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Heat stress is a major concern for the growth of cool-season creeping bentgrass (Agrostis stolonifera L.). Nonetheless, there is a lack in a clear and systematic understanding of thermotolerance mechanisms for this species. This study aimed to assess heat tolerance in experimental lines and cultivars to determine important physiological and biochemical traits responsible for improved tolerance, including the use of OJIP fluorescence. Ten creeping bentgrass lines were exposed to either control (20/15 °C day/night) or high temperature (38/33 °C day/night) conditions for 35 d via growth chambers at Griffin, GA. Principal component analysis and clustering analysis were performed to rank stress performance and divide lines into different groups according to their tolerance similarities, respectively. At the end of the trial, S11 729-10 and BTC032 were in the most thermotolerant group, followed by a group containing BTC011, AU Victory and Penncross. Crenshaw belonged to the most heat-sensitive group while S11 675-02 and Pure Eclipse were in the second most heat-sensitive group. The exceptional thermotolerance in S11 729-10 and BTC032 was associated with their abilities to maintain cell membrane stability and protein metabolism, plus minimize oxidative damages. Additionally, among various light-harvesting steps, energy trapping, dissipation and electron transport from QA to PQ were more heat-sensitive than electron transport from QA to final PSI acceptors. Along with the strong correlations between multiple OJIP parameters and other traits, it reveals that OJIP fluorescence could be a valuable tool for dissection of photosynthetic processes and identification of the critical steps responsible for photosynthetic declines, enabling a more targeted heat-stress screening. Our results indicated that variability in the level of heat tolerance and associated mechanisms in creeping bentgrass germplasm could be utilized to develop new cultivars with improved thermotolerance.

Results suggest that sand topdressing was more consistent at reducing dollar spot (Clarireedia jacksonii) in fairway turfgrass more so than rolling. This practice could be an effective cost-saving alternative to reduce frequent fungicide applications. Research was conducted from 2011 to 2014 on a simulated golf fairway and examined dollar spot severity responses in a mixed-stand of creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua ssp. reptans) to sand topdressing and rolling. Treatments consisted of biweekly sand topdressing, rolling at three frequencies (one, three, or five times weekly), a control, and three replications. Infection was visually estimated. Sand topdressing significantly (P < 0.05) reduced disease up to 50% at the peak of the dollar spot activity in 2011, 2013, and 2014. Results on the effects of rolling on dollar spot were inconsistent.

Hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (HCT) is considered to be an essential enzyme for regulating the biosynthesis and composition of lignin. To investigate the properties and function of ZjHCT4, the ZjHCT4 gene was cloned from Zoysia japonica with a completed coding sequence of 1284-bp in length, encoding 428 amino acids. The ZjHCT4 gene promoter has several methyl jasmonate (MeJA) response elements. According to analysis of expression patterns, it was up-regulated by MeJA, GA3 (Gibberellin), and SA (Salicylic acid), and down-regulated by ABA (Abscisic acid). Ectopic ZjHCT4 expression in creeping bentgrass causes excessive plant elongation. In addition, the content of G-lingnin and H-lingnin fell in transgenic plants, whereas the level of S-lingnin increased, resulting in a considerable rise in the S/G unit ratio. Analysis of the expression levels of lignin-related genes revealed that the ectopic expression of ZjHCT4 altered the expression levels of a number of genes involved in the lignin synthesis pathway. Simultaneously, MeJA, SA, GA3, IAA, BR (Brassinosteroid), and other hormones were dramatically enhanced in transgenic plants relative to control plants, whereas ABA concentration was significantly decreased. Expression of ZjHCT4 impacted lignin composition and plant growth via altering the phenylpropionic acid metabolic pathway and hormone response, as revealed by transcriptome analysis. HCTs may influence plant lignin composition and plant development by altering hormone content. These findings contributed to a deeper comprehension of the lignin synthesis pathway and set the stage for further investigation and application of the HCTs gene.

