
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ACKNOWLEDGMENTS
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The authors thank D. Archibald, R. Knupp, and S. Eisenhauer for their assistance. This study was funded by grants from United States Golf Association (USGA), the Pennsylvania Turfgrass Council (PTC), and Hatch Project PA 3766 and 4086.
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NOTES
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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication December 4, 2007.
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J. Dai, D. R. Huff, and M. J. Schlossberg
Salinity Effects on Seed Germination and Vegetative Growth of Greens-Type Poa annua Relative to Other Cool-Season Turfgrass Species
Crop Sci.,
March 17, 2009;
49(2):
696 - 703.
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TOP
ABSTRACT
INTRODUCTION
