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J.W. Moon Jr., D.M. Kopec, E. Fallahi, C.F. Macino, D.C. Slack, and K. Jordan

Photosynthesis was reduced by 85% to 90% in perennial ryegrass (Lolium perenne L. cv. Derby) following a one-day chilling exposure at 8C day (450 μmol·s-1·m-2 PPF) and 5C night. Seven days of recovery at 22/17C day/night were required for full recovery of photosynthesis. More than 75% of the limitation in photosynthesis following chilling was due to non-stomatal factors, and reduced initial slopes of CO2 assimilation vs. intercellular CO, indicate that photosynthetic capacity was reduced for 5 days following chilling. Carbon dioxide assimilation at saturating intercellular CO2 (>500 μmol·mol-l) was also reduced by chilling, indicating again that stomatal limitations were a minor contributor to the photosynthetic reduction observed under ambient CO2.

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E.H. Ervin and A.J. Koski

A growth chamber and a greenhouse study were conducted to determine if successive applications of trinexapac-ethyl (TE) to developing perennial ryegrass (Lolium perenne L.) plants would reduce leaf elongation rate (LER) while increasing tiller number and root mass. Growth parameters measured were LER, tiller number, and root mass. In the growth chamber, developing perennial ryegrass plants were sprayed twice with TE at 0.24 kg·ha-1 a.i. at 20 and 40 days after emergence. Leaf elongation rate was reduced by ≈35% following two applications of TE in both growth chamber experiments. This treatment increased the number of tillers per plant in the growth chamber at 60 days after emergence and in the greenhouse at 150 days after emergence, but had no effect on root or shoot mass in either location. Multiple applications of TE to developing perennial ryegrass turfs may favor quicker establishment in terms of tillering, while substantially reducing mowing requirement. Chemical names used: 4-cyclopropyl-α-hydroxy-methylene-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl).

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Alejandro Alarcon*, Frederick T. Davies, David Wm. Reed, Robin L. Autenrieth, and David A. Zuberer

Arbuscular mycorhizal fungi (AMF) have been used in phytoremediation and can increase tolerance and growth of plants in contaminated environments. However, little is known about the influence AMF on plant growth to organic contaminants in soils. A greenhouse experiment was conducted to study the response of seedlings of annual ryegrass (Lolium perenne L.) var. Passerel Plus inoculated with Glomus intraradices Schenck & Smith in soil contaminated with sweet Arabian median crude oil. Inoculated (AMF) and non-inoculated (Non-AMF) plants were established in an pasteurized and artificially contaminated sandy loam soil with 0; 3000; 15,000; or 45,000 mg of petroleum kg-1 soil (n = 20). Plants were inoculated with 500 spores of G. intraradices (Mycorise® ASP, PremierTech Biotechnologies, Canada). After 90 days, plant growth of AMF or Non-AMF plants, was drastically affected at all petroleum concentrations. However, G. intraradices enhanced plant growth, chlorophyll content, and gas exchange of plants grown at 3,000 mg kg-1 compared to Non-AMF plants. Total leaf area, chlorophyll, and net photosynthesis were also higher (+380%, +63%, and +81%, respectively) at this concentration. Water use efficiency (net photosynthesis/stomatal conductance) of AMF-plants was three times greater than Non-AMF at 3,000 mg·kg-1. At concentrations of 15,000 and 45,000 mg kg-1 AMF did not have effect, but colonization was observed (11.8% and 18.6%, respectively). These values of colonization were significantly lower than those observed in AMF-plants at 0 (42.5%) and 3,000 mg·kg-1 (55.6%). Studies are currently being conducted to understand the physiological role of AMF on plants exposed to organic contaminants.

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P.H. Demoeden, M.J. Mahoney, and M.J. Carroll

Fenoxaprop (0.027, 0.036, and 0.045 kg·ha-1) was field-applied at either of 2-, 3-, or 4-week intervals to perennial ryegrass (Lolium perenne L.) naturally infested with smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl.] in Maryland (Easton and Silver Spring) during 1989 and 1990. In 1989, fenoxaprop applied at 2- or 3-week intervals at 0.027 kg·ha-1 provided fair (>74%) to good (>80%) smooth crabgrass control. Fenoxaprop applied at 0.036 or 0.045 kg·ha-1 at 2- or 3week intervals provided good to excellent (> 90%) smooth crabgrass control. Four-week intervals generally provided control that was inferior to the shorter application intervals at Silver Spring but not at Easton. In 1990, all rates provided good to excellent smooth crabgrass control when applied at 2- or 3-week intervals in Easton. At Silver Spring, where smooth crabgrass levels were very high, >88% control was provided by 0.036 kg·ha-1 applied at a 2-week interval and by 0.045 kg·ha-1 applied at either a 2- or 3-week interval. Chemical name used: [±]-2-[4-[(6 chloro-2 benzoxazolyl)oxy]phenoxy] propanoic acid (fenoxaprop).

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Michael A. Fidanza and Peter H. Dernoeden

A field investigation was conducted during 1991 and 1992 to determine the effectiveness of enzyme-linked immunosorbent assay (ELISA) to predict brown patch (Rhizoctonia solani Kühn) infection events in `Caravelle' perennial ryegrass (Lolium perenne L.). Turfgrass samples were collected either between 7:00 and 8:00 am or 4:00 and 5:00 pm, and from plots mowed to a height of either 1.7 or 4.5 cm. Pathogen detection levels were generally higher in am-sampled turf and in plots mowed to a height of 4.5 cm. During 2 years, only 7 of 15 infection events were predicted from samples collected from high-cut turf and only three from samples collected from low-cut turf. While this technology is useful for confirming the presence of R. solani, it was unreliable for predicting infection events.

