Warm-season Turfgrass Species Research Articles

Influence of traffic stress on warm season turfgrass species under simulated traffic

Traffic stress causes wear injury and soil compaction. Various anatomical and morphological plant characteristics have been suggested to correspond with turfgrass wear tolerance are well documented in cool season turfgrass but not much with warm season turfgrass. So in order to evaluate warm season turfgrass like cowgrass, Manilagrass and seashore paspalum grass were considered with two levels of traffic; No traffic (T0) and High traffic (T1). Results have shown that high traffic significantly reduced the performance of turfgrasses compared to no traffic. Manilagrass under high traffic recorded the lowest reduction in turf quality, turf cover (19.3% at 90 days after treatment), root length (2.5cm), root fresh (0.61 g) and dry weight (0.31 g), total chlorophyll (0.02 mg/g) and total non-structural carbohydrates content (2.7%) with reduced cellulose (29.27%), hemicelluloses (63.49%) and lignin (5.58%) content. Manilagrass exhibited considerably better performance among evaluated turfgrasses and scored first position in wear tolerance even with increased bulk density.

Effects of Salinity on Warm-season Turfgrass Species Collected in a Mediterranean Environment

Effects of Salinity on Warm-season Turfgrass Species Collected in a Mediterranean Environment

Efficient virus-induced gene silencing in Cynodon dactylon and Zoysia japonica using rice tungro bacilliform virus vectors

Cynodon dactylon and Zoysia japonica are two important warm-season turfgrass species with multiple utilizations. Genetic transformations of Cynodon dactylon and Zoysia japonica are extremely difficult, which severely restrict the gene functional studies and molecular breeding research of the two grasses. By contrast, virus-induced gene silencing (VIGS) presents an effective and rapid alternative method to create targeted gene knock-outs for gene functional studies in plants. In this study, we tested the efficiency of modified rice tungro bacilliform virus (RTBV) vector in silencing Cynodon dactylon and Zoysia japonica phytoene desaturase (PDS) gene through agroinfiltration. The agroinfiltrated leaves of two Cynodon dactylon and two Zoysia japonica cultivars all showed white streaks typical for PDS gene silencing at 21days post agroinfiltration. In Cynodon dactylon and Zoysia japonica plants displaying white streak leaf symptoms, PDS gene expression in leaves were all significantly lower than that of control and mock-infected plants. These results indicated that RTBV-VIGS system is efficient in Cynodon dactylon and Zoysia japonica.

Effects of Genotype and Isolate on Expression of Dollar Spot in Seashore Paspalum

Seashore paspalum (Paspalum vaginatum Swartz) is a warm-season turfgrass species primarily used on golf courses and athletic fields, and is often impacted by the disease dollar spot caused by Sclerotinia homoeocarpa F.T. Bennett. Dollar spot is the most common and economically important turfgrass disease in North America, and current management of this disease relies heavily on frequent fungicide applications. An alternate management strategy is host plant resistance, but a better understanding of the interactions between pathogen isolates and the host species is needed to effectively incorporate this resistance into elite seashore paspalum genotypes. The goal of this study was to gather host plant/isolate response data that could be used to develop an effective and efficient screening protocol for resistance to this important disease. Five genotypes of seashore paspalum (‘Aloha’, ‘SeaIsle 2000’, ‘SeaIsle 1’, ‘SeaIsle Supreme’, and 05-1743) varying in dollar spot resistance were inoculated with five isolates of S. homoeocarpa in repeated field studies during 2012 and 2013. Isolates used were from three warm-season and one cool-season turfgrass species. Inoculated plots were evaluated visually and using digital image analysis (DIA) for disease development over time and for number and area of infection centers at two rating dates each year. Statistical differences among the seashore paspalum genotypes and inoculation/isolate treatments were detected for area under the disease progress curve (AUDPC) values, number of infection centers, and infection center area. A significant interaction between seashore paspalum genotype and S. homoeocarpa isolate effects was not observed, indicating that host plant resistance genes are likely not isolate specific. Using this information, breeders should be able to use one highly virulent S. homoeocarpa isolate to screen for host plant resistance in seashore paspalum.

