Comparative Chemical and Molecular Variability of Cananga odorata ( Lam.) Hook.f. & Thomson forma genuina (Ylang-Ylang) in the Western Indian Ocean Islands: Implication for Valorization by Ce ´ line Benini* a ), Gre ´gory Mahy b ), Jean-Philippe Bizoux b ), Jean-Paul Wathelet c ), Patrick du Jardin a ), Yves Brostaux d ), and Marie-Laure Fauconnier a ) a ) Plant Biology Unit, Gembloux Agro-Bio Tech, University of Lie `ge, 2 Passage des De ´ porte ´ s, BE-5030 Gembloux (phone: þ 32-81622460; e-mail: celine.benini@gmail.com) b ) Biodiversity and Landscape Unit, Gembloux Agro-Bio Tech, University of Lie ` ge, 27 avenue Mare ´ chal Juin, BE-5030 Gembloux c ) General and Organic Chemistry Unit, Gembloux Agro-Bio Tech, University of Lie `ge, 2 Passage des De ´ porte ´s, BE-5030 Gembloux d ) Applied Statistics, Computer Science and Mathematics Unit, Gembloux Agro-Bio Tech, University of Lie `ge, 8 avenue de la Faculte ´ dAgronomie, BE-5030 Gembloux Cananga odorata ( Lam.) Hook.f. & Thomson forma genuina (Annonaceae) is a tropical tree, grown for the production of ylang-ylang essential oil, which is extracted from its fresh and mature flowers. Despite its economic and social importance, very little information is available on its variability and the possible factors causing it. Therefore, the relationship between the genetic structure, revealed by amplified fragment length polymorphism (AFLP), and the essential oil chemical composition, determined by GC/MS analysis, of ylang-ylang grown in semi-managed systems in three Indian Ocean islands (Grande Comore, Mayotte, and Madagascar) was investigated. Our results revealed a low genetic variation within plantations and contrasted situations between islands. Variations of the chemical composition could be observed within plantations and between islands. The genetic differentiation pattern did not match the observed pattern of chemical variability. Hence, the chemical variation could not be attributed to a genetic control. As Grande Comore, Madagascar, and Mayotte present different environmental and agronomic conditions, it can be concluded that the influence of these conditions on the ylang-ylang essential oil composition is consistent with the patterns observed. Finally, several strategies were proposed to valorize the chemical composition variations. Introduction. – The industrial production of essential oils requires not only that the product is available, but also that its quality is stable [1]. It is therefore important to understand the factors that influence the variability in the chemical composition of essential oils, to produce oils that meet the market requirements. Many studies have focused on characterizing the factors responsible for the chemical polymorphism recorded within species, highlighting a set of factors linked to essential oil variability: environmental heterogeneity, cultivation conditions, genetic differences among populations, race or variety of plant species used for the essential oil extraction, influence of the physiology of individual plants, and the agronomic practices related to political and social conditions [1] [2] . The presence of different genetic pools within species, the variation in environmental conditions, and the interaction between these two factors, are particularly important determinants of essential oil variability CHEMISTRY & BIODIVERSITY – Vol. 9 (2012) 1389  2012 Verlag Helvetica Chimica Acta AG, Zürich