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The susceptibility of warm-season turfgrasses such as bermudagrass (Cynodon spp.) to winter injury in the transition zone is a major concern. Therefore, the objective of the study was to evaluate five golf course putting green-type experimental genotypes (OKC6318, OKC0805, OKC1609, OKC0920, and OKC3920) and three commercially available bermudagrasses (‘Champion Dwarf’, ‘TifEagle’, and ‘Tahoma 31’) for freeze tolerance by subjecting them to 11 freezing temperatures (–4 to –14 °C) under controlled environment conditions. The experiment was conducted in batches, with four genotypes per batch, and each batch was replicated in time. The mean lethal temperature to kill 50% of the population (LT₅₀) for each genotype was determined. There were significant differences in LT₅₀ values among the bermudagrass genotypes. ‘Champion Dwarf’ had an LT₅₀ value ranging from –5.2 to –5.9 °C across all three batches. The experimental genotypes tested in this study had LT₅₀ values ranging from –7.0 to –8.1 °C and were each lower than that of ‘Champion Dwarf’. ‘Tahoma 31’, the top performing genotype, had an LT₅₀ value ranging from –7.8 to –9.0 °C across all three batches. OKC 3920 was the only experimental genotype with an LT₅₀ value in the same statistical group as ‘Tahoma 31’. The information gained from this research would be useful for breeders to gauge the genetic gain in freeze tolerance in breeding golf course putting green-type bermudagrass.

Bermudagrass (Cynodon sp.) is one of the most commonly used warm-season turfgrasses in the southern areas and transition zone of the United States. Due to the increasing demand for water resources and periodic drought, it is important to improve the drought resistance of bermudagrass for water savings and persistence under drought stress. This study was conducted to determine whether experimental bermudagrass genotypes have improved drought resistance compared with the standard cultivars Tifway and Riley’s Super Sport (Celebration^®) at Stillwater, OK. The trials were designed as randomized complete blocks with four replications in Expt. I and three replications in Expt. II. In each experiment, genotypes were subjected to progressive acute drought conditions using polyethylene waterproof tarps to exclude precipitation over a period of at least 72 d. Bermudagrass entries were evaluated for turfgrass quality, leaf firing, normalized difference vegetation index, and live green cover at least once each week during the dry-down. Substantial drought response variations were found in this study, and all parameters were positively and highly correlated. A turf performance index (TPI) was assembled based on the number of times an entry ranked in the top statistical group across all testing parameters on each date. ‘DT-1’ (TifTuf^®) and OSU1221 had the top TPI in both experiments. Most of bermudagrass experimental genotypes had equal or greater TPI than the standard Tifway, showing improved drought resistance through breeding effects. The identification of superior drought resistance experimental genotypes provided useful information to breeders on cultivar release.

Turfgrass managers are using reclaimed water as an irrigation resource because of the decreasing availability and increasing cost of fresh water. Much attention, thereby, has been drawn to select salinity-tolerant turfgrass cultivars. An experiment was conducted to evaluate the relative salinity tolerance of 10 common bermudagrasses (Cynodon dactylon) under a controlled environment in a randomized complete block design with six replications. ‘SeaStar’ seashore paspalum (Paspalum vaginatum) was included in this study as a salinity-tolerant standard. All entries were tested under four salinity levels (1.5, 15, 30, and 45 dS·m⁻¹) consecutively using subirrigation systems. The relative salinity tolerance among entries was determined by various parameters, including the normalized difference vegetation index (NDVI), percentage green cover determined by digital image analysis (DIA), leaf firing (LF), turf quality (TQ), shoot vertical growth (VG), and dark green color index (DGCI). Results indicated that salinity tolerance varied among entries. Except LF, all parameters decreased as the salinity levels of the irrigation water increased. ‘Princess 77’ and ‘Yukon’ provided the highest level of performance among the common bermudagrass entries at the 30 dS·m⁻¹ salinity level. At 45 dS·m⁻¹, the percent green cover as measured using DIA varied from 4.97% to 16.11% among common bermudagrasses, where ‘SeaStar’ with a DIA of 22.92% was higher than all the common bermudagrass entries. The parameters LF, TQ, NDVI, DGCI, VG, and DIA were all correlated with one another. Leaf firing had the highest correlation with other parameters, which defined its value as a relative salinity tolerance measurement for common bermudagrass development and selection.