Background Small heat shock proteins (sHSPs) are critical for plant response to biotic and abiotic stresses, especially heat stress. They have also been implicated in various aspects of plant development. However, the acting mechanisms of the sHSPs in plants, especially in perennial grass species, remain largely elusive. Results In this study, AsHSP26.8a, a novel chloroplast-localized sHSP gene from creeping bentgrass (Agrostis stolonifera L.) was cloned and its role in plant response to environmental stress was studied. AsHSP26.8a encodes a protein of 26.8 kDa. Its expression was strongly induced in both leaf and root tissues by heat stress. Transgenic Arabidopsis plants overexpressing AsHSP26.8a displayed reduced tolerance to heat stress. Furthermore, overexpression of AsHSP26.8a resulted in hypersensitivity to hormone ABA and salinity stress. Global gene expression analysis revealed AsHSP26.8a-modulated expression of heat-shock transcription factor gene, and the involvement of AsHSP26.8a in ABA-dependent and -independent as well as other stress signaling pathways. Conclusions Our results suggest that AsHSP26.8a may negatively regulate plant response to various abiotic stresses through modulating ABA and other stress signaling pathways.

Dollar spot is caused by the fungus Clarireedia jacksonii and is the most common disease of golf course turfgrass in temperate climates. Oxalic acid (OA) is an important pathogenicity factor in other fungal plant pathogens, such as the dicot pathogen Sclerotinia sclerotiorum, but its role in C. jacksonii pathogenicity on monocot hosts remains unclear. Herein, we assess fungal growth, OA concentration, and pH change in potato dextrose broth (PDB) following incubation of C. jacksonii. In addition, OA production by C. jacksonii and S. sclerotiorum was compared in PDB amended with creeping bentgrass or common plant cell wall components (cellulose, lignin, pectin, or xylan). Our results show that OA production is highly dependent on the environmental pH, with twice as much OA produced at pH 7 than pH 4 and a corresponding decrease in PDB pH from 7 to 5 following 96 h of C. jacksonii incubation. In contrast, no OA was produced or changes in pH observed when C. jacksonii was incubated in PDB at a pH of 4. Interestingly, C. jacksonii increased OA production in response to PDB amended with creeping bentgrass tissue and the cell wall component xylan, a major component of all walls of grasses. S. sclerotiorum produced large amounts of OA relative to C. jacksonii regardless of treatment and no treatment increased OA production by this fungus, though pectin suppressed S. sclerotiorum OA production. These results suggest that OA production by C. jacksonii is reliant on host specific components within the infection court, as well as the ambient pH of the foliar environment during its pathogenic development.

