Turfgrass Species Research Articles

Validating a practical methodology for thatch—mat—soil distinction in turfgrass soils

AbstractDiscerning thatch and mat in turfgrass soils is important in organic matter research and choosing the correct turfgrass maintenance actions to keep turfgrass healthy and optimize playability. However, determining boundaries of thatch and mat in practice is often experienced as difficult because of inherent ambiguity in terminology and diagnostic techniques. We described a practical method for the distinction of thatch, mat, and soil layers, being a combination of visually and manually observable characteristics. For two widely different turfgrass species, we analyzed total organic matter (TOM) and dry bulk density (ρd) in thin slices of 6 mm (between 0‐ and 10‐cm soil depth), resulting in clear patterns for both soil properties with increasing depth. Statistical analysis of TOM patterns resulted in similar boundary depths between calculated and observed layers, validating our practical method for the distinction of thatch, mat, and soil layers as a reliable method.

LpY3IP1 Enhances the drought and salt tolerance of perennial ryegrass by protecting the photosynthetic apparatus

Perennial ryegrass (Lolium perenne L.), one of the main turfgrass species widely planted, is often subjected to drought and salt stresses due to its perennial nature and worldwide distribution. However, the molecular mechanisms and key genes involved in the adaptation of perennial ryegrass to these environmental stresses are largely unknown. Ycf3-interacting protein 1 (Y3IP1), an auxiliary factor of photosystem I (PSI), has recently been shown to enhance stress tolerance. However, the detailed mechanisms through which Y3IP1 enhances stress resistance remain poorly understood. In this study, we discovered that LpY3IP1 in perennial ryegrass positively regulates the drought and salt tolerance by protecting the photosynthetic apparatus under adverse conditions. Seedlings overexpressing LpY3IP1 exhibited improved photosynthetic performance and survival rates under drought and salt stresses, whereas RNAi lines were more vulnerable. Under drought and salt stresses, overexpression lines maintained higher levels of PSI core subunits, while the RNAi mutants showed a reduction in these subunits. LpY3IP1 promoted cyclic electron flow (CEF) at PSI and inhibited the accumulation of ROS under stress. Chloroplasts in RNAi lines were more disorganized and degraded, exhibiting shrunken structures, low staining vesicles, protrusions, and more unstacked and swollen thylakoids under drought or salt treatment. Nevertheless, these changes were less pronounced in the overexpression lines. Therefore, our results reveal that LpY3IP1 enhances the drought and salt tolerance of perennial ryegrass by promoting CEF and mitigating oxidative damage to chloroplasts under stressful conditions.

Brown patch on tall fescue as influenced by nitrogen and fungicide applications

AbstractTall fescue (Festuca arundinacea Schreb.) is a cool‐season turfgrass species commonly used in the transition zone. Brown patch (Rhizoctonia solani Kuhn) can have a significant impact on quality of tall fescue between late spring and late summer and is impacted by management strategies including fertilization and fungicide use. The objective of this study was to evaluate the influence of four nitrogen (N) sources and two application rates (0, 74 kg ha−1 [low], or 220 kg ha−1 [high] annually) along with fungicide application (azoxystrobin applied or not applied) on tall fescue brown patch infection. Highest quality occurred when tall fescue received the highest level of N and fungicide treatment. If high levels of N were applied and no fungicide was used, quality was reduced significantly when brown patch was observed in tall fescue. For example, on July 21, 2023, when most intense brown patch occurred, tall fescue had variable brown patch levels: low N levels 2%–23% and high N levels 48%–66%. Across three rating dates in summer 2023, tall fescue receiving the low N level exhibited statistically similar brown patch among all N sources. Conversely, brown patch treated with high levels of N had lower brown patch in urea compared to humic‐coated urea and slow‐release N on at least one of the three dates. Applying N at a level of 220 kg ha−1 annually or higher can result in significant brown patch in some summers; lower N levels will reduce brown patch. Desiring high tall fescue quality requires the high N level and inclusion of preventive fungicide applications.

