Bentgrass Cultivars Research Articles

Reaction of Bentgrass Cultivars to a Resistance Activator and Elevated CO2 Levels When Challenged with Microdochium nivale, the Cause of Microdochium Patch

Climate change prediction models forecast increased CO2 levels and temperature changes. Microdochium nivale is a common pathogen of turfgrasses in temperate climates, and these changes may increase Microdochium patch disease severity. This research involved experiments on cultivars of Agrostis spp. and Poa annua inoculated with M. nivale and incubated under two CO2 concentrations. The efficacy of a resistance activator, Civitas + Harmonizer, was tested on eight cultivars that were grown under 400 or 800 ppm of CO2 during a 15°C/10°C (day/night), 16‐h photoperiod. The grasses were treated with water or Civitas + Harmonizer and inoculated 1 wk later with M. nivale. Disease severity was lower at 800 ppm than at 400 ppm of CO2, and the application of Civitas + Harmonizer decreased disease symptoms. This research will be useful for recommendations on turfgrass cultivars for northern temperate zone golf courses and on sustainable management practices to face the challenges of climate change.

Transgenic tobacco plants expressing grass AstEXPA1 gene show improved performance to several stresses

Expansins are cell wall-loosening proteins and now widely accepted to associate with the plant resistance against various abiotic stresses. In this study, we cloned an expansin gene of AstEXPA1 from Agrostis stolonifera, a heat-resistant creeping bentgrass cultivar, and transformed it into tobacco plants. Physiological index test showed that the transgenic lines were resistant to various abiotic stresses of drought, heat, cold, and salt in comparison to non-transgenic plants. Comprehensive analysis of four physiological response indices showed that the transgenic plants performed much better resistance to drought, following to heat, cold and salt stress, respectively. Meanwhile soluble sugar content displayed more weight to plant resistance by over-expressing AstEXPA1 gene, followed as proline content, REL, and MDA content. The results here would expand our understanding of the expansin roles and drive better insights into plant molecular breeding against stress.

Golf Ball Mark Severity and Recovery as Affected by Mowing Height, Rolling Frequency, Foot Traffic, and Moisture

Core Ideas Digital image analysis methods to evaluate putting green ball mark severity and recovery. Firmer surfaces from dry conditions or lightweight rolling increased maximum ball mark injury area. Rate of recovery was similar for all treatments, but increased wear increased time to 50% recovery. Demonstrates positive attributes of dispersing foot and equipment traffic throughout the green. Putting greens experience stress from golf balls striking the surface, maintenance equipment, and foot traffic. Improved creeping bentgrass (Agrostis stolonifera L.) cultivars, sand‐based root zones, and skilled superintendents maintain plant health while providing firmer conditions. Many researchers have studied effects of compaction and wear on putting greens, but few have determined the effect of these stresses on ball marks. The objective of this research was to evaluate ball mark severity and recovery of creeping bentgrass under different mowing heights (2.5, 3.2, and 4.0 mm), rolling frequencies (0, 3, or 6 d wk−1), and foot traffic using digital image analysis. Digital images of golf balls placed in the depression were used to calculate ball mark depth, and a cover analysis was conducted to model ball mark injury area using a one phase decay model to determine theoretical maximum injury, slope, and days to 50% recovery. Soil moisture content was positively correlated with ball mark depth, but common stresses rarely altered ball mark depth. The mean theoretical maximum ball mark injury was 377 mm2 greater for daily rolled treatments in 2010 compared to non‐rolled treatments. The slope of recovery rarely changed among treatments suggesting that theoretical maximum ball mark injury area has a greater effect on recovery. Lastly, combining the lowest mowing height or daily rolling and foot traffic slowed the time ball marks took to reach 50% recovery. This research demonstrates the effects common management practices and soil moisture have on the severity and recovery of ball marks during environmental stress.

