402 research outputs found
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
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
Soil Quality and Region Influence Performance and Ranking of Switchgrass Genotypes
Development of switchgrass (Panicum virgatum L.) as a dedicated bioenergy feedstock requires intensive and extensive breeding programs that include careful and thoughtful consideration of appropriate target populations of environments (TPEs). The purpose of this study was to evaluate region (climate), soil quality, and N fertilization level as potential factors influencing the choice of TPE. A total of 45 switchgrass genotypes were evaluated in uniform field studies at six field sites defined as prime or marginal soils in New Jersey, South Dakota, and Wisconsin. Region and soil quality had strong interactions with genotype, but N fertilization had little impact on genetic variation or ranking of genotypes. Lowland genotypes were considerably more sensitive than upland genotypes to interactions with environmental factors, probably due to these field sites being outside of the traditional lowland adaptation zones. Genotype rankings were highly inconsistent across regions and soil types, indicating that breeding programs that target marginal soils should be located on soils that represent the appropriate TPE. Furthermore, interactions across the three regions suggest that breeding programs for the lowland ecotype should be subdivided into different sets of TPEs, which are largely a function of hardiness zone and annual precipitation. Lastly, even with negligible interactions involving N fertilization level, future definitions of TPEs should be based on minimal or no N fertilizer applications to allow breeders to select plants with greater N-use efficiency, N-scavenging ability, and N-recycling efficiency
Meiotic Stability, Chloroplast DNA Polymorphisms, and Morphological Traits of Upland X Lowland Switchgrass Reciprocal Hybrids
Switchgrass (Panicum virgatum L.) has two cytotypes or cytoplasm types, L and U, that are associated with the lowland and upland ecotypes, respectively. The L cytotypes are tetraploids while the U cytotypes can be either tetraploids or octaploids. The objective of this research was to characterize meiotic stability of reciprocal crosses of U and L plants as indicated by chromosome pairing at meiosis and to determine the mode of inheritance of chloroplast DNA (cpDNA) in the hybrids of these cytotypes. Morphological markers that characterize the parents and hybrids also were investigated to confirm that progeny were true hybrids. Reciprocal crosses were made between Kanlow (L tetraploid) and Summer (U tetraploid) plants. Pubescence on the upper surface of the leaf blade, foliage color, and seed size were evaluated as markers to verify hybridization. Meiotic pairing of some of the hybrids was analyzed at the diakinesis stage of meiosis by means of immature anthers. The clone pRR12 from a spinach (Spinacia oleracea L.) cpDNA library was used as a chloroplast hybridization probe to determine chloroplast inheritance. For all the morphological traits evaluated, the hybrids were intermediate in comparison to the parents except for seed width. Chromosome pairing was primarily bivalent in all hybrids. The viability of the hybrid seed and the normal meiotic chromosome pairing of the hybrids indicate a high degree of similarity between upland and lowland genomes. In the cpDNA analysis, all verified hybrids examined carried a fragment identical in size to the fragment of the female parent, indicating predominance of maternal inheritance of the cpDNA in switchgrass
Genetic variability for mineral element concentration of crested wheatgrass forage
Grass tetany is a complex metabolic disorder that causes substantial
livestock production losses and deaths in temperate regions
of the world. It is caused by low levels of Mg or an imbalance of K,
Ca, and Mg in forage consumed by animals. Development of grasses
with improved mineral balance would be an economical means of
minimizing losses from this malady. This study was conducted to
determine if genetic variability exists among crested wheatgrasses,
Agropyron cristatum (L.) Gaertner and A. desertorum (Fisher ex
Link) Schultes, for forage Mg, Ca, K, Fe, Zn, Mn, Cu, Na, and P
concentrations. Forage of spaced plants of 10 diverse crested wheatgrass
strains was harvested from replicated plots at Lincoln and
Alliance, NE, which differ markedly in climate, and analyzed for
these minerals. There were genetic differences among strains over
locations for Ca, Mg, and Fe concentration in the forage. There were
differences among strains within locations but not over locations for
K. Strain differences in Zn, Mn, Cu, Na, and P concentrations of
the forage were not significant (P > 0.05) when averaged over locations.
Calcium and Mg were positively correlated (r = 0.40).