Suppression of creeping bentgrass (Agrostis stolonifera L.) putting greens from plant growth regulators (PGRs) appears to have declined in recent years. Golf course superintendents on the Southern High Plains of Texas struggle with excessive shoot growth of creeping bentgrass during summer months that can result in reduced turf quality (non-uniform growth or scalping) and performance (slow putting green speeds). Creeping bentgrass in semi-arid regions seems to accelerate in growth as the ambient air temperature increases through the summer. Making sequential applications of PGRs to the putting greens during mid to late summer has little to no suppression of the turf. The objectives of this study were to develop growing degree day (GDD) models of commercially available PGRs and analyze visual turf quality and PGR suppression capacity with sequential applications of PGRs on creeping bentgrass putting greens. This research was conducted on two golf courses in Lubbock, TX in the summer of 2014 and 2015. Modeling PGR applications were allowed 1000 GDDs between applications and sequential applications were made every two weeks. Plant growth regulators commercially available for bentgrass putting greens at this time were trinexapac-ethyl (TE), paclobutrazol, flurprimidol, Legacy (TE and flurprimidol) and Musketeer (TE, paclobutrazol, and flurprimidol). Clippings were collected twice per week from the PGR plots and evaluated against the control plots. Turf quality was evaluated visually and using digital image analysis to calculate percent green cover and dark green color with the plots every two weeks between sequential PGR applications. Peak suppression of the turf on the modeling applications ranged from 24% with flurprimidol to 39% with Musketeer. The variation between these products resulted in an additional 83 GDD of accumulation with Musketeer compared to flurprimidol, which could represent an additional 3 to 7 days before additional applications would be required. Legacy and Musketeer suppressed the turf for a longer period than other PGRs. Turf quality was reduced with initial applications of products containing paclobutrazol due to high phytotoxicity from over suppression of the creeping bentgrass. However, those plots treated with products containing paclobutrazol or flurprimidol provided darker green color compared to the untreated control or TE alone on most dates. Sequential applications of PGRs made later in the summer had limited suppression relative to the control plots. Products containing paclobutrazol suppressed the turf more than other sequential applications of PGRs. Ultimately, this research proves that all commercially available products reduce foliar growth of creeping bengrass following application; however, the level of suppression provided or the length of time between applications differs with external factors. The temperature and growth rate of creeping bentgrass should be considered when selecting a product use rate because moderate rates of some products can result in over suppression if applied during sub-optimal growth periods. Over-suppressing the turf can lead to limited traffic tolerance and recovery or increased disease pressure in some regions. Sequential applications of PGRs made based on GDD are would likely be more consistent at suppressing the turfgrass than applications that based on a Julian calendar. Consistently applying PGRs to creeping bentgrass will likely result in phytotoxicity that significantly reduces percent green cover, but ultimately expresses a much darker green color.

[EN] Methiozolin controls annual bluegrass in creeping bentgrass but application timing and temperature could influence efficacy in turf. In field experiments, sequential methiozolin applications totaling 3.36 kg ai ha(-1) provided excellent (> 90%) annual bluegrass control at 8 wk after initial treatment when treatments were initiated in February/March or May but programs totaling 0.84 and 1.68 kg ha(-1) provided poor control (< 70%) at both timings. Methiozolin at all rates caused minimal turf injury (< 8%) but creeping bentgrass was only injured from February/March applications. In growth chamber experiments, creeping bentgrass injury from methiozolin at 10 C was 2 and 4 times greater than at 20 C and 30 C, respectively, while annual bluegrass injury was similar across temperatures. In laboratory experiments, annual bluegrass had more foliar absorption of C-14-methiozolin than creeping bentgrass at 30/25 C (day/night), compared to 15/10 C, but translocation was similar at both temperatures as > 90% of absorbed C-14 remained in the treated leaf after 72 h. Annual bluegrass distributed and recovered more radioactivity to shoots from root-applied C-14-methiozolin than creeping bentgrass while both species had about 2 times more distribution to shoots at 30/25 C than 15/10 C. Metabolites were not detected in annual bluegrass or creeping bentgrass at 1, 3, or 7 d after treatment when grown at 15/10 C or 30/25 C suggesting uptake and translocation contributes to methiozolin selectivity in turfgrass, The authors would like to thank Bill Nutt, Seth Williams, Fred Brubaker, Harold Ammons, Dr. Qingguo Huang, Dr. Bill Vencill, and Dr. Tim Grey for technical support with this research and Dr. Suk-Jin Koo at Moghu Corp. for providing radiolabeled methiozolin and supporting the work. We would also like to thank the PAID-00-12, I + D Programe from the Universitat Politecnica de Valencia for supporting the sabbatical work of Diego Gomez de Barreda at the University of Georgia.

