Pierre Roumet

Impact of drought stress on the phenology of two soybean ( Glycine max L. Merr) cultivars

Abstract Drought stresses modify the phenology of plants, and thus affect the yield components. The impact of various periods of water stress on the organ appearance rate and on the durations of the main vegetative and reproductive periods was studied under greenhouse conditions on soybean cultivars differing by type of growth. The two cultivars, Weber and Spot, maturity group I, indeterminate and determinate respectively, were subjected to drought stress (30% PAW) during a main developmental stage: i.e., vegetative, flowering, pod lengthening or seed filling. Drought stress seemed to trigger a signal that caused an early switch of plant development from vegetative to reproductive. Appearance of nodes initiated during stress was delayed, resulting in a small number of nodes produced, whereas flower and pod appearance were hastened. Each reproductive phase was shorter under stress, mainly because of the appearance of new organs that prevented the emergence of organs belonging to the earlier ontogenetic phases. The seed-filling stage and the final stage in seed abortion began earlier in stressed plants and the duration of the maturation period was significantly reduced by stress during seed filling, leading to accelerated senescence. The cultivars differed mostly with respect to their strategies of partitioning between the main stem and branches. Under stress, the duration of the main reproductive phase was increased on the main stem but reduced on the branches in cultivar Weber, whereas the opposite response was noted in cultivar Spot.

Environment characterisation for the interpretation of environmental effect and genotype × environment interaction

Increasing attention is being paid to environment characterisation as a means of identifying the environmental factors determining grain protein content (GPC) in durum wheat. New insights in crop physiology and agronomy have led to the development of crop simulation models. Those models can reconstruct plant development for past cropping seasons. One major advantage of these models is that they can also indicate the intensity of limiting factors affecting plants during particular developmental stages. The main environmental factors determining GPC in durum wheat can be investigated by introducing the intensity of limiting factors into genotype × environment (G×E) models. In our case, limiting factors corresponding to water deficit and nitrogen availability were calculated for the development period between booting and heading. These variables were then introduced into a clustering model. This model is an extension of factorial regression applied to discrete environment and genotypic variables. This procedure effectively described the environment main effect: around 30.9% of the sum of squares of the environment main effect was accounted for, using less than 33% of the degrees of freedom. It also partially accounted for G×E interaction. Our methodology, coupling the use of crop simulation and G×E analysis models, is of potential value for improving our understanding of the main development stages and identification of environmental limiting factors for the development of GPC.

Towards a comprehensive characterization of durum wheat landraces in Moroccan traditional agrosystems: analysing genetic diversity in the light of geography, farmers’ taxonomy and tetraploid wheat domestication history

BackgroundCrop diversity managed by smallholder farmers in traditional agrosystems is the outcome of historical and current processes interacting at various spatial scales, and influenced by factors such as farming practices and environmental pressures. Only recently have studies started to consider the complexity of these processes instead of simply describing diversity for breeding purposes. A first step in that aim is to add multiple references to the collection of genetic data, including the farmers’ varietal taxonomy and practices and the historical background of the crop.ResultsOn the basis of interview data collected in a previous study, we sampled 166 populations of durum wheat varieties in two traditional Moroccan agrosystems, in the Pre-Rif and Atlas Mountains regions. Using a common garden experiment, we detected a high phenotypic variability on traits indicative of taxonomical position and breeding status, namely spike shape and plant height. Populations often combined modern (short) with traditional-like (tall) statures, and classical durum squared spike shape (5 flowers/spikelet) with flat spike shape (3 flowers/ spikelet) representative of primitive domesticated tetraploid wheat (ssp. dicoccum). By contrast, the genetic diversity assessed using 14 microsatellite markers was relatively limited. When compared to the genetic diversity found in a large collection of tetraploid wheat, it corresponded to free-threshing tetraploid wheat. Within Morocco, the two studied regions differed for both genetic diversity and variety names. Within regions, neither geography nor variety names nor even breeding status constituted strong barriers to gene exchange despite a few significant patterns.ConclusionsThis first assessment of morphological and genetic diversity allowed pointing out some important factors that may have influenced the structure and evolutionary dynamics of durum wheat in Morocco: the significance of variety names, the occurrence of mixtures within populations, the relative strength of seed exchange between farmers and local adaptation, as well as the fate of modern varieties once they have been introduced. Further, multidisciplinary studies at different spatial scales are needed to better understand these complex agrosystems of invaluable importance for food security.

