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Zhiyong Wang, Paul Raymer and Zhenbang Chen

St. augustinegrass (Stenotaphrum sp.) is a warm-season perennial turfgrass that grows widely in tropical regions around the world. St. augustinegrass is valued for both its turf performance and high levels of resistance to biotic and abiotic stresses. The current study was aimed at developing nuclear microsatellite markers for st. augustinegrass. Pyrosequencing of an enriched microsatellite library on the Roche FLX platform using a 454 Titanium kit produced 57,306 sequence reads; 2614 of which contained short tandem repeats. One hundred primer pairs were tested with 18 accessions from the U.S. Department of Agriculture National Plant Germplasm System st. augustinegrass collection grown in Griffin, GA. This collection contains both Stenotaphrum dimidiatum and Stenotaphrum secundatum accessions. Among revealed 100 primer pairs, 33 were polymorphic. A total of 175 alleles were amplified. The number of observed alleles per primer pair ranged from two to 10, with an average of 5.3. Shannon’s information index and Nei’s genetic diversity values were 0.4403 and 0.2873, respectively. This set of microsatellite markers is useful for assessment of genetic diversity and construction of molecular genetic linkage maps in st. augustinegrass.

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Lusheng Zeng, Jiayang Liu, Robert N. Carrow, Paul L. Raymer and Qingguo Huang

Organic coatings on sand particles can cause soil water repellency (SWR) where a soil does not spontaneously wet; this leads to challenges in water management and crop production. In laboratory studies, we evaluated a novel approach using direct application of 10 enzymes at three (low, medium, high) dosages to remediate SWR on two sand turfgrass soils in a 3-day incubation study and a second study at high dosage with 1-day incubation. A soil:solution ratio of 1:1 (10 g soil and 10 mL solution) was used and a deionized water control included. For Soil 7, a very strongly hydrophobic soil from a localized dry spot turfgrass area with a water drop penetration time (WDPT) of 7440 seconds (untreated) and 332 to 338 seconds (water-treated), the high dosage rates of laccase, chitinase, and protease at 1 and 3 days incubation resulted in WDPT of less than 60 seconds (i.e., hydrophilic soil). Pectinase exhibited similar results only in the 3-day incubation study. On the strongly hydrophobic Soil 21 (WDPT of 655 seconds untreated; 94 to 133 water-treated) from the dry area of a fairy ring-affected area on a turfgrass site, high dosages of chitinase, laccase, pectinase, and protease reduced WDPT to less than 60 seconds in both studies; and medium dosage rates were also effective for all but protease in the 3-day incubation study. Each of the four most effective enzymes for reducing WDPT, noted previously, demonstrated a significant exponential or logarithmic relationship between decreasing WDPT and increasing enzyme dosage. Further studies in field situations will be required to determine enzyme effectiveness on SWR and water management.

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Sudeep S. Sidhu, Qingguo Huang, Robert N. Carrow and Paul L. Raymer

Accumulation of excessive organic matter as thatch restricts permeability of putting greens and is one of the most difficult problems in turfgrass management. A greenhouse experiment using potted bentgrass (Agrostis stolonifera L.) determined the efficacy of a ligninolytic enzyme, laccase, in reducing organic matter accumulation in the thatch-mat layer. Laccase was added biweekly at 0, 0.206, 2.06, and 20.6 units of activity/cm2 with and without guaiacol (2-methoxyphenol), a mediator of laccase, and sampling was performed after two and nine months. Parameters investigated included thickness of the organic layer, thatch layer and mat layer, organic matter content, saturated hydraulic conductivity, and lignin content. Organic matter and thatch layer increased between the two sampling dates in all treatments. Laccase was shown to be effective in slowing the rate of accumulation of organic matter and thatch layer. After two months, application of 20.6 units/cm2 of laccase reduced organic layer thickness by 8.7% and extractive-free total lignin content by 8.4% when compared with non-treated control. After nine months, laccase application rates of 2.06 units/cm2 reduced organic matter and thatch layer thickness by 15.6% and 45.0%, respectively, below levels observed in the non-treated control. Applications using 0.206 units/cm2 of laccase were ineffective. Laccase applications had no influence on turf quality. These positive responses suggest laccase treatments could be a non-disruptive option for thatch and/or mat control in bentgrass.