Annual bluegrass (Poa annua L.) and roughstalk bluegrass (Poa trivialis L.) are among the most troublesome grass weeds on golf courses throughout the United States. Herbicides for selective control of these weeds in cool-season fairways are limited and ineffective. Methiozolin is a new isoxazoline herbicide that controls annual bluegrass on putting greens and shows promise for possible weed control in fairways. Kentucky bluegrass (Poa pratensis L.) is among the most common turfgrass species used for golf fairways in the Northern United States and its response to methiozolin has scarcely been tested. A 2.5-yr field study was conducted at four Virginia locations to evaluate methiozolin efficacy for selective annual bluegrass and roughstalk bluegrass control in creeping bentgrass (Agrostis stolonifera L.) or Kentucky bluegrass fairways. Another study evaluated the response of 110 Kentucky bluegrass varieties to three rates of methiozolin. Annual bluegrass has long been presumed to impact putting green trueness, or the ability of the greens canopy to provide a smooth and directionally-consistent ball roll. Although much research has evaluated the impact of greens management on ball roll distance, no peer-reviewed research has evaluated how canopy surface factors, such as weedy annual bluegrass, will influence ball roll direction. Laboratory and field research was conducted to elucidate and overcome experimental errors that may be limiting assessment of ball directional imprecision caused by greens canopy anomalies. Techniques to minimize experimental error were employed in field studies at two Virginia golf courses to determine the influence of annual bluegrass on ball directional imprecision, bounce, and acceleration. Study results suggest that annual bluegrass patches in a creeping bentgrass putting surface can cause subtle increases in ball directional imprecision and bounce but several sources of error must be controlled before these effects can be measured. By using a mechanical putter to avoid directional errors associated with simulated-putt devices, selecting golf balls with balanced centers of gravity, eliminating legacy or "tracking" effects of repeated ball rolls via canopy brushing, and scoring ball direction 30 cm prior to terminal acceleration, we were able to detect an increase in ball directional imprecision of 8 mm m⁻¹ when balls rolled over a single patch of annual bluegrass compared to adjacent rolls on visually-pure creeping bentgrass. In herbicide efficacy studies, methiozolin-only treatments did not significantly injure creeping bentgrass or Kentucky bluegrass, reduce quality, or reduce normalized difference vegetative index regardless of application timings and rates. In general, fall applications of methiozolin reduced roughstalk bluegrass and annual bluegrass cover more than the spring-only treatments. At 1 year after the last treatment, methiozolin at 1500 g ha⁻¹ applied four times in fall at 2-wk intervals for two consecutive years controlled roughstalk bluegrass and annual bluegrass ≥85% and more consistently than other herbicides or treatment regimes. Spanning 110 Kentucky bluegrass varieties, a commercially-acceptable threshold of 30% Kentucky bluegrass injury required between 3.4 to more than 10 times the methiozolin rate needed for annual bluegrass control. Results indicate that annual bluegrass increases directional imprecision and bounce of golf balls rolling across a greens canopy. Methiozolin could be a viable herbicide for managing annual and roughstalk bluegrass in Kentucky bluegrass and creeping bentgrass fairways but weed control efficacy may be dependent on application timing. By measuring small differences in ball directional imprecision as influenced by greens canopy factors, future research efforts will aim to help turf managers choose appropriate greens management techniques. Ph. D.

Background Genetic engineering offers the opportunity to generate unique genetic variation that is either absent in the sexually compatible gene pool or has very low heritability. The generation of transgenic plants, coupled with breeding, has led to the production of widely used transgenic cultivars in several major cash crops, such as maize, soybean, cotton and canola. The process for regulatory approval of genetically engineered crops is slow and subject to extensive political interference. The situation in forage grasses and legumes is more complicated. Scope Most widely grown forage, turf and bioenergy species (e.g. tall fescue, perennial ryegrass, switchgrass, alfalfa, white clover) are highly self-incompatible and outcrossing. Compared with inbreeding species, they have a high potential to pass their genes to adjacent plants. A major biosafety concern in these species is pollen-mediated transgene flow. Because human consumption is indirect, risk assessment of transgenic forage, turf and bioenergy species has focused on their environmental or ecological impacts. Although significant progress has been made in genetic modification of these species, commercialization of transgenic cultivars is very limited because of the stringent and costly regulatory requirements. To date, the only transgenic forage crop deregulated in the US is 'Roundup Ready' (RR) alfalfa. The approval process for RR alfalfa was complicated, involving several rounds of regulation, deregulation and re-regulation. Nevertheless, commercialization of RR alfalfa is an important step forward in regulatory approval of a perennial outcrossing forage crop. As additional transgenic forage, turf and bioenergy crops are generated and tested, different strategies have been developed to meet regulatory requirements. Recent progress in risk assessment and deregulation of transgenic forage and turf species is summarized and discussed.