Impact of species selection on plant community, sod tensile strength, and translocation rooting of a pollinator‐garden sod

AbstractInterest in pollinator gardens is increasing to address pollinator decline. The establishment of perennial native plants often takes a few years and establishment projects are often lost to competition from unwanted weedy vegetation. Mature sod of pollinator‐serving, native plants that is free of weeds would be highly desirable to conventional turfgrass sod consumers, thus offering a new revenue stream for traditional sod producers. The objective of this study is to evaluate the influence of four foundational species treatments on 3‐year floral biodiversity of pollinator‐serving plants, sod tensile strength, and transplant rooting strength. Results suggest that polycultures of pollinator‐serving forbs can produce a marketable sod with sufficient tensile strength for lifting and translocating and sufficient ability to establish once relocated. Sod tensile strength, however, is insufficient for lifting when the plant community is not grown over plastic or does not contain a high‐shoot density or rhizomatous foundation species such as hard fescue (Festuca longifolia Thuill.) or common yarrow (Achillea millefolium L.). Unfortunately, adding hard fescue or common yarrow markedly reduces the Shannon diversity index and species richness. The force needed to lift transplanted sod after 3 months was 5553 to 6969 N m−2 regardless of foundation species treatment and was numerically higher than the force reported by previous researchers to lift sod of various turfgrass species. Collectively, the data suggest that the best balance between preserving floral biodiversity and maximizing sod handling integrity would be approached by establishing pollinator‐serving forbs alone or with a blend of native grasses over plastic.

Evaluating canopy morphology as predictive indicators of shade tolerance in three warm‐season turfgrass species

AbstractImproving shade tolerance is critical for development of new turfgrass cultivars in the United States. Comparing turfgrass coverage under reduced sun exposure is a popular and effective method for determining shade tolerance, but requires years to evaluate. The objectives were to (i) compare phenotypical differences of experimental genotypes and cultivars of bermudagrass (Cynodon spp.), St. Augustinegrass (Stenotaphrum secundatum), and zoysiagrass (Zoysia spp.) grown under 73% shade and (ii) identify whether genetic improvement for shade adaptation was made in these species. This 3‐year study conducted in Tifton, GA, found phenotypic differences among genotypes within species for turfgrass coverage when exposed to 73% shade. The experimental bermudagrass, 11‐T‐56, possessed the superior combination of high green turfgrass coverage, low canopy height, and season long dark green color under shade. Experimental genotypes in St. Augustinegrass exhibited genetic improvement compared to commercially available cultivars; however, these genotypes should be examined under more intense shade to elicit differences before further selection. Performance of experimental zoysiagrass genotypes from several turfgrass breeding programs did not indicate significant improvement in the shade persistence within Zoysia spp. There appears to be genetic differences in the speed at which newer zoysiagrasses can initially spread by rhizomes and stolons when grown under shade. Further research should be conducted to determine if juvenile growth is an indicator of shade tolerance under natural tree shade or structures. Overall, results indicated that canopy heights cannot be used to directly predict shade tolerance but can be used to identify turfgrasses with reduced mowing frequency requirements.

Influence of Controlled Condition Ice Encasement of Creeping Bentgrass and Annual Bluegrass on Plant Recovery, Gas Evolution, and Metabolites

Two cool-season putting green turfgrass species, annual bluegrass and creeping bentgrass, are differential in ice encasement tolerance. Physiological mechanisms associated with creeping bentgrass ice encasement tolerance and annual bluegrass susceptibility are not understood. The objectives were to evaluate oxygen, ethylene, and CO2 content within the upper soil space of the plants while frozen and immediately after ice melt after 0, 5, 10, 20, and 28 days of ice encasement (2.54 cm of ice) in growth chamber conditions. Following ice melt, plant samples were separated into leaf, crown, and root tissues and used to evaluate carbohydrate and amino acid content. Annual bluegrass exhibited higher damage (slower recovery rates) on most sampling days compared with creeping bentgrass. The organs that were most damaged and exhibited a differential principal component analysis snapshot, were the leaf and crown tissues. Creeping bentgrass may preserve leaf and crown tissues for postwinter recovery whereas significant metabolic changes occur in annual bluegrass leaves and crowns. Creeping bentgrass retained total amino acids in leaves following ice encasement whereas total leaf amino acid levels declined in annual bluegrass. Specific carbohydrates and amino acids such as the ability to maintain high levels of fructose, asparagine, and proline may be important indicators of the tolerance to ice encasement stress. On the basis of more prominent carbohydrate and amino acid loss in leaves and crowns and higher levels of CO2 evolution, annual bluegrass may exhibit a higher metabolism and/or tissue damage during ice encasement compared with creeping bentgrass, which could reduce spring recuperative potential.

