The germination of Kentucky bluegrass, (Poa pratensis L.), seeds is profoundly influenced by two light reactions. One, the phytochrome reaction (P), is promotive, and the other, the so-called “high-energy reaction (HER)”, is inhibitory to germination. The level of germination displayed in 14 days as the resultant of these two opposing reactions is appreciably influenced by temperature.
In darkness, the seeds germinate well at certain temperature alternations but not at constant temperatures. At 15-25°C, the promotive effects of temperature alternation are accomplished in the first 5 to 6 cycles. The promotive effects of alternations are displayed in darkness when the daily period at 25° is between 4 and 14 hours.
Brief daily high-intensity fluorescent illuminances (approximately 4,000 ft-c) during otherwise continuous darkness at constant 20°C induce high germination in most lots. Continuous medium-to-high intensity illumination (approximately 1,200 ft-c) very weakly promotes germination and in potentially promoted seeds inhibits germination to about the level of the dark controls.
Inhibitory effects of continuous light on potentially promoted seeds are best displayed at 20°C constant although, in ‘Newport’ they are observable at 15-25°. The inhibition of ‘Newport’ at 15-25° is to a level below that of the dark controls but above that caused by prolonged illumination at 20°.
Thus conditions most promotive to germination are 15-25°C alternations and brief daily illuminances of high intensity. Simultaneous application of these 2 conditions causes higher germination than when either is applied alone and in one lot of ‘Newport’ the effects are strikingly additive.
. Pergamon Press, Oxford, UK Bushman, B.S. Amundsen, K.L. Warnke, S.E. Robins, J.G. Johnson, P.G. 2016 Transcriptome profiling of kentucky bluegrass ( Poa pratensis L.) accessions in response to salt stress BMC Genomics 17 1 12 Carrow, R.N. Duncan, R.R. 1998
Sods of ‘Merton’ Kentucky bluegrass (Poa pratensis L.) were placed in atmospheres containing 0, 9, 18, or 27% CO2; 0, 2, 4, 8, or 16% O2; and 0, 2, 4, or 8 ppm C2H4. Neither CO2 nor C2H4 toxicity nor O2 deficiency caused sod injury in commercial sod toads. Ventilation tubes inserted in commercial sod toads failed to increase gas exchange and heat dissipation beyond a 3-cm distance.
Four categories of billbug (Sphenophorus parvulus Gyllenhal) resistance were identified and contrasted in terms of anatomical, morphological, and physiological characteristics of 12 Kentucky bluegrass (Poa pratensis L.) cultivars. Discriminant analysis was used as a separatory procedure to determine the relative importance of these plant characteristics to observed billbug resistance and to construct a prediction procedure for potential billbug resistance classes. Variables measured from field-, controlled environment-, and greenhouse-grown plants were analyzed for the most biologically revealing characteristics of potential billbug resistance. Separatory discrimination indicated that cultivars exhibiting moderate and high billbug resistance had tougher tissue than tolerant or susceptible cultivars. Tolerant and highly resistant cultivars differed from those susceptible and moderately resistant by concealing billbug injury. Development of a predictive classification procedure was promising, with percent correct classification ranging from 67% to 94%, depending on number and type of discriminating variables analyzed.
Carbohydrate metabolism is important for plant adaptation to drought stress. The objective of this study was to examine major forms of carbohydrates associated with superior drought tolerance and post-drought recovery in kentucky bluegrass (Poa pratensis) by comparing responses of different forms of carbohydrates with drought stress and re-watering in two cultivars contrasting in drought tolerance. Plants of drought-tolerant ‘Midnight’ and drought-sensitive ‘Brilliant’ were maintained well watered or subjected to drought stress for 10 days by withholding irrigation, and drought-stressed plants were re-watered for 3 days. Physiological analysis (turf quality, relative water content, and electrolyte leakage) confirmed the genetic variability of the two cultivars in drought tolerance. The two cultivars exhibited differential responses to drought stress and re-watering for the content of water-soluble sugars (sucrose, fructose, and glucose) and storage carbohydrates (starch and fructan), and ‘Midnight’ maintained higher sucrose content at 10 days of drought stress and more fructan at 3 days of re-watering. The greater accumulation of sucrose in ‘Midnight’ under drought stress corresponded with higher activities of two sucrose-synthesizing enzymes (sucrose phosphate synthase and sucrose synthase) but was not related to the sucrose-degrading enzyme activity (acid invertase). These results suggested that increased sucrose accumulation resulting from the maintenance of active sucrose synthesis could be associated with superior turf performance during drought stress, whereas increased fructan accumulation could contribute to rapid re-growth and post-drought recovery on re-watering in kentucky bluegrass.