Cadmium (Cd) toxicity seriously affects the growth and development of plants, so studies on uptake, translocation, and accumulation of Cd in plants are crucial for phytoremediation. However, the molecular mechanism of the plant response to Cd stress remains poorly understood. The main objective of this study was to reveal differentially expressed genes (DEGs) under lower (BT2_5) and higher (BT43) Cd concentration treatments in creeping bentgrass. A total of 463,184 unigenes were obtained from creeping bentgrass leaves using RNA sequencing technology. Observation of leaf tissue morphology showed that the higher Cd concentration damages leaf tissues. Four key transcription factor (TF) families, WRKY, bZIP, ERF, and MYB, are associated with Cd stress in creeping bentgrass. Our findings revealed that these four TFs play crucial roles during the creeping bentgrass response to Cd stress. This study is mainly focused on the molecular characteristics of DEGs under Cd stress using transcriptomic analysis in creeping bentgrass. These results provide novel insight into the regulatory mechanisms of respond to Cd stress and enrich information for phytoremediation.

An irrigated field trial was conducted to test the effects of white clover in three turfgrass species (perennial ryegrass, Kentucky bluegrass, and creeping bentgrass) on color, clipping yield, and botanical composition and to estimate nitrogen (N)(2) fixation and N transfer from white clover to associated turfgrass species under different N-fertilization conditions in 1999-2002. Nitrogen fertilizers significantly increased color ratings in all observations. Grass-white clover mixtures had better color ratings than pure grass at all sampling dates and seasonal averages in unfertilized conditions. Fertilized pure grass plots yielded significantly more than control plots in all turfgrass species. Nitrogen fertilization did not affect clipping yield greatly in turfgrass-white clover mixtures. Nitrogen application significantly decreased white clover percentage in the harvested clippings in second and third year. Nitrogen fertilization increased tissue N concentration positively in all turfgrass species grown alone. In contrast, N fertilization did not greatly affect tissue N concentration of either turfgrass species or white clover in the mixtures. Nitrogen fixation of white clover was estimated as 24.6, 30.7, and 33.8 9 m(-2) year(-1) in perennial ryegrass, Kentucky bluegrass, and creeping bentgrass, respectively. The total estimated N-2 fixation gradually decreased with increasing N fertilization. Nitrogen transfer from white clover to the associated turfgrass varied from 4.2 to 13.7% of the total N that the white clover fixed annually.