The relationship between turf quality, EC of dew on turf surface and electrolyte leakage from leaf blade of two creeping bentgrass cultivars in summer

The relationship between turf quality, EC of dew on turf surface and electrolyte leakage from leaf blade of two creeping bentgrass cultivars in summer

Creeping Bentgrass Putting Green Response to Combined Mowing, Rolling, and Foot Traffic Under Environmental Stress

Creeping bentgrass (Agrostis stolonifera L.) putting greens in the transition zone experience high levels of environmental stress during summer months. The interaction of common management practices combined with foot traffic can exacerbate environmental stress. The objective of this study was to determine the effect of management practices combined with foot traffic during high environmental stress in the transition zone. Creeping bentgrass cultivars, SR 1020 and Penn G2, were managed with various mowing heights (2.5, 3.2, or 4.0 mm), rolling frequencies (0, 3, or 6 d per week), and foot traffic. As environmental stress became prominent during summer months, bentgrass maintained at the lowest mowing heights exhibited poorer turf quality, coverage, and wear tolerance compared to the highest mowing height. SR 1020 quality was reduced below acceptable levels in July when mowed at the lowest mowing height in 2011 and 2012. Penn G2 maintained acceptable quality at all mowing heights in 2011, but severe heat and drought stress reduced turf quality regardless of mowing height in 2012. Daily rolling significantly increased wear on both cultivars during high environmental stress that resulted in decreased turf quality and coverage compared to the non‐rolled treatments. The combination of wear from mechanical stress and foot traffic increased wear injury on both cultivars. Under reduced daylengths and optimal air temperatures in September of each year, all response variables improved to similar levels.

한지형 잔디의 피복 율과 생육 증진을 위한 유기질비료 제제의 살포

유기질비료의 원료를 이용하여 한지형 잔디의 종자 파종후 피복율, 생육 및 질의 증진을 위한 유지질비료 제제를 개발하였다. 개발 제제는 한지형 잔디의 생육에 필수적인 무기영양소와 유기물을 함유하고 있다. 유기질비료로 개발한 제제는 4종류로 creeping bentgrass "Penn-A1" 품종과 Kentucky bluegrass 혼합품종(Midnight 33%, Moonlight 33%와 Prosperity 33%)의 종자를 파종 후 50일에 1회 토양 시비로 시험하였다. creeping bentgrass와 Kentucky bluegrass의 피복율, 생장(생장지수) 및 잔디의 질은 2013년 가을부터 2014년 봄철기간 동안 경시적으로 평가를 하였다. 개발제제의 파종 후 1회 토양살포로 잔디 피복율, 잔디 엽색, 엽록소 함량 및 생장에서 통계적인 유의성의 차이를 보였다. creeping bentgrass와 Kentucky bluegrass의 피복율, 엽록소 함량, 잔디 엽색 및 생장은 봄철 6회 조사까지 통계적으로 유의성 있게 증가하였다. 이 결과에 의하면 일부 개발 제제의 사용은 한자형 잔디의 뗏장잔디의 생산과 잔디관리에 도움의 줄 것으로 생각한다. Organic fertilizer preparation was developed with organic materials to improve growth and qualities of cool-season turfgrass species. Organic fertilizer preparation were contained with essential macronutrient elements and organic matter for growth of cool season turfgrass. Four preparations of organic fertilizers were tested on creeping bentgrass (Agrostis palustris Huds) cultivar Penn-A1 and Kentucky bluegrass (Poa pratensis L.) mixed cultivars (Midnight 33%, Moonlight 33%, and Prosperity 33%) by one time application on fifty days after sowing. Two species of cool season turfgrasses were evaluated on turfgrass coverage, growth on NDVI (Normalized Difference Vegetation Index) and qualities from fall season to spring season in sod producing farm. It were found significantly difference found on turfgrass coverage, turf color, chlorophyll contents and growth increase on two species of cool season turfgrasses. Turfgrass coverage, chlorophyll content, turf color and growth increase of organic fertilizer preparation were significantly increased on creeping bentgrass cultivar and Kentucky bluegrass mixed cultivar for six time investigation in spring season. These results may indicate that the use of some preparation is beneficial for sod producing sod and turfgrass management.