These results indicate that it should be possible to breed crested
wheatgrass with increased Mg and Ca concentrations in its forage,
thus reducing grass tetany potential
Forage quality, mineral constituents, and performance of beef yearlings grazing two crested wheatgrasses
In the central Great Plains, crested wheatgrasses (Agropyron cristatum
(L.) Gaetner and A. desertorium (Fischer ex Link) Schultes] are
best utilized for early spring and late fall grazing. The principal objective
of this study was to determine if beef (Bos taurus L.) yearlings
grazing 'Ruff' (A. cristatum) during the spring grazing season had
higher average daily gains and gains per hectare than cattle grazing
`Nordan' (A. desertorum). These cultivars were evaluated in grazing
trials (four replications) in eastern Nebraska in 1985, 1986, and 1987.
The 0.8-ha pastures were seeded in the fall of 1983 on a Typic Argiudoll
soil and were fertilized annually with 68 to 90 kg N ha-1. Grazing
was for 6 wk each spring by yearling steers with a beginning average
weight of 250 kg. Averaged over 3 yr, Ruff produced higher gains
per hectare than Nordan (272 vs 245 kg ha-1) probably because it
produced more herbage because of its better persistence. At the end
of the trial, the averge basal cover of Ruff and Nordan were 21 and
6%, respectively. Three-year mean average daily gains were Ruff =
1.28 vs. Nordan = 1.34 kg d-1, which were unexpected, because Ruff
generally had higher forage quality as measured by an array of parameters.
Ruff forage had a higher, less desirable grass tetany ratio
[K/(Mg +Ca)) than Nordan (2.6 vs. 2.3) averaged over 3 yr. Cattle
grazing Ruff had lower blood serum Mg levels than cattle grazing
Nordan (15.4 vs. 16.2 mg L-1, both of which were below the hypomagnesemia
threshold of 18 mg L-1. This condition may have reduced
intake and animal gains. These results indicate the need for evaluating
pasture and range grass cultivars under grazing conditions
Influence of a classical homogeneous gravitational field on dissipative dynamics of the Jaynes-Cummings model with phase damping
In this paper, we study the dissipative dynamics of the Jaynes-Cummings model
with phase damping in the presence of a classical homogeneous gravitational
field. The model consists of a moving two-level atom simultaneously exposed to
the gravitational field and a single-mode traveling radiation field in the
presence of the phase damping. We present a quantum treatment of the internal
and external dynamics of the atom based on an alternative su(2) dynamical
algebraic structure. By making use of the super-operator technique, we obtain
the solution of the master equation for the density operator of the quantum
system, under the Markovian approximation. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, we investigate the influence of gravity on the
temporal evolution of collapses and revivals of the atomic population
inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting
statistics and quadrature squeezing of the radiation field in the presence of
phase damping.Comment: 25 pages, 15 figure
Life expectancy in older adults with advanced cancer: Evaluation of a geriatric assessment-based prognostic model
Objectives: Oncologists estimate patients' prognosis to guide care. Evidence suggests oncologists tend to overestimate life expectancy, which can lead to care with questionable benefits. Information obtained from geriatric assessment may improve prognostication for older adults. In this study, we created a geriatric assessment-based prognostic model for older adults with advanced cancer and compared its performance to alternative models. Materials and methods: We conducted a secondary analysis of a trial (URCC 13070; PI: Mohile) capturing geriatric assessment and vital status up to one year for adults age ≥ 70 years with advanced cancer. Oncologists estimated life expectancy as 0–6 months, 7–12 months, and > 1 year. Three statistical models were developed: (1) a model including age, sex, cancer type, and stage (basic model), (2) basic model + Karnofsky Performance Status (≤50, 60–70, and 80+) (KPS model), and (3) basic model +16 binary indicators of geriatric assessment impairments (GA model). Cox regression was used to model one-year survival; c-indices and time-dependent c-statistics assessed model discrimination and stratified survival curves assessed model calibration. Results: We included 484 participants; mean age was 75; 48% had gastrointestinal or lung cancer. Overall, 43% of patients died within one year. Oncologists classified prognosis accurately for 55% of patients, overestimated for 35%, and underestimated for 10%. C-indices were 0.61 (basic model), 0.62 (KPS model), and 0.63 (GA model). The GA model was well-calibrated. Conclusions: The GA model showed moderate discrimination for survival, similar to alternative models, but calibration was improved. Further research is needed to optimize geriatric assessment-based prognostic models for use in older adults with advanced cancer
Avaliação laboratorial de compostos fibrosos em alimentos e fezes bovinas sob diferentes ambientes fĂsicos
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