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International audience; Biological invasions are a major threat to the terrestrial ecosystems of the sub-Antarctic islands. While non-native plants generally have negative impacts on native arthropods, few studies have investigated how both native and non-native arthropods and plants interact in the sub-Antarctic islands. This was the aim of our study, which was conducted on three islands of the Kerguelen archipelago. The design was based on the spatial proximity of areas dominated by non-native or native plant species. Trait-based indices were calculated to characterize the functional structure of plant communities, considering plant stature and leaf traits. Native and non-native vegetation had contrasting functional composition but their functional diversity was similar. The effects of the type of vegetation, native or non-native, and plant functional diversity on arthropods were tested. Native macro-arthropod richness and abundance were similar or higher in non-native vegetation, and benefited from greater plant functional diversity. Abundances of macro-herbivores, macro-decomposers and macro-predators were also similar or higher in non-native vegetation. Conversely, the abundances of micro-arthropods, Symphypleona springtails and Oribatida mites, were higher in native vegetation but we also found that plant functional diversity had a negative effect on Symphypleona. Our results suggest that non-native plants can affect micro-arthropods directly or indirectly, likely through their effects on abiotic factors. By affecting macro-arthropod abundances across different trophic groups and by depleting micro-arthropods, non-native plants can alter trophic interactions, functional balances and the functioning of whole ecosystem.

International audience; Plant responses to rising atmospheric carbon dioxide (CO2) concentrations, together with projected variations in temperature and precipitation will determine future agricultural production. Estimates of the impacts of climate change on agriculture provide essential information to design effective adaptation strategies, and develop sustainable food systems. Here, we review the current experimental evidence and crop models on the effects of elevated CO2 concentrations. Recent concerted efforts have narrowed the uncertainties in CO2-induced crop responses so that climate change impact simulations omitting CO2 can now be eliminated. To address remaining knowledge gaps and uncertainties in estimating the effects of elevated CO2 and climate change on crops, future research should expand experiments on more crop species under a wider range of growing conditions, improve the representation of responses to climate extremes in crop models, and simulate additional crop physiological processes related to nutritional quality.Understanding of the effects of elevated CO2 on crops has improved sufficiently that modelling future climatic effects on agriculture should eliminate 'no CO2' simulations. Further advancement in the estimation of the effects can be realized by studying a wider variety of crop species under a wider range of growing conditions, improving the representation of responses to climate extremes in crop models and simulating additional crop physiological processes related to nutritional quality.

Reducing pesticide use has become a goal shared by several European countries and a major issue in public policies due to the negative impacts of pesticides on the environment and on human health. However, since most of the agri-food sector relies on pesticides in these countries, substantially reducing pesticide use is a complex issue. To overcome this situation, we argue that agricultural research has a major role to play and must adopt a pesticide-free paradigm to expect a deep impact on pesticide use. In this article, we explain why this new paradigm is needed and outline research fronts that it will help address. These research fronts are related to five strategies: (1) redesigning cropping systems to enhance prophylaxis, (2) diversifying biocontrol strategies and associated business models, (3) broadening the scope of plant breeding to include functional biodiversity and evolutionary ecology concepts, (4) setting new goals for agricultural machinery and digital technologies, and (5) supporting development of public policies and private initiatives for the transition toward pesticide-free agri-food systems. The corresponding research activities must be managed conjointly to develop systemic and coupled innovations, which are essential for reducing pesticide use significantly. We therefore provide examples of cross-cutting objectives that combine these fronts while also highlighting the need for interdisciplinary research projects. By doing so, we provide an overall orientation for research to achieve sustainable agriculture.