Annual bluegrass is a winter annual grass that is problematic on golf putting greens due to its light green color, prolific seedhead production and intolerance to stress. On creeping bentgrass putting greens, herbicides for annual bluegrass control are limited. A new herbicide, methiozolin, developed by Moghu Research Center, LLC, in Daejeon, South Korea, safely and selectively controls annual bluegrass in creeping bentgrass and several other turfgrass species. Methiozolin typically controls annual bluegrass over several weeks, allowing desirable turfgrass time to grow into areas previously infested by annual bluegrass with little surface disruption. The mode of action of methiozolin is unknown, but has been proposed to act as either a cell wall biosynthesis inhibitor (CBI) or an inhibitor of tyrosine aminotransferase (TAT). Field studies were conducted at Virginia Tech to investigate strategies promoting surface recovery on putting greens following atypically rapid annual bluegrass loss resulting from methiozolin application, intensive core-cultivation as well as potential interactions with plant growth regulators (PGR's), like ethephon. In the rapid annual bluegrass removal study, all treatments receiving additional fertility via synthetic fertilizer with or without trinexapac-ethyl or biostimulant recovered 1 to 3 weeks more quickly than treatments that did not include additional fertility. Addition of the PGR trinexapac-ethyl inconsistently regulated speed of canopy recovery, both increasing and decreasing recovery speed. Under normal maintenance conditions, methiozolin does not negatively influence putting green recovery, however, if the putting green is exposed to droughty conditions, methiozolin can reduce recovery time by several weeks. Core-cultivation should be avoided in conjunction with methiozolin and ethephon applications because when this procedure was conducted on the same day as herbicide application it significantly damaged creeping bentgrass, reducing cover to 19% at 2000 g ai ha⁻¹, compared to the non-treated at 62%. Regarding the question of methiozoling mode of action, laboratory studies supported the claim that addition of exogenous 4-hydroxyphenylpyruvate (4-HPP) alleviates symptoms of methiozolin exposure in lesser duckweed, a model monocot species, but feeding various turfgrass species and annual bluegrass exogenous 4-HPP did not alleviate symptoms. Creeping bentgrass secondary root length and density was not affected by methiozolin, although annual bluegrass, Kentucky bluegrass and perennial ryegrass secondary root lengths were reduced. Based on these data, it does not appear that TAT inhibition is a primary mode of action of methiozolin in turfgrass. Studies were conducted to determine if methiozolin inhibited cell wall biosynthesis in desirable turfgrass species and annual bluegrass. All species exhibited decreased enrichment of ¹³C in cell-wall sugars form ¹³C-glucose in response to methiozolin and a known cell wall biosynthesis inhibitor, indaziflam. Indaziflam and methiozolin at 0.01 µM inhibited ¹³C enrichment of all sugars less than methiozolin at 1.0 µM, for xylose, arabinose and glucose, but not galactose. Addition of 4-HPP increased incorporation of ¹³C into xylose, but had no other influence on ¹³C incorporation into other cell wall sugars. Lack of species specific response indicates that cell wall biosynthesis inhibition is probably not the source of interspecific species responses observed in the field. Ph. D.

International audience; Background and Aims To improve the management of grass communities, early plant development was compared in three species with contrasting growth forms, a caespitose ( Lolium perenne), a rhizomatous (Poa pratensis) and a caespitose-stoloniferous species (Agrostis stolonifera). Methods Isolated seedlings were grown in a glasshouse without trophic constraints for 37 d (761 degrees Cd). The appearance of leaves and their location on tillers were recorded. Leaf appearance rate ( LAR) on the tillers and site-filling were calculated. Tillering was modelled based on the assumption that tiller number increases with the number of leaves produced on the seedling main stem. Above- and below- ground parts were harvested to compare biomass. Key Results Lolium perenne and A. stolonifera expressed similar bunch-type developments. However, root biomass was approx. 30% lower in A. stolonifera than in L. perenne. Poa pratensis was rhizomatous. Nevertheless, the ratio of above-ground : below- ground biomass of P. pratensis was similar to that of L. perenne. LAR was approximately equal to 0.30 leaf d(-1) in L. perenne, and on the main stem and first primary tillers of A. stolonifera. LAR on the other tillers of A. stolonifera was 30% higher than on L. perenne. For P. pratensis, LAR was 30% lower than on L. perenne, but the interval between the appearance of two successive shoots from rhizomes was 30% higher than the interval between two successive leaf stages on the main stem. Above- ground parts of P. pratensis first grew slower than in the other species to the benefit of the rhizomes, whose development enhanced tiller production. Conclusions Lolium perenne had the fastest tiller production at the earliest stages of seedling development. Agrostis stolonifera and P. pratensis compensated almost completely for the delay due to higher LAR on tillers or ramets compared with L. perenne. This study provides a basis for modelling plant development