Gamma-ray Irradiation Induces Useful Morphological Variation in Bermudagrass

Bermudagrass, Cynodon dactylon (L.) Pers. is a widely used warm-season turfgrass species in warmer regions of the world. Gamma (ɣ) irradiation has been used to generate useful variations in turfgrass breeding for various morphological traits. The objective of the present study was to measure and determine variations in morphology and turfgrass characteristics of a native drought resistant bermudagrass germplasm irradiated with 70, 90 or 110 Gy using a 60Co source. The stolons containing a single node were irradiated and immediately planted for regeneration in a greenhouse at the Akdeniz University, Antalya, Turkey. Selected mutants regenerated from the irradiated stolons were clonally propagated and transplanted into plastic pots for further observations of turfgrass characteristics. Survival rates of stolons exposed to 70, 90 and 110 Gy were 76%, 43% and 17% respectively, 6 weeks after treatment. Dosages of 85 and 57 Gy were determined as LD50 and LD20 for the cuttings, respectively. The linear reduction of survival rate with increasing gamma-rays was highly correlated (r2=0.99). A total of four mutant lines (0.3 % of the irradiated plants) showed a distinct dwarfed growth habit. Three of these lines were originated from 70 Gy and one from 110 Gy. These mutant lines exhibited more dwarf growth habit, higher shoot density, finer leaf texture than parental genotype. Mutant lines developed in this study can be used for the development of improved bermudagrass cultivars for landscaping and sports turf.

Doveweed (Murdannia nudiflora) Control in Warm-Season Turfgrass Species

Doveweed is an aggressive, naturalized summer annual weed that rapidly invades warm-season turfgrass species, especially in residential lawns, and few herbicides can effectively control it. Because of these challenges, a well-designed management strategy is necessary for doveweed control. This 4-page fact sheet describes identification, growth requirements, chemical control and cultural practices. Written by Ramon G. Leon and Bryan Unruh, and published by the UF Department of Agronomy, June 2015.

Cold Acclimation Treatment–induced Changes in Abscisic Acid, Cytokinin, and Antioxidant Metabolism in Zoysiagrass (Zoysia japonica)

Zoysiagrass (Zoysia spp.), a warm-season turfgrass species, experiences freezing damage in many regions. The mechanisms of its cold acclimation and freezing tolerance have not been well understood. This study was designed to investigate effects of cold acclimation treatment on leaf abscisic acid (ABA), cytokinin (transzeatin riboside (t-ZR), and antioxidant metabolism associated with freezing tolerance in zoysiagrass (Zoysia japonica). ‘Chinese Common’ zoysiagrass was subjected to either cold acclimation treatment with temperature at 8/2 °C (day/night) and a photosynthetically active radiation (PAR) of 250 µmol·m−2·s−1 over a 10-hour photoperiod or normal environments (temperature at 28/24 °C (day/night), PAR at 400 µmol·m−2·s−1 and 14-hour photoperiod) for 21 days in growth chambers. Cold treatment caused cell membrane injury as indicated by increased leaf cell membrane electrolyte leakage (EL) and malondialdehyde (MDA) content after 7 days of cold treatment. Cold treatment increased leaf ABA and hydrogen peroxide content and reduced t-ZR content. Leaf superoxide dismutase (SOD), ascorbate peroxidase (APX) activity, and proline content increased, whereas catalase (CAT) and peroxidase (POD) activity declined in response to cold treatment. Cold treatment increased freezing tolerance as LT50 declined from −4.8 to −12.5 °C. The results of this study indicated that cold acclimation treatment might result in increases in ABA and H2O2, which induce antioxidant metabolism responses and improved freezing tolerance in zoysiagrass.

