Eco-geographic patterns of genetic diversity of African rice, Oryza glaberrima, in Benin (West Africa)

Genetic erosion is a phenomenon that is currently of concern because of the loss of biodiversity, especially from crop populations in centers of origin and diversity due to a narrowing of the genetic base caused by various factors. The rate of erosion depends on the crop, the region, and the specific environment and cropping conditions. There is now a need for new gene sources and reinstatement of genetic diversity. Studies on the genetic diversity available, especially in traditional agricultural ecosystems are therefore needed. The genus Oryza contains 22 species: two are cultivated, Asian rice ( Oryza sativa) and African rice (Oryza glaberrima) and 20 are wild. In West Africa, which is considered the center of origin of Oryza glaberrima, the two cultivated species are often grown alongside one another on farmers' fields. Yet, few investigations have been undertaken to study African rice landraces (traditional varieties) in West Africa, and the impact of the introduction of new varieties on their diversity. The main goal of this dissertation is to explore the spatial distribution of Oryza glaberrima and its landraces managed at the farmer's level in different geographical regions and help supply a basis for further investigations for the management of Oryza glaberrima landraces in Benin, West Africa. Various methodologies were utilized and focused on three modes of inquiry: the collection of socio-economic data using 150 ethnographic surveys; molecular analysis of 253 rice accessions collected in the field from farmers using 12 fluorescent labeled microsatellites organized in 3 panels; and the utilization of Geographic Information Systems to integrate physical and socio-economic conditions to identify the areas of unique and high diversity. The results show that 1) landraces and modern cultivars are grown in conjunction on farmers' fields, 2) peak genetic diversity occurs in areas with intermediate environmental variables, and 3) a systematic rather than opportunistic targeting of populations and areas for both ex situ and in situ conservation can be elaborated. These results can be used as part of a national program to complement the rice germplasm collection and the genetic analysis ongoing in Benin, to effectively target the area of greatest diversity, and to identify the most effective strategy for the conservation of this diversity.;Keywords: Agrobiodiversity, Ethnographic surveys, ex situ and in situ conservation, Genetic diversity, Landraces, Geographic Information Systems, Oryza glaberrima, Oryza sativa..