Michael D. Peel

Characterization of physiological responses of two alfalfa half-sib families with improved salt tolerance

Alfalfa (Medicago sativa L.) is a major forage crop worldwide that is relatively sensitive to soil salinity. Improved cultivars with high production on saline soil will benefit many producers and land managers. This study reports the characterization of physiological responses of two unrelated experimental alfalfa half-sib families, HS-A and HS-B, selected for their improved survival under saline conditions (up to EC 18). Six-week-old plants were subjected to NaCl-nutrient solution treatment for three weeks starting at an electrical conductivity (EC) of 3 dS m(-1) with incremental increases of 3 dS m(-1) every week, reaching 9 dS m(-1) in the third week. HS-B showed greater leaf number (72%) and stem length (44%) while HS-A showed better leaf production (84%) under salt treatment compared to the initial genetic backgrounds from which they were developed. This improved growth is associated with 208% and 78% greater accumulation of chlorophyll content in HS-B and HS-A, respectively. Both HS-A and HS-B also showed improved capability to maintain water content (RWC) under salt stress compared to the initial populations. Differing from its initial populations (P-B), HS-B did not accumulate Na in shoots after salt treatment. HS-B also maintained K(+)/Na(+) and Ca(2+)/Na(+) ratios, while P-B showed 59% and 69% decrease in these ion ratios, respectively. Na(+) content in HS-A was not different from its initial populations (P-A) after salt treatment. However, HS-A showed an enhanced accumulation of Ca(2+) and maintained the levels of Mg(2+) and K(+) in shoots compared to the P-A populations. This study provides physiological support of improved salt tolerance in HS-A and HS-B and suggests that these plants maintain ion homeostasis but have different mechanisms of coping with high salinity.

Stand Establishment and Persistence of Perennial Cool-Season Grasses in the Intermountain West and the Central and Northern Great Plains

Abstract The choice of plant materials is an important component of revegetation following disturbance. To determine the utility and effectiveness of various perennial grass species for revegetation on varied landscapes, a meta analysis was used to evaluate the stand establishment and persistence of 18 perennial cool-season grass species in 34 field studies in the Intermountain and Great Plains regions of the United States under monoculture conditions. Combined across the 34 studies, stand establishment values ranged from 79% to 43% and stand persistence values ranged from 70% to 0%. Intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D. R. Dewey), tall wheatgrass (Thinopyrum ponticum [Podp.] Z.-W. Liu & R.-C. Wang), crested wheatgrass (Agropyron spp.), Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy), and meadow brome (Bromus riparius Rehmann) possessed the highest stand establishment (≥ 69%). There were no significant differences among the 12 species with the largest stand persistence values. Basin wildrye (Leymus cinereus (Scribn. & Merr.) Á. Löve), Altai wildrye (Leymus angustus [Trin.] Pilg.), slender wheatgrass (Elymus trachycaulus [Link] Gould ex Shinners), squirreltail (Elymus spp.), and Indian ricegrass (Achnatherum hymenoides [Roem. & Schult.] Barkworth) possessed lower stand persistence (≤ 32%) than the majority of the other species, and Indian ricegrass (0%) possessed the lowest stand persistence of any of the species. Correlations between environmental conditions and stand establishment and persistence showed mean annual study precipitation to have the most consistent, although moderate effect (r = ∼0.40) for establishment and persistence. This relationship was shown by the relatively poor stand establishment and persistence of most species at sites receiving less than 310 mm of annual precipitation. These results will be a tool for land managers to make decisions concerning the importance of stand establishment, stand persistence, and annual precipitation for revegetation projects on disturbed sites.

A molecular genetic linkage map identifying the St and H subgenomes of Elymus (Poaceae: Triticeae) wheatgrass

Elymus L. is the largest and most complex genus in the Triticeae tribe of grasses with approximately 150 polyploid perennial species occurring worldwide. We report here the first genetic linkage map for Elymus. Backcross mapping populations were created by crossing caespitose Elymus wawawaiensis (EW) (Snake River wheatgrass) and rhizomatous Elymus lanceolatus (EL) (thickspike wheatgrass) to produce F(1) interspecific hybrids that were then backcrossed to the same EL male to generate progeny with segregating phenotypes. EW and EL are both allotetraploid species (n = 14) containing the St (Pseudoroegneria) and H (Hordeum) genomes. A total of 387 backcross progeny from four populations were genotyped using 399 AFLP and 116 EST-based SSR and STS markers. The resulting consensus map was 2574 cM in length apportioned among the expected number of 14 linkage groups. EST-based SSR and STS markers with homology to rice genome sequences were used to identify Elymus linkage groups homoeologous to chromosomes 1-7 of wheat. The frequency of St-derived genome markers on each linkage group was used to assign genome designations to all linkage groups, resulting in the identification of the seven St and seven H linkage groups of Elymus. This map also confirms the alloploidy and disomic chromosome pairing and segregation of Elymus and will be useful in identifying QTLs controlling perennial grass traits in this genus.