Consumptive water use and crop coefficients for warm-season turfgrass species in the Southeastern United States

Increased urban demand for landscape irrigation, as well as interest in promoting water-use efficient species by municipalities, water purveyors, and homeowners associations emphasize the need for comparative data on consumptive water use by warm-season lawn grasses. The objective of this study was to quantify actual evapotranspiration (ETa) and to develop crop coefficients (Kc) for four warm-season turfgrass species, namely ‘Tifway’ bermudagrass (Cynodon dactylon (L.) Pers. x Cynodon transvaalensis Burtt-Davy), ‘Empire’ zoysiagrass (Zoysia japonica Steud.), ‘Floratam’ St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze], and ‘Argentine’ bahiagrass (Paspalum notatum Flugge). Crop coefficients were derived by dividing ETa (measured directly from lysimeter weight change over 24 to 72-h periods) by reference evapotranspiration (ETo) calculated from the ASCE–EWRI Standardized Method using onsite weather station data. Data were collected over three seasons from non-stressed, well-watered turf. For 17 of the 30 measurement periods, Kc did not differ among the 4 species, and on 24 of 30 periods zoysiagrass, bermudagrass, and St. Augustinegrass Kc did not differ from one another. A trend toward elevated Kc was observed in bahiagrass in years 2 and 3, particularly during early spring measurement periods. Kc values for all species fluctuated across seasons and years, peaking to ∼0.8 during active growth periods when vapor pressure deficit and solar radiation were greatest, and declining to ∼0.3 in late fall and winter. Root growth differences among the species appeared to have a stronger relationship to ET rates than did shoot growth rate. Results demonstrated that the commonly recommended warm-season turf coefficient of 0.6, while approximating overall average annual ETa, under-predicted ETa during active growth periods and over-predicted ETa during late fall and winter periods, when turf was slowly growing or quiescent. The results indicate seasonal refinement of Kc values may be needed to more effectively meet consumptive water use requirements of warm-season turfgrasses.

Performance of warm-season turfgrasses in an area of central Italy

Traditionally, in Italy, the C3 cool-season grasses have been the dominant species used for turfs, even though they do not appear to be the most suitable for the Mediterranean climate. However, recent limited water availability and the need to reduce energy inputs have placed drought tolerant warm-season turfgrasses under the spotlight. These species combine aesthetics with performance advantages in terms of water consumption, and with regard to the reduction of fertilizer and pesticides use. The present research was aimed to test the performance of warm-season turfgrass species (three cultivars of Cynodon dactylon, two cultivars of Paspalum vaginatum and two of Zoysia japonica) in a climatic transition zone in Tuscany, to evaluate their potential for use in this environment. The assessment of several parameters, which were estimated periodically, permitted performance evaluation of each species/cultivar, thereby enhancing the existing knowledge of these species and their potentiality in this environment. Results showed that the species with the best adaptation to the environment was Cynodon dactylon, which had higher performances compared to the other species. Paspalum vaginatum reported good quality in terms of color and density, but was damaged by low temperatures during winter. Zoysia japonica displayed a poor performance during the first year, but quality increased during the second year, yielding satisfactory results.

Ground level air convection produces frost damage patterns in turfgrass.

Frost injury patterns are commonly observed on the warm-season turfgrass species bermudagrass (Cynodon species Rich.), zoysiagrass (Zoysia species Willd.), and buffalograss [Bouteloua dactyloides (Nutt.) J.T. Columbus] in cool-temperate and subtropical zones. Qualitative observations of these injury patterns are presented and discussed. A model for the formation of such patterns based on thermal instability and convection of air is presented. The characteristic length scale of the observed frost pattern injury requires a temperature profile that decreases with height from the soil to the turfgrass canopy surface followed by an increase in temperature with height above the turfgrass canopy. This is justified by extending the earth temperature theory to include a turf layer with atmosphere above it. Then the theory for a thermally unstable layer beneath a stable region by Ogura and Kondo is adapted to a turf layer to include different parameter values for pure air, as well as for turf, which is treated as a porous medium. The earlier porous medium model of Thompson and Daniels proposed to explain frost injury patterns is modified to give reasonable agreement with observed patterns.

