167 research outputs found
Screening genetic variation for photosynthetic capacity and efficiency in wheat
The world population is rising, placing increasing
demands on food production. One way to contribute to food
security is by improving yields of staple crops like wheat. Yield
can be calculated from the product of plant biomass and harvest
index (the ratio of grain yield to above ground biomass). Since
harvest index of wheat has already reached its maximum biological
limit in some environments, attention is now focused on
increasing crop biomass. Efficient interception of
photosynthetically active radiation and effective photosynthetic
sugar production underpin yield, however, little breeding has
been done for photosynthetic performance. Exploiting existing
genetic variation for important photosynthetic traits such as
photosynthetic capacity (Pc) and photosynthetic efficiency (Peff)
will help to improve wheat yield. CO2 assimilation rate, which is
a commonly measured parameter for assessing photosynthetic
performance, is found to vary across wheat genotypes. Two
additionally important parameters are Rubisco activity (Vcmax)
and electron transport rate (J). There is much less information
reported regarding genetic variation of these two latter
parameters because measurements of CO2 response curves with gas
exchange used to derive Vcmax and J are slow and unsuitable for
rapid screening of many genotypes in the field. The two main
objectives of this project were firstly, to find out if there is
genetic variation for these important photosynthetic traits in
wheat, and secondly, to develop a rapid method for screening
photosynthetic and leaf attributes in different wheat genotypes.
To deal with variable leaf temperatures in the field and
accurately estimate Vcmax and J, improved values for the
temperature dependence of several Rubisco kinetic parameters were
needed. These temperature-dependencies were derived from
measurements made under controlled conditions. A method for
rapidly estimating variation in Pc components Vcmax and J and in
other photosynthetic traits was developed based on calibration of
leaf reflectance spectra against photosynthetic parameters
derived using conventional gas exchange, morphological (leaf mass
per unit area, LMA) and chemical (nitrogen and chlorophyll per
unit area) measurements of 76 wheat genotypes screened in several
different environments. When observed data were compared against
predictions from reflectance spectra, correlation coefficients
(R2 values) of 0.62 for Vcmax25, 0.71 (J), 0.89 (LMA) and 0.93
(Narea), were obtained. Reflectance spectra from an additional
458 elite and landrace wheat genotypes were measured to further
assess variation in photosynthetic traits. There were significant
differences between wheat genotypes in Vcmax25 per unit N, which
is a good measure of Peff. Environment presented interaction with
genotypes for Pc and Peff when measurements performed in
glasshouse & field or in Australia & Mexico were compared. In
future, linking genotypic variation for photosynthetic traits to
DNA-based genetic markers will permit even faster selection of
genotypes in breeding. Reflectance spectra should be a good tool
to accelerate identification and selection of wheat genotypes and
detection of important genomic regions for photosynthetic
capacity and efficiency in wheat
Photons to food: genetic improvement of cereal crop photosynthesis
Photosynthesis has become a major trait of interest for cereal yield improvement as breeders appear to have reached the theoretical genetic limit for harvest index, the mass of grain as a proportion of crop biomass. Yield improvements afforded by the adoption of green revolution dwarfing genes to wheat and rice are becoming exhausted, and improvements in biomass and radiation use efficiency are now sought in these crops. Exploring genetic diversity in photosynthesis is now possible using high-throughput techniques, and low-cost genotyping facilitates discovery of the genetic architecture underlying this variation. Photosynthetic traits have been shown to be highly heritable, and significant variation is present for these traits in available germplasm. This offers hope that breeding for improved photosynthesis and radiation use efficiency in cereal crops is tractable and a useful shorter term adjunct to genetic and genome engineering to boost yield potential.the New South Wales Environmental Trust (2016/RD/0006), the Cotton Research
and Development Corporation (CRDC), and the Grains Research and Development Corporation (GRDC
Pulse Root Ideotype for Water Stress in Temperate Cropping System
Pulses are a key component of crop production systems in Southern Australia due to their rotational benefits and potential profit margins. However, cultivation in temperate cropping systems such as that of Southern Australia is limited by low soil water availability and subsoil constraints. This limitation of soil water is compounded by the irregular rainfall, resulting in the absence of plant available water at depth. An increase in the productivity of key pulses and expansion into environments and soil types traditionally considered marginal for their growth will require improved use of the limited soil water and adaptation to sub soil constrains. Roots serve as the interface between soil constraints and the whole plant. Changes in root system architecture (RSA) can be utilised as an adaptive strategy in achieving yield potential under limited rainfall, heterogenous distribution of resources and other soil-based constraints. The existing literature has identified a ââSteep, Deep and Cheapâ root ideotype as a preferred RSA. However, this idiotype is not efficient in a temperate system where plant available water is limited at depth. In addition, this root ideotype and other root architectural studies have focused on cereal crops, which have different structures and growth patterns to pulses due to their monocotyledonous nature and determinant growth habit. The paucity of pulse-specific root architectural studies warrants further investigations into pulse RSA, which should be combined with an examination of the existing variability of known genetic traits so as to develop strategies to alleviate production constraints through either tolerance or avoidance mechanisms. This review proposes a new model of root system architecture of âWide, Shallow and Fineâ roots based on pulse roots in temperate cropping systems. The proposed ideotype has, in addition to other root traits, a root density concentrated in the upper soil layers to capture in-season rainfall before it is lost due to evaporation. The review highlights the potential to achieve this in key pulse crops including chickpea, lentil, faba bean, field pea and lupin. Where possible, comparisons to determinate crops such as cereals have also been made. The review identifies the key root traits that have shown a degree of adaptation via tolerance or avoidance to water stress and documents the current known variability that exists in and amongst pulse crops setting priorities for future research
