Foliar Oil Research Articles

Taxonomic treatment of Myrtaceae based on leaf morphology, architecture, foliar oil glands and molecular characteristics

Taxonomic treatment of Myrtaceae based on leaf morphology, architecture, foliar oil glands and molecular characteristics

Eucalyptus bakeri: a potential source species for eucalyptus oil production in the subtropics

ABSTRACT There is a paucity of eucalypt species in tropical Australia that produce a foliar essential oil in high concentration and rich in 1,8-cineole, the sought-after component of medicinal eucalyptus oils. Eucalyptus bakeri, a mallee from the dry subtropical parts of northern New South Wales and Queensland, is an exception, with limited earlier studies reporting that this species produced foliar oil with commercial characteristics. The aim of this study was to determine the variation in foliar oil characteristics throughout the natural range of E. bakeri as a precursor to the more intensive field-testing of the species as a commercial source of eucalyptus oil. Mature leaves and, when available, coppice leaves for comparison were collected over three separate field trips in 2020 from individual trees representing each of 17 provenances throughout the natural range of E. bakeri in Queensland. Foliar oil concentrations on a fresh-weight basis throughout the provenances sampled were relatively high, averaging 2.3% for mature leaves and 2.8% for coppice leaves, with an individual tree high of 4.1% for both leaf categories. 1,8-Cineole was the dominant compound in all foliar oils sampled, averaging 89.3% (range 70.2–94.6%) in oils from mature leaves and 87.6% (range 79–92.5%) from coppice leaves. Sabinene levels, restricted to a maximum of 0.3% in some oil standards, averaged 0.3% (range trace – 1.5%) in oils from mature leaves and 0.4% (range trace – 0.7%) from coppice leaves. The high foliar oil concentrations and consistency in oil qualities mark this species as a potential candidate as a eucalyptus oil source species for the dry subtropics. Provenance/progeny trials are now needed to determine which provenances produce adequate growth rates and the silviculture required to manage the species as an oil-producing crop, as well as to investigate variations in oil characteristics, including sabinene levels, when all sources are grown at a common site.

Accuracy of Genomic Prediction for Foliar Terpene Traits in Eucalyptus polybractea.

Unlike agricultural crops, most forest species have not had millennia of improvement through phenotypic selection, but can contribute energy and material resources and possibly help alleviate climate change. Yield gains similar to those achieved in agricultural crops over millennia could be made in forestry species with the use of genomic methods in a much shorter time frame. Here we compare various methods of genomic prediction for eight traits related to foliar terpene yield in Eucalyptus polybractea, a tree grown predominantly for the production of Eucalyptus oil. The genomic markers used in this study are derived from shallow whole genome sequencing of a population of 480 trees. We compare the traditional pedigree-based additive best linear unbiased predictors (ABLUP), genomic BLUP (GBLUP), BayesB genomic prediction model, and a form of GBLUP based on weighting markers according to their influence on traits (BLUP|GA). Predictive ability is assessed under varying marker densities of 10,000, 100,000 and 500,000 SNPs. Our results show that BayesB and BLUP|GA perform best across the eight traits. Predictive ability was higher for individual terpene traits, such as foliar α-pinene and 1,8-cineole concentration (0.59 and 0.73, respectively), than aggregate traits such as total foliar oil concentration (0.38). This is likely a function of the trait architecture and markers used. BLUP|GA was the best model for the two biomass related traits, height and 1 year change in height (0.25 and 0.19, respectively). Predictive ability increased with marker density for most traits, but with diminishing returns. The results of this study are a solid foundation for yield improvement of essential oil producing eucalypts. New markets such as biopolymers and terpene-derived biofuels could benefit from rapid yield increases in undomesticated oil-producing species.

Differential metabolic specialization of foliar oil glands in Eucalyptus brevistylis Brooker (Myrtaceae).

