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 “‘Steep, Deep and Cheap” 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 “Wide, Shallow and Fine” 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 ‘gene bank’ 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

K∗^{*}(892)±^{\pm} resonance production in Pb−-Pb collisions at sNN\sqrt{s_{\rm NN}} = 5.02 TeV

International audienceThe production of K$^*$(892)$^\pm$ meson resonance is measured at midrapidity ($|y|8$ GeV/$c$, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium

Multiplicity and event-scale dependent flow and jet fragmentation in pp collisions at s\sqrt{s} = 13 TeV and in p−-Pb collisions at sNN\sqrt{s_\mathrm{NN}} = 5.02 TeV

International audienceLong- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at $\sqrt{s}=13$ TeV and p$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The correlation functions are measured as a function of relative azimuthal angle $\Delta\varphi$ and pseudorapidity separation $\Delta\eta$ for pairs of primary charged particles within the pseudorapidity interval $|\eta| < 0.9$ and the transverse-momentum interval $1 < p_{\rm T} < 4$ GeV/$c$. Flow coefficients are extracted for the long-range correlations ($1.6 < |\Delta\eta| <1.8$) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events

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 $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV to probe the CMW. In particular, the slope of the normalized difference in elliptic ($v_{2}$) and triangular ($v_{3}$) 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 $r_{3}^{\rm Norm}$ is found to be larger than zero and to have a magnitude similar to $r_{2}^{\rm Norm}$, thus pointing to a large background contribution for these measurements. Furthermore, $r_{2}^{\rm Norm}$ 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 ($f_{\rm CMW}$) contribution to this measurement which is compatible with zero. This measurement provides the very first upper limit for $f_{\rm CMW}$, and in the 10-60% centrality interval it is found to be 26% (38%) at 95% (99.7%) confidence level

Light-flavor particle production in high-multiplicity pp collisions at s=13\mathbf{\sqrt{\textit{s}} = 13} TeV as a function of transverse spherocity

International audienceResults on the transverse spherocity dependence of light-flavor particle production ($\pi$, K, p, $\phi$, ${\rm K^{*0}}$, ${\rm K}^{0}_{\rm{S}}$, $\Lambda$, $\Xi$) at midrapidity in high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV were obtained with the ALICE apparatus. The transverse spherocity estimator ($S_{{\rm O}}^{{\it p}_{\rm T}=1}$) categorizes events by their azimuthal topology. Utilizing narrow selections on $S_{\text{O}}^{{\it p}_{\rm T}=1}$, 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 $S_{{\rm O}}^{{\it p}_{\rm T}=1}$ estimator is found to effectively constrain the hardness of the events when the midrapidity ($\left | \eta \right |< 0.8$) 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 $S_{{\rm O}}^{{\it p}_{\rm T}=1}$

Skewness and kurtosis of mean transverse momentum fluctuations at the LHC energies

International audienceThe first measurements of skewness and kurtosis of mean transverse momentum ($\langle p_\mathrm{T}\rangle$) fluctuations are reported in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV, Xe$-$Xe collisions at $\sqrt{s_\mathrm{NN}}$$=$ 5.44 TeV and pp collisions at $\sqrt{s} = 5.02$ TeV using the ALICE detector. The measurements are carried out as a function of system size $\langle \mathrm{d}N_\mathrm{ch}/\mathrm{d}\eta\rangle_{|\eta|<0.5}^{1/3}$, using charged particles with transverse momentum ($p_\mathrm{T}$) and pseudorapidity ($\eta$), in the range $0.2 < p_\mathrm{T} < 3.0$ GeV/$c$ and $|\eta| < 0.8$, respectively. In Pb$-$Pb and Xe$-$Xe collisions, positive skewness is observed in the fluctuations of $\langle p_\mathrm{T}\rangle$ for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum bias pp collisions are also reported here. Kurtosis of $\langle p_\mathrm{T}\rangle$ fluctuations is found to be in good agreement with the kurtosis of Gaussian distribution, for most central Pb$-$Pb collisions. Hydrodynamic model calculations with MUSIC using Monte Carlo Glauber initial conditions are able to explain the measurements of both skewness and kurtosis qualitatively from semicentral to central collisions in Pb--Pb system. Color reconnection mechanism in PYTHIA8 model seems to play a pivotal role in capturing the qualitative behavior of the same measurements in pp collisions