Relation entre les caractères morphologiques observés sur des plantes espacées et les indices de compétition intra et inter-spécifiques chez la luzerne

Relation entre les caractères morphologiques observés sur des plantes espacées et les indices de compétition intra et inter-spécifiques chez la luzerne. 2. Rencontres Francophones sur les Légumineuses (RFL2

Structuration de la diversité génétique chez la luzerne cultivée, conséquence pour l'identification de gènes liés à des caractères agronomiques

La luzerne, espèce allogame et autotétraploïde, est une légumineuse fourragère dont l’intérêt connaît un renouveau certain grâce à ses atouts pour le développement durable de l’agriculture. L’amélioration des variétés nécessite de mieux connaître les ressources génétiques, pour les exploiter, que ce soit en sélection classique ou en utilisant les outils moléculaires pour implémenter la sélection assistée par marqueurs. En étudiant 10 variétés européennes, nous avons montré que la diversité à l’intérieur des variétés est grande (hétérozygotie attendue de 0.75, déviation standard de 0.80, pour des caractères phénotypiques et des marqueurs moléculaires neutres, respectivement). La différenciation entre variétés est notable pour les caractères phénotypiques. Cette structuration de la diversité est favorable à l’utilisation de la génétique d’association basée sur des gènes candidats pour identifier des gènes liés à des caractères agronomiques. Une telle étude a permis de montrer que le gène Constans-like contribue à expliquer les différences de longueur de tiges chez la luzerne, une composante du rendement fourrager. Alfalfa, an allogamous and autotetraploid species, is a forage legume for which a renewed interest has raised because of its advantages for a sustainable agriculture. Variety improvement requires a better knowledge of the genetic resources in order to exploit them, with classical breeding methods or with molecular tools to implement marker assisted selection. We have described 10 European varieties and found a large within-variety diversity (expected heterozygozity of 0.75, standard deviation of 0.80, with phenotypic traits and neutral molecular markers, respectively). Differentiation between varieties was noticeable for phenotypic traits. This genetic structure of diversity is favourable to the use of association genetics based on candidate genes to identify genes related to agronomic traits. Such a study showed that Constans-like gene contributes to explain differences in alfalfa stem length, a component of forage yield

Association study between the gibberellic acid insensitive gene and leaf length in a Lolium perenne L. synthetic variety

<p>Abstract</p> <p>Background</p> <p>Association studies are of great interest to identify genes explaining trait variation since they deal with more than just a few alleles like classical QTL analyses. They are usually performed using collections representing a wide range of variability but which could present a genetic substructure. The aim of this paper is to demonstrate that association studies can be performed using synthetic varieties obtained after several panmictic generations. This demonstration is based on an example of association between the gibberellic acid insensitive gene (GAI) polymorphism and leaf length polymorphism in 'Herbie', a synthetic variety of perennial ryegrass.</p> <p>Methods</p> <p>Leaf growth parameters, consisted of leaf length, maximum leaf elongation rate (LERmax) and leaf elongation duration (LED), were evaluated in spring and autumn on 216 plants of Herbie with three replicates. For each plant, a sequence of 370 bp in GAI was analysed for polymorphism.</p> <p>Results</p> <p>Genetic effect was highly significant for all traits. Broad sense heritabilities were higher for leaf length and LERmax with about 0.7 in each period and 0.5 considering both periods than for LED with about 0.4 in each period and 0.3 considering both periods. GAI was highly polymorphic with an average of 12 bp between two consecutive SNPs and 39 haplotypes in which 9 were more frequent. Linkage disequilibrium declined rapidly with distance with r ²values lower than 0.2 beyond 150 bp. Sequence polymorphism of GAI explained 8-14% of leaf growth parameter variation. A single SNP explained 4% of the phenotypic variance of leaf length in both periods which represents a difference of 33 mm on an average of 300 mm.</p> <p>Conclusions</p> <p>Synthetic varieties in which linkage disequilibrium declines rapidly with distance are suitable for association studies using the "candidate gene" approach. GAI polymorphism was found to be associated with leaf length polymorphism which was more correlated to LERmax than to LED in Herbie. It is a good candidate to explain leaf length variation in other plant material.</p