Trees and shrubs from the genus Eucalyptus are characterized by the presence of numerous foliar oil glands that generally house mono- and sesquiterpenes. In some species, glands are also known to house substantial quantities of unrelated secondary metabolites such as volatile, aromatic β-triketones. It is not known if these compounds are co-housed with terpenes or if they are produced in distinct, metabolically specialized glands. We showed that Eucalyptus brevistylis-a species with appreciable foliar quantities of both β-triketones and terpenes-contains two visually distinct gland types in leaves, one that is translucent and the other golden-brown. Gas chromatographic analyses of solvent extracts of the two gland types showed that the translucent glands contain sesquiterpene alcohol cubenols and cubebols (termed 'sesquiterpene glands'), whereas the golden-brown glands contain predominantly the β-triketone conglomerone with lesser amounts of sesquiterpene hydrocarbon caryophyllenes (termed 'triketone glands'). Analysis of leaves from trees of different ages, from young saplings through to advanced age trees, showed a gradual increase in the abundance of sesquiterpene glands relative to triketone glands as plants aged. Such ontogenetic regulation of foliar secondary metabolite concentration appears to be a common feature of Eucalyptus species, albeit at different temporal scales. A similar ontogenetic pattern was observed in ageing leaves, with mature leaves having a higher proportion of sesquiterpene glands than young leaf tips. It is concluded that regulation of the relative abundances of the two gland types with ontogeny likely reflects the different herbivores present at the different life stages of leaves and whole plants. In particular, leaf tips and young plants may be advantaged by deploying higher amounts of insecticidal β-triketones. The concurrent deployment of two metabolically distinct gland types in leaves is a rare phenomenon and a novel finding for myrtaceous trees.

A modified, hypoallergenic variant of the Ricinus communis Ric c1 protein retains biological activity.

Ric c1, an allergenic protein from castor oil plants (Ricinus communis), is an insect α-amylase inhibitor that has become an occupational allergen. Ric c1 can cross-react with allergens from wheat, soybean, peanut, shrimp, fish, gluten, house dust, tobacco and air fungus, thereby amplifying the concern and risks caused by castor oil plants (COP) allergens. Two continuous IgE-binding epitopes were identified in Ric c1, both containing glutamic acid residues involved in IgE-binding and allergic challenges. We produced recombinant Ric c1 (rRic c1) in Escherichia coli, using primers from foliar castor oil plant DNA, and a mutant (Glu-Leu) recombinant protein (mrRic c1) in the same system using synthetic genes. rRic c1 preserved both allergenic and α-amylase inhibitory properties, and mrRic c1 drastically reduced allergenic properties. These results can help to establish meaningful relationships between structure, defence and allergenicity, important steps for producing engineered plants and developing new approaches for immunotherapy.

Assessment of a non-destructive method to predict oil yield in Eucalyptus polybractea (blue mallee)

Eucalyptus oil is produced from a number of “oil mallee” species with high concentration of foliar essential oils, high proportion of 1,8-cineole and the ability to re-sprout with multiple stems from lignotubers after coppicing. Eucalyptus polybractea is one of the most planted mallees in Australia, but few efforts have been made to improve crop yields through selection or breeding programs, with the exception of seed collection from trees with high oil and 1,8-cineole concentration. The yield of essential oil from commercial eucalypt plantations is subject to several quantitative traits that interact, both positively and negatively. Using non-destructive methods we assessed traits relating to oil yield (quantitative and qualitative variation of foliar essential oils and biomass-related parameters) for their variability, heritability as well as phenotypic and genetic interactions in an open-pollinated progeny trial with 40 families and 480 individuals of E. polybractea. From this we built models to predict family yield performance and compared our predictions to commercial scale harvests of the same trial.Our models show that relying on oil concentration and 1,8-cineole proportion alone is not ideal for selection of top performing families. Rather a mixture of biomass related traits, foliar oil concentration, 1,8-cineole proportion and leaf architecture contribute to the top performing families in varying ways.

Comparative study of the volatile oil content and antimicrobial activity of Psidium guajava L. and Psidium cattleianum Sabine leaves

