Previous studies into the population structure of Melaleuca alternifolia by both isozyme and microsatellite analysis revealed little evidence for genetic structuring within genetic provenances. In contrast, analysis of the oil composition within these same regions showed distinct clustering of chemotypes within the provenances suggesting either that chemotype was not under genetic control, or that there is strong environmental selection for plant chemotypes. To investigate the level of genetic control of monoterpene composition in the essential oil of M. alternifolia, individuals representing the three extreme chemotypes of high terpinen-4-ol, high 1,8-cineole and high terpinolene were crossed with an individual with the commercially desirable high terpinen-4-ol oil profile. The progeny resulting from these crosses displayed oil profiles that were intermediate to that of the parent. Further analysis of the survey of oil chemotypes within the natural population also suggests that these intermediate chemotypes may arise naturally between regions containing high proportions of the extreme chemotypes. These results imply that there is a level of genetic structure for chemotype determination within the genetic provenance that is undetected by isozyme and microsatellite analysis. This information could play a vital role in the selection of appropriate genetic material to be used in future essential oil selection and breeding programs.

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