Response of sod webworm Chrysoteuchia topiaria Zeller (Lepidoptera: Crambidae) to endophyte infection and mycotoxin profiles of cool‐season turfgrass species grown for seed in Oregon

AbstractThe subterranean sod webworm, also known as cranberry girdler (Chrysoteuchia topiaria), is one of the most damaging insect pests in cool‐season grass grown for seed crops in Oregon. Chemical control options are limited and require irrigation or rainfall for adequate insecticide incorporation to control C. topiaria larvae. Epichloë endophytes associated with cool‐season turfgrass species and their mycotoxin profiles are well‐documented in offering plant protection against invertebrates; these fungi may offer sustainable pest management tools. Our objectives were to characterize endophyte‐mediated resistance to C. topiaria in 19 commercially available cultivars of tall fescue, perennial ryegrass, and fine fescue grown for seed in Oregon. Endophyte status (presence and viability) of fungal endophytes and their mycotoxin profiles were measured using polymerase chain reaction, and liquid chromatography‐tandem mass spectrometry, respectively. No‐choice assays were conducted in the laboratory to measure the impact of endophyte status on C. topiaria larvae in two separate no‐choice experiments. Our results suggested that increased mortality of C. topiaria larvae (R2 = 0.8526, Experiment 1; R2 = 0.6628, Experiment 2) in tall fescue cultivars was most influenced by total peramine and ergot alkaloid, and total ergoline concentrations in Experiment 1 and 2, respectively. However, no significant effect on insect mortality was found in the perennial ryegrass and fine fescue cultivars included in this study. Overall, these findings suggest a viable grass–endophyte association can be utilized as a sustainable alternative to foliar insecticides for C. topiaria management in tall fescue seed crops.

Single-cell RNA-sequencing provides new insights into the cell-specific expression patterns and transcriptional regulation of photosynthetic genes in bermudagrass leaf blades

As an important warm-season turfgrass species, bermudagrass (Cynodon dactylon L.) flourishes in warm areas around the world due to the existence of the C4 photosynthetic pathway. However, how C4 photosynthesis operates in bermudagrass leaves is still poorly understood. In this study, we performed single-cell RNA-sequencing on 5296 cells from bermudagrass leaf blades. Eight cell clusters corresponding to mesophyll, bundle sheath, epidermis and vascular bundle cells were successfully identified using known cell marker genes. Expression profiling indicated that genes encoding NADP-dependent malic enzymes (NADP-MEs) were highly expressed in bundle sheath cells, whereas NAD-ME genes were weakly expressed in all cell types, suggesting C4 photosynthesis of bermudagrass leaf blades might be NADP-ME type rather than NAD-ME type. The results also indicated that starch synthesis-related genes showed preferential expression in bundle sheath cells, whereas starch degradation-related genes were highly expressed in mesophyll cells, which agrees with the observed accumulation of starch-filled chloroplasts in bundle sheath cells. Gene co-expression analysis further revealed that different families of transcription factors were co-expressed with multiple C4 photosynthesis-related genes, suggesting a complex transcription regulatory network of C4 photosynthesis might exist in bermudagrass leaf blades. These findings collectively provided new insights into the cell-specific expression patterns and transcriptional regulation of photosynthetic genes in bermudagrass.

Brown patch severity of five tall fescue cultivars as influenced by summer nitrogen rates

Turf-type tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.: TTTF] is a predominant turfgrass species for lawns throughout cool-humid regions, yet brown patch (caused by Rhizoctonia and Rhizoctonia-like species) can cause severe damage during the summer months. Hypothesized strategies to help minimize brown patch severity and decrease fungicide use includes establishing TTTFs with a high level of host resistance and minimizing summer nitrogen (N) applications. A two-year field study was conducted in West Lafayette, IN to determine the influence of late-spring and summer applied N at two application rates among five TTTF cultivars. Urea-N was applied monthly at two rates from April to July, totaling to 73.5 and 245.0 kg N ha−1. Turf performance was determined using visual ratings for turf quality, relative canopy greenness, disease severity (0–100%), and seasonal brown patch as calculated by area under the disease progress curve (AUDPC). Brown patch was generally not affected by N-rate for any cultivar in either study year. While none of the TTTF cultivars had complete brown patch resistance, cultivar differences were observed, with disease severity ranging from 9.8 to 39.0% and 20.0–51.9% in 2021 and 2022, respectively. Selecting a brown patch resistant cultivar reduced seasonal brown patch severity by 61% across study years compared to the most susceptible cultivars. This study demonstrates that summer N applications to TTTF lawns should not be completely avoided to reduce brown patch as previously suggested and emphasizes the importance of host resistance for disease management.