Classification of bentgrass (Agrostis) cultivars and accessions based on microsatellite (SSR) markers

Genetic relationships among Agrostis species used for turf have been difficult to discern. Recent studies have either confirmed or contradicted previously proposed genetic relationships based on chromosome pairing behavior of inter-specific hybrids. The objective of the current study was to assess genetic relationships among Agrostis cultivars and accessions by using newly available A. stolonifera microsatellite (SSR) markers. Nuclear SSR (nuSSR) and chloroplast SSR (cpSSR) markers were used to genotype 16 individuals from each of 74 Agrostis cultivars and accessions. Genetic relationships based on nuSSR markers most closely resembled species relationships proposed by Jones in the 1950s. Contrary to the work of Jones, genetic relationships based on cpSSR markers indicated that A. canina was more closely related to A. stolonifera than to A. capillaris. We hypothesize that chloroplast introgression via interspecific hybridization between A. canina and A. stolonifera resulted in these species sharing common chloroplast genome lineages, while maintaining disparate nuclear genome lineages. Genetic relationships within Agrostis species based on nuSSR markers closely matched known pedigree relationships. Bayesian clustering analysis of nuSSR markers indicated that most modern seeded A. stolonifera cultivars exhibited high levels of admixture. Our study confirms that nuSSR markers distinguish Agrostis species and cultivars, and are valuable for studying genetic diversity and genetic relationships within the genus Agrostis.

Suitability of Creeping Bentgrass and Bermudagrass Cultivars for Black Cutworms and Fall Armyworms (Lepidoptera: Noctuidae).

The black cutworm, Agrotis ipsilon Hufnagel, and fall armyworm, Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), are common turfgrass pests of golf courses in the southeastern United States. Heat-tolerant bentgrass (Agrostis stolonifera L.) cultivars are expanding the range of bentgrass further south, but these cultivars have not been studied for their potential host plant resistance to black cutworm or fall armyworm. The goals of the study were to investigate feeding response of black cutworm and fall armyworm to these newer heat-tolerant creeping bentgrass cultivars, as well as commonly used cultivars of bermudagrass [Cynodon dactylon (Loppers.)]. Choice and no-choice feeding assays and fecundity tests were conducted in the laboratory and greenhouse to evaluate performance and preference of the two insects. When given a choice, neither black cutworm nor fall armyworm showed a preference for the majority of new cultivars tested. There were no differences in leaf area consumption or insect development for either pest in no-choice feeding assays. Black cutworm females preferred laying eggs in bentgrass compared with bermudagrass, but will oviposit onto bermudagrass, suggesting that both turf species are suitable hosts of this pest. The broad host ranges of generalist caterpillar pests of turfgrass hinder the application of host plant resistance in integrated pest management on golf courses.

Phytohormone Responses and Cell Viability during Salinity Stress in Two Creeping Bentgrass Cultivars Differing in Salt Tolerance

Salinity stress is becoming more prevalent in turfgrass management with the increasing use of recycled water for irrigation. Creeping bentgrass (Agrostis stolonifera) is a cool-season turfgrass species that contains significant cultivar variation in salt stress tolerance, but the mechanism related to this cultivar variation is not well understood. Our objectives were to determine whether differential hormone content could play a role in cultivar variation of salt responses and to evaluate whether cell viability assays using dye techniques could differentiate salt stress damage levels in turfgrass species. Therefore, a growth chamber study with potted plants was conducted to evaluate salt ion concentrations, physiological responses, and hormone analysis [abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), salicylic acid (SA), zeatin riboside (ZR), and ethylene] at 4, 8, and 12 dS·m−1 in relatively salt-tolerant ‘Mariner’ compared with salt-sensitive ‘Penncross’ creeping bentgrass. A hydroponics-based growth chamber study was performed for evaluation of whether dead-cell stains coupled with image analysis could be a quick method for indicating cell viability variation between cultivars. Greater salt tolerance was evident in ‘Mariner’ at 12 dS·m−1, which showed significantly lower electrolyte leakage, higher leaf relative water content (RWC), osmotic potential, photochemical efficiency, and photochemical yield compared with ‘Penncross’. A higher K+ and lower Na+ content was maintained in leaves of ‘Mariner’ compared with ‘Penncross’ while roots of ‘Mariner’ maintained higher Ca2+ content under stressed and nonstressed conditions. Phytohormone levels showed a decline in salt-stressed roots compared with nonstressed plants but ‘Mariner’ roots were able to maintain levels higher than ‘Penncross’. ‘Mariner’ leaves showed an increased accumulation of ABA, JA, SA, and ZR while roots maintained higher IAA and SA compared with ‘Penncross’. The results suggest that ‘Mariner’ was able to mitigate salt stress by better ion regulation and differential regulation of hormones compared with ‘Penncross’. ‘Mariner’ leaves and roots showed significantly lower dead cells compared with ‘Penncross’ under salt stress. The results suggest that staining for cell viability could be a useful technique for studying turfgrass stress or other cellular responses.

