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[PHD] THESE. Coexistence and performance of diploid and polyploid Acacia senegal (L.) Willd. : Implications for adaptation and domestication in the Sahel [texte imprimé] / Adia Madjiguène Diallo, Auteur . - Danemark : University of Copenhagen, 2015. Langues : Anglais ( eng) Catégories : | FORESTERIE
| Mots-clés : | Acacia senegal, adaptation, distribution, drought, genetic differentiation, genetic relationship, gum arabic, heritability, origins, polyploidy, Sahel regions | Index. décimale : | K030- Génétique et amélioration des plantes | Résumé : | Acacia senegal, is the most important gum arabic producer and represents an active component in traditional dryland agroforestry systems in Africa. The species has been recently found to consist of both diploid and polyploid individuals, which opens for interesting questions since polyploidy is considered a major evolutionary process in plants. This thesis aims to contribute new knowledge about potential role of polyploidization in A. senegal in relation to adaptation, gum arabic production and evolutionary success. For these purposes, different approaches such as field trial assessment, stress trial experiment, microsatellite markers and flow cytometry were used. Results reveal polyploid individuals are also found in Senegal, but frequences vary among populations. Comparision of growth performance in both a progeny trial and in a growth chamber under drought stress test indicated that polyploids perform better than diploid under dry conditions. The quantitative genetic analysis reveal different sibling-relationship between diploids and polyploids were observed. Diploids were mainly outcrossed and families consisted of half-sib progenies. In contrast, polyploid individuals within families were more related than half-sib. Narrow sense heritability was estimated to 0.38 for gum yield suggesting that a breeding program for increased gum yield can be effective in providing gain after selection of trees with superior phenotypes based on careful testing. The study of distribution of polyploids and their genetic structure compared to diploids across different environmental ranges in Senegal show no simple geographic pattern in the level of polyploids in natual populations, but frequency of polyploids appeared to be positively correlated with increased salinity. Polyploids were found to be more genetically differentiated compared to diploids and based on study of genetic relationship between cytotypes, it is argued that polyploid A. senegal are likely to have multiple origins |
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