Interspecific hybrids between texas bluegrass (Poa arachnifera Torr.) and kentucky bluegrass (Poa pratensis L.) are known to exhibit good heat tolerance, which has aided in their adaptation to the warmer climates of the southern United States, but their tolerance to shade has not been investigated. The objectives of this study were to 1) evaluate the growth responses of interspecific bluegrass hybrids (P. arachnifera × P. pratensis) in comparison with kentucky bluegrasses and a shade-tolerant cultivar of tall fescue (Festuca arundinacea Schreb.) under full sunlight and shaded environments, 2) identify optimum times to evaluate shade tolerance using the selected growth measurements, 3) calculate the minimum daily light requirements to retain acceptable turfgrass quality, and 4) determine if trinexapac-ethyl (TE) applications enhance hybrid bluegrass quality under shade. Two 10-week greenhouse experiments (late spring and early fall) were conducted in Dallas, TX. Within each of three light environments a randomized complete block design was used to accommodate three replications of eight genotypes treated with and without TE (0 or 0.228 kg·ha−1 a.i.). Turfgrass quality, leaf elongation rates, clipping dry weights, and percent green cover were measured. Meaningful comparisons were best during the late spring when daily light integrals (DLI) were optimum for healthy plant growth. Shade-tolerant hybrid bluegrasses (DALBG 1201 and TAES 5654) were identified using turfgrass quality and leaf elongation rates. These genotypes exhibited above-acceptable turfgrass quality in all environments, and a reduced leaf elongation rate similar to the tested dwarf-type tall fescue. DLI requirements of DALBG 1201 and TAES 5654 were ≤4 to achieve acceptable quality. TE applications generally did not improve turfgrass quality of genotypes, although leaf elongation rates were significantly reduced in all environments.
Meghyn Meeks, Ambika Chandra and Ben G. Wherley
Daniel Hargey, Benjamin Wherley, Andrew Malis, James Thomas and Ambika Chandra
During water conservation periods, municipal water purveyors often limit irrigation for established lawns to once every 7 to 14 days, although a 4- to 6-week variance to these restrictions is often permitted for turfgrass establishment. Therefore, establishment practices promoting rapid development of a deep and expansive root system during this time may support long-term success of the turf once irrigation is scaled back. Sod producers and turf managers could benefit from information on the influence of mowing practices and plant growth regulator (PGR) applications on turf root development during this initial establishment period. The objectives of this greenhouse study were to 1) evaluate the effects of mowing and trinexapac-ethyl (TE) application on final turf quality and root development characteristics (weight, total length, and extension rate) of st. augustinegrass (Stenotaphrum secundatum) sod during a 35-day establishment period, and 2) compare the quality and rooting potential of ‘TamStar’, a newly released, embryo-rescue-derived cultivar possessing good drought resistance, with ‘Floratam’, the current industry standard for drought resistance. Weekly mowing reduced both total (2.5 to 90 cm) and deep (45 to 90 cm) root weight and root length in both cultivars. TE had no effect on visual quality of ‘TamStar’, but decreased turf quality in ‘Floratam’. TE reduced clipping yields of both cultivars but did not improve root development for either cultivar. Depth of maximal root extension during establishment was unaffected by cultivar, mowing, or TE treatment. At the conclusion of the 35-day establishment period, ‘TamStar’ exhibited superior turf quality and root weight relative to ‘Floratam’, but also produced higher rates of shoot growth. Results emphasize the importance of withholding mowing during st. augustinegrass establishment, particularly for improving total root length and deep root production, and also show that TE does not improve root development of st. augustinegrass during establishment.
Ben Wherley, Ambika Chandra, Anthony Genovesi, Mason Kearns, Tim Pepper and Jim Thomas
St. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is considered to be one of the most shade-tolerant warm-season turfgrasses, yet information is lacking on intraspecies developmental responses and performance in shade. This greenhouse study was conducted to 1) compare quality, development, and physiological responses of 10 commercial and experimental lines of st. augustinegrass in moderate and heavy [32% and 15% photosynthetic photon flux (PPF), respectively] shade environments’ and 2) evaluate physiological and morphological indicators that could be used in rapid screening for shade tolerance among st. augustinegrass progeny from a segregating population. A range of shade tolerance was observed between the entries, as noted by quality and percent green cover after 10 weeks of imposed shade conditions. In moderate shade, most entries maintained acceptable (6 or greater) quality and greater than 50% green cover. However, in heavy shade, only ‘Captiva’, ‘Amerishade’, and ‘PI 600734’ maintained acceptable quality, with only PI 600734 and Captiva maintaining greater than 50% cover. ‘TAES 5732-6’, an embryo rescue-derived hybrid from ‘Floratam’, exhibited the least shade tolerance of the group in both shade environments. Neither chlorophyll content nor total nonstructural carbohydrates related well to observed shade quality differences between the entries. A strong correlation existed between shoot elongation rate of a cultivar and its corresponding final percent green cover in moderate shade (R 2 = 0.66) but not in heavy shade (R 2 = 0.19), suggesting that moderate shade may be the better environment for discriminating genetic differences among st. augustinegrass germplasm for shade tolerance.
