Intraspecific variation in oil components of Boronia megastigma Nees. (Rutaceae) flowers

Abstract

Intraspecific variation in the oil composition of Boronia megastigma Nees. (Rutaceae) was examined. Boronia absolute is extracted from blossom primarily for use as a food additive. A major component is β-ionone and B. megastigma is one of the commercial, natural sources of this compound. Genotypes superior in production of β-ionone and low in monoterpene hydrocarbons were sought from natural populations in the south west of Western Australia as part of a breeding programme. Flowers were collected from 25 plants in each of 29 different populations. Blossom was extracted with ethanol and analysed using a gas liquid chromatograph fitted with ionisation detectors. The contents of β-ionone, dodecyl acetate, α-pinene, β-pinene and limonene in the oil extract were compared. Intrapopulation variation was as great as inter-population variation and no distinct chemotypes were found. Considerable variation existed in the content of components. The highest β-ionone content was 1787 mg g-1 f. wt. Some genotypes contained all five components analysed, others lacked one or more of the monoterpenes: α-pinene, β-pinene or limonene. Principle components analysis indicated that contents of β-ionone and dodecyl acetate were associated and that they were distinct from the content of the monoterpenes, which were associated with each other. Natural shading was associated with lower levels of monoterpenes but other oils were unaffected. Young plants contained less pinenes than older plants and old plants contained the most dodecyl acetate. Vigorous plants produced more pinenes. Red flowers contained the least β-ionone and dodecyl acetate.