Selection gains for essential oil traits using micropropagation of Eucalyptus polybractea

The value of eucalyptus oil for medicinal purposes is based largely on its cineole content, and the prime commercial species for pharmaceutical grade eucalyptus oil is Eucalyptus polybractea (blue mallee). This study applies a recently developed micropropagation protocol to selected elite oil yielding blue mallee seedlings and investigates the potential of a trial plantation based on micropropagated clones to increase cineole yields. The study aims to assess two micropropagated clones of blue mallee for growth and key essential oil traits in comparison to two related half-sibling families, and to assess consistency for oil traits within clones. After 23 months growth in a plantation, all ramets from the micropropagated clones appeared healthy and showed similar growth forms to the half-sibling saplings at the time of harvest. Total above ground biomass was significantly greater in the half-sibling families compared to their relative clones. Nevertheless, the foliar essential oil concentration and the proportion of the total oil as cineole was greatest in the clones compared to their related half-sibling families, reflecting the oil traits of the ortets. The oil composition profiles were very consistent within clones. This was particularly evident for cineole which had the remarkably narrow ranges of 90–92% in one clone and 92–94% in the other, suggesting strong genetic control of essential oil composition. Overall, the results suggest that micropropagation has great potential for the establishment of blue mallee plantations using genotypes selected for key oil traits. The application of the micropropagation protocol to older plants of blue mallee (for which both key oil and biomass traits are known) is likely to produce greater selection gains for cineole yield.