Genetic variances for dry matter yield, nitrogen content, and nitrogen yield in crested wheatgrass-alfalfa mixtures

Since its introduction from Asia in the early 1900s, crested wheatgrass [Agropyron cristatum (L.)Gaertner, A. desertorum (Fisch. ex Link) Schultes et al.] has had a major impact on the improvement of western rangelands of North America. Most of the early seedings with this cool-season grass were made as monocultures. Present and projected use of rangelands, however, prescribe that future crested wheatgrass cultivars have the genetic potential to be an effective component in a species complex including other grasses, shrubs, and forbs. The present study was conducted to evaluate the effect of associated alfalfa (Medicago sativa L.) on the performance and genetic variability in a 50-clone sample of a tetraploid crested wheatgrass breeding population. Significant (P<0.05) differences were found among the clonal lines for dry matter (DM) yield, nitrogen (N), and N yield. Opportunities for genetic improvement, as indicated by the magnitude of the genetic variation for these characters, was significantly increased when the grasses were grown in association with alfalfa. Significant (P<0.01) and positive correlations of clonal means between stand types indicated that differences among the clonal lines in DM yield, N content, and N yield were relatively consistent when grown with or without alfalfa. These results indicate that initial screening could be effectively done in tetraploid crested wheatgrass in the presence or absence of alfalfa. Final evaluation of breeding lines and experimental strains, however, should be done with alfalfa if the object is to develop cultivars to be grown in combination with that species

Genetic variability of Mg, Ca, and K in crested wheatgrass

Increasing available Mg in crested wheatgrass (Agropyron spp.) could reduce the incidence of grass tetany (hypomagnesemia) in ruminants glazing this forage. Raising the Mg levels might be done through genetic processes if enough variation in ion concentration existed in the Agropyrons. The purpose of this study was to determine the genetic variation in Mg, Ca, and K concentrations in 2 crested wheatgrass populations. Parent plants were vegetatively propagated to provide 6 replicates each of 12 clones of crested wheatgrass (A. desertorum) and 16 F3 clones of colchicine-induced tetraploid A. cristatum X natural tetraploid A. desertorum. Each plant was selected on a basis of seedling and mature plant vigor, forage, and seed yield, leafiness, resistance to pests, and response to environmental stress. The 2 populations were grown in separate, space-planted nurseries at Logan, Utah. Herbage was harvested at the pre-boot and early flowering stage in each of 2 years. Magnesium and Ca were determined by atomic absorption and K by flame emission. A reduced tetany potential (RTP) index for each clone was calculated as the sum of normalized Mg and (Ca+Mg)/K values. Significant (P<0.01) differences for all traits were detected among clones in each population. All traits, except K and RTP, were closely correlated. Broad-sense heritability values for most traits ranged from 0.61 to 0.84. Enough genotypic variation existed in both populations to warrant breeding lines with higher concentrations of Mg and larger RTP values. Such changes could reduce the incidence of grass tetany in livestock grazing crested wheatgrass

Genetic variability for elements associated with grass tetany in Russian wildrye

Grass tetany (hypomagnesemia) may be an important factor limiting productivity of animals grazing Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski]. This malady is associated with relatively low concentrations in the forage of Mg and Ca, and high values for K and K/(Ca+Mg). We studied the genetic variablity in a Russian wildrye breeding population for mineral elements that relate to grass tetany in ruminants. Forty-five progeny lines, established as spaced plants in a randomized complete block, were sampled at the pre-boot and boot stages in each of 2 years and analyzed for Mg, Ca, K, and P. Although seasonal variation was evident, K/(Ca+Mg) of the progeny lines ranged from 3.2 to 4.6, well above the 2.2 level at which a 5% incidence of grass tetany has been found in dairy cattle. With few exceptions, progenies differed for all traits evaluated. Differences among progenies were relatively consistent over harvests for all traits. A reduced tetany potential (RTP) was computed as the sum of normalized Mg and reciprocal of K/(Ca+Mg) values, providing an estimate of the grass tetany risk for individual progeny lines. The variation among progenies, and the magnitude of broad-sense heritability estimates for RTP (0.48) and K/(Ca+Mg) values (0.31), indicate that mineral ion composition of this breeding population can be altered through breeding. The high K/(Ca+Mg) values in the population suggest that it may be helpful to introduce genetic factors conditioning lower grass tetany potential from other sources. Intercharacter correlations suggest that breeding for higher levels of Mg will be accompanied by increased Ca and, to a lesser extent, increased K