Annual bluegrass (Poa annua L.) is the most problematic weed to control in creeping bentgrass (Agrostis stolonifera L.) putting greens. The objective of this study was to transition a mixed putting green stand of annual bluegrass and creeping bentgrass to a monoculture by using fertilizers and plant growth regulators that selectively inhibit annual bluegrass. A 25 year old loamy sand rootzone research green, planted with \'Penn-Eagle\' creeping bentgrass, with roughly 45% initial annual bluegrass coverage was utilized. The biweekly application of ammonium sulfate (4.8 kg ha-1) with treatments of ferrous sulfate at rates of 0, 12.2, 24.4, and 48.8 kg ha-1 and in combination with seaweed extract (12.8 L ha-1) or paclobutrazol (0.37 L ai ha-1 spring and fall; 0.18 L ai ha-1 summer) were applied March to October, 2011 and 2012. Plots receiving the highest rate of ferrous sulfate resulted in annual bluegrass infestation declines from an early trial amount of 45% to a final average of 20% but also resulted in unacceptable late-summer events of annual bluegrass collapse. The ferrous sulfate medium rate resulted in a smooth transition from early-trial annual bluegrass infestation of 45% to an end of trial infestation of 20% and had the highest putting green quality. Previous research has reported that consistent use of paclobutrazol can effectively and safely reduce annual bluegrass infestations. In this trial annual bluegrass was reduced to 9% infestation after three months of application. Two unexpected observations from this trial were that ferrous sulfate, applied at medium to high rates, significantly reduced silvery thread moss (Bryum argentum Hedw.) populations and occurrences of dollar spot (Sclerotinia homoeocarpa F. T. Bennett) disease. Dollar spot control with ferrous sulfate has not previously been reported in the literature, so additional studies were designed to investigate this phenomenon further. A creeping bentgrass putting green study was conducted to determine if sulfur, iron, or the two combined as ferrous sulfate decreases dollar spot activity. Ferrous sulfate resulted in the highest turf quality and suppressed S. homoeocarpa infection, even during high disease pressure. Fe-EDTA suppressed dollar spot infection as well as ferrous sulfate but quality declined to unacceptable levels during the summer, due to Fe-EDTA only. Sulfur did not affect or increased S. homoeocarpa infection, indicating that a high and frequent foliar rate of iron is responsible for dollar spot control. An in-vitro study was conducted to determine if agar pH in combination with iron concentrations affects mycelial growth of S. homoeocarpa. Results from this trial indicated that 5.4 agar pH is an optimal pH for mycelial growth. The 10 to 100 mg iron kg-1 concentration had little effect on mycelial growth at 5.0 and 5.5 pH, but increased growth at 4.5 and 6.5 pH. As the iron concentration was increased from 10 to 100 to 1000 mg kg-1, mycelial growth decreased or stopped. Our final conclusions are that seasonal biweekly foliar applications of the medium rate of ferrous sulfate (24.4 kg ha-1) safely and effectively reduced annual bluegrass infestation out of a creeping bentgrass putting green, while also effectively suppressing silvery thread moss and dollar spot incidence. Master of Science

