15 décembre 2003
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Parmi les légumineuses, les espèces du genre Hedysarum constituent un patrimoine phytogénétique performant pour la production de fourrage et la valorisation des parcours dégradés, notamment dans les régions semi-arides et arides. La conservation de ces ressources nécessite une évaluation préalable de leur diversité génétique. L'analyse moléculaire par AFLP de 10 populations spontanées et 2 cultivées de l'espèce H. coronarium L., a permis de recenser un total de 207 bandes dont 178 se sont révélées polymorphes, qui constituent des marqueurs puissants pour décrire la variabilité chez H. coronarium. La variabilité génétique est importante (taux de bandes polymorphes de 86% pour l'ensemble des populations analysées). La diversité génétique intrapopulation représente la majeure partie de la diversité génétique totale. Les distances génétiques établies à partir des données AFLP montrent la ressemblance des deux cultivars provenant de la région de Béja et de Mateur, et leur éloignement des populations spontanées Zit et Makthar à tendance orthotropique. Le cultivar Béja présente une relative proximité avec la population spontanée de la même localité.
The conservation of bio-diversity among cultivated plants and their wild relatives is of particular importance in Tunisia, where a severe genetic erosion has been observed. Among the forage legumes (family Leguminosae = Fabaceae), the genus Hedysarum is of great importance, since it can provide new phytogenetic resources able to increase the value of pastoral lands and the benefits derived from them. The diploid and tetraploid Mediterranean species (x=8) of this genus differ by their morphological habits, pollination system, biological cycle and geographical origin. Among them, all nutritious and highly palatable to sheep, only H. coronarium L. (commonly called Sulla or Spanish Sainfoin), a native of Italy, is grown for fodder : e.g. in Spain, Greece and North Africa. In this study, the genetic diversity of H. coronarium was ascertained by an AFLP analysis of 180 individual plants belonging to ten spontaneous local populations and to two cultivars. A total of 207 bands were amplified, among which 178 (86%) revealed polymorphism. These were scored as AFLP bands and computed with the Shannon index. In addition, polymorphic bands were also analysed to produce a genetic distance matrix following NEI and LIs (1979) formula. A cluster analysis using the UGPMA method (Unweighted Pair Group Method using Arithmetic Average) was also performed, using Neighbors programme. Our data show that the AFLP method is an efficient tool to examine the genetic diversity among and within accessions of H. coronarium. The great discriminative power of AFLP markers and their ability to represent genetic relationships among Hedysarum plants was confirmed. Our data exhibit evidence of great similarity between the two cultivars originating from Béja and Mateur, and also a relative distance from the spontaneous populations of Jebel Zit and Makthar, which are characterized by an orthotropic form. In addition, the Béja cultivar is relatively close to the spontaneous population of same origin.
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