Comprehensive assessment of turfgrass wear tolerance: A study on mechanical and chemical traits

A key criterion in the selection process for turfgrass breeding is effective wear tolerance, indicating the plant's capacity to endure forces that may impact leaves, stems, crowns, and roots. In this study, the correlation between mechanical and chemical traits and the wear tolerance of 37 cultivars belonging to seven turfgrass species was examined. Mechanical properties and fiber characteristics of wide range of turfgrass cultivars were determined and compared for the first time. The evaluation of turf wear tolerance (described as turf cover index, TCI) was conducted through a three-year field trial using a Brinkman traffic simulator. Tensile tests were conducted to determine biomechanical parameters. According to the TCI, the most wear-resistant cultivars were those of Lolium perenne, Most of these cultivars demonstrated a TCI below 0.1. The cultivar 'Nira' was the most resistant, with a TCI of − 0.285. The least resilient cultivars belonged to Festuca ovina and Festuca rubra, all exhibiting TCI values above 0.6. Agrostis stolonifera and Agrostis capillaris were characterised by lower cellulose and acid detergent fiber content but high hemicellulose content. The opposite result was determined for Festuca rubra and Festuca ovina. The highest hemicellulose ratio was obtained for Poa pratensis. Lolium perenne was characterised by relatively high content of cellulose, lignin and hemicellulose. Cultivars of Festuca arundinace distinctly differed from other cultivars, demonstrating higher mechanical resistance with an average force-to-break of 3.73 N. Cultivars of Agrostis stolonifera and Agrostis capillaris reached force-to-break values up to 1.0 N. The relationships between TCI and fiber composition of turfgrass leaves were significant for crude fiber, NDF and hemicellulose content. Thus higher NDF and hemicellulose content resulted in higher force-to-break and work-to-break parameters.

Quality and Establishment of Some Water-Conserving Turfgrass Species for Sustainable Development and Some Ecosystem Services in Arid Urban Environments

Turfgrasses are essential landscape plants with social, environmental, and aesthetic services for urban ecosystems. However, more is needed to know how to establish them so that they can benefit from their ecosystem services in urban environments. This research examined some quality and morphological and physiological factors for the establishment and social and environmental service assessment of three warm-season turfgrasses, including Kikuyu grass (Pennisetum clandestinum), bermuda grass (Cynodon dactylon), and buffalo grass (Buchloe dactyloides), compared to the cool-season grass of tall fescue (Festuca arundinacea Schreb.). The experiment was split-plot in time, based on a randomized complete block design with eight replications. The main plot was the season with four levels, and the subplot was the four turfgrass species types. The results indicated that seasons and turfgrass types and their interaction significantly impacted most measured variables (p ≤ 0.01). Some quality measurements like turf density, color, texture, coverage, and quality after clipping and establishment confirmed the superiority of Buchloe dactyloides over the other species. Also, kikuyu grass showed higher turfgrass density, more potential for weed control, and higher coverage and growth rate but also showed invasiveness features. Tall fescue had the lowest visual aesthetic compared with the other turfgrass species. Warm-season turfgrasses adaptable to the ecology of the region should be used compared to tall fescue to achieve better turfgrass quality and social and ecosystem services for the sustainable development of arid urban environments.

Brown patch severity as affected by cool‐season turfgrass species, cultivar, and nitrogen rate

