Achievements in forest tree genetic improvement in Australia and New Zealand 2: Development of Corymbia species and hybrids for plantations in eastern Australia

This paper describes the establishment of provenance seedling seed orchards of three spotted gums and cadaga (all species of Corymbia ex Eucalyptus). It also discusses the limitations of growing the spotted gums as pure species including: lack of mass flowering, susceptibility to a fungal shoot blight and low amenability to vegetative propagation. These limitations, together with observation of putative natural hybrids of the spotted gums with cadaga, and the early promise of manipulated hybrids, led to an intensive breeding and testing program. Many hybrid families have significant advantages in growth and tolerance to disease, insects and frost, and can be vegetatively propagated. They also exhibit broad environmental plasticity, allowing the best varieties to be planted across a wider range of sites than the spotted gums, resulting in more land being suitable for plantation development.

Eriophyid mites on spotted gums: population and histological damage studies of an emerging pest

A suite of co-occurring eriophyid mite species are significant pests in subtropical Australia, causing severe discolouration, blistering, necrosis and leaf loss to one of the region's most important hardwood species, Corymbia citriodora subsp. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson (Myrtaceae). In this study, we examined mite population dynamics and leaf damage over a 1-year period in a commercial plantation of C. citriodora subsp. variegata. Our aims were to link the incidence and severity of mite damage, and mite numbers, to leaf physical traits (moisture content and specific leaf weight (SLW)); to identify any seasonal changes in leaf surface occupancy (upper vs. lower lamina); and host tree canopy strata (upper, mid or lower canopy). We compared population trends with site rainfall, temperature and humidity. We also examined physical and anatomical changes in leaf tissue in response to mite infestation to characterize the plants' physiological reaction to feeding, and how this might affect photosynthesis. Our main findings included positive correlations with leaf moisture content and mite numbers and with mite numbers and damage severity. Wet and dry leaf mass and SLW were greater for damaged tissue than undamaged tissue. Mites were distributed equally throughout the canopy and on both leaf surfaces. No relationships with climatic factors were found. Damage symptoms occurred equally and were exactly mirrored on both leaf surfaces. Mite infestation increased the overall epidermal thickness and the number and size of epidermal cells and was also associated with a rapid loss of chloroplasts from mesophyll cells beneath damage sites. The integrity of the stomatal complex was severely compromised in damaged tissues. These histological changes suggest that damage by these mites will negatively impact the photosynthetic efficiency of susceptible plantation species.

Eriophyid mites on spotted gums: population and histological damage studies of an emerging pest

A suite of co-occurring eriophyid mite species are significant pests in subtropical Australia, causing severe discolouration, blistering, necrosis and leaf loss to one of the region's most important hardwood species, Corymbia citriodora subsp. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson (Myrtaceae). In this study, we examined mite population dynamics and leaf damage over a 1-year period in a commercial plantation of C. citriodora subsp. variegata. Our aims were to link the incidence and severity of mite damage, and mite numbers, to leaf physical traits (moisture content and specific leaf weight (SLW)); to identify any seasonal changes in leaf surface occupancy (upper vs. lower lamina); and host tree canopy strata (upper, mid or lower canopy). We compared population trends with site rainfall, temperature and humidity. We also examined physical and anatomical changes in leaf tissue in response to mite infestation to characterize the plants' physiological reaction to feeding, and how this might affect photosynthesis. Our main findings included positive correlations with leaf moisture content and mite numbers and with mite numbers and damage severity. Wet and dry leaf mass and SLW were greater for damaged tissue than undamaged tissue. Mites were distributed equally throughout the canopy and on both leaf surfaces. No relationships with climatic factors were found. Damage symptoms occurred equally and were exactly mirrored on both leaf surfaces. Mite infestation increased the overall epidermal thickness and the number and size of epidermal cells and was also associated with a rapid loss of chloroplasts from mesophyll cells beneath damage sites. The integrity of the stomatal complex was severely compromised in damaged tissues. These histological changes suggest that damage by these mites will negatively impact the photosynthetic efficiency of susceptible plantation species.

Toughening of Fibre Composite Resins through Modification of Plant Oils

Extract from the executive summary: A collaborative scoping research project to identify plant oil species with potential value in the production of fibre composite resins and assess their suitability to Queensland’s regions has been conducted by QDPI&F, USQ and Loc Composites Pty Ltd. The use of plant-oil based resins in the production of fibre composites will contribute to the Queensland economy through establishing sustainable high technology building products from renewable sources while decreasing the reliance of resin production on fossil fuels. The main objective of this project was to indentify a suite of plant oil species that show agronomic adaptability to the Australian environment (e.g. climate, soils) and economic viability of extracting plant oils for resin production within a highly competitive supply and demand production market.

Resin-foraging by colonies of Trigona sapiens and T. hockingsi (Hymenoptera: Apidae, Meliponini) and consequent seed dispersal of Corymbia torelliana (Myrtaceae).