Creeping bentgrass (Agrostis stolonifera L.) is a major low-cut cool-season turfgrass used worldwide. The objectives of this research were to: 1) to gain insight into the diurnal fluctuation of N metabolism and effects of cytokinin (CK) and nitrate; 2) to characterize the impacts of N and CK on creeping bentgrass under heat stress; 3) to investigate the simultaneous effects of CK and N on the antioxidant responses of heat stressed creeping bentgrass; and 4) to examine the expression pattern of the major heat shock proteins (HSPs) in creeping bentgrass during different heat stress periods, and then to study the influence of N on the expression pattern of HSPs. The transcript abundance of nitrate reductase (NR), nitrite reductase (NIR), plastidic glutamine synthetase (GS2), ferredoxin-dependent glutamate synthase (Fd-GOGAT), and glutamate dehydrogenase (GDH) and N metabolites in shoots were monitored during the day/night cycle (14/8 h). All the measured parameters exhibited clear diurnal changes, except GS2 expression and total protein. Both NR expression and nitrate content in shoots showed a peak after 8.5 h in dark, indicating a coordinated oscillation. Nitrate nutrition increased diurnal variation of nitrate content compared to control and CKHowever, CK shifted the diurnal in vivo NR activity pattern during this period. Grass grown at high N had better turf quality (TQ), higher Fv/Fm, normalized difference vegetation index (NDVI), and chlorophyll concentration at both 15 d and 28 d of heat stress than at low N, except for TQ at 15 d. Shoot NO3-, NH4+, and amino acids increased due to the high N treatment, but not water soluble proteins. High N also induced maximum shoot nitrate reductase activity (NRmax) at 1 d. CK increased NDVI at 15 d and Fv/Fm at 28 d. In addition, grass under 100 µM CK had greatest NRmax at both 1 d and 28 d. Under high N with 100 µM CK, root tZR and iPA were 160% and 97% higher than under low N without CK, respectively. Higher O2- production, H2O2 concentration, and higher malonydialdehyde (MDA) content in roots were observed in grass grown at high N. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (POD) in roots were enhanced by high N at 19, 22, and 24% levels, respectively, relative to low N. Twenty-eight days of heat stress resulted in either the development of new isoforms or enhanced isoform intensities of SOD, APX, and POD in roots compared to the grass responses prior to heat stress. However, no apparent differences were observed among treatments. No CK effects on these antioxidant parameters were found in this experiment. At week seven, grass at medium N had better TQ, NDVI, and Fv/Fm accompanied by lower shoot electrolyte leakage (ShEL) and higher root viability (RV), suggesting better heat resistance. All the investigated HSPs (HSP101, HSP90, HSP70, and sHSPs) were up-regulated by heat stress. Their expression patterns indicated cooperation between different HSPs and that their roles in creeping bentgrass thermotolerance were affected by N level. Ph. D.

Soil temperature has a crucial impact on physiological processes and growth of plants with important consequences for plant productivity and food safety including nitrate accumulation in leaf blades of leaf vegetables. Consumer demand for high-quality, fresh-cut vegetables has increased rapidly in the last decades, and temperature modulation can help control nitrate concentration in fresh vegetables, an important trait of product safety. Corn salad plants [Valerianella locusta (L.) Laterr., cultivar Gala] were grown at three root temperatures (15, 20, and 25 °C) in a floating system. This experimental setup allowed to directly evaluate the effect of root temperature on yield and plant quality excluding the effect on soil processes and properties. Nutrient solution was renewed weekly and kept aerated while air temperature was maintained constant at 20 °C for all treatments during the entire time of experiments. At harvest, plants were collected, the shelf life evaluated, and the nutrient uptake [NO3−, iron (Fe) from 59Fe-o,oEDDHA, and 35SO42−] and mineral content were determined. Results showed that growing conditions at 20 °C of the nutrient solution led to the best plant performance in terms of yield, nitrate content at leaf level, root biomass, leaf area, and greenness with positive effects on postharvest quality, i.e., less rapid leaf loss of greenness and leaf fresh weight (FW) loss during conservation at 4 °C. At this temperature condition of the nutrient solution, it has also been observed an enhanced functionality of mechanisms involved in the acquisition of nutrients like NO3−, Fe, and SO42−, which are known to play an important role in nitrate level in leaf tissues of crops. Plants grown at 15 °C showed minor growth, whereas the nutrient solution at 25 °C caused stress for the plants affecting negatively the quality and yield. Overall, the results obtained showed that root temperature plays a fundamental role in several plant processes that affect yield and its quality; for hydroponic system cultivations, a level of growing-medium temperature close to that of the surrounding air seems suitable.