Abscisic acid (ABA) and glycine betaine (GB) may regulate plant responses to drought or salinity stress. The objectives of this controlled-environment study were to determine whether foliar application of ABA or GB improves turf quality under drought or salinity and whether improved stress responses were associated changes in antioxidant metabolism in two C3 turfgrass species, creeping bentgrass (Agrostis stolonifera) and kentucky bluegrass (Poa pratensis). Physiological parameters evaluated included turf quality, leaf relative water content, membrane electrolyte leakage (EL), membrane lipid peroxidation [expressed as malondialdehyde (MDA) content], and activity of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX). Abscisic acid and GB were both effective in mitigating physiological damage resulting from drought or salinity for both grass species, but effects were more pronounced on kentucky bluegrass. The most notable effects of ABA or GB application were the suppression of EL and MDA accumulation and an increase in APX, POD, and SOD activities after prolonged periods of drought (21 days) or salinity stress (35 days). These results suggest foliar application of ABA or GB may alleviate physiological damage by drought or salinity stress in turfgrass and the maintenance of membrane stability and active antioxidant metabolism could contribute to the positive effects in the stress mitigation effects.
The effectiveness of ethephon for reducing the growth of annual bluegrass (Poa annua L.), when grown as single plants in pot culture in the greenhouse or outdoors, and within a Kentucky bluegrass (Poa pratensis L.) sod, was evaluated. Ethephon reduced the growth of annual bluegrass more than that of Kentucky bluegrass. Concentration was more important in reducing plant spread than the number of applications. Ethephon applied to field grown turf reduced the leaf area per tiller of annual bluegrass but not Kentucky bluegrass. Leaves per tiller and the shoot dry weight of field grown Kentucky bluegrass increased with increasing ethephon rates compared to nontreated plots. Although significant growth retardation occurred for both species in pot culture, only Kentucky bluegrass canopy height decreased in the field with increasing ethephon rates. Decreased Kentucky bluegrass canopy height resulted from reduced sheath length. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon).
High temperatures during simulated shipping were more consistently injurious to ‘Merion’ Kentucky bluegrass (Poa pratensis L.) sod than other factors tested. Sod produced with increasing amounts of nitrogen had increased rates of temperature rise. Higher nitrogen levels also increased respiration, percent leaf kill, and ethylene production. There was no consistent effect of 6-benzylamino purine (BA) on sod storage life. Mowing to 2 cm prior to harvest reduced the amount of living tissue, causing lower temperatures, lower respiration rates, and less sod injury. Root production after sod transplanting was greatest from sod grown with 0 and 100 kg/ha of nitrogen fertilization and decreased with higher nitrogen rates.
The distribution of photosynthetically fixed carbon within a turfgrass sod was investigated following a routine mowing. The partitioning of 14C-labeled photosynthate was monitored in Kentucky bluegrass (Poa pratensis L. cvs. Baron and Merion) turf 2, 24, and 72 hr after mowing at 3.8 cm. Circles of turf (15 cm in diameter) were exposed to 14CO2 for 15 min, 10-cm-diameter plugs were removed 2 and 24 hr after exposure, and the plants were assayed for radioactivity. Experiments were conducted in late spring, midsummer, and early autumn for 2 years in field plots on a silt loam. Photosynthate translocation from leaf blades to leaf sheaths and crowns was reduced by as much as 25% within 2 hr after mowing but generally returned to a constant and greater rate within 24 hr. Midsummer mowing temporarily inhibited photosynthate transport more than mowing in spring or fall. Photosynthate distribution within turfgrass plants was influenced more by time of year and nutritional status than by mowing. Kentucky bluegrass maintained as closely mowed turf sustains only a slight and temporary disturbance in energy partitioning in response to mowing.
A turfgrass blend of ‘Parade’, ‘Adelphi’, ‘Glade’, and ‘Rugby’ Kentucky bluegrasses (Poa pratensis L.) was treated with N-[2,4-dimethyl-5-[[(trifluromethyl) sulfonyl] phenyl] acetamide (mefluidide) at 0.28 and 0.56 kg ha−1; (2-chloroethyl) phosphonic acid (ethephon) at 2.24, 4.48, and 6.72 kg ha−1; 5-(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo [5,4,1,02,6,08,11]dodeca-3,9-diene (BAS 106 00 W) at 1.68, 3.36, and 5.04 kg ha−1, and α-(1-methylethyl)-α-[4-(trifluromethoxy) phenyl]-5-pyrimidinemethanol (EL-500) at 0.84, 1.21, and 1.40 kg ha−1 in field and greenhouse studies. Each of the materials investigated was effective in retarding Kentucky bluegrass growth in field studies. However, effects on growth inhibition and turfgrass quality varied between years. Ethephon was the only material not effective in reducing clipping yield in the greenhouse, whereas none of the growth retardants inhibited root organic matter production or rhizome weight in the greenhouse study.