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Qi Zhang and Kevin Rue

Saline and alkaline conditions often coexist in nature. Unlike salinity that causes osmotic and ionic stresses, alkalinity reflects the impact of high pH on plant growth and development. In this research, seven turfgrass species, tall fescue (Festuca arundinacea Schreb.), kentucky bluegrass (Poa pratensis L.), creeping bentgrass (Agrostis stolonifera L.), perennial ryegrass (Lolium perenne L.), zoysiagrass (Zoysia japonica Steud.), bermudagrass [Cynodon dactylon var. dactylon (L.) Pers.], and alkaligrass [Puccinellia distans (Jacq.) Parl.], were germinated under 10 saline–alkaline conditions [two salinity concentrations (25 and 50 mm) × five alkalinity levels (pH = 7.2, 8.4, 9.1, 10.0, 10.8)] in a controlled environment. Seed germination was evaluated based on final germination percentage and daily germination rate. Alkaligrass and kentucky bluegrass showed the highest and lowest germination under saline conditions, respectively. Limited variations in germination were observed in other species, except bermudagrass, which showed a low germination rate at 50 mm salinity. Alkalinity did not cause a significant effect on seed germination of tested turfgrass species.

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Qi Zhang and Kevin Rue

Exogenous application of glycinebetaine (GB), an osmoprotectant, increases tolerance to stresses including salinity in various plants. Information on turfgrass, however, is limited. In this study, GB was used to prime turfgrass seeds to enhance salinity tolerance during germination and seedling growth stage when plants are more sensitive to stresses. Unprimed and primed (50, 100, 150, or 200 mm solution of GB or distilled water) seeds of perennial ryegrass (Lolium perenne L.) (PR), tall fescue (Festuca arundinacea Schreb.) (TF), creeping bentgrass (Agrostis palustris Huds.) (CB), and kentucky bluegrass (Poa pratensis L.) (KB) were germinated in solutions of distilled water, mannitol (causing osmotic stress only), or NaCl (causing both osmotic and ionic stresses). Their osmotic potential (ψS) and salinity level were -0.1 MPa and 0.1 dS·m−1 (no stress), –1.0 MPa and 0.1 dS·m−1 (moderate osmotic stress), and –1.0 MPa and 14.6 dS·m−1 (moderate osmotic and ionic stresses), respectively. Seeds primed with GB showed a higher germination rate (11.0% to 13.9% increase) and seedling growth (19.3% to 20.7% increase) in mannitol or NaCl solution than in distilled water. Different turf species showed different responses to osmotic and ionic stresses. No differences in germination and seedling growth of PR, TF, and KB were observed between mannitol and NaCl treatments, indicating that osmotic stress appeared to more critical than ionic stress under saline conditions. For CB, the seed germination rate and seedling growth were lower (19.3% to 44.2% reduction) in NaCl than in mannitol, showing an accumulative effect of both osmotic and ionic stresses under saline conditions.

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Sheng Wang and Qi Zhang

Many golf courses and turfgrass managers use recycled water, which contains high salts, as part or a sole irrigation source to lower costs and comply with governmental restrictions on water use. High salinity negatively affects turfgrass performance. Using salt-tolerant species or cultivars is one the most effective methods to address salinity problems. Twenty-six commercially available creeping bentgrass (Agrostis stolonifera) cultivars were evaluated for salt tolerance during in vitro germination on 1% agar media supplemented with NaCl at 0, 5, 10, 15, or 20 g·L−1 at 25/15 °C (day/night) under fluorescent light (36 μmol·s−1·m−2) with an 8- to16-h photoperiod. Significant variations in salinity tolerance were observed among the cultivars. Final germination rate (FGR, %) and daily germination rate (DGR, %/d) decreased linearly or quadratically as salinity levels increased. ‘Declaration’, ‘Seaside II’, ‘T-1’, and ‘Bengal’ were the most salt-tolerant, requiring salt levels at or greater than 16.0 and 10.0 g·L−1, respectively, to reduce FGR and DGR by 50%. In contrast, ‘Tyee’, ‘Kingpin’, and ‘SR1150’ required average salinity levels of 11.6 and 6.5 g·L−1 to cause 50% reduction in FGR and DGR, respectively, showing that they were the least salt-tolerant cultivars. The largest difference between FGR (1.9%) and DGR (26.2%) reduction under saline conditions was observed at 5 g·L−1, indicating that DGR was more sensitive to salinity changes than FGR. Therefore, DGR might be a more reliable method to be used for salt selection.