Mining for allelic gold : finding genetic variation in photosynthetic traits in crops and wild relatives
Improvement of photosynthetic traits in crops to increase yield potential and crop resilience has recently become a major breeding target. Synthetic biology and genetic technologies offer unparalleled opportunities to create new genetics for photosynthetic traits driven by existing fundamental knowledge. However, large âgene bankâ collections of germplasm comprising historical collections of crop species and their relatives offer a wealth of opportunities to find novel allelic variation in the key steps of photosynthesis, to identify new mechanisms and to accelerate genetic progress in crop breeding programmes. Here we explore the available genetic resources in food and fibre crops, strategies to selectively target allelic variation in genes underpinning key photosynthetic processes, and deployment of this variation via gene editing in modern elite material
Observation of medium-induced yield enhancement and acoplanarity broadening of low- jets from measurements in pp and central PbPb collisions at TeV
International audienceThe ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high ) hadron trigger in protonproton and central PbPb collisions at TeV. A data-driven statistical method is used to mitigate the large uncorrelated background in central PbPb collisions. Recoil jet distributions are reported for jet resolution parameter , 0.4, and 0.5 in the range GeV and triggerrecoil jet azimuthal separation . The measurements exhibit a marked medium-induced jet yield enhancement at low and at large azimuthal deviation from . The enhancement is characterized by its dependence on , which has a slope that differs from zero by 4.7. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation
Probing the Chiral Magnetic Wave with charge-dependent flow measurements in Pb-Pb collisions at the LHC
International audienceThe Chiral Magnetic Wave (CMW) phenomenon is essential to provide insights into the strong interaction in QCD, the properties of the quark-gluon plasma, and the topological characteristics of the early universe, offering a deeper understanding of fundamental physics in high-energy collisions. Measurements of the charge-dependent anisotropic flow coefficients are studied in Pb-Pb collisions at center-of-mass energy per nucleon-nucleon collision 5.02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic () and triangular () flow coefficients of positively and negatively charged particles as a function of their event-wise normalized number difference, is reported for inclusive and identified particles. The slope is found to be larger than zero and to have a magnitude similar to , thus pointing to a large background contribution for these measurements. Furthermore, can be described by a blast wave model calculation that incorporates local charge conservation. In addition, using the event shape engineering technique yields a fraction of CMW () contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for , and in the 10-60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level
Charged-particle production as a function of the relative transverse activity classifier in pp, pPb, and PbPb collisions at the LHC
International audienceMeasurements of charged-particle production in pp, pPb, and PbPb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum () in the range GeV. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier, , is used to group events according to their UE activity, where is the charged-particle multiplicity per event in the transverse region and is the mean value over the whole analysed sample. The energy dependence of the distributions in pp collisions at , 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particle spectra as a function of in the three azimuthal regions in pp, pPb, and PbPb collisions at TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and pPb)
Light-flavor particle production in high-multiplicity pp collisions at = 13 TeV as a function of transverse spherocity
Results on the transverse spherocity dependence of light-flavor particle production (, K, p, , , , , ) at midrapidity in high-multiplicity pp collisions at = 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator () categorizes events by their azimuthal topology. Utilizing narrow selections on , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The estimator is found to effectively constrain the hardness of the events when the midrapidity () estimator is used. The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced. The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of .Results on the transverse spherocity dependence of light-flavor particle production (, K, p, , , , , ) at midrapidity in high-multiplicity pp collisions at TeV were obtained with the ALICE apparatus. The transverse spherocity estimator () categorizes events by their azimuthal topology. Utilizing narrow selections on , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The estimator is found to effectively constrain the hardness of the events when the midrapidity () estimator is used. The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced. The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of
Prompt and non-prompt J production at midrapidity in PbPb collisions at = 5.02 TeV
International audienceThe transverse momentum () and centrality dependence of the nuclear modification factor of prompt and non-prompt J, the latter originating from the weak decays of beauty hadrons, have been measured by the ALICE collaboration in PbPb collisions at = 5.02 TeV. The measurements are carried out through the decay channel at midrapidity ( 5 GeV/, which becomes stronger with increasing collision centrality. The results are consistent with similar LHC measurements in the overlapping intervals, and cover the kinematic region down to = 1.5 GeV/ at midrapidity, not accessible by other LHC experiments. The suppression of prompt J in central and semicentral collisions exhibits a decreasing trend towards lower transverse momentum, described within uncertainties by models implementing J production from recombination of c and quarks produced independently in different partonic scatterings. At high transverse momentum, transport models including quarkonium dissociation are able to describe the suppression for prompt J. For non-prompt J, the suppression predicted by models including both collisional and radiative processes for the computation of the beauty-quark energy loss inside the quarkgluon plasma is consistent with measurements within uncertainties
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