Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV

Two-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe

Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at root(NN)-N-S=2.76 TeV

Peer reviewe

Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions

We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Pseudorapidity and transverse-momentum distributions of charged particles in proton-proton collisions at root s=13 TeV

The pseudorapidity (eta) and transverse-momentum (p(T)) distributions of charged particles produced in proton-proton collisions are measured at the centre-of-mass energy root s = 13 TeV. The pseudorapidity distribution in vertical bar eta vertical bar <1.8 is reported for inelastic events and for events with at least one charged particle in vertical bar eta vertical bar <1. The pseudorapidity density of charged particles produced in the pseudorapidity region vertical bar eta vertical bar <0.5 is 5.31 +/- 0.18 and 6.46 +/- 0.19 for the two event classes, respectively. The transverse-momentum distribution of charged particles is measured in the range 0.15 <p(T) <20 GeV/c and vertical bar eta vertical bar <0.8 for events with at least one charged particle in vertical bar eta vertical bar <1. The evolution of the transverse momentum spectra of charged particles is also investigated as a function of event multiplicity. The results are compared with calculations from PYTHIA and EPOS Monte Carlo generators. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe

Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb-Pb collisions at root s(NN)=2.76TeV

The elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

Management of Ditylenchus africanus (Nematoda : Tylenchidae) on groundnut (Arachis hypogaea)

PhD, North-West University, Potchefstroom CampusMANAGEMENT OF DITYLENCHUS AFRICANUS (NEMATODA: TYLENCHIDAE) ON GROUNDNUT (ARACHIS HYPOGAEA) Groundnut production has decreased in South Africa over the past seven years in spite of an increase in grain yield potential of the crop. This decrease in production, associated with a decrease in area planted to the crop, is ascribed to poor kernel quality that renders production of groundnut uneconomical. Ditylenchus africanus has a major effect of groundnut downgrading and is suspected to be the primary cause of the decline in national groundnut production. The objective of the study was to find an economically feasible management strategy for the nematode on groundnut. In order to evaluate and develop control strategies for D. africanus, relationships between nematode population densities and damage symptoms with groundnut downgrading disorders and calculation of income, as stipulated by the local agricultural products standards act, was established. This relationship was used throughout the study to determine the economical feasibility of control strategies in field or near field conditions, viz. microplots. Nematicides applied at prescribed rates on groundnut gave inconsistent results in terms of D. africanus population reduction and yield improvement. Nematicide efficacy was higher under irrigation than rain-fed conditions. Inconsistent efficacy of systemic nematicides under dry land production conditions lead to the conclusion that groundnut production under marginal conditions is uneconomical, irrespective of nematode control. Production of the crop under marginal conditions should be discouraged because of the great economic risk. Spread of D. africanus may be enhanced as a result of abstinence from additional nematode control inputs under such conditions. Neither reduced nor increased dosage rates of systemic nematicides justified concomitant reductions or increases in cost of application. Integration of different planting dates of groundnut and systemic nematicide application is not a feasible management option for D. africanus. Nematicide efficacy and variation in environmental conditions are too unpredictable to serve as a basis for planning nematode control measures and optimum groundnut yield. Tolerance levels of the cultivar Kwarts are not adequate to be included in a management strategy for D. africanus populations. Integration of chemical control with differential nematode susceptibility of groundnut cultivars that are currently available is also not economically feasible. Application of ethylene dibromide at planting at reduced rates of 10 to 15 //ha proved to be effective in D. africanus management and groundnut yield improvement. The reduced costs of these application rates and the increase in income obtained by these applications provide an economically feasible alternative management strategy to groundnut producers. Adoption of a strategy such as this may serve to increase national groundnut production and restore areas lost to groundnut production over the past few years.Doctora

Host suitability of selected South African maize genotypes to the root-knot nematode species Meloidogyne incognita race 2 and Meloidogynejavanica: a preliminary study