International audience; Selection of grazing-tolerant lucerne (Medicago sativa) germplasm with low autumn dormancy and erect growth habit, suitable to environments with mild winters, is hindered by genetically-based tradeoffs among these traits. Marker-assisted selection (MAS) may help overcoming the difficulty of phenotypic selection and hasten the breeding process. Over 400 progenies from four bi-parental crosses between contrasting parents from two cultivars were phenotyped for grazing tolerance and six other morpho-physiological characters. In parallel, genotyping-by-sequencing marker data were generated, with the objective to facilitate the multi-trait MAS by identifying quantitative trait loci (QTL) for the traits and assessing the extent of their co-location. In total, 9594 markers, with less than 20% missing data, segregated as simplex markers in at least one progeny family. Twenty-seven QTL were identified for six traits in the different bi-parental crosses. QTL were found to a different extent on all homology groups except homology group 4. No QTL was found for dry-matter yield before grazing imposition. The number of QTL for other traits varied from one (basal plant diameter) to nine (plant growth habit). Only for growth habit were QTL observed in all four crosses. The QTL analysis largely confirmed the association between grazing tolerance, non-erect growth habit and autumn dormancy. However, the absence of complete co-location of QTL highlighted a partly different genetic control of these traits, thereby offering scope for MAS exploitation to select genotypes carrying useful trait combinations.

International audience; Key message Exposure of N. wightii seeds to liquid nitrogen allows for dormancy breaking and promotes plant establishment without adverse effects on yield. One of the most widespread legume species in the world is N. wightii, which is used as a cover crop for animal feed and has positive environmental impacts. However, plant establishment is difficult due to the dormancy of seeds. There are several methods available to break dormancy, with exposure to low temperature being the strategy most frequently used. This current study investigated exposure of seeds of N. wightii to liquid nitrogen (LN) and subsequent field evaluation of growth and development of plants until harvest. Exposure of seeds to LN improved plant growth and reproductive development. At 7 days of planting, cryo-exposed seeds showed a 12.5-fold increase in plant emergence compared with controls, but this difference progressively declined reaching only a 2.7-fold difference at 42 days. Plant height and the number of leaves per plant were consistently higher in plants formed from cryo-exposed seeds. They reached 1.5-fold increase of plant height and 1.3-fold increase of leaf number at 42 days. The effect of LN on leaf coverage was substantially higher when evaluated from 60 to 150 days, but declined by 180 days. The highest number of inflorescences was recorded at 104 days of planting with plants derived from cryo-exposed seeds displaying a 1.9-fold increase over the control plants. This also resulted in cryo-exposed plants producing significantly more fruit and pods than control plants (1.8 and 1.7-fold more, respectively). Contrastingly, the pod length, the number of seeds per pod and the weight of 1000 seeds did not show statistically significant differences. The results from this study showed that exposure of N. wightii seeds to LN allows for dormancy breaking and promotes plant establishment without adverse effects on yield.

Aims Little is yet known about the component traits that control the deployment of root architecture in most grassland species. The aim of this study was to compare patterns of root growth in contrasting forage legumes and to analyse their dependency to shoot development. Methods The parameters of a dynamic simulation model were identified for seven contrasting species in a series of greenhouse experiments in order to characterize root elongation, root branching and taproot growth. The model allowed us to explore the interactions between root development and whole plant growth. Results Most of the root morphogenetic parameters studied displayed significant inter-specific variability. Several traits appeared to be correlated, indicating a close association between extreme root tip diameters, the branching ability of roots and their maximal elongation rate. The species differed along two PCA axes which accounted respectively for the branching ability of fine roots and taproot development. Quite remarkably, the group of species identified for root development did not coincide with those previously identified for shoots, suggesting a degree of independence between the morphogenetic traits that control shoot and root architecture. However, both plant parts remained tightly linked through the trophic relationship represented by root biomass allocation. Conclusions Our results suggest that the concomitant analysis of root and shoot development is necessary to properly decipher rooting strategies in forage legumes.

