Essential oil variation in Eucalyptus crebra, E. melanophloia (Myrtaceae) and their hybrids

The leaf essential oils obtained from Eucalyptus melanophloia F.Muell., E. crebra F.Muell. and their hybrids from four widely separated sites were investigated. The major components that were observed, of the predominantly monoterpenoid oils, were α-pinene (1–58%), 1,8-cineole (0.2–60%) and p-cymene (0.2–21%). Oils tended to be unique to each locality investigated and although the parental species were discrete on their profiles, the oils of the hybrids appeared not to differ from those of their putative parents when commonly used methods of analysis (e.g. principal components analysis, PCA) were applied. Leaf oils are a complex mixture of components and elucidating differences among large datasets such as these can be difficult by traditional methods of analysis. Linear discriminant analysis (LDA) was applied to the oils data and it was found that with a forward stepwise LDA with 13 or 16 components of 70, it was possible to distinguish between the parents and their hybrids at a particular site or where the parents and hybrids originated.