Growth performance, ruminal fermentation profiles, and carcass characteristics of beef steers grazing tall fescue without or with nitrogen fertilization1

A 2-yr study was conducted to evaluate the effects of finishing beef cattle grazed on tall fescue (TF) pastures without or with N fertilization on growth performance, ruminal fermentation, and carcass characteristics. In each grazing season, 18 Angus crossbred steers were arranged in a completely randomized design with repeated measures on the following 2 treatments: TF without N fertilizer (TF–NF) and TF with N fertilizer (TF+NF). Three replicated pastures with 3 steers per replicate were assigned to each treatment. A total of 168 kg/ha N fertilizer was applied in 3 split applications at 56 kg/ha each to the TF+NF in each grazing season. Steers rotationally grazed on 0.47-ha pasture for 7 d with a 28-d rotation interval for a total of 16 wk. Body weight data and pasture forage samples were collected every 4 wk, whereas ruminal fluid was collected at wk 4, 10, and 16. After the completion of 16-wk grazing, ultrasound measurement was performed to assess carcass characteristics. In response to N fertilization, greater CP concentration was detected on TF+NF compared with TF–NF in 2011 (11.9 vs. 10.6% DM, respectively; P < 0.01). Overall ADG was greater in steers that grazed TF+NF pastures (P < 0.05) in the 2-yr grazing seasons, and tended to increase (P = 0.07) overall DMI and G:F in 2010. Regardless of N fertilization, ADG peaked between wk 4 and 8 (1.05 kg/d; P < 0.01), and then declined until wk 16. A gradual decline of G:F was noticed with progression in grazing seasons (P < 0.05). Greater total VFA concentrations were detected in ruminal fluid of steers that grazed TF+NF (P < 0.01), but a minor effect was shown on individual VFA (acetate, propionate, and butyrate) concentrations and acetate-to-propionate ratio. Ruminal ammonia-N (NH3-N) concentration increased (P < 0.01) with N fertilization, whereas NH3-N:total VFA increased (P < 0.01) with the progression of grazing seasons. Backfat thickness, ribeye area, and intramuscular fat concentration did not differ between treatments. Overall results of this study indicate that N fertilization on TF affected ruminal fermentation which positively influenced growth performances, but did not affect carcass characteristics of grazing beef steers. In addition, readily fermentable carbohydrate supplementation is needed to improve utilization of increased dietary CP due to N fertilization and consequently enhance growth performances of grazing steers.

Physiological and molecular characterisation of lucerne (Medicago sativa L.) germplasm with improved seedling freezing tolerance

Abstract. We conducted greenhouse experiments to compare 14 lucerne (alfalfa, Medicago sativa L.) germplasms for their survival following freezing. Some are collections adapted to the Grand River National Grasslands in South Dakota. We hypothesised that these collections might have developed a tolerance to survive the frigid growth conditions common there. Two of these collections, River side (RS) and Foster ranch (FR), showed greater freezing tolerance than the other germplasms tested, based on their consistent survival rates with or without cold acclimation. In multiple freezing studies, RS and FR had average survival rates of 74% and 79%, respectively, in contrast to the commercial cultivars Apica and CUF-101 (CUF) (64% and 24%, respectively). The average temperature at which 50% of ions in plant tissues leak out (LT50) by freezing based on leaf electrolyte leakage was closely correlated with survival rates. Leaf LT50 improved 2–3-fold after 3 days of cold acclimation, based on leaf electrolyte leakage analysis, reaching −18°C, –9.6°C, –8.5°C, and −5°C for RS, FR, Apica, and CUF, respectively. Comparison of total soluble sugars and relative water content in shoots before and after cold acclimation showed that they were not well correlated with freezing tolerance and could not explain the superior responses of RS and FR during cold acclimation. Transcript analysis of cold-responsive MsCBF1, MsCBF2 and CAS15B genes showed that RS, FR, Apica and CUF exhibited distinct patterns of cold induction. Although RS, FR and Apica showed a rapid or greater increase in expression level of one or two of these genes, CUF showed only a moderate induction in MsCBF2 and CAS15B transcripts, suggesting that expression of these genes may be a good molecular marker for freezing tolerance in lucerne. The findings provide evidence that freezing tolerance in lucerne is a complex trait and that a combination of different mechanisms may greatly improve freezing tolerance. RS and FR are potential resources in breeding for improving freezing tolerance in lucerne.

Effects of energy supplementation in pasture forages on in vitro ruminal fermentation characteristics in continuous cultures1

ABSTRACT A dual-flow, continuous-culture system was used to assess the effects of energy supplementation with 4 pasture forages on in vitro ruminal fermentation characteristics. Twelve dietary treatments were tested in a split-plot design: energy supplementation (no concentrate, 30% ground corn, or 30% dried distilled grains with solubles) as a whole plot and pasture forages [tall fescue (TF) without N fertilizer, TF with N fertilizer (TF+NF), TF-alfalfa mixture, and TF-birdsfoot trefoil mixture (TF+BFT)] as a subplot. Three replicated runs lasted 9 d each, with 7 d for adaptation period and 2 d for data collection. The greatest total VFA and propionate concentrations (P

Fatty acid composition in adipose tissue of pasture- and feedlot-finished beef steers1