Growth and Enzymatic Activity of Four Warm-season Turfgrass Species Exposed to Waterlogging

Waterlogging (WL) negatively affects plant growth and development, but the physiological responses of turfgrass species to WL are not well understood. The objective of this study was to examine growth and physiological mechanisms of WL tolerance in warm-season turfgrass species. Knotgrass (Paspalum paspaloides), spiny mudgrass (Pseudoraphis spinescens), seashore paspalum (Paspalum vaginatum), and centipedegrass (Eremochloa ophiuroides) were subjected to 30 days of WL. At the end of the treatment, knotgrass and spiny mudgrass maintained the shoot and root biomass while seashore paspalum and centipedegrass showed reductions in biomass under WL. Root oxidase activity (ROA) was unaffected until after 12 or 18 days of WL but decreased by 14.3%, 17.8%, 32.0%, and 68.7% at 30 days of WL for knotgrass, spiny mudgrass, seashore paspalum, and centipedegrass, respectively. Waterlogging increased root activities of lactate dehydrogenase and alcohol dehydrogenase, but generally to a lesser extent in knotgrass and spiny mudgrass. The leaf and root activities of superoxide dismutase (SOD) and peroxidase (POD) were induced after 6 or 12 days of WL, but to a greater extent for knotgrass and spiny mudgrass. At 30 days of WL, the increased leaf and root activities of SOD and POD were higher in knotgrass and spiny mudgrass than that of seashore paspalum and centipedegrass; while centipedegrass showed 37.8% reduction in root SOD activity. The total soluble protein (TSP) concentration remained unchanged in both leaves and roots during the entire WL treatment for knotgrass, while a decreased leaf TSP was found in the other three species after 12 or 24 days of WL as well as in the roots of seashore paspalum and centipedegrass. More reductions in leaf or root TSP were observed in seashore paspalum and centipedegrass than in knotgrass and spiny mudgrass at 30 days of WL. The results indicated that higher ROA, activities of antioxidant enzymes and TSP contributed to WL tolerance of warm-season turfgrass species.

Weed control spectrum and turfgrass tolerance to bioherbicide Phoma macrostoma

Phoma macrostoma is a bioherbicide being developed for selective weed control in turfgrass. The previous research with this product is limited to cool-season turfgrass systems with little information available on appropriate application rates or weed control spectrum for weeds common to warm-season turf. Studies were conducted to evaluate application rates and weed control spectrum of P. macrostoma on common dandelion (Taraxacum officinale G.H. Weber ex Wigg.), slender aster (Aster subulatus var. ligulatus Shinners), common mallow (Malva neglecta Wallr.), common purslane (Portulaca oleracea L.), California burclover (Medicago polymorpha L.), and annual sow thistle (Sonchus oleraceus L.). Although most weeds exhibited susceptibility to P. macrostoma, control differed by weed species and study. P. macrostoma had the greatest efficacy on dandelion, but provided little efficacy on common purslane and common mallow. Warm-season turfgrass tolerance was also evaluated across five commonly used warm-season turfgrass species. No turfgrass injury was observed at any rate on any species; however, weed control data suggest that P. macrostoma may not offer effective broad-spectrum weed control similar to common synthetic herbicides, when applied at the rates used in this study.

Warm-season Turfgrass Species Generate Sports Surfaces with Different Playability

Synthetic sports surfaces are increasingly subject to standardization of athlete-surface and ball-surface interactions (playability parameters). Such standardizations have led to an increase in the level of the engineering and predictability of these surfaces, and as such may be beneficial also for natural turf. In warm and temperate climates, many natural turf sports surfaces are established with warm-season (C4) turfgrass species due to their suitability to the environment in such areas. This study was aimed at evaluating the Féderation Internationale de Football Association (FIFA)-standard playing characteristics of different sports turf surfaces obtained from three commonly used C4 turfgrass species: 1) ‘Tifway 419’ hybrid bermudagrass (Cynodon dactylon var. dactylon × C. transvaalensis), 2) ‘Zeon’ manilagrass (Zoysia matrella), and 3) ‘Salam’ seashore paspalum (Paspalum vaginatum) for factors concerning leaf tissue (silica, lignin, water content) and canopy structure (shoot density, leaf architecture, stolon density, etc.). Results showed that surfaces of different C4 turfgrass species generate different playability parameters, with seashore paspalum being a harder faster surface, manilagrass being a softer slower surface, and hybrid bermudagrass showing intermediate characteristics. These playing quality results were associated with certain specific canopy biometrical/morphological parameters such as shoot density, horizontal stem density (HSD), leaf section, and, to a lesser extent, to certain plant tissue compounds (lignin, silica).