Genotyping by Sequencing Using Specific Allelic Capture to Build a High-Density Genetic Map of Durum Wheat

Targeted sequence capture is a promising technology which helps reduce costs for sequencing and genotyping numerous genomic regions in large sets of individuals. Bait sequences are designed to capture specific alleles previously discovered in parents or reference populations. We studied a set of 135 RILs originating from a cross between an emmer cultivar (Dic2) and a recent durum elite cultivar (Silur). Six thousand sequence baits were designed to target Dic2 vs. Silur polymorphisms discovered in a previous RNAseq study. These baits were exposed to genomic DNA of the RIL population. Eighty percent of the targeted SNPs were recovered, 65% of which were of high quality and coverage. The final high density genetic map consisted of more than 3,000 markers, whose genetic and physical mapping were consistent with those obtained with large arrays.

Calibration of a chemometrical model from field hyperspectral close-range images: Taking into account leaf inclination and multiple reflection effects

The aim of the study was to test the potentiality of field close-range hyperspectral images to obtain nitrogen content of wheat leaves in field. Field measurements imply several potential disturbances of the recorded signal: illumination level, specular reflection, multiple reflections, etc. Chemo-metrical model calibration procedure has to take them into account. We tested the following methodology. First we calibrated a chemometrical model between nitrogen content and non-disturbed reflectance signal of flat isolated leaves. Thus we evaluated the quality of such a model. Then, we identified and qualified each phenomenon effects and proposed a solution to overcome each issue. Finally, we verified that all the disturbances could be taken into account while preserving satisfactory model prediction quality.

Anchoring durum wheat diversity in the reality of traditional agricultural systems: varieties, seed management, and farmers’ perception in two Moroccan regions

BackgroundTraditional agrosystems are the places were crop species have evolved and continue to evolve under a combination of human and environmental pressures. A better knowledge of the mechanisms underlying the dynamics of crop diversity in these agrosystems is crucial to sustain food security and farmers’ self-reliance. It requires as a first step, anchoring a description of the available diversity in its geographical, environmental, cultural and socio-economic context.MethodsWe conducted interviews with farmers cultivating durum wheat in two contrasted traditional agrosystems of Morocco in the Pre-Rif (163 farmers) and in the oases of the Atlas Mountains (110 farmers). We documented the varietal diversity of durum wheat, the main characteristics of the farms, the farming and seed management practices applied to durum wheat, and the farmers’ perception of their varieties.ResultsAs expected in traditional agrosystems, farmers largely practiced diversified subsistence agriculture on small plots and relied on on-farm seed production or informal seed exchange networks. Heterogeneity nevertheless prevailed on many variables, especially on the modernization of practices in the Pre-Rif region. Fourteen (resp. 11) traditional and 5 (resp. 3) modern varieties were identified in the Pre-Rif region (resp. in the Atlas Mountains). The majority of farmers grew a single variety, and most traditional varieties were distributed in restricted geographical areas. At the farm level, more than half of the varieties were renewed in the last decade in the Pre-Rif, a more rapid renewal than in the Atlas Mountain. Modern varieties were more prevalent in the Pre-Rif region and were integrated in the traditional practices of seed production, selection and exchange. They were clearly distinguished by the farmers from the landraces, the last ones being appreciated for their quality traits.ConclusionsThe surveyed traditional agrosystems constitute open, dynamic and heterogeneous entities. We suggest that competing factors could favour or limit the cultivation of improved varieties and the erosion of original durum wheat diversity. This first description opens the way to focused further investigations, including complementing variety names with cultural, genetic and phenotypic information and unravelling the multidimensional factors and consequences of modern variety adoption.

Epistatic determinism of durum wheat resistance to the wheat spindle streak mosaic virus

Key messageThe resistance of durum wheat to the Wheat spindle streak mosaic virus (WSSMV) is controlled by two main QTLs on chromosomes 7A and 7B, with a huge epistatic effect.AbstractWheat spindle streak mosaic virus (WSSMV) is a major disease of durum wheat in Europe and North America. Breeding WSSMV-resistant cultivars is currently the only way to control the virus since no treatment is available. This paper reports studies of the inheritance of WSSMV resistance using two related durum wheat populations obtained by crossing two elite cultivars with a WSSMV-resistant emmer cultivar. In 2012 and 2015, 354 recombinant inbred lines (RIL) were phenotyped using visual notations, ELISA and qPCR and genotyped using locus targeted capture and sequencing. This allowed us to build a consensus genetic map of 8568 markers and identify three chromosomal regions involved in WSSMV resistance. Two major regions (located on chromosomes 7A and 7B) jointly explain, on the basis of epistatic interactions, up to 43% of the phenotypic variation. Flanking sequences of our genetic markers are provided to facilitate future marker-assisted selection of WSSMV-resistant cultivars.

A spectral correction method for multi-scattering effects in close range hyperspectral imagery of vegetation scenes: application to nitrogen content assessment in wheat

A method able to overcome multiple scattering effects in close range hyperspectral imagery of vegetation scenes is presented. It has been developed using canopy and light propagation simulation tools and evaluated on real crop plants in the context of nitrogen content assessment.