AbstractBrown patch (caused by various Rhizoctonia and Rhizoctonia‐like species) is a major summer disease for several cool‐season turfgrass species, including creeping bentgrass (CBG) (Agrostis stolonifera L.), colonial bentgrass (CLBG) (Agrostis capillaris L.), perennial ryegrass (PRG) (Lolium perenne L.), and turf‐type tall fescue (TTTF; [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]). Elevated nitrogen (N) rates are suggested to enhance development of brown patch symptoms. A controlled environment study was conducted to determine the influence of two N rates among four cool‐season turfgrass species maintained at 1.9 cm after inoculation with R. solani. Field‐grown plants of four CBG cultivars, a CLBG cultivar, a PRG blend, and two TTTF cultivars were fertilized weekly, totaling 49 and 196 kg N ha−1 across four applications. Turfgrass responses were measured as relative growth rate, brown patch severity, and seasonal brown patch using area under the disease progress curve (AUDPC). On average, peak brown patch severity among the species and cultivars was between 22.6% and 68.1% for Raptor III TTTF and Penn A‐1 CBG, respectively. Turf‐type tall fescue cultivars decreased brown patch by 61% compared to CBG, CLBG, and PRG. The lower N rate reduced brown patch AUDPC by 17% and 33% for CBG and PRG, respectively, but N rate generally had no effect for CLBG and TTTF. These results reinforce the importance of planting disease‐resistant species and cultivars. Additionally, N rate may be an important factor affecting brown patch severity for select intensively managed turfgrass species.

Genome-Wide Identification and Expression Analysis of the PUB Gene Family in Zoysia japonica under Salt Stress.

The U-box protein family of ubiquitin ligases is important in the biological processes of plant growth, development, and biotic and abiotic stress responses. Plants in the genus Zoysia are recognized as excellent warm-season turfgrass species with drought, wear and salt tolerance. In this study, we conducted the genome-wide identification of plant U-box (PUB) genes in Zoysia japonica based on U-box domain searching. In total, 71 ZjPUB genes were identified, and a protein tree was constructed of AtPUBs, OsPUBs, and ZjPUBs, clustered into five groups. The gene structures, characteristics, cis-elements and protein interaction prediction network were analyzed. There were mainly ABRE, ERE, MYB and MYC cis-elements distributed in the promoter regions of ZjPUBs. ZjPUBs were predicted to interact with PDR1 and EXO70B1, related to the abscisic acid signaling pathway. To better understand the roles of ZjPUBs under salt stress, the expression levels of 18 ZjPUBs under salt stress were detected using transcriptome data and qRT-PCR analysis, revealing that 16 ZjPUBs were upregulated in the roots under salt treatment. This indicates that ZjPUBs might participate in the Z. japonica salt stress response. This research provides insight into the Z. japonica PUB gene family and may support the genetic improvement in the molecular breeding of salt-tolerant zoysiagrass varieties.

Chromosome-scale genome assembly of Poa trivialis and population genomics reveal widespread gene flow in a cool-season grass seed production system.

Poa trivialis (L.) is a cool-season grass species found in various environments worldwide. In addition to being a desired turfgrass species, it is a common weed of agricultural systems and natural areas. As a weed, it is an important contaminant of commercial cool-season grass seed lots, resulting in widespread gene flow facilitated by human activities and causing significant economic losses to farmers. To better understand and manage infestations, we assembled and annotated a haploid genome of P. trivialis and studied troublesome field populations from Oregon, the largest cool-season grass seed producing region in the United States. The genome assembly resulted in 1.35 Gb of DNA sequence distributed among seven chromosome-scale scaffolds, revealing a high content of transposable elements, conserved synteny with Poa annua, and a close relationship with other C3 grasses. A reduced-representation sequencing analysis of field populations revealed limited genetic diversity and suggested potential gene flow and human-assisted dispersal in the region. The genetic resources and insights into P. trivialis provided by this study will improve weed management strategies and enable the development of molecular detection tests for contaminated seed lots to limit seed-mediated gene flow. These resources should also be beneficial for turfgrass breeders seeking to improve desirable traits of commercial P. trivialis varieties and help to guide breeding efforts in other crops to enhance the resiliency of agricultural ecosystems under climate change. Significance Statement: The chromosome-scale assembly of Poa trivialis and population genomic analyses provide crucial insights into the gene flow of weedy populations in agricultural systems and contribute a valuable genomic resource for the plant science community.

Confirmation and differential metabolism associated with quinclorac resistance in smooth crabgrass (Digitaria ischaemum)