Development and characterization of genomic SSR markers in Cynodon transvaalensis Burtt-Davy

Simple sequence repeat (SSR) markers are a major molecular tool for genetic and genomic research that have been extensively developed and used in major crops. However, few are available in African bermudagrass (Cynodon transvaalensis Burtt-Davy), an economically important warm-season turfgrass species. African bermudagrass is mainly used for hybridizations with common bermudagrass [C. dactylon var. dactylon (L.) Pers.] in the development of superior interspecific hybrid turfgrass cultivars. Accordingly, the major objective of this study was to develop and characterize a large set of SSR markers. Genomic DNA of C. transvaalensis '4200TN 24-2' from an Oklahoma State University (OSU) turf nursery was extracted for construction of four SSR genomic libraries enriched with [CA](n), [GA](n), [AAG](n), and [AAT](n) as core repeat motifs. A total of 3,064 clones were sequenced at the OSU core facility. The sequences were categorized into singletons and contiguous sequences to exclude redundancy. From the two sequence categories, 1,795 SSR loci were identified. After excluding duplicate SSRs by comparison with previously developed SSR markers using a nucleotide basic local alignment tool, 1,426 unique primer pairs (PPs) were designed. Out of the 1,426 designed PPs, 981 (68.8 %) amplified alleles of the expected size in the donor DNA. Polymorphisms of the SSR PPs tested in eight C. transvaalensis plants were 93 % polymorphic with 544 markers effective in all genotypes. Inheritance of the SSRs was examined in six F(1) progeny of African parents 'T577' × 'Uganda', indicating 917 markers amplified heritable alleles. The SSR markers developed in the study are the first large set of co-dominant markers in African bermudagrass and should be highly valuable for molecular and traditional breeding research.

Comparative analyses of physiological responses of Cynodon dactylon accessions from Southwest China to sulfur dioxide toxicity.

Sulfur dioxide (SO2), a major air pollutant in developing countries, is highly toxic to plants. To achieve better air quality and landscape, planting appropriate grass species in severe SO2 polluted areas is very critical. Cynodon dactylon, a widely used warm season turfgrass species, has good SO2-tolerant ability. In this study, we selected 9 out of 38 C. dactylon accessions from Southwest China as representatives of high, intermediate SO2-tolerant and SO2-sensitive accessions to comparatively analyze their physiological differences in leaves under SO2 untreated and treated conditions. Our results revealed that SO2-tolerant C. dactylon accessions showed higher soluble sugar, proline, and chlorophyll a contents under both SO2 treated and untreated conditions; higher chlorophyll b and carotenoid under SO2 treated condition; lower reactive oxygen species (ROS) level, oxidative damages, and superoxide dismutase (SOD) activities under SO2 treated condition; and higher peroxidase (POD) activities under SO2 untreated condition. Further results indicated that SO2-tolerant C. dactylon accessions had higher sulfur contents under both SO2 treated and untreated conditions, consistent with higher SO activities under both SO2 treated and untreated conditions, and higher SiR activities under SO2 treated condition. Taken together, our results indicated that SO2 tolerance of C. dactylon might be largely related to soluble sugar, proline and chlorophyll a contents, and SO enzyme activity.

Improving Cold Tolerance through In Vitro Selection for Somaclonal Variations in Seashore Paspalum