Pigment Changes in Cool‐Season Turfgrasses in Response to Ultraviolet‐B Light Irradiance

Pigments and phenolics that absorb ultraviolet light (UV) are involved in the protection of the photosynthetic apparatus during periods of high ultraviolet‐B (UV‐B) radiation and can be of benefit to turfgrasses. This study initiated in October 2010 and repeated in March 2011 aimed to characterize protective pigment responses to elevated UV‐B in cool‐season turfgrass. Tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.), and creeping bentgrass (Agrostis stolonifera L.) cultivars L93 and Penncross were tested. Turfgrass pigment responses were measured over a 1‐wk period during which they were subjected to 16 kJ m−2 d−1 of UV‐B in growth chambers. Photoperiod was 14 h and plants were subjected to 26.2 mol m−2 d−1 photosynthetically active radiation (PAR) at 20° C day and 17°C night. Turfgrass samples were collected at Day 0, 1, 3, 5, and 7. Measurements included chlorophyll fluorescence, chlorophyll pigmentation, and flavonoid, phenolic, anthocyanins, and carotenoid concentrations. Chlorophyll fluorescence increased and chlorophyll quantities decreased significantly (P < 0.05) in UV‐B conditions compared to control. All species had significantly (P < 0.05) higher quantities of total phenolics and flavonoids at the top of the tissue canopy relative to roots and shoot tissue near the soil surface. Anthocyanins were only found in creeping bentgrass L93. Carotenoids, zeaxanthin, and β‐carotene declined in the UV‐B treatment for both creeping bentgrass L‐93 and Penncross after 7 d, but did not decrease for perennial ryegrass or tall fescue. Carotenoids may play a greater role in UV‐B tolerance than anthocyanins in cool‐season turfgrasses due to their ubiquitous presence.

Sclerotinia homoeocarpa overwinters in turfgrass and is present in commercial seed.

Dollar spot is the most economically important disease of amenity turfgrasses in the United States, yet little is known about the source of primary inoculum for this disease. With the exception of a few isolates from the United Kingdom, Sclerotinia homoeocarpa, the causal agent of dollar spot, does not produce spores. Consequently, it was assumed that overwintering of this organism in soil, thatch, and plant debris provides primary inoculum for dollar spot epidemics. Overwintering of S. homoeocarpa in roots and shoots of symptomatic and asymptomatic creeping bentgrass turfgrass was quantified over the course of a three-year field experiment. Roots did not consistently harbor S. homoeocarpa, whereas S. homoeocarpa was isolated from 30% of symptomatic shoots and 10% of asymptomatic shoots in the spring of two out of three years. The presence of stroma-like pathogen material on leaf blades was associated with an increase in S. homoeocarpa isolation and colony diameter at 48 hpi. Commercial seed has also been hypothesized to be a potential source of initial inoculum for S. homoeocarpa. Two or more commercial seed lots of six creeping bentgrass cultivars were tested for contamination with S. homoeocarpa using culture-based and molecular detection methods. A viable, pathogenic isolate of S. homoeocarpa was isolated from one commercial seed lot and contamination of this lot was confirmed with nested PCR using S. homoeocarpa specific primers. A sensitive nested PCR assay detected S. homoeocarpa contamination in eight of twelve (75%) commercial seed lots. Seed source, but not cultivar or resistance to dollar spot, influenced contamination by S. homoeocarpa. Overall, this research suggests that seeds are a potential source of initial inoculum for dollar spot epidemics and presents the need for further research in this area.

