Analysis of Genetic Changes in Single-Variety Ryegrass Swards

Ryegrass varieties are synthetics, with a wide within-variety genetic variance for most traits. Ryegrass swards are likely to experience genetic changes with seasons and years because of plant death, asymmetric vegetative reproduction or plant recruitment through reproduction or seed immigration. These changes may be related to or induce changes in agronomic traits, such as biomass production or dry matter composition. The present research was undertaken to measure genetic changes in swards obtained from sowings of a single variety of ryegrass. These changes were evaluated using both neutral molecular markers and morphological traits. The present paper deals with the molecular markers

Estimation of the Coefficient of Double-Reduction in Autotetraploid Lucerne

Polyploidy plays an important role in the evolution of species and many cultivated species, particularly in angiosperms, are polyploids (Bever and Felber, 1992; Gallais, 2003). Autopolyploid species that show a tetrasomic inheritance have complex genetics. However, some theoretical models were built for: (1) genetic mapping (Hackett et al., 1998), (2) quantitative genetics (Gallais, 2003) and (3) population genetics (Ronfort et al., 1998). But in practice, most data analyses ignore one essential feature of tetrasomic inheritance that is double-reduction. Indeed, in an autotetraploid species, homologous chromosomes can form tetravalents at meiosis. In this case, a double-reduction is observed if crossing-over occurs between a locus and its centromere, and if the sister chromatids migrate to the same pole at anaphase I. The gametes may, thus, carry a pair of sister alleles. Double-reduction frequency is represented by the index of separation (α) (Demarly, 1963; Mather, 1935; Mather, 1936). The parameter α is considered as a product of four probabilities: α = q e a s (Gallais, 2003) in which “ q ” is the probability of multivalent formation, “ e ” the probability of first equational division, related to the frequency of crossing-over, “ a ” is the probability of non-disjunction at first anaphase and “s” is the probability of having two sister chromatids in the same gamete. If separation during anaphase II is random, s = ½. Consequently, α will be low for a gene located in the vicinity of the centromere and will increase with distance between the gene and the centromere. It was demonstrated that double-reduction events alter the rate of progression towards equilibrium under inbreeding or under random mating, modify the recombination rate between loci and also alter the rate of decay of linkage disequilibrium under random mating (Bever and Felber, 1992). Current theoretical models allow drawing genetic maps taking into account double-reduction (Luo et al., 2004). Thus, it is possible to estimate α for codominant loci in tetraploid species. To date, we have few estimates of the double-reduction frequency. Haynes and Douches (1993) on potato and Julier et al. (2003) on lucerne found that double-reduction occurs sporadically. In both studies, the low number of progenies hampered a precise estimation of α. The aim of our study was to estimate the frequency of double-reduction in a mapping population of lucerne that includes a large number of individuals

A CONSTANS-like gene candidate that could explain most of the genetic variation for flowering date in Medicago truncatula

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

Dry Matter Accumulation and Partitioning between Vegetative and Reproductive Organs in Alfalfa (\u3ci\u3eMedicago sativa\u3c/i\u3e L.)

This work investigated the partitioning of dry matter between vegetative and reproductive plant organs in alfalfa during the reproductive period under field conditions. Two French varieties (Europe and Magali) were studied. Both varieties showed similar growth pattern of the different plant organs in 1998 and 1999. The mean dry matter of vegetative organs (shoots and leaves) over the two years was higher in Europe (567g/m2) than Magali (470g/m2). No vegetative growth was observed during the reproductive period. The root organs (measured to a depth of 0.20 m) and the reproductive organs showed an increase in dry matter accumulation during the first 300 °Cd and 600 °Cd, respectively. It indicated that dry matter was preferentially partitioned to the reproductive organs during the first 600 °Cd. The root organs seem to be a competing sink during the early seed growth (200 °Cd to 300 °Cd). The dry matter partitioning was not affected by the year. Thus, when dry matter accumulation ceased only 30% in Europe and 27% in Magali of the aboveground dry weight was in the reproductive organs. The mean inflorescence weight reached its maximum after 450 °Cd from inflorescence flowering

Grasslands and herbivore production in Europe and effects of common policies

The European project Multisward (http://www.multisward.eu/multisward_eng/) aims at supporting developments and innovations in grassland use and management in different European farming systems (including low-input and organic farming systems), pedoclimatic and socio-economic conditions i) to enhance the role of grasslands at farm and landscape levels to produce environmental goods and to limit the erosion of biodiversity and ii) to optimise economic, agronomic and nutritional advantages for the development of innovative and sustainable ruminant production systems. The identification of the innovations and their implementation required an exhaustive analysis of the state of grasslands and herbivore production in Europe including how they changed over decades. The effects of public policies were investigated. The results of this analysis are published in the present book

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

Agronomic Value of Mixture of Perennial Rye-Grass Cultivars: Preliminary Results

Mixtures of grass and legume species are commonly used in sown grasslands. Mixtures have been shown to be favourable for stable production over cycles and years due to a succession of species over time (Mosimann & Charles, 1996 ; Nie et al, 2004). However, little is known whether the genetic variation in pure stands has an influence on the agronomic value and its variation over seasons

C and O isotope compositions of modern fresh-water mollusc shells and river waters from Himalaya and Ganga plain

The aim of this paper is to unfold the relationship between O and C isotope compositions of modern fresh-water mollusc shells and water in order to refine the basis of interpretation for paleoenvironnemental reconstruction in the sub-Himalayan river basins. Large number of mollusc shells and associated host water from both running water and closed body of water were analysed including intra-shell variability in a few cases. The O isotopic compositions of river waters in the Himalayas and Ganga plain have a large range, from -18‰ in the north of the High range up to -8 to -4 ‰ in the Ganga plain. d18O of rivers are also seasonally variable, especially in foothills rivers whereas the seasonal contrast is smoothed out for main Himalayan rivers having large catchments. O isotopic compositions of bulk shells (Aragonite) vary between -15 and -5 ‰. Average d18OAra values are consistent with precipitation at equilibrium with host waters at a temperature range of 20-25°C suggesting that shell growth may be favoured during non-monsoon conditions. Shells collected along main Himalayan rivers have d18O values uniformly distributed within -11 and -6 ‰ reflecting the minimal seasonal contrast shown by these rivers. In contrast, O isotopic compositions of shells from foothills rivers vary only by 4‰. This shows that, depending on the type of river where the molluscs grow, the information in term of d18O amplitude will be different for identical climatic conditions. In closed or pond water bodies significant enrichment in 18O due to evaporation is observed. The C isotopic compositions of river dissolved inorganic carbon (DIC) decrease downstream from 0 to -10 ‰ reflecting input of soil derived alkalinity and plant productivity in the river. d13C of shells are systematically lower than compositions calculated for equilibrium with river DIC indicating that in addition to DIC, a significant fraction of carbon is derived from metabolic sources. Intra-shell d13C are stable compared to the seasonal variability of DIC suggesting that the pool of organic carbon changes throughout year