Correction de la notice https://prodinra.inra.fr/record/471516 ; 10.1007/s13593-019-0570-6; International audience; Historically, the agronomic focus of crop mineral nutrition has yielded responses to individual elements (N, P, K...) to determine the economically optimum fertilization rates. This prognostic approach required several parameters for crops, climates, and soils that are often estimated with large uncertainty leading to over-fertilization and environmental problems in some systems (e.g., maize in China), and under-fertilization and soil mining in other systems (e.g., wheat in Australia). In this review, an alternative approach is developed for reducing the uncertainty intrinsically linked to this prognostic approach. Our approach is based on four propositions: (1) the evidence of an allometry between the metabolic shoot mass (scaling with leaf area) and the structural shoot mass (supporting and vascular tissues) within plants that allows the formulation of critical N dilution curves and the determination of the Nitrogen Nutrition Index (NNI) for estimating the N nutrition status of field crops; (2) the co-regulation of crop N uptake dynamics by both soil N supply and crop N demand in relation with its growth capacity that allows a better, more generalizable estimation of timing and rate of fertilizer; (3) a better understanding of the effects of genotype-environment-management interactions on N use efficiency in cropping systems reducing then drastically uncertainties linked to the classical prognostic approach for N fertilization; (4) as P and K also relate allometrically with biomass, P and K concentrations can be directly related to N concentration for the formulation of a multi-element diagnosis of crop nutrition. Here, we develop the theoretical background supporting these four propositions and outline implications for both fertilization management and crop phenotyping.

International audience; Variety registration of lucerne often fails because of the difficulty to pass the distinction test. This test is presently based on phenotypic traits. We proposed to evaluate if high-throughput genotyping of varieties with genotyping-by-sequencing markers could help to distinguish among 20 varieties and if the genetic distances were correlated to phenotypic ones. Genotyping was performed either on 40 individuals or on 4 bulks of 100 plants per variety. At the methodological level, we obtained a high number of polymorphic markers, a precise determination of the allele dosage on the individuals, a high reproducibility of allele frequency estimated on bulks and a good correlation between allele frequencies scored on individuals or on bulks. Each pair of the 20 varieties was significantly distinct when using the markers. In addition, the varieties grouped in a way that was consistent with their genetic origin. Genetic distances were correlated to phenotypic distances obtained from data collected in the distinction tests. We suggest that molecular markers could be useful to assist distinction tests during the official trials for registration of lucerne varieties.

Background Genetic studies and breeding of agricultural crops frequently involve phenotypic characterization of large collections of genotypes grown in field conditions. These evaluations are typically based on visual observations and manual (destructive) measurements. Robust image capture and analysis procedures that allow phenotyping large collections of genotypes in time series during developmental phases represent a clear advantage as they allow non-destructive monitoring of plant growth and performance. A L. perenne germplasm panel including wild accessions, breeding material and commercial varieties has been used to develop a low-cost, high-throughput phenotyping tool for determining plant growth based on images of individual plants during two consecutive growing seasons. Further we have determined the correlation between image analysis-based estimates of the plant’s base area and the capacity to regrow after cutting, with manual counts of tiller number and measurements of leaf growth 2 weeks after cutting, respectively. When working with field-grown plants, image acquisition and image segmentation are particularly challenging as outdoor light conditions vary throughout the day and the season, and variable soil colours hamper the delineation of the object of interest in the image. Therefore we have used several segmentation methods including colour-, texture- and edge-based approaches, and factors derived after a fast Fourier transformation. The performance of the procedure developed has been analysed in terms of effectiveness across different environmental conditions and time points in the season. Results The procedure developed was able to analyse correctly 77.2 % of the 24,048 top view images processed. High correlations were found between plant’s base area (image analysis-based) and tiller number (manual measurement) and between regrowth after cutting (image analysis-based) and leaf growth 2 weeks after cutting (manual measurement), with r values up to 0.792 and 0.824, respectively. Nevertheless, these relations depend on the origin of the plant material (forage breeding lines, current forage varieties, current turf varieties, and wild accessions) and the period in the season. Conclusions The image-derived parameters presented here deliver reliable, objective data, complementary to the breeders’ scores, and are useful for genetic studies. Furthermore, large variation was shown among genotypes for the parameters investigated. Electronic supplementary material The online version of this article (doi:10.1186/s13007-016-0132-8) contains supplementary material, which is available to authorized users.