David O. Okeyo, Jack D. Fry, Dale J. Bremer, Ambika Chandra, Dennis Genovesi and Milton C. Engelke
Zoysiagrass (Zoysia spp.) is recognized for its low requirements for pesticide and fertilizer input, but Meyer (Z. japonica Steud.), the cultivar commonly used in the transition zone of the United States, is slow to establish. We evaluated new zoysiagrass progeny for stolon growth characteristics and rate of establishment and determined the relationship between stolon growth characteristics and coverage. ‘Meyer’, DALZ 0102 (a Z. japonica), and 18 progeny from crosses of ‘Emerald’ (Z. japonica × Z. tenuifolia Willd. ex Thiele) or a Z. matrella (L.) Merr. × Z. japonica were planted as 6-cm diameter plugs on 30.5 × 30.5-cm centers in 1.5 × 1.5-m plots in 2007 and as single 10-cm diameter plugs in 1.2 × 1.2-m plots in 2008 in Manhattan, KS. Data were collected weekly on number of stolons initiated per plug, stolon elongation, and number of stolon branches. Two researchers rated coverage visually near the end of each growing season. Rate of stolon initiation ranged from 2.2/week to 8.6/week. Elongation rate ranged from 18.8 to 65.1 mm/week. At 11 weeks after planting in 2007, four of 18 progeny had superior coverage to ‘Meyer’; at 11 weeks after planting in 2008, 13 of 18 progeny had superior coverage to ‘Meyer’. Rate of stolon initiation was positively correlated (P < 0.01) with zoysiagrass coverage (r = 0.66, in 2007; r = 0.94 in 2008); likewise, stolon elongation was positively correlated with coverage in 2007 (r = 0.52, P < 0.01) and 2008 (r = 0.53, P < 0.05). Stolon initiation or elongation could be used in short-term evaluations to predict rate of zoysiagrass coverage from plugs. Greater stolon initiation or elongation of experimental some zoysiagrass progeny makes them promising for alternatives to ‘Meyer’ for overcoming slow establishment rates.
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.
David O. Okeyo, Jack D. Fry, Dale J. Bremer, Ambika Chandra, A. Dennis Genovesi and Milton C. Engelke
Zoysiagrass (Zoysia spp.) grown under shade on golf courses and in home lawns is slow to recover from damage and declines in quality over time. We evaluated stolon growth and tillering of ‘Meyer’ and Chinese Common (both Z. japonica Steud.); ‘Zorro’, ‘Diamond’, and ‘Cavalier’ [all Z. matrella L. (Merr.)]; ‘Emerald’ (Z. matrella × Z. pacifica Goudsw.); and six experimental progeny from ‘Emerald’ × Z. japonica and reciprocal crosses of Z. japonica × Z. matrella under silver maple (Acer saccharinum L.) shade and in full sun in 2008 and 2009 in Manhattan, KS. A single 6-cm diameter plug was planted in the center of 1.2 m × 1.2-m plots, and data were collected weekly on the number of stolons, stolon elongation, and number of stolon branches. Tiller number was collected at the start and end of each study period, and biomass (excluding roots) was determined at the end of each season. Zoysiagrasses under an average of 76% tree shade exhibited reductions of 38% to 95% in stolon number; 9% to 70% in stolon length; 10% to 93% in stolon branching; and 56% to 98% in biomass. Seven of the 10 grasses exhibited a decline in tiller number in each experiment; none of the grasses differed from ‘Meyer’ in percentage change in tiller number under shade. ‘Emerald’, ‘Cavalier’, ‘Zorro’, and several progeny from crosses between ‘Emerald’ × Z. japonica or reciprocal crosses of Z. matrella × Z. japonica produced more, longer, or more highly branched stolons than ‘Meyer’, suggesting they may have improved recovery potential in shade.
Jennifer A. Kimball, M. Carolina Zuleta, Matthew C. Martin, Kevin E. Kenworthy, Ambika Chandra and Susana R. Milla-Lewis
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.
Karen R. Harris-Shultz, Susana Milla-Lewis, Aaron J. Patton, Kevin Kenworthy, Ambika Chandra, F. Clint Waltz, George L. Hodnett and David M. Stelly
Zoysiagrass (Zoysia sp.) is used as a warm-season turfgrass for lawns, parks, and golf courses in the warm, humid and transitional climatic regions of the United States. Zoysiagrass is an allotetraploid species (2n = 4x = 40) and some cultivars are known to easily self- and cross-pollinate. Previous studies showed that genetic variability in the clonal cultivars Emerald and Diamond was likely the result of contamination (seed production or mechanical transfer) or mislabeling. To determine the extent of genetic variability of vegetatively propagated zoysiagrass cultivars, samples were collected from six commercially available zoysiagrass cultivars (Diamond, Emerald, Empire, JaMur, Meyer, Zeon) from five states (Arkansas, Florida, Georgia, North Carolina, Texas). Two of the newest cultivar releases (Geo and Atlantic) were to serve as outgroups. Where available, one sample from university research plots and two samples from sod farms were collected for each cultivar per state. Forty zoysiagrass simple sequence repeat (SSR) markers and flow cytometry were used to compare genetic and ploidy variation of each collected sample to a reference sample. Seventy-five samples were genotyped and an unweighted pair group method with arithmetic mean clustering revealed four groups. Group I (Z. japonica) included samples of ‘Meyer’ and Empire11 (‘Empire’ sample at location #11), Group II (Z. japonica × Z. pacifica) included samples of ‘Emerald’ and ‘Geo’, Group III (Z. matrella) included samples of ‘Diamond’ and ‘Zeon’, and Group IV (Z. japonica) consisted of samples from ‘Empire’, ‘JaMur’, ‘Atlantic’, and Meyer3 (‘Meyer’ at sample location #3). Samples of ‘Empire’, ‘Atlantic’, and ‘JaMur’ were indistinguishable with the markers used. Four samples were found to have alleles different from the respective reference cultivar, including two samples of ‘Meyer’, one sample of ‘Empire’, and one sample of ‘Emerald’. Three of these samples were from Texas and one of these samples was from Florida. Three of the four samples that were different from the reference cultivar were university samples. In addition, one sample, Empire11, was found to be an octoploid (2n = 8x = 80). For those samples that had a fingerprint different from the reference cultivar, contamination, selfing, and/or hybridization with other zoysiagrasses may have occurred.