AbstractQuinclorac controls crabgrass (Digitaria spp.) in cool- and warm-season turfgrass species. Herbicide-resistant smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] biotypes have evolved due to recurrent usage of quinclorac. Two Mississippi populations (MSU1 and MSU2) of D. ischaemum were characterized using standard greenhouse dose–response screens to assess their resistance relative to known susceptible populations. Subsequent investigations explored mechanisms of resistance, including examining cyanide accumulation, glutathione S-transferase (GST) activity, and the potential involvement of cytochrome P450s in MSU1, MSU2, and a susceptible (SMT2). Resistant populations MSU1 and MSU2 required 80 and 5 times more quinclorac, respectively, to reach 50% biomass reduction than susceptible populations. The SMT2 biotype accumulated three times more cyanide than the resistant MSU1 and MSU2 populations. GST activity was elevated in resistant MSU1 and MSU2 populations. Furthermore, quinclorac concentrations in treated resistant populations were elevated when plants were pretreated with the P450 inhibitor malathion. These findings suggest a non–target site based mechanism of resistance involving the accumulation of cyanide. This may provide a scientific basis for understanding the occurrence of quinclorac-resistant D. ischaemum, although further research is needed to investigate potential target-site mechanisms of resistance.

Nutrition of Florida lawns when summer fertilizer blackout period is enforced

AbstractIn Florida, multiple counties restrict the application of N to turfgrass and landscapes during the summer rainy season. These summer fertilizer blackout periods could impact turfgrass quality and the functionality of warm‐season turfgrass species. A 2‐year study was conducted at the University of Florida's Fort Lauderdale Research and Education Center (FLREC) and West Florida Research and Education Center (WFREC) to assess turfgrass performance of ‘Floratam’ and ‘Classic’ St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] as well as ‘Empire’ and ‘Palisades’ zoysiagrass (Zoysia japonica Steud.), respectively, receiving no N fertilization during summer blackout period using eight fertilization programs compared to an unfertilized control. Visual quality, normalized difference vegetation index, percentage green cover, and dark green color index were assessed biweekly. Roots were collected before and after the fertilizer blackout period to determine root dry weight. While no differences were detected in St. Augustinegrass at the FLREC and zoysiagrass at the WFREC, all fertilized treatments except urea reached and maintained an acceptable turfgrass quality (≥6) throughout the blackout period, suggesting that urea by itself was not sufficient to support an optimal turfgrass performance during a fertilizer blackout period. The addition of P to nutrition programs did not influence turfgrass quality. Results indicate that N source is the most important factor to sustain turfgrass quality year‐round in Florida.

Growth Suppression of Hybrid Bermudagrass with Imazapic

Imazapic is an acetolactate synthase-inhibiting herbicide labeled for weed control in pastures, rangeland, and noncrop areas. Field research was conducted in Knoxville, TN, USA, during 2020 and 2021 to evaluate the tolerance of four hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis Burtt Davy) cultivars to applications of imazapic for growth suppression. Separate experiments were conducted on ‘TifTuf’, ‘Tifway’, ‘Tahoma 31’, and ‘Latitude 36’ hybrid bermudagrass. Experiments included plots (1.5 m2) arranged in a randomized complete block design with four replications and were repeated. Treatments were applied 14 Aug 2020 and 6 Aug 2021, and were mixed with methylated seed oil. Imazapic rates were 0, 35, 52.5, 70, or 105 g⋅ha–1. Cultivar tolerance was assessed via visual ratings of turfgrass injury relative to untreated check plots. Normalized differential vegetation index data were collected on each date turfgrass injury was evaluated. Growth suppression was quantified via reductions in dry clipping weight after mowing. Hybrid bermudagrass injury increased with imazapic rate for all cultivars, and peak injury (> 30%) following all imazapic treatments occurred within 14 days. At the lowest imazapic rate (35 g⋅ha–1), injury was transient, with all hybrid bermudagrass cultivars fully recovered by 28 days. All rates of imazapic reduced hybrid bermudagrass dry clipping weight for 21 days for all cultivars. Further research is warranted to explore lower application rates than those tested in our study, in addition to determining tolerance and growth suppression of other turfgrass species commonly managed on golf courses.

Warm‐season turfgrass species genotype‐by‐environment interaction for turfgrass quality under drought