Tolerance of Bentgrass (Agrostis) Species and Cultivars to Methiozolin

Methiozolin is a new herbicide from South Korea currently under development in the United States for PRE and POST annual bluegrass control in bentgrass and most other cool- and warm-season turfgrasses. Greenhouse studies were conducted in 2012 at the University of California, Riverside, CA, and Auburn University, Auburn, AL, to evaluate the relative tolerance of three bentgrass species comprised of nine creeping bentgrass (CRBG) cultivars, velvet bentgrass (VBG) and colonial bentgrass (COBG) to methiozolin at 0, 0.6, 1.1, 2.2, 4.5 and 9.0 kg ai ha−1. Methiozolin was applied 7 wk after seeding, followed by a second application 5 wk later. Methiozolin rates that produced 25% injury (TI25) and 50% clipping dry weight reduction (GR50) relative to a nontreated control for each species or cultivar were calculated using four-parameter logistic regression. Turf injury rates at 21 d after second treatment (DAT2) were the most consistent in describing relative tolerance among bentgrass species. Overall, CRBG was more tolerant to methiozolin than VBG or COBG. After two applications, methiozolin rates that caused TI25 were 1.1, 0.2, and 0.3 kg ha−1 for CRBG (across all cultivars), VBG, and COBG, respectively. VBG and COBG were not tolerant of sequential methiozolin applications at rates necessary to control annual bluegrass under field conditions. Herbicide rates that caused TI25 and GR50 decreased with the second application. ‘Penn A-4’ CRBG exhibited the highest TI25 28 d after initial treatment (DAIT) at University of California at Riverside (4.5 kg ha−1), but only 2.5 kg ha−1 with two applications by 21 DAT2. All CRBG cultivars tested tolerated methiozolin at 0.5 kg ha−1, the recommended sequential use rate for putting greens in Korea.

Development of SCAR marker for the detection of QTL for resistance to dollar spot in creeping bentgrass (Agrostis stolonifera L.)

Dollar spot (caused by Sclerotinia homoeocarpa F. T. Bennett) is the most economically important fungal turf disease on golf courses in North America. This disease is mainly controlled by using multiple fungicides. However, the causal fungus has developed resistance to seveal classes of fungicides and host resistance is an alternative control strategy. A creeping bentgrass (Agrostis stolonifera L.) cultivar improved with dollar spot resistance would greatly reduce the costs and environmental impacts of fungicide applications. Our previous QTL analysis in the creeping bentgrass ‘549 × 372’ population detected one QTL with a large effect for dollar spot resistance and several QTLs with smaller effects. One RAPD primer, AW10, amplified an 650-bp band in the parent ‘372’, was named 3.AW10.650. This RAPD marker was located on linkage group 7.1 and was significantly (p < 0.0001) associated with the QTL for dollar spot resistance based on 697 progeny of the ‘549 × 372’ population. In this study, we converted the RAPD marker 3.AW10.650 into a sequence characterized amplified region (SCAR) marker, named CreepDSp.650. The SCAR marker showed a significant association (p = 0.006) with dollar spot resistance in an additional segregating population developed at the University of Illinois. We report here the first PCR-based SCAR marker associated with a major-effect QTL for dollar spot resistance in creeping bentgrass. This SCAR marker will facilitate evaluating relatively large numbers of breeding progeny for marker-assisted selection (MAS) in bentgrasses.