Resins are a critical resource for stingless bees and resin-collecting bees act as seed dispersers in tropical plants. We describe the diurnal foraging patterns of colonies of Trigona sapiens and T. hockingsi on resin and pollen. We also document patterns of waste removal and seed dispersal of Corymbia torelliana. At most, only 10% of foragers collected resin or dispersed seed. Nevertheless, bees dispersed 1-3 seeds outside the nest per 5 minutes, and 38-114 seeds per day for each nest. The proportion of returning bees carrying pollen was highest in the morning for both species. The proportion of foragers returning with resin loads showed no significant diurnal variation in any season. Waste removal activity peaked in the afternoon for T. sapiens and in the morning for T. hockingsi. Seed removal peaked in the afternoon in one year only for T. sapiens. Bees dispersed thousands of seeds of C. torelliana over the season even though only a small proportion of the colony was engaged in seed transport.

Reproductive Biology of Corymbia citriodora subsp. variegata and Effective Pollination across its Native Range.

The spotted gum species complex represents a group of four eucalypt hardwood taxa that have a native range that spans the east coast of Australia, with a morphological cline from Victoria to northern Queensland. Of this group, Corymbia citriodora subsp. variegata (CCV) is widespread in south-eastern Queensland and northern New South Wales. It is currently the most commonly harvested native hardwood in Queensland. However, little basic knowledge of the reproductive biology of the species is available to inform genetic improvement and resource management programmes. Here we take an integrative approach, using both field and molecular data, to identify ecological factors important to mating patterns in native populations of CCV. Field observation of pollinator visitation and flowering phenology of 20 trees showed that foraging behaviour of pollinator guilds varies depending on flowering phenology and canopy structure. A positive effect of tree mean flowering effort was found on insect visitation, while bat visitation was predicted by tree height and by the number of trees simultaneously bearing flowers. Moreover, introduced honeybees were observed frequently, performing 73% of detected flower visits. Conversely, nectar-feeding birds and mammals were observed sporadically with lorikeets and honeyeaters each contributing to 11% of visits. Fruit bats, represented solely by the grey-headed flying fox, performed less than 2% of visits. Genotyping at six microsatellite markers in 301 seeds from 17 families sampled from four of Queensland's native forests showed that CCV displays a mixed-mating system that is mostly outcrossing (tm = 0.899 ± 0.021). Preferential effective pollination from near-neighbours was detected by means of maximum-likelihood paternity analysis with up to 16% of reproduction events resulting from selfing. Forty to 48% of fertilising pollen was also carried from longer distance (>60 m). Marked differences in foraging behaviour and visitation frequency between observed pollinator guilds suggests that the observed dichotomy of effective pollen movement in spotted gums may be due to frequent visit from introduced honeybees favouring geitonogamy and sporadic visits from honeyeaters and fruit bats resulting in potential long-distance pollinations.

Revisiting genetic structuring in spotted gums (genus Corymbia section Maculatae) focusing on C. maculata, an early diverged, insular lineage

Species delineation in the spotted gum complex was revisited focusing on Corymbia maculata. This study expands the range of C. maculata analysed with microsatellite markers to include populations from the north of the species range. It supported earlier findings that it is a cohesive genetic entity, well resolved from northern spotted gum taxa, Corymbia citriodora and Corymbia henryi; and inferences that its insularity is due to early lineage divergence and historical isolation. The northern extent of C. maculata sampled, as defined by chloroplast and nuclear genomes predominantly of C. maculata character, was the location of Kiwarrak, south of the Manning River near Taree in New South Wales. Trees from a recognised intergrade zone at the Yarratt locality, around 26 km north of Kiwarrak, also possessed a uniquely C. maculata chloroplast haplotype, but their nuclear genomes were predominantly of northern taxa ancestry. Range expansion of northern taxa leading to southerly gene movement into populations formerly C. maculata, would account for this apparent instance of chloroplast capture. Two subpopulations were identified in C. maculata, a northern population of which the Ourimbah locality was the most southerly studied, and a southern population of which Wingello was the most northerly locality studied. Diminished levels of northern taxa ancestry, i.e. C. citriodora or C. henryi, in individuals from the southern, relative to the northern subpopulation of C. maculata, suggested that secondary contact with northern taxa contributes to its substructure.

Optimisation of resin extraction from an Australian arid grass ‘Triodia pungens’ and its preliminary evaluation as an anti-termite timber coating

Spinifex grasses are the dominant vegetative component in Australian grassland habitats, covering approximately 26% of the Australian landmass. Our ongoing work explores the utility of both the cellulosic and resinous components of this abundant biomass for modern applications and a potential economy for our Aboriginal collaborators. This study is focused on the optimisation of a resin extraction process using solvent, and the subsequent evaluation, via a field trial, of the potential use and efficacy of the resin as an anti-termite coating material. Termiticidal performance was evaluated by re-dissolving the extracted resin in acetone and coating on pine timber blocks. The resin-coated and control blocks were then exposed to a colony of Mastotermes darwiniensis’ (Froggatt) termites, which are the most primitive alive and destructive species in subterranean area, at a trial site in northeast Australia, for six months. The results clearly showed that spinifex resin effectively protected the timber from termite attack, while the uncoated control samples were extensively damaged. By demonstrating an enhanced termite resistance, we here report that plant resins that are produced by arid/semi-arid grasses could be potentially used as treatments to prevent termite attack.