Genetic structure of a population evolving under traditional farming system

Citrullus lanatus var. lanatus oleaginous type offers a particularly interesting study case of a minor crop evolving in a traditional farming system. The general objective of this thesis was to understand precisely how the mating system in combination with the cultivation practices affect the genetic structure and diversity of C. lanatus oleaginous type and its evolution in time. The genetic diversity and structure of 15 fields of C. lanatus oleaginous type in Côte d’Ivoire was characterized with the use of microsatellite markers. The reproduction biology of the C. lanatus oleaginous type was also studied, with an emphasis on the mating system and the magnitude of inbreeding depression. The outcrossing rate turned out to be high (0.76), and no sign of inbreeding depression was found. Then each factor among the natural evolutionary forces (outcrossing rate, inbreeding depression) and cultivation practices (size of the fields, partial exchange of seeds between farmers, mode of selection of the seeds, reduction of the number fields) was analyzed, and its potential impact on the genetic diversity was quantified by means of Monte Carlo techniques. Eventually, the different evolutive forces were analyzed in a more inclusive approach in which the interplay between these forces was investigated. Based on the previously-mentioned experimental results, constraints on each evolution factors were derived. The analysis suggested that the outcrossing rate was likely to vary among the fields, and that the degree of genetic differentiation was likely to originate from a non-random selection of the seeds for the next crop cycles. This work also demonstrated the capabilities of a Monte Carlo based approach to quantify the risk of genetic erosion in traditionally cultivated crops.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201