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Georg August University of Göttingen (2006)

Development of microsatellites in Prosopis spp. and their application to study the reproduction system

Mottura, Martín Carlos

Titre : Development of microsatellites in Prosopis spp. and their application to study the reproduction system

Entwicklung von Mikrosatelliten für Prosopis spp. und ihre Anwendung zur Untersuchung des Reproduktionssystems

Auteur : Mottura, Martin Carlos

Université de soutenance : Georg August University of Göttingen

Grade : Doctor of Forestry Science 2006

Résumé
Prosopis chilensis and Prosopis flexuosa, two hardwood arboreal species, constitute important natural resources. They play a vital role in the ecology and the economy of arid and semi-arid zones in Argentina. In spite of their importance, the exploration of the genetic resources of both species is in an early stage. Highly polymorphic molecular markers are indispensable for the study of the genetic resources of these species. Microsatellite markers (SSRs = Simple Sequence Repeats) offer a great potential for the analysis of gene flow and mating system.The aim of the present study was first to develop microsatellite markers for the genus Prosopis ; and secondly to use the developed markers in a study of the reproduction system of a hybrid swarm between Prosopis chilensis and Prosopis flexuosa.SSR loci were isolated for the species Prosopis chilensis using an enrichment protocol developed by Fischer and Bachmann (1998). Six primer pairs were obtained. These primers showed a Polymorphism Information Content between 0.14 and 0.70 in P. chilensis and, between 0.41 and 0.85 in P. flexuosa. Expected heterozygosity ranged from 0.14 to 0.73 in P. chilensis, and from 0.46 to 0.86 in P. flexuosa. A test for cross-species amplification in seven other Prosopis species revealed a broad cross-species affinity.The developed SSR markers were applied to study genetic variation and reproductive system of a hybrid swarm between Prosopis chilensis and P. Flexuosa. 100 flowering Prosopis trees (adult population) were studied. Morphological assignment was performed by means of qualitative and quantitative morphological characters. Three morphological groups were obtained : Group 2, Prosopis flexuosa ; Group 3, P. chilensis ; and Group 1, intermediate individuals. Total number of alleles over all groups and at six SSR loci was 70 (average number of alleles/locus = 11.67). Estimate gene diversity (He) showed the highest mean value in Group 2 (He = 0.730), followed by Group 1 (He = 0.605), and Group 3 (He = 0.554).For the study of the reproduction system, twenty three open-pollinated trees were selected. 516 seeds (seed population) were collected. Seed population was divided into groups according to the morphological classification of the mother trees. 41 different alleles were found in the seed population. Genetic parameters showed the highest differentiation between Group 3 and 2 in the seed population as well as in the effective pollen cloud. Reduction in genetic differentiation was observed over all groups comparing the seed population and effective pollen cloud to the adult population.Paternity analysis, conducted by categorical allocation and based on multilocus genotypes, was used in order to asses more precisely the gene flow between groups. Among the 420 progenies that had their male parent within the stand, 170 resulted from hybridization events between groups.Results point towards strong gene flow between morphological groups. A considerable reduction in the genetic differentiation among morphological groups was observed in just one generation. Mating system analysis indicates that gene flow is asymmetric. For the formation of intermediate individuals, Group 2 receives more pollen from Group 3 than the opposite. Hybridization is accompanied by introgression. A higher mating rate of intermediate individuals with Group 3 generates greater levels of introgression towards this group.

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Page publiée le 17 mars 2008, mise à jour le 2 janvier 2019