Use of microsatellite DNA markers to investigate the level of genetic diversity and population genetic structure of coconut (Cocos nucifera L.) L. Perera, J.R. Russell, J. Provan, and W. Powell Abstract: We have used eight pairs of simple sequence repeat (SSR) primers to analyse the genetic diversity in 130 in- dividuals of coconut (Cocos nucifera L.) comprising 75 tall individuals and 55 dwarf individuals, representing 94 dif- ferent coconut ecotypes throughout the world. A total of 51 alleles were detected, with an average of 6.4 alleles per locus. Fifty alleles were detected in tall coconuts (talls; mean alleles/locus 6.3) compared with only 26 (mean/ locus 3.3) in dwarfs, and the average diversity value in talls (0.589) was also significantly higher than that in dwarfs (0.348). Using the eight SSRs we were able to uniquely discriminate 116 of the 130 individuals. A phenetic tree based on D AD (absolute distance) values clustered individuals into five groups, each mainly composed of either talls or dwarfs. These results provide evidence in support of previous hypotheses concerning the dissemination of coconut, as well as important new information for conservation and breeding purposes. Key words: coconut, Cocos nucifera, microsatellites, SSR, genetic diversity. Résumé : Des paires d’amorces spécifiques à huit microsatellites (SSRs) ont été employées pour analyser la diversité génétique parmi 130 cocotiers (Cocos nucifera L., 75 de grande taille et 55 nains) représentant 94 écotypes différents provenant de partout dans le monde. Au total, 55 allèles ont été détectés pour une moyenne de 6,4 allèles par locus. Cinquante allèles ont été détectés parmi les cocotiers de grande taille (une moyenne de 6,3 allèles par locus) alors que seuls 26 allèles étaient présents chez les cocotiers nains (une moyenne de 3,3 allèles par locus). La valeur moyenne de diversité génétique chez les grands cocotiers (0,589) était supérieure à celle observée chez les cocotiers nains (0,348). À l’aide des huit microsatellites, il a été possible de distinguer 116 des 130 individus. Un arbre fondé sur les valeurs D AD a groupé les individus en cinq groupes, chacun composé principalement de cocotiers grands ou nains. Ces résultats appuient les hypothèses concernant la dissémination du cocotier et apportent d’importantes informations nouvelles en vue de la conservation et de l’amélioration génétique du cocotier. Mots clés : cocotier, Cocos nucifera, microsatellites, SSR, diversité génétique. [Traduit par la Rédaction] Perera et al. 21 Introduction Coconut is the most extensively grown and used nut in the world, playing a significant role in the economic, cultural, and social life of over 80 tropical countries. Currently, coco- nut is mainly an oil crop; rich in lauric acid, with a variety of other uses in addition to commercial oil production (Harries 1995). Coconut is a member of the monocotyled- enous family Arecaceae (Palmaceae), subfamily Cocoideae and the monospecific genus Cocos. The existence of related genera of coconut in South America (Cook 1910; Purseglove 1985) and coconut’s long history in the Eastern hemisphere has led to controversy over its centre of diversity. Fremond et al. (1966) summarised the main reasons for considering a Southeast Asian origin for coconut, and Melanesia is consid- ered as the most likely region for coconut domestication along the coasts and islands between Southeast Asia and the Western Pacific (Harries 1995). According to Whitehead (1976), coconut spread both west and east from this putative centre of diversity. Purseglove (1985) suggested an alterna- tive route for the evolution of coconut from a South Ameri- can ancestor that could have been disseminated by ocean currents from South America to Polynesia. Coconut has been distributed to many different parts of the world including Central and South America, East and West Africa, Southeast Asia, East Asia and the Pacific is- lands. Dissemination was achieved by floating in sea cur- rents (Ohler 1984) and subsequent germination on the shore, followed by further human dispersal. Geographic isolation, introgressive hybridisation, mutation, and selection are the Genome 43: 15–21 (2000) © 2000 NRC Canada 15 Corresponding Editor: B. Golding. Received December 17, 1998. Accepted July 2, 1999. L. Perera, J.R. Russell, 1 J. Provan, and W. Powell. Department of Cell and Molecular Genetics, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, U.K. 1 Author to whom all correspondence should be addressed (e-mail: J.Russell@scri.sari.ac.uk).