Bermudagrass (Cynodon sp.) is a highly productive, warm-season, perennial grass that has been grown in the United States for turfgrass, forage, pasture, rangeland, and roadside use. At the same time, many bermudagrass production and reclamation sites across the United States are affected by soil salinity issues. Therefore, identifying bermudagrass with improved salinity tolerance is important for successfully producing bermudagrass and for reclaiming salt-affected sites with saline irrigated water. In this project, the relative salinity tolerance of seven clonal-type bermudagrass was determined, including industry standards and an Oklahoma State University (OSU) experimental line. The experiment was conducted under a controlled environment with six replications of each treatment. Seven bermudagrass entries were exposed to four salinity levels (1.5, 15, 30, and 45 dS·m⁻¹) consecutively via subirrigation systems. The relative salinity tolerance among entries was determined by normalized difference vegetation index (NDVI), digital image analysis (DIA), leaf firing (LF), turf quality (TQ), shoot dry weight (SW), visual rating (VR), and dark green color index (DGCI). Results indicated that there were variable responses to salinity stress among the entries studied. As salinity levels of the irrigation water increased, all evaluation criterion decreased, except LF. All entries had acceptable TQ when exposed to 15 dS·m⁻¹. When exposed to 30 dS·m⁻¹, experimental entry OKC1302 had less LF than all other entries except ‘Tifway’, while ‘Midlawn’ showed more LF than all the entries. Leaf firing ranged from 1.0 to 2.7 at 45 dS·m⁻¹, where ‘Tifway’ outperformed all other entries. At 45 dS·m⁻¹, the live green cover as measured using DIA ranged from 3.07% to 24.72%. The parameters LF, TQ, NDVI, DGCI, SW, and DIA were all highly correlated with one another, indicating their usefulness as relative salinity tolerance measurements.

Cell and plastid membranes play a critical role in plant response to chilling stress. Fall color retention (chilling tolerance) of bermudagrass (Cynodon sp.) is known to vary with cultivar and management practices. A growth chamber study was conducted to characterize the lipid composition of three bermudagrasses in response to chilling stress. The grasses selected were ‘Tahoma 31’ (chilling-sensitive) and ‘Tifway’ (chilling-tolerant) interspecific hybrid bermudagrass (C. dactylon × C. transvaalensis) and ‘Celebration’ common bermudagrass (C. dactylon), which served as an internal standard. Plants were subjected to simulated fall conditions defined as an 8/2 °C (day/night) temperature regime with 10-hour photoperiod and evaluated for chilling response for 42 days before allowing plants to enter an apparent dormancy. Plant leaves were sampled for lipidomics analysis at 0, 14, and 42 days of chilling treatment (DOT) and again after 40 days of recovery from dormancy (during which temperatures were adjusted to mimic average spring conditions for Oklahoma). ‘Tifway’ demonstrated the lowest electrolyte leakage (EL) and visual discoloration at 42 DOT, while ‘Tahoma 31’ had the greatest EL and discoloration on the same date, and ‘Celebration’ was intermediate of the two. Prolonged exposure to chilling stress generally increased digalactosyldiacylglycerol and phosphatidylcholine (PC) content and decreased monogalactosyldiacylglycerol (MGDG) content, with ‘Tahoma 31’ showing the greatest increase in PC and decrease in MGDG. The double bond index, an indicator of fatty acid unsaturation, was greatest in ‘Tifway’ at 42 DOT. Each cultivar increased in fatty acid unsaturation, with Tifway demonstrating the greatest increase in MGDG unsaturation. Multivariate discriminant analysis identified six individual lipid species that contributed most to the cultivar response to chilling. These findings suggest unsaturation level of plastid lipids, particularly MGDG, is important for chilling tolerance and therefore fall color retention of bermudagrass. Furthermore, this study provides evidence that chilling tolerance can be negatively associated with freezing tolerance in bermudagrass.