Seasonal trends in herbage yield and quality of Agropyrons

Crested wheatgrasses (Agropyron spp.) are grown on 6 million ha in the U.S. and Canada, where they provide excellent early-season forage, but lose nutritional quality by midsummer. Some producers believe that A. fragile maintains its quality longer than other crested wheatgrasses. This study compared herbage yield and quality of 3 A. fragile entries with A. desertorum, A. cristatum, 1-28 (induced tetraploid of A. cristatum), and the hybrid 'Hycrest'. Entries were established near Logan, Ut., on 1-m spacings. Herbage yield and quality were determined in year 2 and 3 at vegetative, boot, flower, seed ripe, and post-seed-ripe maturity stages (harvests 1 through 5) and on regrowth following the vegetative and boot-stage harvests. All entries flowered within 1 to 2 days of each other. Dry-matter yield increased for all grasses, but digestibility (IVDMD), crude protein, and elemental concentrations declined with maturity. Mean IVDMD values for all grasses were 741,642,534,485, and 444 mg g-1 for harvests 1 through 5 and 490 and 560 mg g-1 for the regrowth following harvest 1 and 2. The A. fragile entries had higher N, Ca, P, and Ca/P, but lower yield, IVDMD, and grass tetany potential values than other Agropyrons. Contrary to expectations, IVDMD of A. fragile decreased to 500 mg g-1 , 6 to 11 days earlier than for the other Agropyrons. The 1-28 and Hycrest entries had higher yield, IVDMD, K, and grass tetany risk and lower N, Ca, P, and Ca/P than the other Agropyrons

Response to Selection for Reduced Grass Tetany Potential in Crested Wheatgrass

Grass tetany (hypomagnesemia) has caused substantial economic losses in ruminant animals grazing crested wheatgrass (Agropyron spp.) and other cool-season (C3) grasses. This malady is most prevalent in early lactating animals grazing forage that is deficient in Mg, Ca, and carbohydrates and with high levels of K. The K/(Ca + Mg) ratio expressed as moles of charge is often used to estimate the grass tetany potential of forage samples. Previous studies have shown that heritable variation exists in crested wheatgrass populations for traits associated with grass tetany, and research was conducted to determine the genetic response to selection for these traits. Selections were made during 1985 from two crested wheatgrass breeding populations in Utah (`I-28' and Hycrest) based on a reduced grass tetany potential (RTP) index, which incorporates the K/(Ca + Mg) ratio along with concentrations of Ca, Mg, and K. Mean values for the K/(Ca + Mg) were reduced by 5% in 1-28 and 11% in Hycrest after one cycle of selection. Narrow-sense heritability values based on actual genetic advance and parent-progeny regression ranged from 0.62 to 0.82 in analyses of data combined across two sampling dates and two years (1988 and 1989). Genetic response to selection on the basis of RTP index was closely associated with the K/(Ca + Mg) ratio and concentrations of Ca and Mg but not with levels of K. Correlations between the K/(Ca + Mg) ratio and crude protein content and digestibility suggested that selection for RTP would likely be accompanied by improved forage quality in the Hycrest breeding population

Genetic variation for Ca, Mg, and K concentrations in Agropyrons and Psathyrostachys

We had three goals in this series of studies. We wished to 1) determine the extent of genetic variability and broad sense heritability for Ca, Mg and K concentrations in these forage grasses, 2) obtain an estimate of the relative magnitude of genotype x environment interaction, and 3) develop a breeding and selection program for lines having reduced tetany potential (RTP) indices

Ash, carbon isotope discrimination, and silicon as estimators of transpiration efficiency in crested wheatgrass

Breeding and selection for higher transpiration efficiency (W) has been hampered by tedious and costly methodology. Rapid and less costly methods are needed for screening W in plant improvement programmes. We report the relationship of ash, silicon (Si) concentration, and Si uptake to W in crested wheatgrass (Agropyron desertorum [Fischer ex Link] Schultes), an important C3 range grass in western North America. Clones of crested wheatgrass were grown under three water levels in a field rainout shelter and as potted plants under two water levels in the field and greenhouse. Ash and Si concentrations were compared to previously determined values of shoot mass, transpiration, W, and carbon isotope discrimination (A). Ash and Si concentrations were not consistently related to ? and W across all environments; however, ash concentration was positively correlated with ? (r=0•69**, df = 22) and negatively correlated with W (r= -0•61**, df=22) in the well-watered field environment. Across all environments and studies, the ranges in the coefficients of variation (CV, %) for clonal means were: W, 4-15; ?, 1-4; ash concentration, 6-14; Si concentration, 13-30; and Si uptake, 21-33. The generally lower CV for W, ?, and ash concentration suggest that these traits were more repeatable than Si concentration or uptake. Although a consistent relationship was not observed between Si and W and between ash and W, the correlations of ash and W from the well-watered field environment were encouraging. In view of the low cost for ash analysis, we conclude that further research is needed to evaluate the potential of ash as a criterion in selecting for improved W, particularly during the early phases of a breeding programme when large populations are usually involved. Later selections could be based on the more precise and accurate, but costly, ? analysis