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Qi Zhang, Kevin Rue and Jeanna Mueller

Glycinebetaine (GB) seed priming enhances stress tolerance in various plants during the germination and seedling growth stage; however, information regarding turfgrass is limited. In this study, GB at 5 to 50 mm was used to prime seeds of six turfgrass species to evaluate the potential of GB priming in enhancing tolerance to drought, salinity, and sub-optimal temperature during germination. Stress tolerance was determined as relative final germination percentage (FGP) and daily germination percentage (DGP), expressed as percentage of germination under stress conditions compared with the control treatment (i.e., unprimed seeds germinated under non-stress condition) for each species. Daily germination percentage was more sensitive to stress than FGP. Perennial ryegrass (Lolium perenne L.) showed high tolerance to drought, salinity, and chilling temperatures (5 and 10 °C below optimal germination temperature) followed by tall fescue (Festuca arundinacea Schreb.) and creeping bentgrass (Agrostis palustris L.), whereas kentucky bluegrass (Poa pratensis L.), bermudagrass [Cynodon dactylon var. dactylon (L.) Pers.], and zoysiagrass (Zoysia japonica Steud.) were stress-sensitive. Kentucky bluegrass and bermudagrass showed higher germination at 10 mm GB under temperature stress and drought and temperature stresses, respectively; however, other grasses showed limited responses to seed priming. Our results showed that the efficacy of GB priming is plant-, GB concentration-, and stressor-dependent.

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Sheng Wang, Qi Zhang and Eric Watkins

Prairie junegrass (Koeleria macrantha) is a perennial, cool-season, native grass that has shown potential for use as a turfgrass species in the northern Great Plains; however, limited information is available on its salt tolerance. In this study, salinity tolerance of four junegrass populations from North America (Colorado, Minnesota, Nebraska, and North Dakota) and two improved turf-type cultivars from Europe (‘Barleria’ and ‘Barkoel’) was evaluated and compared with kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne), sheep fescue (Festuca ovina), hard fescue (F. brevipila), and tall fescue (F. arundinacea). Salinity tolerance was determined based on the predicted salinity level causing 50% reduction of final germination rate (PSLF) and daily germination rate (PSLD) as well as electrolyte leakage (EL), tissue dry weight (DW), and visual quality (VQ) of mature plants. All populations of prairie junegrass showed similar salt tolerance with an average of PSLF and PSLD being 7.1 and 5.3 g·L−1 NaCl, respectively, comparable to kentucky bluegrass and hard and sheep fescue but lower than tall fescue and perennial ryegrass. Larger variations were observed in VQ in the junegrasses compared with EL and DW, in which ‘Barleria’ from the European population showed the highest VQ, following two salt-tolerant grasses, tall fescue and sheep fescue. Nebraska population was the least salt-tolerant within the species but still exhibited similar or higher tolerance than kentucky bluegrass and perennial ryegrass cv. Arctic Green. Overall, junegrass was more salt-sensitive during germination but more tolerant to salinity when mature. Salinity tolerance of junegrass may be further improved through turfgrass breeding because salinity tolerance varied in different populations.

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Qi Zhang, Liqi Yang and Kevin Rue

Drought is the most important abiotic stress in crop production including turfgrass management. Using drought tolerant plants can help minimize stress damage. In this study, 23 commercially available cultivars of creeping bentgrass (Agrostis stolonifera) were evaluated for their responses to drought stress that was induced by polyethylene glycol (PEG) 6000 in a hydroponic system during the seed germination and seedling growth stage. In such a system, water potential was adjusted to 0.0 (the control), −0.3, and −0.6 MPa to mimic the drought condition. The absolute water content (AWC), shoot dry weight (SDW), root dry weight (RDW), longest root length (LRL), specific root length (SRL), and root-to-shoot dry weight ratio (RSR) in the plants grown for 4 weeks in the treatment were determined. Results showed that SDW and LRL were unaffected by drought; however, RDW and RSR increased, whereas SRL and AWC were reduced under drought. Among the 23 creeping bentgrass cultivars evaluated, Independence and Crystal Bluelinks had a higher turfgrass performance index (TPI), which represented the number of times a cultivar ranked in the top statistical group across all parameters. The results suggest that ‘Independence’ and ‘Crystal Bluelinks’ may be more adapted to drought than the other cultivars at the seedling stage.