The chemical composition of the hydrodistilled oils of the leaves of Psidium guajava L. (guava leaf) and Psidium cattleianum Sabine (strawberry guava) was determined by GC/MS analysis to identify their chemotypes. Moreover, in vitro antimicrobial activity of these volatile oils against selected bacteria, yeast, and mycelia fungi was studied. The yield of the volatile oil hydrodistilled from the leaves of P. guajava L. and P. cattleianum Sabine was 1.6 and 2.69g/kg on fresh weight basis, respectively. Limonene was the major identified hydrocarbon in P. guava leaves’ oil (54.70%), whereas, 1, 8-cineole was the major identified oxygenated monoterpenoid (32.14%) in common guava leaves. The foliar oil of P. cattleianum was predominated by the sesquiterpene hydrocarbon; β-caryophyllene representing 28.83% of the total oil make-up. The antibacterial activity of guava leaf oil was more pronounced against Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa than that of strawberry guava leaves, while P. cattleianum showed a higher activity against ess. The MIC of the volatile oil of the leaves of P. guajava against S. aureus was 6.75μg/ml, while that of P. cattleianum exhibited MIC value of 13.01μg/ml against Neisseria gonorrhoeae. Results demonstrated that the volatile oil of both Psidium species showed different chemotypes. Moreover, the volatile oils of guava and strawberry guava leaves might be good candidates as antimicrobial agents.

Genomic approaches to selection in outcrossing perennials: focus on essential oil crops.

The yield of essential oil in commercially harvested perennial species (e.g. 'Oil Mallee' eucalypts, Tea Trees and Hop) is dependent on complex quantitative traits such as foliar oil concentration, biomass and adaptability. These often show large natural variation and some are highly heritable, which has enabled significant gains in oil yield via traditional phenotypic recurrent selection. Analysis of transcript abundance and allelic diversity has revealed that essential oil yield is likely to be controlled by large numbers of quantitative trait loci that range from a few of medium/large effect to many of small effect. Molecular breeding techniques that exploit this information could increase gains per unit time and address complications of traditional breeding such as genetic correlations between key traits and the lower heritability of biomass. Genomic selection (GS) is a technique that uses the information from markers genotyped across the whole genome in order to predict the phenotype of progeny well before they reach maturity, allowing selection at an earlier age. In this review, we investigate the feasibility of genomic selection (GS) for the improvement of essential oil yield. We explore the challenges facing breeders selecting for oil yield, and how GS might deal with them. We then assess the factors that affect the accuracy of genomic estimated breeding values, such as linkage disequilibrium (LD), heritability, relatedness and the genetic architecture of desirable traits. We conclude that GS has the potential to significantly improve the efficiency of selection for essential oil yield.

Estimating terpene and terpenoid emissions from conifer oleoresin composition

The following algorithm, which is based on the thermodynamics of nonelectrolyte partitioning, was developed to predict emission rates of terpenes and terpenoids from specific storage sites in conifers:Ei=xoriγoripi∘where Ei is the emission rate (μg C gdw−1 h−1) and pi∘ is the vapor pressure (mm Hg) of the pure liquid terpene or terpenoid, respectively, and xori and γori are the mole fraction and activity coefficient (on a Raoult's law convention), respectively, of the terpene and terpenoid in the oleoresin. Activity coefficients are calculated with Hansen solubility parameters that account for dispersive, polar, and H-bonding interactions of the solutes with the oleoresin matrix. Estimates of pi∘ at 25 °C and molar enthalpies of vaporization are made with the SIMPOL.1 method and are used to estimate pi∘ at environmentally relevant temperatures. Estimated mixing ratios of terpenes and terpenols were comparatively higher above resin-acid- and monoterpene-rich oleoresins, respectively. The results indicated a greater affinity of terpenes and terpenols for the non-functionalized and carboxylic acid containing matrix through dispersive and H-bonding interactions, which are expressed in the emission algorithm by the activity coefficient. The correlation between measured emission rates of terpenes and terpenoids for Pinus strobus and emission rates predicted with the algorithm were very good (R = 0.95). Standard errors for the range and average of monoterpene emission rates were ±6 – ±86% and ±54%, respectively, and were similar in magnitude to reported standard deviations of monoterpene composition of foliar oils (±38 – ±51% and ±67%, respectively).

Differential patterns of mono- and sesquiterpenes with leaf ontogeny influence pharmaceutical oil yield in Eucalyptus polybractea R.T. Baker

Pharmaceutical 1,8-cineole oil is commercially harvested from Eucalyptus polybractea R.T. Baker grown in short rotation coppice cultivation. Harvests occur throughout the year, with no consideration given to the proportion of leaves present at different ontogenetic stages, and the effect leaf ontogeny may have on harvested oil quality and quantity. To determine the optimal leaf stage to harvest pharmaceutical-grade oil, we quantified the relationship between leaf ontogeny and foliar oil quantity and quality, secretory cavity size, and abundance along branches of two E. polybractea clones. The results show that the desirable attributes of oil yield and 1,8-cineole proportion both reach their maximum in fully expanded leaves and that this coincides with maximum secretory cavity size. Across all leaf ages the amount of various monoterpenes were highly correlated with 1,8-cineole, suggesting a single, multi-product monoterpene synthase may be responsible. In the very young leaves, sesquiterpenes such as β-elemene were the most abundant constituents of the essential oil. This study suggests that there may be differential transcriptional regulation of mono- and sesquiterpene synthases with leaf ontogeny such that sesquiterpene biosynthesis is at a maximum only in young leaves, and that monoterpene biosynthesis dominates during leaf and concomitant cavity expansion. Given E. polybractea leaves are produced during major seasonal flushes, there are times throughout the year when the numbers of young leaves with inferior oil quantity and quality are likely to be proportionally decreased. Therefore harvesting times could be manipulated to take advantage of such times and ensure abundant high quality oil is harvested.

Using the Eucalyptus genome to understand the evolution of plant secondary metabolites in the Myrtaceae

Background Eucalyptus trees (family Myrtaceae) are well-known for their high foliar content of several classes of secondary metabolites and these have a strong effect on the feeding patterns of several species of marsupials and at least some insects. Best known are the essential oils, which is mostly a mixture of terpenoids, but there are also significant concentrations of flavonoid and formylated phloroglucinol compounds. There is extensive quantitative and qualitative variation within and between species of Myrtaceae in these chemical groups and all appear to be under strong genetic control with heritabilities (H 2 ) between 0.3 and 0.9. As well as being important ecologically, the terpenes in particular are valued as industrial and medicinal products and Australia supports a strong essential oil industry focused on Eucalyptus and Melaleuca foliar oils. Results and discussion The Eucalyptus grandis genome provides the opportunity to discover the genetic makeup of the biosynthetic pathways for secondary metabolites. We present data from pathways leading into the biosynthesis of terpenes, flavonoids and lignins. The homology of genes and gene families were investigated and compared to a variety of other species including poplar (Populus trichocarpa), grape (Vitis vinifera) and apple (Malus x domesticus). For example, terpene synthases (the gene family responsible for the final step in the terpene biosynthesis) has 120 members in the genome of Eucalyptus grandis, compared to 44 and 99 in poplar and grape, respectively (Table 1). Genes of the biosynthetic pathways for secondary metabolites were mapped to the Eucalyptus grandis genome and their location was compared to a number of quantitative trait loci (QTL) studies that investigated variability in secondary metabolites and wood properties in eucalypts. This approach allowed the discovery of candidate genes for a large number of QTL. Understanding the genetic basis of variations in quantitative traits provides insights into ecosystem function and at the same time may help breeders in the essential oil industry. We have characterized trait associations with polymorphisms from Eucalyptus globulus ,i nvestigating 200 SNPs and roughly 40 traits ranging from terpenoids to terpene-adducts to flavonoids and to tanninrelated traits. We discovered several significant trait associations between allelic variants in the chloroplastic MEP pathway and monoterpenes and between the cytosolic MVA pathway and sesquiterpenes, as well as one allelic variant in a prenyl pyrophosphate synthase that associates with the ratio of monoterpenes to sesquiterpenes. Loci with significant associations were mapped to the Eucalyptus grandis genome and compared to published QTL datasets that investigated similar traits. These results represent the first species wide analysis of

Corymbia leaf oils, latitude, hybrids and herbivory: A test using common‐garden field trials

AbstractFoliar oils, particularly monoterpenes, can influence the susceptibility of plants to herbivory. In plants, including eucalypts, monoterpenes are often associated with plant defence. A recent analysis revealed an increase in foliar oil content with increasing latitudinal endemism, and we tested this pattern using three eucalypt taxa comprising a latitudinal replacement cline. We also examined the relative concentrations of two monoterpenes (α‐pinene and 1,8‐cineole), for which meta‐analyses also showed latitudinal variation, using hybrids of these three taxa with Corymbia torelliana. These, and pure C. torelliana, were then assessed in common‐garden field plots for the abundance and distribution of herbivory by four distinct herbivore taxa. Differing feeding strategies among these herbivores allowed us to test hypotheses regarding heritability of susceptibility and relationships to α‐pinene and 1,8‐cineole. We found no support for an increase in foliar oil content with increasing latitude, nor did our analysis support predictions for consistent variation in α‐pinene and 1,8‐cineole contents with latitude. However, herbivore species showed differential responses to different taxa and monoterpene contents. For example, eriophyid mites, the most monophagous of our censused herbivores, avoided the pure species, but fed on hybrid taxa, supporting hypotheses on hybrid susceptibility. The most polyphagous herbivore (leaf blister sawfly Phylacteophaga froggatti) showed no evidence of response to plant secondary metabolites, while the distribution and abundance patterns of Paropsis atomaria showed some relationship to monoterpene yields.

The influence of micropropagation on growth and coppicing ability of Eucalyptus polybractea

A micropropagation protocol was recently developed for Eucalyptus polybractea R.T. Baker, a commercially important eucalypt grown in short-rotation coppice cultivation and harvested for its foliar 1,8-cineole oil. Micropropagation of elite E. polybractea trees has resulted in selection gains for foliar oil traits, but decreased above-ground biomass accumulation has been observed in clones compared to related half-sibling families. This study aims to use a greenhouse study to investigate if micropropagation induces somaclonal variation that can account for the reduction in above-ground biomass in E. polybractea clones. Secondly, the study aims to compare the coppicing ability of micropropagated clones with related half-sibling seedlings using de-topped plantation-grown saplings. The results of the greenhouse study suggest that micropropagation of E. polybractea induces somaclonal variation that manifests in more mature leaf morphologies such as increased foliar oil concentrations and lower specific leaf area (SLA), attributable to an isobilateral arrangement of increased palisade mesophyll layers. Lower SLA, rather than differences in root allocation, is likely to be a key contributor to the lower relative growth rates observed in early sapling growth of micropropagated clones. In the field study, all micropropagated and seedling-derived E. polybractea saplings coppiced vigorously in the 12 months after de-topping. The coppice growth was so vigorous in the 12 months after de-topping that total above-ground biomass equalled that of the 27-month-old saplings, irrespective of propagation source. The morphological distinction between leaves of micropropagated and seed-derived plants was no longer evident in the coppice regrowth. The results presented here suggest that the micropropagated leaf morphology and the resultant growth reduction is transient and micropropagated plants coppice just as vigorously as seed-derived plants. Therefore, micropropagation is unlikely to detrimentally influence above-ground biomass accumulation beyond the first harvest rotation.

Latitudinal trends in foliar oils of eucalypts: Environmental correlates and diversity of chrysomelid leaf-beetles

Eucalypts are characterized by their oleaginous foliage, yet no one has considered the universality of oil expression or its ecological associations and implications for biodiversity. Published literature on the oils of 66 eucalypts was combined with geographic distribution information contained in the Australian National Herbarium (ANHSIR) database to investigate continent-scale changes in oil yield and composition. The exposure to fire and rainfall of each eucalypt was considered in reference to Walker's data on fire frequency and Australian Bureau of Meteorology 97-year records of rainfall variability. Host collection records for 69 species of chrysomelid leaf-beetle were collated from entomologists to consider patterns of association with a subset of 16 eucalypts. Eucalypts endemic to the seasonally arid, sub-tropical to tropical climates of northern Australia have less oleaginous and aromatic leaves than species endemic to the mesic, temperate climates of the southern parts of the continent. Maximum oil yield and the concentrations of cineole and pinene were positively correlated with minimum fire interval but not with rainfall variability. Low oil contents in more northerly distributed species may facilitate persistence in highly fire-prone habitats. There were no patterns in the diversity of chrysomelid leaf-beetles with either the oil yield or the concentrations of 1,8-cineole or α-pinene in their hosts. When taken in consideration with the apparent strategy of eucalypts to tolerate insect herbivory, current evidence augurs against high concentrations of cineole or pinene acting alone as antibiotic plant secondary metabolites.

Effect of nitrogen‐application rate on the biomass, concentration, and composition of essential oils in the leaves and roots of three types of parsley

AbstractThe effect of four levels of nitrogen (N) application (3.2, 16.2, 32.4, and 48.6 g m–2) on the biomass and concentration and composition of essential oils of three parsley types (plain leaf, turnip‐rooted, curl leaf) was investigated in order to determine the optimum N level for oil production by this crop. The concentration of essential oils in the roots and leaves of plain leaf parsley and turnip‐rooted parsley was not affected by N application, but decreased with increasing N rate in curl leaf parsley. However, because the mean foliage biomass for all three types was about 2.5 times higher at 16.2 g m–2 N than in the low‐N‐rate treatment, the mean foliar oil yield increased from 0.68 to 1.38 g m–2. Root biomass increased by a factor of 1.7 at 16.2 g m–2 N (compared to the low‐N‐rate treatment), but oil yield increased only marginally from 0.3 to 0.4 g m–2. The composition of the essential oils of roots and leaves differed between parsley types. Increasing N application caused a reduction in the percentage of β‐phellandrene in the essential oils of parsley leaves. In turnip‐rooted parsley, increasing N caused a reduction in the percentage of myristicin and apiole. Because these three components of the essential oils contribute to parsley aroma, it may be concluded that although application of N fertilizer leads to higher parsley biomass and oil yield per plant, the essential oil components may change and aroma quality may be affected negatively.

Discrimination between seedlings of Eucalyptus globulus, E. nitens and their F1 hybrid using near-infrared reflectance spectroscopy and foliar oil content

Summary Identification of plant hybrids produced from closely related species can be difficult using morphological characteristics alone, particularly when identifying young seedlings. In this study, we compared the performance of three calibration models developed to discriminate between seedlings of Eucalyptus globulus, E. nitens and their first-generation hybrid using either foliar oil chemistry or near-infrared reflectance spectral data from fresh, whole leaves. Both oil and near-infrared reflectance spectroscopy (NIRS) models were developed using partial least-squares discriminant analysis and showed high classification accuracy, all correctly classifying more than 91% of samples in cross-validation. Additionally, we developed a larger, “global” and independently validated NIRS model specifically to discriminate between E. globulus and F1 hybrid seedlings of different ages. This model correctly classified 98.1% of samples in cross-validation and 95.1% of samples from an independent test set. These results show that NIRS analysis of fresh, whole leaves can be used as a rapid and accurate alternative to chemical analysis for the purpose of hybrid identification.

PENINGKATAN GENETIK PADA PEMULIAAN Melaleuca cajuputi subsp. cajuputi

The breeding program of Melaleuca cajuputi subsp. cajuputi in Indonesia was started in 1994 by the Institute for Biotechnology and Forest Tree Improvement in cooperation with CSIRO-Australia. An assessment of progeny test of M. cajuputi at Paliyan at 23 months and at Sukun-Ponorogo at 36 months old were conducted to ascertain the patterns of genetic variation in growth and foliar oil and to estimate genetic parameters in growth and foliar oil . Based on the evaluation, genetic variation on growth and oil yield were high. Genetic gain estimation for growth and oil yield were 11.83 to 20.38 % in the progeny test seedling seed orchard of M. Cajuputi at Sukun, Ponorogo.

Research note: Micropropagation of Eucalyptus polybractea selected for key essential oil traits.

A protocol for the micropropagation of Eucalyptus polybractea R.T. Baker (blue mallee) using axillary bud proliferation from lignotuber-derived explants is described. Three different ages of plants were used as explant sources: glasshouse-grown seedlings, field-grown saplings, and coppice of field-grown mature lignotubers. Explants from each source initiated successfully and no significant difference was observed for shoot proliferation, rooting success or hardening success between explant sources. Leaf oil quantity and quality for hardened clones transplanted to a field plantation were assessed after 3 months of growth. Ramets of all clones contained high quality oil with over 80% 1,8-cineole. For seedling-derived clones, foliar oil concentrations of ramets were higher than those of the ortets from which they were derived. For sapling and mature lignotuber derived clones the opposite was the case. This suggests that ontogenetic and physiological constraints may be influencing yield in the young ramets. The age of the explant source did not appear to influence the success of micropropagation, and as a result older plants (for which key oil traits are known) can be selected as elite plants for multiplying selected genotypes via micropropagation.