고산지역에서의 크리핑 벤트그래스 품종 생육특성 비교

고산지역 기후 환경에서 크리핑 벤트그래스품종의 생육특성을 비교 분석하여 그린과 페어웨이조건에 적합한 품종을 선발하기 위해본 실험을 실시하였다. 먼저 경기중부, 영서시내, 영서 고산지대의 기후환경 데이터를 비교 분석하였을 때, 고도에 따른 기후의 차이가 위도에 따른 지역 차이보다 큰 것으로 분석되었다. 영서산악지대에 USGA 방식의 그린용 지반과 캘리포니아식의 페어웨이 지반의 시험포장을 조성한 후 5가지 종류의 크리핑 벤트그래스 품종을 파종하여 두 지반에 따라 깎는 높이를 달리하여 3년간 생육기간의 품종별 생육특성을 비교 분석하였다. 봄철 그린 업 측정한 결과 'T-1'과 'CY-2'는 타 품종들 보다 좀 그린업이 빨랐으나 'Penncross'는 그린업이 가장 더딘 것으로 나타났다. 그린과 페어웨이 예고환경에서 비슷한 결과가 나타났다. 실험기간 중 'T-1' 품종이 전반적인 시각적 품질평가 결과와 전반적인 뿌리길이에서 가장 우수하였으나 하절기에는 'Penncross'의 뿌리 길이와 건중량이 높았고, 'Penn A-1' 품종이 가장 낮은 결과를 보였다. 전반적으로 페어웨이에서도 그린조건에서와 같이 'T-1', 'CY-2' 품종이 엽색, 피복도, 뿌리길이 등 양호한 생육특성을 보였다. This experiment was carried out for the selection of suitable cultivars on the green and fairway at the mountain area. The climate data showed that differences of altitude influenced greater than latitude on temperature and rainfall when compared with 3 areas of the central of Gyeong-gi and Yeong-seo, and the mountain area at Yeong-seo. The plot was prepared with the USGA profiles for green and modified California style for fairway at the mountain golf course in Wonju, Korea. The growth characteristics were compared on two different profiles for 3 years of growing seasons after seeding with 5 creeping bentgrass cultivars. 'T-1' and 'CY-2' showed a rapid greenup compare with other cultivars in spring of 2010 with the both green and fairway mowing height. However, 'Penncross' resulted the slowest among cultivars. 'T-1' showed the most prominent visual quality of overall rate and the deepest root length after one year of seeding, while 'Penncross' showed an excellent result of root length and weight during summer season. However, 'Penn A-1' had an imperial result in that season. Comparison of the growth characteristics under green and fairway conditions, 'T-1' and 'CY-2' showed exellent overall results at the mountain area at Yeong-seo area in Korea.

Physiological Responses of Creeping Bentgrass Cultivars to Carbonate, Chloride, and Sulfate Salinity

ABSTRACTEvaluation of creeping bentgrass (Agrostis stolonifera L.) salt tolerance often showed inconsistent results. The objective of this study was to investigate the reactions of ‘Seaside II’ and ‘T‐1’ to NaCl, Na2CO3, Na2SO4, and CaCl2, each at concentrations of 0, 25, 75, 125, 175, and 225 mM. Chlorophyll a (Chla) content was the lowest in the CaCl2 treatment followed by Na2CO3 and Na2SO4 and highest in NaCl whereas chlorophyll b (Chlb) content was lowest in Na2CO3 followed by CaCl2 and Na2SO4 and highest in NaCl. Turfgrass visual quality and green density were reduced the most by the Na2CO3 and CaCl2 treatments. Evapotranspiration (ET) decreased in the order of treatments CaCl2, Na2SO4, Na2CO3, and NaCl at 1 wk after treatment (WAT), but at 4 WAT there were no difference among CaCl2, Na2SO4, and Na2CO3. Significant salt type × concentration interaction existed, and the first order or second order coefficient of regression equation ranked the changing rate of physiological parameters differently in different salts. Leaf K+:Na+ ratio was affected differently by salts and a threshold of 1 appeared at different salt concentrations depending on salt types and cultivars. The pH, osmotic potential, and electrical conductivity of salt solutions were confounded making the interpretation of mechanisms of physiological stress difficult. Nevertheless, this study showed that different salts rank creeping bentgrass salt tolerance differently.