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Qi Chai, Xinqing Shao and Jianquan Zhang

Understanding turfgrass response to silicon (Si) application under salinity conditions is important to find a way to improve turfgrass salt tolerance for turf management. The objective of the study was to investigate effects of increasing amendment concentrations of Na2SiO3 on turf growth and distribution of Na+ and K+ in seedlings of kentucky bluegrass (KBG) (Poa pratensis L.) under salinity stress. This growth chamber experiment was consisted of a control (no salinity and no Si) and five Si amendment treatments (0, 0.24, 0.48, 0.72, and 0.96 g Si/kg saline soil) under 10 g·kg−1 salinity conditions. Seed germination rate was significantly increased after 12 d under 0.48 g·kg−1 Si treatment. Plant height and canopy coverage were increased under 0.72 g·kg−1 Si treatment after 40 and 44 d of treatment, respectively, and tiller number was increased under 0.96 g·kg−1 Si treatment compared with 0 Si under saline conditions. With the supplement of Si at 0.48 to 0.96 g·kg−1, the ratio of Na+/K+ in shoots was decreased and individual leaf area was increased compared with 0 Si under saline conditions. The increase in individual leaf area was mainly the result of the increase in the leaf blade length. The concentration of K+ in shoots was significantly increased, whereas the concentrations of Na+ in roots were significantly decreased under all Si amendment treatments. The content of K+ was higher in shoots than in roots, but the ratio of Na+/K+ in roots was higher than in shoots in all Si amendment treatments. The results indicate that under saline conditions, Si induced the transfer of K+ from roots to shoots but inhibited the absorption and transfer of Na+, which may contribute to better turf quality and growth with Si treatment under saline conditions.

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Qi Zhang, Sheng Wang and Kevin Rue

Salinity tolerance of 12 turfgrasses in four groups, creeping bentgrass (Agrostis stolonifera L.), fescues (Festuca spp.), kentucky bluegrass (Poa pratesis L.), and alkaligrass [Puccinellia distans (Jacq.) Parl.], was evaluated using three germination methods. Seeds were germinated on 1% agar medium, on germination paper, or in a hydroponic system under salinity levels of 0, 5, 10, 15, or 20 g·L−1 NaCl. Germination rate and seedling growth of each grass were determined. Salinity reduced the final germination rate (FGR), daily germination rate (DGR), and seedling leaf area (LA) in all tests. On agar medium, no significant difference in salinity tolerance was observed among the four turf groups; however, ‘Turf Blue’ kentucky bluegrass with a corn starch-based coating (coated ‘Turf Blue’) showed a significant higher salinity tolerance than the uncoated one. Using germination paper, creeping bentgrass required the highest salinity level to cause 50% reduction in FGR followed by alkaligrass, fescues, and kentucky bluegrass. Kentucky bluegrass required the lowest salinity level (9.5 g·L−1) to reduce DGR by 50%. With the hydroponic system, alkaligrass required a salinity level of 26.3 g·L−1 to reduce FGR by 50%, the highest among the four groups. Alkaligrass showed again the highest salinity tolerance with an average of 12.7 g·L−1 needed to reduce LA by 50%. Among the grasses, coated ‘Turf Blue’ kentucky bluegrass, ‘Declaration’ creeping bentgrass, and ‘Fults’ alkaligrass showed the highest salinity tolerance when evaluated on agar medium, on germination paper, or in the hydroponic system, respectively. The present study determined the salinity tolerance of 12 turfgrasses at seed germination and early seedling growth stages and showed that the germination method was a factor affecting the evaluation result and it should be considered in a seed germination test of turfgrass for salinity tolerance.