Evaluation of the phenotypic variation in kikuyu populations

A series of cutting experiments evaluated the phenotypic variation in populations of kikuyu in Australia to assess their capacity to provide sufficient variability to sustain a breeding and selection program. The aim of such a program would be to develop a high quality cultivar without compromising stand vigour. Single plants, generated either from seed of commercial cultivars or accessions, seed treated by mutagenic chemicals or from randomly-chosen runners from stands across Australia, were sown singularly in randomised block experiments under irrigation at two sites in subtropical eastern Australia. There were significant differences between kikuyu cultivars in leaf, stem and runner dry matter yields, plant height and quality (crude protein, neutral detergent and acid detergent fibre content and in vitro digestibility). Variation between individual plants was also substantial, with 7, 3 and 3 % improvement over the population mean for crude protein content, in vitro digestibility, and metabolisable energy respectively, and a reduction of 5 and 8 % in neutral and acid detergent fibre content. It was also associated with a forage yield twice the population mean from these elite plants. Mutagenesis of seed from a commercial cultivar produced greater within-population variation for quality, but less for agronomic, traits compared with the natural population. Gene fingerprinting suggested that the material distributed across Australia came from two main sources, one related to cv. Whittet and the other to a ‘common’ lower yielding type. It was concluded that the currentlyavailable material within Australia, although from limited genetic base, contained sufficient variation to achieve a significant improvement in quality without reducing plant vigour

Evaluation of the phenotypic variation in kikuyu populations

A series of cutting experiments evaluated the phenotypic variation in populations of kikuyu in Australia to assess their capacity to provide sufficient variability to sustain a breeding and selection program. The aim of such a program would be to develop a high quality cultivar without compromising stand vigour. Single plants, generated either from seed of commercial cultivars or accessions, seed treated by mutagenic chemicals or from randomly-chosen runners from stands across Australia, were sown singularly in randomised block experiments under irrigation at two sites in subtropical eastern Australia. There were significant differences between kikuyu cultivars in leaf, stem and runner dry matter yields, plant height and quality (crude protein, neutral detergent and acid detergent fibre content and in vitro digestibility). Variation between individual plants was also substantial, with 7, 3 and 3 % improvement over the population mean for crude protein content, in vitro digestibility, and metabolisable energy respectively, and a reduction of 5 and 8 % in neutral and acid detergent fibre content. It was also associated with a forage yield twice the population mean from these elite plants. Mutagenesis of seed from a commercial cultivar produced greater within-population variation for quality, but less for agronomic, traits compared with the natural population. Gene fingerprinting suggested that the material distributed across Australia came from two main sources, one related to cv. Whittet and the other to a ‘common’ lower yielding type. It was concluded that the currentlyavailable material within Australia, although from limited genetic base, contained sufficient variation to achieve a significant improvement in quality without reducing plant vigour

Plant breeding influences the performance of temperate pasture species in the subtropics

Data from a series of experiments over a 15-year period in the subtropics were interrogated to determine whether plant breeding had influenced the performance of ryegrass and lucerne in the subtropics of Australia. It was found that, within sets of plant breeders' lines available for sowing in any one experiment, yield of the best experimental lines of perennial and annual ryegrasses and lucerne were almost always above that of standard cultivars. The range in rust resistance was not as great in annual ryegrass, with breeders' lines rarely being superior to the standard cultivars. However in perennial ryegrass and lucerne, the range of disease: resistance was greater and did show improvement relative to the standard cultivars. There was also a trend towards improved performance of breeders' lines over time. Those available between 1996 and 1999 showed an overall increase in yield over the general experimental mean, and the performance of the best and worst experimental lines in ryegrass and lucerne at the commencement of the study period (1978 for lucerne and 1992 for ryegrasses). Persistence of lucerne showed the reverse trend with an overall fall in the general experimental mean. Resistance to Phythophthora root rot (PRR) and leaf diseases improved over time but that for Colletotrichum crown rot (CCR) declined. The reasons for these trends are discussed

Performance of temperate perennial pastures in the Australian subtropics 2. Milk production

Milk production from irrigated, pure stands of perennial ryegrass (Lolium perenne cv. Yatsyn), prairie grass (Bromus willdenodii cv. Matua) and tall fescue (Festuca arundinacea cv. AU Triumph) were compared with that achieved from Italian ryegrass (L. multiflorum cv. Concord) over 3 lactations of multiparous Holstein–Friesian cows at Mutdapilly in south-east Queensland. Pastures were fertilised with 50 kg nitrogen/ha . month as urea and annual dressings of 20 kg phosphorus/ha and 50 kg potassium/ha (as superphosphate and muriate of potash respectively). There were 4 pasture treatments grazed at 3 cows/ha in a 1-week-on, 3-weeks-off rotation with 2 replicates and 3 cows/treatment block. Cows grazed the pastures day and night from May to November. Over summer, cows grazed the pastures during the night and were fed supplements (silage in the first lactation, and lucerne hay in the second and third lactations) during the day because there was no shade available in the irrigation areas. In autumn, the animals were removed from the ryegrass and prairie grass pastures for 8 weeks to allow seedling re-establishment, either by oversowing (ryegrasses) or natural reseeding (prairie grass). Cows continued to graze the fescue pastures at night during autumn. All cows received a ration of 4 kg/cow of a grain–minerals mixture in the first lactation and 5 kg/cow in the second and third lactations. Milk production from perennial ryegrass was higher than from fescue in the first lactation and Italian ryegrass in the second and third lactations. Prairie grass gave similar milk production to perennial ryegrass in all 3 years. In the third year, perennial ryegrass, prairie grass and fescue gave similar milk production. Milk quality from the 4 grasses was similar except in the third lactation when the lactose content of milk from perennial ryegrass pastures was lowest. There were also small and inconsistent differences in milk component yields between the 4 grasses. Liveweight changes were small except in the second lactation when the cows grazing fescue lost weight relative to the other treatments. Mean liveweight at calving increased over the 3 lactations. It was concluded that all 3 temperate perennial grasses demonstrated useful traits for use in subtropical dairy pastures. Perennial ryegrass produced the most milk from the lowest amount of dry matter on offer. Prairie grass produced similar milk yields to perennial ryegrass, was well eaten by cattle and was self regenerating. Although fescue was slower to establish and needed more intensive management to control maturity, it was the most persistent and was the only grass to provide autumn grazing. In the second year this attribute resulted in a lower requirement for supplementary feeding. Fescue produced the highest gross margin in the second lactation and was only marginally less than prairie grass in the third. The performance of Italian ryegrass was as good as that of perennial ryegrass in the first lactation but fell substantially in the second and third lactations as the level of summer grass invasion increased

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters