Genetic parameters and expected gains from selection for monoterpene yields in Petford Eucalyptus camaldulensis.
Genetic parameters were estimated for yield of 1,8-cineole [eucalyptol] and total monoterpenes as a fraction of leaf weight in nineteen open-pollinated families of Petford origin at 3.75 years old in two progeny/provenance trials of E. camaldulensis at Mtao and Forest Hill in Zimbabwe. Only data from the Mtao provenance trial were used to estimate genetic gains and correlations, although data on plant composition for both sites are tabulated. Both traits appeared to be highly heritable and, as expected, were strongly genetically correlated, with narrow-sense individual heritabilities of about 0.50. Expected gain in the first generation following individual selection in the trials of one tree in 10 for either trait was about 25-32%. Genetic correlations between growth traits and 1,8-cineole yield were small. This indicates that both traits might be improved concurrently, thus enhancing the economics of growing Petford E. camaldulensis for both wood and essential oil production. However, the presence of moderate and unfavourable genetic correlations between growth traits and total yield of monoterpenes warrants further study. It was not possible to gauge the significance of apparent family × site interaction for 1,8-cineole yield in this study. However, a test of rank correlation showed an association (Ip <0.01) between family rankings on each site and the highest-yielding trees on both sites came from the same families. This raises the possibility of being able to select individuals for cloning that yield well over a range of site conditions.