ABSTRACT Twenty-seven Angus crossbred steers were used to evaluate the effects of finishing beef cattle on pasture without or with N fertilization of the pasture versus feedlot finishing beef steers on fatty acid composition in subcutaneous adipose tissue. A completely randomized design with repeated measures was used to arrange steers into 3 treatments: grazing on tall fescue (TF) without N fertilizer (TF−NF), grazing on TF with N fertilizer (TF+NF), and feeding TMR on feedlot (FLT). For the pasture treatments, it was hypothesized that N fertilization would affect fatty acid composition of adipose tissue in pasture-fed beef steers because of its potential effects on nutrient and energy utilization. Three replicated pastures or group pens with 3 steers per replicate were assigned into each treatment. A total of 168 kg of N fertilizer per hectare was applied in 3 split applications at 56 kg/ha to the TF+NF. From May through September 2010 (total of 16 wk), pasture-finished steers were grazed on replicated 0.47-ha paddocks, while steers on the FLT were fed a finishing diet containing 76% barley grain. Subcutaneous adipose tissue biopsies were obtained on wk 4, 12, and 16. Total fat percentage in TF pasture did not differ due to N fertilization, and similar total fat concentrations were also measured between TF pasture and the FLT on wk 12 and 16. Nitrogen fertilization increased PUFA proportion (mg/100 mg of total fatty acid) in TF grass on wk 4 and 12, including C18:3 n-3 (P

Comparison of alfalfa, birdsfoot trefoil, and cicer milkvetch in combination with 25, 50, or 75% tall fescue in a continuous-culture system1

ABSTRACT A continuous-culture experiment was performed to investigate the effects of tall fescue (TF)-to-legume ratios (TF:legume = 75:25, 50:50, or 25:75 on a DM basis) of 3 different TF-legume mixed diets [TF-alfalfa (TF+AF), TF-birdsfoot trefoil (TF+BT), or TF-cicer milkvetch (TF+CM)] on in vitro fermentation characteristics. Nine dietary treatments were tested in a 3 (TF-legume ratio) × 3 (TF-legume mixed diet) split-plot design. Dietary treatments did not affect the concentrations of total VFA, acetate, and butyrate, whereas increasing legume proportion increased propionate concentration (P = 0.03). Regardless of TF-legume ratio, feeding TF+CM re sulted in the greatest propionate concentration, whereas TF+AF and TF+BT maintained a similar concentration of propionate. The TF+AF combination resulted in a greater acetate-to-propionate ratio than TF+BT or TF+CM (P = 0.03). Decrease in ammonia-N concentration (P

Breeding meadow bromegrass for forage characteristics under a line-source irrigation design

Production from less productive lands limited by irrigation can be increased if genetically improved pasture grasses are developed with increased dry matter production (DMY) and nutritional quality. In 2000, 18 half-sib families of meadow bromegrass were seeded in a modified strip-plot design with four replications and water levels (WL) applied as nonrandom strips ranging from 10.1 mm wk-1 at WL-5 to 36.8 mm wk-1 at WL-1. The objective was to estimate genetic variability and parameters as affected by irrigation level and harvest date for DMY, crude protein (CP), in vitro true digestibility (IVTD), neutral detergent fiber (NDF), and digestible neutral detergent fiber (dNDF). Low h2 estimates for DMY suggest that gains in total DMY from selection within these half-sib families (HSF) are not likely. Crude protein concentrations were more influenced by harvest date than WL. Heritability estimates were relatively high regardless of WL or harvest date for IVTD. The effect of WL on h2 estimates for NDF were less...

Tall fescue forage mass in a grass-legume mixture: predicted efficiency of indirect selection

High fertilizer prices and improved environmental stewardship have increased interest in grass-legume mixed pastures. It has been hypothesized, but not validated, that the ecological combining ability between grasses and legumes can be improved by breeding specifically for mixture performance. This experiment examined the predicted efficiency of selection in a grass monoculture environment to indirectly improve tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) forage mass in a grass-legume mixture. Heritability, genetic and rank correlations, and selection efficiencies were estimated for forage mass in a tall fescue half-sib population grown as spaced-plants overseeded with either turf-type tall fescue (monoculture) or alfalfa (mixture). Heritability for tall fescue forage mass in monoculture ranged from 0.32 to 0.70 and were always similar or greater than those in mixture (range 0.27–0.55) for four successive harvests and annual total. Genetic correlations between monoculture and mixture tall fescue forage mass varied with values of 0.48, 0.92, −0.31, 0.70, and 0.25 in June, July, August, October, and annual total, respectively. Indirect selection efficiencies exceeded or approached direct selection for mixtures only in July and October (1.29, and 0.73, respectively). Whereas, indirect selection efficiencies were low in June, August, and annual forage mass (0.58, −0.31, and 0.28, respectively). Moreover, low Spearman’s rank correlations (−0.03 to 0.35) indicated differing half-sib family performance between the monoculture and mixture environments. Results indicate that direct selection should be used to improve tall fescue forage mass in a grass-legume mixture, and support the hypothesis of increasing ecological combining ability by breeding for mixtures per se.