Examination of the consistency of plant traits driving oil yield and quality in short-rotation coppice cultivation of Eucalyptus polybractea

The value of eucalyptus oil for medicinal purposes is based largely on its cineole content. The prime commercial species for cineole production in Australia is Eucalyptus polybractea (blue mallee). Despite the long history of blue mallee harvesting in Australia, there has been little research on the establishment of plantations of the species or on the efficacy of short-rotation coppice cultivation with respect to the consistency of oil yield and quality from rotation to rotation. This study aims to assess if subsequent coppice oil traits reflect sapling traits and if the coppice oil traits under short-rotation cultivation are consistent from one rotation to the next. A trial plantation was established in a key eucalyptus oil harvesting district in Victoria. Firstly, the oil-related traits of 20 saplings harvested 3.5 years after planting were compared with those of their subsequent coppice harvested after 12 months regrowth. Despite the expected differences in total biomass, the oil-related traits of blue mallee saplings were mostly well reflected in their subsequent coppice. Total above ground biomass and foliar oil concentration were significantly related between saplings and coppice, and cineole proportion showed a Pearson's correlation of 0.93 between harvests. Nevertheless, the mean foliar oil concentration in the coppice was 148 mg g −1 dw compared with 107 in the saplings, and the coppice foliage, on average, showed significantly reduced cineole with a mean of 87% in the saplings (maximum of 95.6%) compared to a mean of only 80% in the coppice (maximum of 87.0%). Secondly, the oil traits of 20 coppice plants from one 12-month harvest rotation to the next were compared. Again, total above ground biomass, foliar oil concentration and cineole proportion were significantly related between the harvests, with cineole proportion having a Pearson's correlation of 0.90 between rotations. The coppice between rotations were remarkably consistent in terms of biomass and oil traits and indeed mean coppice cineole yields were 28.6 and 29.7 g in rotations 1 and 2, respectively. The results support the screening of key oil-related traits in saplings for the selection of elite genotypes for plantations, and the use of short-rotation cultivation of the plantations for continued oil harvesting. Furthermore, no relationship was observed between biomass and oil concentration in the blue mallee saplings or coppice, suggesting selection gains in a given key oil trait will not result in losses in another.

Screening selected myrtaceous tree species for production of essential oils in northern Queensland

Trials to identify alternative cropping options to Melaleuca alternifolia for northern Queensland essential oil growers were established at Dimbulah and Innot Hot Springs in 2001. Seed sources of Asteromyrtus symphyocarpa (1,8-cineole form), Eucalyptus staigeriana (citral), Melaleuca cajuputi subsp. cajuputi (trans-nerolidol), M. ericifolia (d-linalool), M. quinquenervia (trans-nerolidol and viridiflorol forms) and M. viridiflora (methyl cinnamate) with potential to produce commercial foliar oils were evaluated. Information was gathered on their adaptability, growth and oil yields over 49 months and 52 months (two harvests) from planting at Dimbulah and Innot Hot Springs, respectively. Of the species and chemotypes evaluated, M. quinquenervia showed potential for commercial production of trans-nerolidol, a compound used in perfumery. It had a very high survival rate (96%) and yields could be expected to improve dramatically from the average 100 kg/ha per harvest achieved in these trials with further research into selection of seed source, control of insect damage and breeding for genetic improvement. M. cajuputi subsp. cajuputi gave a similar performance to M. quinquenervia. The rarity of the trans-nerolidol form of this species and remoteness of its natural occurrence are impediments to further planting and research. E. staigeriana, with second harvest yields of ~600 kg/ha, performed exceptionally well on both sites but potential for development is limited by the ready availability of competitively priced E. staigeriana oil produced in South America. Survival of M. ericifolia ranged from 62% to 82% at 32 months (second harvest) at Innot Hot Springs and was deemed a failure at Dimbulah with poor growth and low survival, raising a major question about the suitability of this species for cultivation in the seasonally dry tropics. Planting of this species on a wider scale in northern Queensland cannot be recommended until more is known about factors affecting its survival. A. symphyocarpa and M. viridiflora were too slow-growing to warrant further consideration as potential oil-producing species at this time.