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Timothy L. Grey, David C. Bridges, Paul Raymer, Don Day and D. Scott NeSmith

Field studies were conducted to determine the tolerance of 11 sweet corn (Zea mays L.) cultivars to the herbicides nicosulfuron and primisulfuron. The su cultivar `Merit' was intolerant of nicosulfuron and primisulfuron, as indicated by significant differences from the untreated check for all measured variables. Most other su cultivars exhibited stunting, but injury was ≤19% (0% = no injury; 100% = dead) with nicosulfuron and primisulfuron in 1992. The se cultivars Alpine and Harris Moran Silverado exhibited variable stunting to nicosulfuron (25% and 23% injury, respectively) and primisulfuron (43% and 50%, respectively) in 1992. The sh2 cultivar Supersweet Jubilee was injured less by nicosulfuron (16%) than by primisulfuron (33%) in 1992. All cultivars except Merit recovered from early-season herbicide injury in 1992 and 1993. Significant differences among the se, su, and sh2 cultivars were recorded for the remaining variables (stalk height, marketable ear number and yield, ear length and diameter), but no patterns with respect to a specific sugary genetic background developed in 1992 or 1993. Nicosulfuron and primisulfuron were safely applied to the cultivars Alpine, Harris Moran Silverado, Royal Gold, Seneca Chief, Calumet, Jubilee, and Supersweet Jubilee without reductions in fresh ear yield. Chemical names used: {2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide} (nicosulfuron); {methyl 2[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzonate} (primisulfuron).

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Sang In Shim, Jun-Cheol Moon, Cheol Seong Jang, Paul Raymer and Wook Kim

Germination of seashore paspalum (Paspalum vaginatum Swartz) is a critical factor influencing seedling establishment when seeded directly in fields. In this research, pregermination priming with osmotic solution was used to improve the germination percentage of seashore paspalum. The goal of this study was to develop techniques that improve the germination of a seashore paspalum cultivar (SeaSpray). Seeds were subjected to priming in petri dishes with solutions of KNO3 at 25 °C for 24, 48, and 72 h in growth chambers. Germination percentage differed by priming duration as well as concentration of priming media. Based on the germination percentage 14 days after imbibition, the most promising priming condition was the treatment with 0.2% or 0.5% KNO3 for 72 h at a constant temperature of 30 °C and 0.2% or 0.5% KNO3 for 48 to 72 h at alternating temperature of 25/35 °C. Both concentrations showed reasonable germination percentage greater than 85% at alternating temperature condition. Priming with KNO3 solution for 48 to 72 h improved not only germination percentage, but also uniformity. The increased duration of priming with KNO3 was positively correlated with an improved germination percentage. The effect of increasing concentration was the most apparent at a constant temperature (30 °C) regime with the treatment of 0.2% KNO3 priming. Germination percentage was increased from 34.3% to 68.0% 2 weeks after imbibition (WAI) as the priming duration was increased from 24 to 72 h. Priming with KNO3 for 3 days also had a modest effect on germination percentage (greater than 74.7%) at 1 WAI. Therefore, priming with 0.2% or 0.5% solution of KNO3 for 72 h is a recommended method that can be practically applied for increasing germination of paspalum under an alternating temperature (25/35 °C) condition. The regression analysis between odds of germination percentage and germination time showed that priming treatment increased internal activities during the second stage of seed germination.

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Sudeep S. Sidhu, Qingguo Huang, Robert N. Carrow and Paul L. Raymer

Organic layer formation in the form of thatch is a major problem in managed turfgrass systems. Biweekly application of laccase enzyme has been well-documented to facilitate the degradation of thatch and reduce the accumulation rate of organic matter in ‘Crenshaw’ creeping bentgrass (Agrostis stolonifera L.). A field experiment involving creeping bentgrass was conducted to evaluate the residual effects on thatch accumulation after ceasing laccase applications. A significant reduction in thatch layer thickness was observed at 6, 12, and 18 months after treatment initiation when laccase was applied at different rates and frequencies. Residual effects of laccase application were observed for thatch layer thickness, but no additional accumulation of thatch was observed 6 months after treatment cessation. At 18 months after treatment initiation, a significant increase in the thatch layer was observed where treatments had been ceased for 12 months, but no thatch accumulation was observed for laccase treatment for a second 6-month period during the second year. This information is critical to turf practitioners when developing laccase application protocols. Limiting laccase applications for a period of 6 months during 1 year was shown to be effective for thatch control.