Quantifying Nitrogen Requirement for Creeping Bentgrass Putting‐Green Cultivars

Nitrogen is perhaps the most important nutrient for turfgrasses because it improves color, density, and recuperative ability when applied at adequate rates. Although numerous unique traits, such as dark genetic color and improved stress tolerance have been identified, there is a lack of published data comparing creeping bentgrass cultivar N use. Therefore, a field study was initiated in 2009 and 2010 to identify creeping bentgrass (Agrostis stolonifera L.) putting‐green cultivars that required the least amount of N to maintain acceptable color while maintaining desirable agronomic traits and good overall playability. Eighteen creeping bentgrass cultivars were planted on 2 July 2006 and maintained at a 3.2‐mm mowing height. Nitrogen, liquid urea, was applied at 49, 147, or 294 kg ha−1 yr−1. Nitrogen applications were applied every 2 wk from April to October. Data collection included turfgrass color, relative chlorophyll index (RCI), clipping yield, lateral regrowth, ball‐roll distance, and thatch accumulation. Increasing N rates resulted in higher RCI, more top growth, faster lateral regrowth, and shorter ball‐roll distances. Regarding thatch accumulation, no significant differences were detected between cultivars. Overall, the creeping bentgrass cultivars that maintained acceptable color with the least amount of N input included ‘007’, ‘Authority’, ‘Penn A‐4’, ‘Shark’, and ‘T‐1’. These cultivars also maintained desirable agronomic traits, such as high RCI, reduced clipping yield, increased lateral regrowth, and adequate ball‐roll distance. This research indicates creeping bentgrass cultivar is an important selection criterion if a reduction in N use is a relevant consideration.

First Report of Dollar Spot Caused by Sclerotinia homoeocarpa on Agrostis stolonifera in North Dakota.

Dollar spot disease is a major concern for golf courses nationwide, resulting in poor turf quality and significant damage to playing surfaces. To manage this disease effectively, fungicides need to be applied regularly. This management strategy represents a significant cost to turfgrass managers and may impact the economics of the industry in North Dakota. In the summer of 2011, small, circular, sunken brown patches of dead turf approximately 5 cm in diameter and resembling dollar spot disease were observed on a creeping bentgrass (Agrostis stolonifera L.) variety trial at the North Dakota State University Agricultural Experiment Station in Fargo, ND. Fresh individual leaf specimens with distinct lesions having straw colored centers and reddish brown margins were collected. Leaves were surface disinfected in a 0.05% sodium chloride solution for 60 s, rinsed three times in sterile distilled water, then placed onto potato dextrose agar (PDA). Three isolates were obtained from the disease infested leaves with similar morphology to that described for Sclerotinia homoeocarpa F.T. Bennett (1). Fungal colonies were initially colorless followed by the development of sparse white columnar aerial mycelia with cinnamon colored bases. Hyphae were 5 to 8 μm wide and thin walled with dense granular contents and septations at irregular intervals. Fourteen days after culturing, dark brown to black mycelial stroma developed. A single representative isolate was selected to conduct inoculations. Inoculum was produced by placing six 5-mm-diameter plugs of PDA with actively growing mycelium into an Erlenmeyer flask with 40 g of sterile millet seed. The inoculum was incubated for 14 days at ambient temperature (20 to 25°C). Three creeping bentgrass cultivars, Crenshaw, Declaration, and L-93, were inoculated (two pots per cultivar). Following inoculation, the pots were misted with water, sealed in separate plastic bags, and placed in the dark for 48 h. For the next 5 days, plants were placed for 8 h outside of bags on a bench with full spectrum fluorescent bulbs, followed by 16 h in plastic bags in the dark. Finally, pots were placed on a bench for 48 h. Signs and symptoms of S. homoeocarpa developed on all pots, whereas the controls remained asymptomatic. The same fungus was reisolated from grass leaves, satisfying Koch's postulates. To confirm the identity of the fungus, the internal transcribed spacer was amplified using the ITS4 and ITS5 primers (2). The amplicon was sequenced, generating a 549-bp sequence (Accession No. JQ735942) with 100% similarity to sequences of S. homoeocarpa in GenBank (Accession Nos. GQ924924.1, GQ924923.1, and EU123801.1). To our knowledge, this is the first confirmed report of dollar spot in North Dakota.

Construction of a linkage map for quantitative trait loci associated with economically important traits in creeping bentgrass (Agrostis stolonifera L.)

