Implications for in situ genetic resource conservation from the ecogeographical distribution of rice genetic diversity in Maritime Guinea M. B. Barry 1 , J. L. Pham 2 , J. L. Noyer 3 , B. Courtois 3 , C. Billot 3 and N. Ahmadi 4 * 1 Institut de Recherche Agronomique de Guine ´e, PB 1523, Conakry, Guinea, 2 UMR DGPC / IRD, Av Agropolis, 34398 Montpellier Cedex 5, France, 3 UMR PIA, CIRAD, Av Agropolis, 34398 Montpellier Cedex 5, France and 4 UR Peuplements de riz, CIRAD, TA70/03, Av Agropolis, 34398 Montpellier Cedex 5, France Received 15 March 2006; Accepted 21 August 2006 Abstract Genetic resource conservation is widely acknowledged as important. The implementation of conservation requires an insight into the distribution of genetic diversity at the scale of small regions or villages. We present an analysis of rice diversity at such a scale, in a region where traditional farming still prevails. Regional allelic diversity was comparable to that noted worldwide for Asian rice (Oryza sativa), but not as high for African rice (O. glaberrima). Each village pooled more than half of the regional allelic diversity. Genetic differentiation between varieties from the same village accounted for 70% of the regional variation. The differ- entiation associated with lowland and upland rice-growing ecosystems was 23%, while that associated with differences between villages within the same ecosystem was 7%. In the upland ecosystem, geographical distance had a significant effect on the F ST between pairs of villages. In the lowland ecosystem, differences in soil salinity between villages affected F ST . Genetic diversity within a single village may have up to three components: an ancient gla- berrima component shared with neighbouring or ethnically related villages; a relatively ancient sativa component which was hardly or no longer shared with other villages due to local differentiation; and a recently introduced sativa component shared with other villages. Genetic resource conservation could be achieved, in terms of allelic diversity, through strati- fied sampling according to described genetic differentiation factors, whereas current farming systems must be preserved to ensure conservation of the diversity of allelic associations. Keywords: diversity partition; Guinea rice; in situ conservation Introduction Awareness of the importance of the genetic diversity of crop plants has been increasing since the early 1970s, which has prompted much investment in genebank development and maintenance (Hawkes, 1983). More recently, the concept of on-farm in situ conservation has emerged (Altieri and Merrick, 1987; Maxted et al., 1997), involving permanent cropping and management of crop populations within the environment where the species has evolved (Bellon et al., 1997). It is now widely recognized that these two approaches are comp- lementary and should be jointly included in conservation strategies (Olfield and Alcorn, 1987; International Plant Genetic Resources Institute, 1993; Brush, 1999; Wood * Corresponding author. E-mail: ahmadi@cirad.fr q NIAB 2007 ISSN 1479-2621 Plant Genetic Resources: Characterization and Utilization 5(1); 45–54 DOI: 10.1017/S1479262107390898