Construction of two genetic linkage maps in cultivated tetraploid alfalfa (Medicago sativa) using microsatellite and AFLP markers

BACKGROUND: Alfalfa (Medicago sativa) is a major forage crop. The genetic progress is slow in this legume species because of its autotetraploidy and allogamy. The genetic structure of this species makes the construction of genetic maps difficult. To reach this objective, and to be able to detect QTLs in segregating populations, we used the available codominant microsatellite markers (SSRs), most of them identified in the model legume Medicago truncatula from EST database. A genetic map was constructed with AFLP and SSR markers using specific mapping procedures for autotetraploids. The tetrasomic inheritance was analysed in an alfalfa mapping population. RESULTS: We have demonstrated that 80% of primer pairs defined on each side of SSR motifs in M. truncatula EST database amplify with the alfalfa DNA. Using a F1 mapping population of 168 individuals produced from the cross of 2 heterozygous parental plants from Magali and Mercedes cultivars, we obtained 599 AFLP markers and 107 SSR loci. All but 3 SSR loci showed a clear tetrasomic inheritance. For most of the SSR loci, the double-reduction was not significant. For the other loci no specific genotypes were produced, so the significant double-reduction could arise from segregation distortion. For each parent, the genetic map contained 8 groups of four homologous chromosomes. The lengths of the maps were 2649 and 3045 cM, with an average distance of 7.6 and 9.0 cM between markers, for Magali and Mercedes parents, respectively. Using only the SSR markers, we built a composite map covering 709 cM. CONCLUSIONS: Compared to diploid alfalfa genetic maps, our maps cover about 88–100% of the genome and are close to saturation. The inheritance of the codominant markers (SSR) and the pattern of linkage repulsions between markers within each homology group are consistent with the hypothesis of a tetrasomic meiosis in alfalfa. Except for 2 out of 107 SSR markers, we found a similar order of markers on the chromosomes between the tetraploid alfalfa and M. truncatula genomes indicating a high level of colinearity between these two species. These maps will be a valuable tool for alfalfa breeding and are being used to locate QTLs

La distinction des variétés de luzerne pourrait s’appuyer sur les marqueurs moléculaires

La distinction des variétés de luzerne pourrait s’appuyer sur les marqueurs moléculaires. 2. Rencontres Francophones sur les Légumineuses (RFL2

La diversité variétale à l’échelle d’un territoire est-elle un levier pour améliorer les performances agronomiques de la luzerne ? Analyse d’une étude de simulation avec le modèle STICS

La diversité variétale à l’échelle d’un territoire est-elle un levier pour améliorer les performances agronomiques de la luzerne ? Analyse d’une étude de simulation avec le modèle STICS. 2. Rencontres Francophones sur les Légumineuses (RFL2

Genome-wide genotyping data renew knowledge on genetic diversity of a worldwide alfalfa collection and give insights on genetic control of phenology traits

China’s and Europe’s dependence on imported protein is a threat to the food self-sufficiency of these regions. It could be solved by growing more legumes, including alfalfa that is the highest protein producer under temperate climate. To create productive and high-value varieties, the use of large genetic diversity combined with genomic evaluation could improve current breeding programs. To study alfalfa diversity, we have used a set of 395 alfalfa accessions (i.e. populations), mainly from Europe, North and South America and China, with fall dormancy ranging from 3 to 7 on a scale of 11. Five breeders provided materials (617 accessions) that were compared to the 400 accessions. All accessions were genotyped using Genotyping-by-Sequencing (GBS) to obtain SNP allele frequency. These genomic data were used to describe genetic diversity and identify genetic groups. The accessions were phenotyped for phenology traits (fall dormancy and flowering date) at two locations (Lusignan in France, Novi Sad in Serbia) from 2018 to 2021. The QTL were detected by a Multi-Locus Mixed Model (mlmm). Subsequently, the quality of the genomic prediction for each trait was assessed. Cross-validation was used to assess the quality of prediction by testing GBLUP, Bayesian Ridge Regression (BRR), and Bayesian Lasso methods. A genetic structure with seven groups was found. Most of these groups were related to the geographical origin of the accessions and showed that European and American material is genetically distinct from Chinese material. Several QTL associated with fall dormancy were found and most of these were linked to genes. In our study, the infinitesimal methods showed a higher prediction quality than the Bayesian Lasso, and the genomic prediction achieved high (&gt;0.75) predicting abilities in some cases. Our results are encouraging for alfalfa breeding by showing that it is possible to achieve high genomic prediction quality