Plant reproductive systems present a gradient of gender ranging from unisexuality to hermaphrodism. This variability in sex expression can be found within species and has been found to be influenced by external factors such as resource levels. The sexual strategy selected will depend not only on the number of pollen grains and seeds an individual can produce but also on the chance of success of this production. Production depends on trade-offs between female and male functions of hermaphrodites according to resource level and subsequent fate is influenced by selfing, inbreeding depression and competition among offspring. The goal of this study is to determine how interactions between these key parameters, resources availability, selfing and density-dependent competition within offspring influence the evolution of reproductive systems. We showed with a theoretical approach that (i) a change in resource level at the population level affects sexual strategies only in certain conditions; (ii) density-dependent seedling mortality disadvantages females compared to hermaphrodites and interacts strongly with resource level.

Forage quality combines traits related to protein content and energy value. High-quality forages contribute to increase farm autonomy by reducing the use of energy or protein-rich supplements. Genetic analyses in forage legume species are complex because of their tetraploidy and allogamy. Indeed, no genetic studies of quality have been published at the molecular level on these species. Nonetheless, mapping populations of the model species M. truncatula can be used to detect QTL for forage quality. Here, we studied a crossing design involving four connected populations of M. truncatula. Each population was composed of ca. 200 recombinant inbred lines (RIL). We sought population-specific QTL and QTL explaining the whole design variation. We grew parents and RIL in a greenhouse for 2 or 3 seasons and analysed plants for chemical composition of vegetative organs (protein content, digestibility, leaf-to-stem ratio) and stem histology (stem cross-section area, tissue proportions). Over the four populations and all the traits, QTL were found on all chromosomes. Among these QTL, only four genomic regions, on chromosomes 1, 3, 7 and 8, contributed to explaining the variations in the whole crossing design. Surprisingly, we found that quality QTL were located in the same genomic regions as morphological QTL. We thus confirmed the quantitative inheritance of quality traits and tight relationships between quality and morphology. Our findings could be explained by a co-location of genes involved in quality and morphology. This study will help to detect candidate genes involved in quantitative variation for quality in forage legume species.

International audience; Background and aims Plant litter quality and water availability both control decomposition. The interaction of both parameters was never studied. We used a grassland site, where litter of contrasting quality, i.e. green litter (fresh leaves; high quality) and brown litter (dead leaves, which underwent senescence but which are still attached to the plant; low quality), is returned to soil. Green and brown litter were exposed in the field under regular weather and drought conditions. The objective of this study was to evaluate the effect of drought on the decomposition of both litter types. Methods We incubated green and brown litter of three different grassland species (Lolium perenne, Festuca arundinacea and Dactylis glomerata) alone or as litter mixture (1/3 of each of the three grassland species) in litterbags for 28 weeks. Drought conditions were simulated by rainfall exclusion. After incubation, litter residues were analysed for C and nitrogen (N) content and stable isotope composition. Additionally, we determined the response of the lignin and carbohydrate signatures to the contrasting conditions. Results C decomposition kinetics of green and brown litter under drought conditions could be explained by two pools of contrasting turnover times. Drought decreased leaf litter C and N decomposition by more than 50% compared to regular weather conditions, mainly by strongly decreasing the decomposition rate constants. The lowest C decomposition occurred for mixtures of litter from all three grassland species. Brown litter showed on average 15% higher reduction in carbon decomposition than green litter following drought. Lignin content remained similar for green and brown litter after drought and regular weather conditions, while sugar content remained similar in green litter and decreased by 18% for brown litter under drought conditions. Conclusions Our results showed different response of decomposition of litter with contrasting quality to drought. Low quality brown litter is likely to be more affected than high quality green litter. Thus, litter quality must be taken into account, when assessing the effect of drought on decomposition.