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Manuel Chavarria, Benjamin Wherley, James Thomas, Ambika Chandra and Paul Raymer

As population growth places greater pressures on potable water supplies, nonpotable recycled irrigation water is becoming widely used on turfgrass areas including golf courses, sports fields, parks, and lawns. Nonpotable recycled waters often have elevated salinity levels, and therefore turfgrasses must, increasingly, have good salinity tolerance to persist in these environments. This greenhouse study evaluated 10 commonly used cultivars representing warm-season turfgrass species of bermudagrass (Cynodon spp.), zoysiagrass (Zoysia spp.), st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and seashore paspalum (Paspalum vaginatum Swartz) for their comparative salinity tolerance at electrical conductivity (EC) levels of 2.5 (control), 15, 30, and 45 dS·m–1. Salinity treatments were imposed on the grasses for 10 weeks via subirrigation, followed by a 4-week freshwater recovery period. Attributes, including turf quality, the normalized difference vegetation index (NDVI), canopy firing, and shoot biomass reductions were evaluated before and after salinity stress, as well as after the 4-week freshwater recovery period. Results showed considerable differences in salinity tolerance among the cultivars and species used, with the greatest tolerance to elevated salinity noted within seashore paspalum cultivars and Celebration® bermudagrass. In comparison with growth in 2.5-dS·m–1 control conditions, increased shoot growth and turf quality were noted for many bermudagrass and seashore paspalum cultivars at 15 dS·m–1. However, st. augustinegrass and some zoysiagrass cultivars responded to elevated salinity with decreased growth and turf quality. No cultivars that had been exposed to 30- or 45-dS·m–1 salinity recovered to acceptable levels, although bermudagrass and seashore paspalum recovered to acceptable levels after exposure to 15-dS·m–1 salinity. More severe salinity stress was noted during year 2, which coincided with greater greenhouse temperatures relative to year 1.

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Brian M. Schwartz, Ryan N. Contreras, Karen R. Harris-Shultz, Douglas L. Heckart, Jason B. Peake and Paul L. Raymer

Seashore paspalum is a salt tolerant, predominately diploid (2n = 2x = 20) species that is well adapted to coastal regions in tropical and subtropical environments. Because a majority of the available cultivars are propagated vegetatively and most genotypes are cross-fertile, a sterile cultivar that does not produce segregating seedlings would benefit sod growers and turfgrass managers who demand uniformity for certification and performance. Therefore, an experiment was conducted to create a colchicine-induced polyploid seashore paspalum. One triploid (2n = 3x = 30) genotype (11-TSP-1) was identified and remains stable. Although there is a possibility that this event was triggered by the colchicine treatment, a more likely explanation is that it resulted from the union of a reduced and an unreduced gamete. Pollen shed was observed from 11-TSP-1 in 2011, but individual pollen grains stained with iodine–potassium iodide were irregularly shaped and typically had lower starch content than pollen from several diploid cultivars. The leaf width of 11-TSP-1 was statistically equal to that of the seashore paspalum cultivar SeaStar, indicating its potential for use as a fine turf. 11-TSP-1 had both superior visual color and a dark green color index when compared with ‘SeaStar’. Future study of the reproductive fertility and more extensive field testing of this genotype should be carried out to determine its turfgrass potential. Chemical names used: 4′, 6-diamidino-2-phenylindole (DAPI), dimethyl sulfoxide (DMSO), iodine-potassium iodide (I2-KI), propidium iodide (PI).

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Clinton J. Steketee, Alfredo D. Martinez-Espinoza, Karen R. Harris-Shultz, Gerald M. Henry and Paul L. Raymer

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.

Open access

Brian M. Schwartz, Wayne W. Hanna, Lisa L. Baxter, Paul L. Raymer, F. Clint Waltz, Alec R. Kowalewski, Ambika Chandra, A. Dennis Genovesi, Benjamin G. Wherley, Grady L. Miller, Susana R. Milla-Lewis, William C. Reynolds, Yanqi Wu, Dennis L. Martin, Justin Q. Moss, Michael P. Kenna, J. Bryan Unruh, Kevin E. Kenworthy, Jing Zhang and Patricio R. Munoz