PhD defense: Adja Madjiguene Diallo – Københavns Universitet

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PhD defense: Adja Madjiguene Diallo

Adja Madjiguene Diallo defends his thesis: 

Coexistence and performance of diploid and polyploid Acacia senegal (L.) Willd.: implications for adaptation and domestication in the Sahel

Principal supervisor

Professor Erik Dahl Kjær
Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

Co-supervisors

Associate Prof. Lene Rostgaard Nielsen
Associate Prof. Anders Ræbild
Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

Assessment Committee

Associate Professor Thure Hauser (chair)
Department of Plant and Environmental Sciences, University of Copenhagen, DK
Head of Research Group Jean -Marc Bouvet
CIRAD – Agricultural Research for Development, F

Researcher Myriam Heuertz
INRA & University of Bordeaux, F   

Abstract

Acacia senegal, is the most important gum arabic producer and the tree species 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 provides new knowledge about the potential role of polyploidization in A. senegal in relation to adaptation, gum arabic production and evolutionary success. The findings are based on a combinaton of different approaches such as field trial assessment, stress trial experiment, microsatellite markers and flow cytometry were used. 

The thesis reveals that polyploid individuals are also found in Senegal, and the frequences vary among populations. Comparision of growth performance in a progeny trial and in a growth chamber under drought stress test suggested that polyploids perform better than diploid under dry conditions.

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 narrowl related than half-sibs. Narrow sense heritability was estimated to 0.38 for gum yield and suggested 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 thesis includes a study of the distribution and  genetic structure of polyploids compared to diploids across different environmental ranges in Senegal. No simple geographic pattern in the level of polyploids in natural populations were identified, 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 a study of genetic relationship between cytotypes, it is argued that polyploid A. senegal are likely to have multiple origins.

After the PhD defense there will be a reception at Rolighedsvej 23, in meeting room Von Langen.