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T.K. Danneberger, M.B. McDonald Jr., C.A. Geron, and P. Kumari

This study evaluates the effects of seed osmoconditioning on germination and seedling growth of perennial ryegrass (Lolium perenne L.). Seeds were osmoconditioned in polyethylene glycol 8000 with water potentials ranging from 0 to -1.4 MPa for 48 hours. Osmoconditioning for this crop at -1.1 MPa resulted in a 35% germination increase after 48 hours under optimum (15/25C) germination conditions. This promotive effect was observed until 104 hours for percentage germination and root growth and 118 hours for shoot growth. Rate of seed germination and seedling root growth of osmoconditioned seeds also was enhanced when seeds were placed under suboptimum germination temperatures of 5, 10, and 15C. These results suggest that while osmoconditioning enhanced initial germination rate and seedling root growth under laboratory conditions, it did not do so under prolonged favorable conditions. However, the promotive effects of osmoconditioning were more beneficial when seeds were exposed to less favorable germination conditions.

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J.A. Doty, W.S. Braunworth Jr., S. Tan, P.B. Lombard, and R.D. William

Evapotranspiration (ET) of three perennial ryegrass (Lolium perenne L.) cultivars and one cultivar each of colonial bentgrass (Agrostis tenuis L.) and tall fescue (Festuca arundinacea L.) was measured in the field. Soil water depletion was measured with a neutron probe. Under minimal maintenance (i.e., no irrigation and infrequent mowing), ET was not significantly different for five perennial grasses. All grasses used more water than the bare-ground treatment. Soil water uptake was greatest in the upper soil layer (O to 25 cm) and decreased with depth. Few differences in water uptake were noted among grasses within each soil layer.

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A.R. Mazur and J.S. Rice

Research was conducted to determine the influence of the rate of seeding perennial ryegrass (Lolium perenne L.) over bermudagrass [Cynodon dactylon (L.) Pers × C. transvaalensis Burtt-Davy] on both the establishment of the ryegrass and the quality of bermudagrass golf greens. Increasing seeding rate from 90 to 180 g·m–2 resulted in more rapid establishment and a linear increase in turf quality. Turf density, as measured by leaf number, displayed linear and quadratic responses to seeding rates, with higher rates producing the greatest leaf numbers. Leaf width declined linearly with seeding rate, suggesting higher putting quality, as did tillers per plant. Spring transition to bermudagrass was slowed at high (150–180 g·m–2) seeding rates, with significantly more ryegrass present in late May. Emergence and growth of bermudagrass were suppressed longer at the higher overseeding rates. We conclude that the choice of seeding rate for ryegrass is a compromise between rapid development of, and maintenance of, quality turf vs. early smooth transition to bermudagrass in the spring.

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J.S. Ebdon, R.A. Gagne, and R.C. Manley

Turf loss from freezing injury results in costly reestablishment, especially with turfgrasses such as perennial ryegrass (Lolium perenne L.) having poor low-temperature tolerance. However, no studies have been conducted to investigate the relative importance of low-temperature tolerance and its contribution to turfgrass quality (performance) in northern climates. The objective of this research was to compare critical freezing thresholds (LT50) of 10 perennial ryegrass cultivars representing contrasting turf-quality types (five high- and five low-performance cultivars). Cultivar selection was based on turfgrass quality ranking (top and bottom five) from the 1997 National Turfgrass Evaluation Program (NTEP) trial conducted at the Maine (Orono) location. Ten freeze-stress temperatures (-3 to -21 °C) and a nonfrozen control (5 °C) were applied to 5-month-old plants. Acclimated (AC) plant material maintained in an unheated polyhouse during the fall and winter in Massachusetts was compared to nonacclimated (NA) plant material (grown at 18 °C minimum in a greenhouse). Low-temperature tolerance was assessed using whole-plant survival and electrolyte leakage (EL). Estimates of LT50 were derived from fitted EL and survival curves using nonlinear regression. High-performance cultivars were able to tolerate significantly lower freeze-stress temperatures indicated by less EL and greater survival compared to low-performance cultivars. The EL method had good predictive capability for low-temperature survival. Acclimated tissues and high-performance cultivars had significantly flatter EL curves and lower mortality rates. These results underscore the importance of selecting cold-tolerant perennial ryegrass genotypes for adaptation to northern climates.

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Daniel C. Bowman and Jack L. Paul

The absorption and assimilation of 15N-labeled urea, (NH4)2 S O4, and KNO applied to the foliage of perennial ryegrass (Lolium perenne L.) turf were examined under a controlled environment. Each source of N was dissolved in deionized water to a final concentration of 25 g N/liter and spray-applied at a rate of 5 g N/m2. Absorption of the fertilizer-N over 48 hours, as measured by 15N analysis of tissue digests, amounted to 35%, 39%, and 40% for the urea, (NH4)2 S O4, and KNO3, respectively. Absorption was also estimated by a washing procedure that measured the urea remaining on the foliage and by the increase in total N in the ryegrass tissue. There were no significant differences between the three methods for absorption of (NH4) 2SO4 and KNO3. The washing method, however, significantly overestimated absorption of urea. Partitioning of the absorbed N between tissues was similar at 48 hours for all three N sources, averaging 32% in new leaves, 52% in old leaves and shoot tissue, and 16% in the roots. Most of the absorbed urea- and NH4 -N was assimilated by 48 hours, whereas only half of the NO3 -N was reduced during that period.