Creeping bentgrass (Agrostis stolonifera L.) is the most widely cultivated and high-value turfgrass species. Genetic linkage maps of creeping bentgrass were constructed for quantitative trait loci (QTL) analysis of gray snow mold (Typhula incarnata) resistance, recovery and leaf width. A segregating population of 188 pseudo-F2 progeny was developed by two-way pseudo-testcross mapping strategy. Amplified fragment length polymorphism, new developed Agrostis specific expressed sequence tag-single sequence repeat (SSR), random amplified polymorphic DNA and genomic SSR markers corresponding to DNA polymorphisms heterozygous in one parent and null in the other, were scored and placed on two separate genetic linkage maps, representing each parent. In the male parent map, 100 markers were mapped to 14 linkage groups covering a total length of 793 cM with an average interval of 8.2 cM. In the female parent map, 146 markers were clustered in another 14 linkage groups spanning 805 cM with an average distance of 5.9 cM between adjacent markers. We identified three putative QTL for leaf width and one QTL for snow mold disease resistance. The construction of a linkage map and QTL analysis are expected to facilitate the development of disease resistant creeping bentgrass cultivars by using molecular marker-assisted selection.

Seasonal Development of Dollar Spot Epidemics in Six Creeping Bentgrass Cultivars in Maryland

This 3-year field study evaluated the incidence and severity of dollar spot (Sclerotinia homoeocarpa F.T. Bennett) in six creeping bentgrass (Agrostis stolonifera L.) cultivars maintained as a golf course fairway. Comparison of area under the disease progress curve (AUDPC) data clearly indicted two resistance groups among the six cultivars. ‘Crenshaw’ and ‘Backspin’ were classified as highly susceptible (HS) and the other four cultivars (i.e., ‘Penncross’, ‘Providence’, ‘L-93’, and ‘007’) were classified as moderately susceptible (MS) to dollar spot. In all three study years, there were three epidemics that began in May. Data could not be collected in HS cultivars after the first epidemic in each year as a result of severe damage. In MS cultivars, the first epidemic ended and a second began between early July and late August. The second epidemic ended approximately mid-October and a third epidemic appeared in MS cultivars between late October and early December. The second epidemic was longest and most severe, and the third fall epidemic was least severe and of shortest duration. The first epidemic in HS cultivars developed up to two weeks earlier and progressed more rapidly and severely than in MS cultivars. A growing degree-day (GDD) model, using a base air temperature of 15 °C and a start date of 1 Apr., was accurate in predicting the onset of the first epidemic in HS (60 to 70 GDD) and MS (105 to 115 GDD) cultivars during each of the three study years. Growing degree-day models are greatly influenced by the many microclimates found on golf courses and need to be evaluated for accuracy in diverse environments.

Lateral Spread and Dry Matter Partitioning of Creeping Bentgrass Cultivars

ABSTRACTCreeping bentgrass (Agrostis stolonifera L.) cultivars are available that possess varying vegetative characteristics. A better understanding of the vegetative growth among creeping bentgrass cultivars is essential to its culture and would aid breeders in selecting for improved turf characteristics in germplasm screening programs. Our objectives were to identify differences in establishment rates among cultivars of creeping bentgrass and to determine the factors associated with differing growth rates by using growth analysis techniques. Spaced plantings of 24 cultivars of creeping bentgrass were evaluated for stolon characteristics and lateral spread. Two cultivars with differing lateral spread were used for further growth analysis in a growth chamber. ‘Penncross’ exhibited greater lateral spread and longer internodes compared with recently developed cultivars. ‘Bengal’ had the slowest lateral spread and the shortest mean stolon and internode length. Internode and stolon length were positively correlated as well as internode length and establishment rate indicating that cultivars with long internodes also possess fast establishment rates and longer stolons. Growth analysis indicated that Penncross and Bengal produce similar amounts of dry matter but Penncross allocates more dry matter into stolons than leaves. Variation in dry matter partitioning could partially explain differences in lateral spread among cultivars of creeping bentgrass. The vegetative characteristics should be matched with desired site usage requirements for optimum performance when selecting cultivars of creeping bentgrass.