Thirty-one commercial maize (Zea mays L.) hybrids and open-pollinated varieties (OPV's) were screened in separate greenhouse trials with a resistant inbred line MP712W as reference genotype for host suitability to Meloidogyne incognita race 2 and Meloidogyne javanica. Approximately 10 000 eggs and second-stage juveniles (J2) of the appropriate root-knot nematode species were inoculated on roots of each maize seedling 10 days after plant emergence. The numbers of eggs and J2 per root system were counted, while it was also calculated g-1 root. In addition, percentage resistance in relation to the most susceptible genotype and nematode reproduction factors (Rf) were calculated for the maize genotypes screened. Substantial variation existed among the maize hybrids and OPV's with regard to the nematode parameters evaluated. A number of genotypes could be regarded as highly resistant to M. incognita race 2 based on the fact that they supported less than 10% of the population of this root-knot nematode species, compared to that supported by the most susceptible genotype. Several hybrids and OPV's were identified with Rf values less than one for M. incognita race 2 and M. javanica respectively, indicating antibiosis resistance to these parasites. Screenings of maize genotypes in this study have provided a clear indication of the genetic variability within the maize genome, also with regard to susceptibility of the crop to root-knot nematodes. This substantiates the fact that maize could not be regarded as a non-host to root-knot nematodes on a generic basis, particularly in terms of commercial hybrids. It is suggested that commercial maize hybrids are screened on a continuous basis against root-knot nematodes, which would facilitate selection of hybrids that are less susceptible to both nematode species but that would perform optimally in soils conducive to root-knot-nematode infestation

Sampling variation in the quantification of fumonisins in maize samples

Fumonisins produced by F. verticillioides and F. proliferatum cause mycotoxicoses in horses, swine and rats and have been associated with oesophageal cancer in humans. Accurate measurement of mycotoxins is essential for determining the safety of grain and their products for consumption. Four sources of variation were studied, namely sub-sample size, variation within a single maize sub-sample, number of replicates and toxin detection techniques used by independent laboratories. Variation in detected fumonisin levels within a single maize sample was high using the 25 g sub-samples proposed in the Neogen Veratox protocols. A 250 g subsample significantly reduced variation in fumonisin levels of samples. An incremental increase in sample size also improved the number of positive samples recorded. Increasing the number of replicates using the recommended sub-sample size (25 g) did notreduce variation except when the sample had high fumonisin levels. Improved accuracy was recorded when a 250 g sub-sample was used in conjunction with increased replicates. Data from laboratory analyses indicated that ELISA reactions (Agricultural Research Council - Grain Crops Institute) correlated significantly with HPLC results of the Medical Research Council (MRC), but neither of these correlated with results from an independent laboratory. Concentrations determined using ELISA were consistently higher than those from the HPLC (MRC) technique. Quantification technique, sample size, replicate number and laboratory where analyses are conducted, appear to be important sources of variation for quantification of fumonisins

Differential responses of resistant and susceptible groundnut genotypes at cellular level to Ditylenchus africanus

Ditylenchus africanus causes cellular breakdown in pod tissue of susceptible groundnut cultivars. The histopathology of this nematode on a resistant genotype was studied using light microscopy and compared with the histopathology of D. africanus on a susceptible genotype. Plants of breeding line PC254K1 and cv. Sellie were propagated in a glasshouse, inoculated with D. africanus at inoculum levels of 2000, 5000 and 7000 nematodes per plant and the pods were collected at 90, 120 and 150 days after planting. In contrast to the susceptible genotype, only a small number of nematodes were observed in restricted areas of the pod tissue of the resistant genotype. Furthermore, the resistant genotype showed neither external symptoms nor cellular breakdown in reaction to D. africanus. According to results of this study, the mechanism of resistance involved may be the inhibition of proper development, migration and reproduction of this nematode, thus preventing it building up to damaging population levels.http://dx.doi.org/10.1163/138855410X508723http://booksandjournals.brillonline.com/content/10.1163/138855410x50872