Cold stress is a major factor limiting the growth of warm-season turfgrass species. Cold tolerance in warm-season turfgrass species could be improved through in vitro selection for somaclonal variations. The objectives of this study were to establish an effective in vitro culture protocol for generating plants from calli using mature seeds of seashore paspalum (Paspalum vaginatum) and to determine whether in vitro cold selection of somaclonal variations would lead to improved cold tolerance in seashore paspalum. The optimal concentrations of supplemental compounds in the culture medium for callus induction, embryogenic callus formation, and plant regeneration were determined. The supplemental compounds included 2,4–dichlorophenoxy acetic acid (2,4-D), 6-benzylaminopurine (6-BA), kinetin (KT), naphthalene-1-acetic acid (NAA), CuSO4, and acidic hydrolysis casein (AHC). The highest rates of callus induction (97.50%), embryogenic callus formation (66.88%), and regeneration (55.94%) were obtained with the supplemental compounds of 3.0 mg·L−1 2,4-D and 10.0 mg·L−1 CuSO4 for callus induction; with 3.0 mg·L−1 2,4-D, 15 mg·L−1 CuSO4, and 1.0 g·L−1 AHC for embryogenic callus formation; and with 8.0 mg·L−1 6-BA, 0.2 mg·L−1 KT, 0.5 mg·L−1 NAA, and 10 mg·L−1 CuSO4 for plant regeneration. Embryogenic calli were subjected to 2 or 6 °C treatment for 90 days for in vitro cold selection of somaclonal variation. Plants regenerated from calli surviving cold treatment (cold-selected) for 45 or 60 days were then exposed to low temperatures [15/10 or 5/3 °C (day/night)]. Plant variants derived from cold-selected calli exhibited significant improvement in their tolerance to low temperature of either 15/10 or 5/3 °C (day/night), as manifested by higher turf quality, leaf chlorophyll content, and membrane stability as well as lower levels of lipid peroxidation compared with the control plants. This study demonstrated the feasibility of in vitro selection for cold tolerance in seashore paspalum. The cold-tolerant variants could be useful germplasm for breeding programs and further molecular characterization of cold tolerance mechanisms.

Strategies for Converting Tall Fescue to Warm-season Turf in a Mediterranean Climate

Replacing cool-season turf with more drought and heat tolerant warm-season turfgrass species is a viable water conservation strategy in climates where water resources and precipitation are limited. Field studies were conducted in Riverside and Irvine, CA, to investigate three methods (scalping, eradication with a nonselective herbicide, planting into existing turf) of converting an existing tall fescue (Festuca arundinacea) sward to warm-season turf. Cultivars established vegetatively by plugging were ‘De Anza’ hybrid zoysiagrass [Zoysia matrella × (Z. japonica × Z. tenuifolia)], ‘Palmetto’ st. augustinegrass (Stenotaphrum secundatum), ‘Tifsport’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis), ‘Sea Spray’ seashore paspalum (Paspalum vaginatum), and ‘UC Verde’ buffalograss (Buchloe dactyloides). Cultivars established from seeds were ‘Princess-77’ bermudagrass (C. dactylon) and ‘Sea Spray’ seashore paspalum. Neither scalping nor planting into existing tall fescue were effective conversion strategies, as none of the warm-season turfgrasses reached 50% groundcover within 1 year of planting. All of the species except for st. augustinegrass reached a higher percentage of groundcover at the end of the study when glyphosate herbicide was applied to tall fescue before propagation compared with the other conversion strategies. Bermudagrass and seashore paspalum established from seeds and hybrid bermudagrass from plugs provided the best overall establishment with 97%, 93%, and 85% groundcover, respectively, when glyphosate was used before establishment. Quality of seeded cultivars matched or exceeded that of cultivars established vegetatively by plugging. These results suggest that eradication of tall fescue turf followed by establishment of warm-season turf from seeds is the best and easiest turf conversion strategy.

Lateral Spread of Three Warm-season Turfgrass Species as Affected by Prior Summer Water Stress at Two Root Zone Depths

As a result of increasing demand for potable water, local and national initiatives to conserve municipal water supplies have been implemented. Many of these initiatives focus on reducing irrigation of turfgrass in urban landscapes and may totally ban irrigation during periods of severe water shortage. Proper selection of adapted turfgrass species and cultivars is vital to long-term water conservation initiatives. Turfgrasses that can survive and recover from extended hot and dry periods under limited to no irrigation would best meet water conservation objectives. The present study was conducted to evaluate the recuperative potential of transplanted plugs of 24 commonly grown cultivars of three warm-season turfgrass species after incremental increases in water stress imposed by withholding all water for up to 60 days. A 2-year field study was conducted consisting of eight blocks containing 25 plots each. Each block was planted with one plot each of eight cultivars of bermudagrass (Cynodon dactylon sp.), seven cultivars of st. augustinegrass (Stenotaphrum secundatum sp.), and nine cultivars of zoysiagrass (five of Zoysia japonica sp. and four of Zoysia matrella sp.). Four blocks were planted on native soil with no restriction to rooting, whereas the other four had an effective root zone of only 10 cm of soil. Cup cutter plugs were collected at predetermined intervals, transported to College Station, TX, replanted, and grown under well-watered conditions. Measurements of the lateral spread of the plugs were taken every 10 to 14 days for the first 60 to 70 days after planting (DAP). The lateral spread of plugs collected after 0 days of summer dry-down (DSD) was greatest for bermudagrass, intermediate for st. augustinegrass, and lowest for zoysiagrass. In most cases there were no consistent differences between cultivars within a species. All species grown on the 10-cm deep root zone were unable to survive the 60-day period without water and died within the first 40 days. For each species, lateral spread was increasingly delayed or reduced with increasing DSD. Although all three species grown on native soil were able to survive and recover from a 60-day period without water, the bermudagrass cultivars had the most rapid recovery rates measured as lateral spread of transplanted plugs.

Assessment of Molecular Variation within ‘Raleigh’ St. Augustinegrass using Amplified Fragment Length Polymorphism Markers

St. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a popular turfgrass in the southern United States as a result of its superior shade tolerance and relatively low input requirements. However, it is the least cold-tolerant of commonly used warm-season turfgrass species. ‘Raleigh’, released in 1980, has superior cold tolerance and is adapted and widely used in U.S. Department of Agriculture hardiness zones 8 to 9. More than 25 years after its release, ‘Raleigh’ is still the industry’s standard in terms of cold tolerance. However, the original foundation and breeder stock fields of the cultivar have been lost, placing the integrity of the cultivar at risk. The objectives of this study were to investigate whether current ‘Raleigh’ production fields across the southern United States are true to the original source. In this study, 15 amplified fragment length polymorphism (AFLP) primer combinations were used to assess levels of genetic variability among three original stocks of ‘Raleigh’ and 46 samples obtained from sod farms and universities in six states. Genetic similarities among the original stocks were Sij = 1, whereas similarities between this group and all other samples ranged from 0.24 to 1.0. Results based on cluster analysis, principal coordinate analysis, and analysis of molecular variance (AMOVA) revealed separation between original stocks of ‘Raleigh’ and some commercial samples. Results from this study offer further evidence that molecular markers provide a useful and powerful technique for identity preservation of clonally propagated cultivars and the detection of genetic variants in sod production fields and turfgrass breeding programs.

Identification of a New Waitea circinata Variety Causing Basal Leaf Blight of Seashore Paspalum.

Seashore paspalum (Paspalum vaginatum) is a saline-tolerant, warm-season turfgrass species popular for golf course use in tropical and subtropical climates. A new variety of Waitea circinata (proposed as W. circinata var. prodigus) is described as the causal agent of basal leaf blight, a novel disease of seashore paspalum. Foliar necrosis and canopy thinning of seashore paspalum were observed on three different golf course fairways in Florida over an 18-month period. Five isolates with profuse, pink to yellow mycelia and small, salmon-colored or yellow to light-brown sclerotia were cultured from diseased turf foliage. Isolates grew rapidly over a temperature range of 25 to 35°C and were initially identified as an uncharacterized variety of W. circinata. Internal transcribed spacer sequences of rDNA from the isolates were compared with sequences from previously described W. circinata varieties. The paspalum isolates formed a phylogenetic clade that was distinct from the other W. circinata varieties. Pathogenicity was confirmed on 'SeaDwarf' and 'SeaIsle Supreme' seashore paspalum, 'Penncross' creeping bentgrass (Agrostis stolonifera), 'Senesta' bermudagrass (Cynodon dactylon), and 'Dark Horse' roughstalk bluegrass (Poa trivialis). The geographical distribution and potential impact of basal leaf blight is unknown. However, the range of potential turfgrass hosts and environmental conditions conducive for disease development suggest that the pathogen may infect other species in addition to seashore paspalum.