Flowering is a critical period during a plant's life cycle, and thus the identification and characterization of genes involved in flowering date control are of great importance in agronomy, breeding, population genetics and ecology. The model species Medicago truncatula can be used to detect genes explaining the variation for flowering date, which could also explain this variation in legume crops. The objective of this study was to identify the most promising candidate gene explaining a major quantitative trait locus (QTL) for flowering date previously found in three M. truncatula mapping populations. Fine mapping and bioinformatic analysis of bacterial artificial chromosomes (BACs) in the confidence interval of the QTL showed six genes potentially involved in the control of flowering date. Two of these genes, similar to CONSTANS and FT of Arabidopsis thaliana respectively, had genomic mutations when compared to the parents. The transcriptomic study of these genes by semi-quantitative RT-PCR in leaves and flowers sampled at two developmental stages showed that the CONSTANS-like gene was differentially expressed in the two parental lines. A gene belonging to the CONSTANS-like family could explain the major QTL for flowering date segregating in M. truncatula progenies.

Contact: bernadette.julier@lusignan.inra.fr; International audience; In alfalfa (Medicago sativa), an autotetraploid forage legume, stem length is a major component of forage yield, quality and competing ability. In this species, flowering date is not a breeding criterion. Association mapping based on a candidate gene approach has given good results in plants, including autotetraploid species for which genetic analyses are complex. The role of a CONSTANS-LIKE gene, identified as a candidate for stem elongation and flowering date in the model legume M. truncatula, was tested for association with the same traits in alfalfa. Four hundred genotypes from ten cultivars were evaluated for stem height and flowering date in two locations during 4 years. They were genotyped with simple sequence repeat markers and a low structuration was noticed. Primers were designed to amplify and sequence two regions of the alfalfa gene homologous to CONSTANS-LIKE. Single nucleotide polymorphisms (SNPs) were detected and their allelic dose in each genotype was scored. Linkage disequilibrium within CONSTANS-LIKE rapidly decreased as expected. Eight SNPs with a frequency above 10% were detected over 1,010 bp (one SNP every 126 bp on average) in the 400 genotypes. This number was lower than observed in a neutral gene (a SNP every 31 bp on average). Highly significant associations of three SNPs to flowering date and stem height were identified. Each SNP explained up to 4.2% of the genetic variance. Thus, as in the model species, the CONSTANS-LIKE gene was shown to be involved in flowering date and stem height in alfalfa

Feral populations of cultivated crops may act as reservoirs for novel traits and aid in trait movement across the landscape. Knowledge on the genetic diversity of feral populations may provide new insights into their origin and evolution and may help in the design of efficient novel trait confinement protocols. In this study, the genetic diversity of 12 feral alfalfa (Medicago sativa) populations originating from southern Manitoba (Canada) and 10 alfalfa cultivars and a M. falcata germplasm were investigated using eight SSR markers (i.e., microsatellites) and 14 phenotypic traits. We found that the genetic diversity observed in feral populations was similar to the diversity detected among the 10 cultivars. Analysis of molecular variance revealed that there was great genetic variation within (99.8%) rather than between different feral populations. Cluster analysis (unweighted pair-group method using arithmetic average) revealed no differentiation between feral populations and cultivars for neutral loci. High levels of population differentiation for phenotypic traits (and not for neutral markers) suggest the occurrence of heterogeneous selection for adaptive traits. The phenotypic traits we studied did not distinctly separate feral populations from cultivars but there was evidence of natural selection in feral populations for traits including winter survivability, rhizome production, and prostrate growth habit. Our results suggest that feral alfalfa populations need to be considered in the risk assessment of alfalfa containing novel genetically modified (GM) traits. Further, feral alfalfa populations may be regarded as a source of new germplasm for plant improvement.