Etude génétique et physiologique de l'architecture déterminée chez le lupin blanc d'hiver. Conséquences agronomiques et en sélection

As on other grain legumes, the determinate architecture seemed promising to reduce vegetative development and improve seed yield and yield stability in autumn-sown white lupin (Lupinus albus). The consequences of this architecture on plant development and yield elaboration was studied through genetic and physiological approaches. The inheritance of determinate architecture was shown to be monogenic and recessive, which allows an easy management of this character in plant breeding. Vegetative development was reduced, because all buds became floral early in the season. Each branch carried fewer leaves than in indeterminates, and the number of vegetative levels was reduced. The profils of number of leaves on the branches had a characteristic bell shape. This structure of branches was modelled. A large genetic variability existed for the architecture, even if the relationship between flowering earliness and vegetative development was strong. Light interception by canopy in terms of thermal time from sowing was similar for the determinates and the indeterminates. Proportion of light reaching the mainstem leaves was higher. Seed yield of determinate genotypes was similar to that of indeterminate genotypes. Dry matter production was lower but harvest index higher than for indeterminates. Maturity date was earlier, especially on cool, wet climates, and yield stability was increased. These trends were linked to the reduction of vegetative development, and to a lower competition between vegetative and reproductive developments than observed in indeterminates. Mainstem and first-order branches mainly contributed to total seed yield, and these orders were less influenced by climatic variation tha upper branch orders. Genetic variability for yield components was large. An extremely reduced vegetative development as well as an excessive development were detrimental to yield. Traits related to branch development (number of leaves and number of branch orders) are valuable breeding criteria on determinate lupins.Comme chez de nombreux protéagineux, l'architecture déterminée a semblé une voie prometteuse pour réduire le développement végétatif et améliorer le rendement et la stabilité du rendement du lupin blanc d'hiver (Lupinus albus L.). Une étude à la fois génétique et physiologique de ce type architecturale et de ses conséquences sur le développement et la mise en place du rendement a donc été entreprise. L'hérédité du caractère d'architecture déterminée est monogénique récessive, ce qui permet une utilisation simple en sélection. Le développement végétatif est réduit car tous les bourgeons passent à l'état floral précocément dans le cycle. Les ramifications portent chacune moins de feuilles que chez les indéterminés, et le nombre de niveaux végétatifs est réduit. La distribution des feuilles sur les ramifications suit un profil caractéristique en forme de cloche. La structure des ramifications a pu être modélisée. Il existe une grande variabilité génétique pour l'architecture, bien que la relation positive entre tardiveté de floraison et développement végétatif soit forte. L'interception de la lumière par le couvert en fonction du temps est similaire chez les déterminés et les indéterminés. Cependant, les déterminés atteignent une interception maximale moins importante en raison de leur développement végétatif restreint. La proportion de lumière qui parvient jusqu'aux feuilles de la tige principale est accrue. Le rendement des génotypes déterminés semble compétitif avec celui des génotypes indéterminés. La production de matière sèche est plus faible mais l'indice de récolte est supérieur. La date de maturité est sensiblement avancée, surtout sous des climats frais et humides, et la stabilité du rendement est plus grande. Ces caractéristiques sont liées à la réduction du développement végétatif, et à une compétition entre développement végétatif et développement reproducteur plus faible que celle observée chez les indéterminés. Le rendement est produit essentiellement sur la tige principale et le premier niveau de ramifications, et ces sites sont moins sujets à des aléas climatiques que les niveaux supérieurs. La variabilité génétique pour les composantes du rendement est large. On met en évidence des relations entre certains caractères d'architecture et les potentialités de rendement. Un développement végétatif trop restreint aussi bien qu'un développement excessif nuisent au rendement. Les caractères de développement des ramifications (nombre de feuilles et nombre de niveaux végétatifs) sont des critères de sélection pertinents chez les lupins déterminés