Drought stress is a major limiting factor for warm-season turfgrass growth during the summer in the U.S. transition zone. Genotypic variation in drought resistance exists among bermudagrasses (Cynodon sp.), but the mechanisms of drought resistance are poorly understood. Our objectives were to investigate physiological changes in three bermudagrass cultivars under a well-watered condition and drought stress. to determine expression differences in soluble protein and dehydrin of the three cultivars under well-watered and drought stress conditions, and to identify the association between dehydrin proteins and drought tolerance. Grasses included a high drought-resistant cultivar, Celebration, a low drought-resistant cultivar, Premier, and a newly released cultivar, Latitude 36. In both well-watered and drought treatments, ‘Latitude 36’ had the highest visual quality and lower or medium electrolyte leakage among three cultivars. In the drought treatment, 16- and 23-kDa dehydrin proteins were observed in ‘Latitude 36’ but not in ‘Celebration’ or ‘Premier’. Our results indicate that the 16- and 23-kDa dehydrin expressions could be associated with drought tolerance and contribute to drought tolerance in bermudagrass.

Turfgrass varietal identification is critical and allows turfgrass professionals to manage the turf based on the cultural requirements of the variety. On the Oklahoma State University (OSU) Baseball Field (OSUBF) in Stillwater, OK, some bermudagrass (Cynodon sp.) plants exhibited desirable traits but their exact identities were unknown due to the installation of multiple varieties over time. Accordingly, the major objective of this study was to identify if the desirable bermudagrass plants were from commercially available known varieties. Recently, the OSU turf bermudagrass breeding program developed and entered three fairway-type clonal bermudagrasses in the 2013 National Turfgrass Evaluation Program (NTEP) bermudagrass trial: OKC 1131, OKC 1163, and OKC 1302. The secondary objective was to create molecular marker profiles for these three experimental lines. Five OSUBF samples were analyzed using simple sequence repeat (SSR) markers, along with 24 clonal, commercially available turf bermudagrass varieties widely used in Oklahoma, the three OSU experimental clones, six randomly selected single plants from ‘Riviera’, and two controls for common bermudagrass (Cynodon dactylon) and african bermudagrass (Cynodon transvaalensis). SSR marker genotyping data indicated that the five OSUBF plants were clones of an identical bermudagrass. The OSUBF bermudagrass had the same fingerprint as ‘Astro-DLM’ bermudagrass for 14 out of 16 SSRs genotyped. Fifteen out of 30 additional SSR markers also showed differences between the OSUBF bermudagrass and ‘Astro-DLM’. The three OSU experimental clones were different from each other and had different fingerprints from the other tested varieties based on SSR profiles, indicating they are new breeding lines. These four distinct lines have potential to be released as new varieties if they demonstrate superior turf quality traits and adaptation over time.

Suitable tensile strength is essential for sod harvest, transport, and installation. Thirty-nine bermudagrass (Cynodon sp.) entries were evaluated for sod handling quality (SHQ) and sod tensile strength (STS) during 2014–15. The SHQ (a discontinuous qualitative parameter) was evaluated using a 1 to 5 scale with 1 = complete pad separation during handling and 5 = no cracking or separation in the sod pad with excellent quality. The STS (a quantitative parameter) was determined using the force required to shear/separate the sod pad. Sod harvests were conducted at 14, 22, and 24 months after planting (MAP). The entry, harvest date, and their interaction affected STS and SHQ. Entries OKC 1302 and 12-TSB-1 had greater STS than ‘Patriot’ but less STS than ‘Latitude 36’, ‘Tifway’, ‘Astro’, and ‘TifGrand’. The seeded entry PST-R6T9S had the lowest STS and SHQ. The overall mean STS and SHQ were lowest at 22 MAP, which could be attributed to the slow recovery of the entries after Winter 2014. A strong positive correlation (r = 0.92) between STS and SHQ suggests that SHQ can be used as a rapid field method to estimate suitability for sod harvest. A predictive linear relationship between overall STS and overall SHQ (r ² = 0.85) found predicted STS values of 8.5, 22.6, 36.8, and 51.0 kg⋅dm^–2 for overall mean SHQ ratings of 2, 3, 4, and 5, respectively. The results of this work will help sod producers in cultivar selection and will aid breeders in making commercialization decisions.