Conservation and management of a threatened traditional agroresource, ylang-ylang Cananga odorata [Lam.] Hook f. & Thomson forma genuina, in the Indian Ocean islands

In order to handle future economic, social and environmental changes, the assessment, management and conservation of the local genetic resources of cash crop species is a fundamental requirement. We investigated the pattern of genetic and morphological diversity of Cananga odorata (Lam.) Hook f. & Thomson forma genuina, an important essential oil tree for the perfume industry in the introduction area of the western Indian Ocean islands. We sought to identify key elements for developing a conservation and management strategy for ylang-ylang genetic resources. Genetic and morphological variations were assessed using Amplified Fragments Length Polymorphism and morphometrics traits and information about farmers' practices were collected. The existence of substantial overall genetic diversity (HT = 0.2599) and the grouping of plantations into different genetic groups suggest that there have been a series of introduction events in the area, with limited exchanges of genetic material within and between islands, which is not what is suggested in the historical records. The morphological study revealed high phenotypic variability despite very similar agronomical practices throughout the studied area. The morphological and genetic variability might have been created and maintained without any planned or conscious management, and this has largely determined the genetic structuring in the area (11.74% genetic variation among islands and 20.68% among plantations). With this species, where past introduction events and farmers’ practices have shaped the genetic variation, on-farm preservation and the maintenance of the current management practices is recommended. Ex situ conservation efforts should also be undertaken, if economically affordable.