AbstractOne of the biggest challenges the turfgrass industry is currently facing is limitations of available water for irrigation of turfgrass areas. Efforts on breeding for drought resistance have increased over the past several years across the United States. Thus, the objectives of this study were to evaluate the performance of bermudagrass (Cynodon spp. Rich.), St. Augustinegrass (Stenotaphrum secundatum (Walter) Kuntze), seashore paspalum (Paspalum vaginatum Swartz) and zoysiagrass (Zoysia spp. Willd.) breeding lines from five different breeding programs under drought and estimate genetic parameters in order to increase selection efficiency for drought resistance improvement in these breeding programs. The germplasm sources were bermudagrass from Oklahoma State University and University of Georgia (UGA); St. Augustinegrass from North Carolina State University, Texas A&M University System (TAMUS) and University of Florida (UF); zoysiagrass from UF and TAMUS; seashore paspalum from UGA. Field trials were conducted from 2016 to 2019 at research facilities in Citra, FL and Dallas, TX. The response variables evaluated were per cent living ground cover (%GC), and turfgrass quality under normal or non‐drought (TQND) and drought conditions (TQD). The genetic variance was significant for TQND and TQD in bermudagrass, TQD in St. Augustinegrass and all traits in zoysiagrass. The heritability estimates were higher for TQD than for TQND in bermudagrass and St. Augustinegrass. Genetic correlation estimates showed that indirect selection can be effective to select drought‐resistant genotypes. Several genotypes performed better than all commercial cultivars in both St. Augustinegrass and zoysiagrass.

Overexpression of PvWAK3 from seashore paspalum increases salt tolerance in transgenic Arabidopsis via maintenance of ion and ROS homeostasis

Seashore paspalum (Paspalum vaginatum O. Swartz) is an important warm-season turfgrass species with extreme salt tolerance, but investigations on its salt tolerance mechanism are limited. A salt induced PvWAK3 from halophyte seashore paspalum was identified in this study. Overexpression of PvWAK3 in Arabidopsis led to increased salt tolerance. Transgenic plants had higher levels of seed germination rate, root length, number of lateral roots, shoot weight, survival rate, Fv/Fm, ETR, and NPQ compared with the wild type (WT) under salt stress. Na+ content was increased and K+ content was decreased after salinity treatment, with lower levels of Na+ and Na+/K+ ratio but higher level of K+ in transgenic plants than in WT under salt stress. The improved maintenance of Na+ and K+ homeostasis was associated with the higher transcript levels of K + -Uptake Permease 4 (KUP4), Potassium Transport 2/3 (AKT2), Salt Overly Sensitive 1 (SOS1) and High-Affinity K + Transporter 5 (HAK5) in transgenic plants compared with WT. Superoxide dismutase (SOD), catalase (CAT) and ascorbate-peroxidase (APX) activities, proline concentration, and P5CS1 transcript were increased after salinity treatment, with higher levels in transgenic lines compared with WT, which led to reduced accumulation of O2·− and H2O2 under salt stress. It is suggested that PvWAK3 regulates salt tolerance positively, which is associated with promoted Na+ and K+ homeostasis, activated antioxidant enzymes, and proline biosynthesis under salt stress.

Assessing the Impact of Water Conservation on Cooling Potential of Two Turfgrass Species

Highlights Empirical CWSI was developed for 'Westcoaster' tall fescue and ‘Tifgreen’ hybrid bermudagrass. The canopy temperature of both species was monitored under multiple irrigation scenarios. Deficit irrigation might reduce the cooling benefits of irrigated urban lawns. Abstract. Canopy temperature provides valuable information for efficient irrigation management and for detecting drought injury in a fast and non-destructive way. It also helps quantify the trade-offs between water conservation and the cooling benefit of the irrigated urban landscape, a critical issue in semiarid inland southern California with limited available water resources. Two adjacent hybrid bermudagrass and tall fescue irrigation trials were conducted to determine canopy temperature changes under a wide range of irrigation treatments from 2017 to 2019 in Riverside, California, USA. The canopy temperature data were also used to develop an empirical crop water stress index (CWSI) for each species. The CWSI values ranged from -0.15 to 0.71 for tall fescue and from -0.28 to 0.54 for hybrid bermudagrass. We observed a moderate correlation between visual rating scores (VR) and CWSI values for tall fescue (r = -0.68) and hybrid bermudagrass (r = -0.61). The fitted linear regression between VR and CWSI data suggested CWSI thresholds close to zero for both species to maintain their acceptable visual quality. The irrigation level consistently showed a significant effect on canopy temperature for both species. On average, a 10% decrease in irrigation application increased the canopy temperature of tall fescue and hybrid bermudagrass by 1.3°C and 0.9°C, respectively. Therefore, deficit irrigation might reduce the cooling benefits of irrigated urban lawns in the semiarid climate of inland southern California. Keywords: Canopy temperature, Evapotranspiration, Smart irrigation controller, Urban heat island, Urban irrigation, Water conservation.