Using plant breeding and genetics to overcome the incidence of grass tetany

Plant breeders developing cultivars to minimize the hazards of grass tetany are concentrating largely on increasing herbage Mg concentrations in cool-season (C3) grasses. Significant genetic variation has been found for Mg, Ca and K concentrations within C3 grass species studied to date. For most C3 forage grass species, heritability estimates are highest for Mg, slightly lower for Ca and lowest for K concentrations. The largest genotype x environmental interactions are found for K values, whereas small environmental effects have been observed for Mg and Ca values. No C3 forage grass cultivar has been developed to date that would eliminate hypomagnesemia. Grass breeders need to develop more experimental C3 plant populations that have high Mg and Ca concentrations. These experimental synthetics with genetically altered mineral concentrations need to be fed to ruminants susceptible to grass tetany to determine whether grass tetany can be eliminated or reduced. Limited feeding trials using ruminants show that improved animal performance can be expected when feeding forage grasses bred for higher Mg concentrations

Variation in agronomic and morphological traits among Russian Wildrye accessions

Russian wildrye [Psathyrostachys juncea (Fischer) Nevski] accessions in the U.S. National Plant Germplasm System have not been adequately characterized for agronomic and morphological traits. Such characterization would be helpful in development of improved cultivars. Objectives of this study were to (i) measure consistency of dry-matter and seed yields as well as plant height and vigor of 65 Russian wildrye accessions and four cultivars at three diverse test sites, (ii) characterize phenotypic diversity among these accessions using duster analysis, and (iii) define needs for future evaluation and collection of Russian wildrye germplasm. Field tests were conducted at Logan, UT; Mandan, ND; and Swift Current, Saskatchewan, Canada. Dry-matter and seed yields were not consistent among accessions and cultivars at the three locations, and testing at each location was necessary to identify accessions that were best suited to a specific location. Variance component estimates were small and of little consequence for accession x year interaction effects. The 69 entries were grouped into 10 clusters based on multivariate analysis of 17 classification variables. Accessions in Cluster 3 averaged well above the overall test mean for dry-matter yield, seed yield, and plant vigor and have high utility in plant breeding programs in North America. Only four accessions had high levels of resistance to Septoria spraguei Uecker & J.M. Krupinsky, an important foliar disease. Accessions from a defined geographic area tended to cluster, but some accessions from a particular area were spread among several clusters. This emphasizes the value of sampling diverse collection sites within a defined geographic area

Variation in mineral concentration and grass tetany potential among Russian Wildrye accessions

Grass tetany or hypomagnesemic tetany in cattle (Bos taurus) is caused by an imbalance of K, Ca, and Mg in the diet. Indications of grass tetany range from reduced milk yield or weight gain to severe convulsions and death. The risk of grass tetany dramatically increases when the K/(Mg + Ca) ratio of forage exceeds 2.2, especially for dams during early lactation. Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], a valuable forage species, has ratios well above this level. Our objectives were to determine the mineral concentration and ratio values for 65 accessions of Russian wildrye to select germplasm sources with low tetany ratio and to determine the effects of year, location, and their interactions with accessions. Seedlings of each accession and two checks, Syn A and Mankota, were established in replicated space-plant nurseries at Logan, UT, Mandan, ND, and Swift Current, Saskatchewan, Canada. Years-within-location effects generally produced the largest variance component, while the accession variance was larger than location x accession and location X accession x year interaction variances for K, Ca, Mg, KJ(Mg + Ca) ratio, and Reduced Tetany Potential (RTP) index. Selection for these traits in Russian wildrye germplasm will require multiple years to characterize adequately accessions, breeding lines, or synthetics. The K/(Ca + Mg) ratio of the accessions tested ranged from 2.2 to 3.0 when averaged across sites and years for V4 growth stage. A similar range of ratio values and ranking of the accessions was observed at the E2 growth stage. The three tetraploid accessions evaluated were among the five accessions with the highest tetany ratios. Previously reported forage yield and seed yield means were significantly correlated with K, Mg, and N concentrations and K/(Ca + Mg) ratio. The RTP index was not correlated with forage yield, seed yield, or N concentration. Therefore, selection in Russian wildrye should be based on increased RTP index rather than K concentration or K/(Ca + Mg) ratio to avoid concomitant unintentional selection of reduced forage yield and seed yiel