Km Barry

Comparison of Antifungal and Antioxidant Activities of Acacia mangium and A. auriculiformis Heartwood Extracts

The effect of heartwood extracts from Acacia mangium (heartrot-susceptible) and A. auriculiformis (heartrot-resistant) was examined on the growth of wood rotting fungi with in vitro assays. A. auriculiformis heartwood extracts had higher antifungal activity than A. mangium. The compounds 3,4′,7,8-tetrahydroxyflavanone and teracacidin (the most abundant flavonoids in both species) showed antifungal activity. A. auriculiformis contained higher levels of these flavonoids (3.5- and 43-fold higher, respectively) than A. mangium. This suggests that higher levels of these compounds may contribute to heartrot resistance. Furthermore, both flavonoids had strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and laccase inhibition. This suggests that the antifungal mechanism of these compounds may involve inhibition of fungal growth by quenching of free radicals produced by the extracellular fungal enzyme laccase.

Crown-scale evaluation of spectral indices for defoliated and discoloured eucalypts

Remote sensing for evaluation of canopy health in plantation eucalypts is a realistic option for forest managers in the near future if reliable and robust methods of spectral analysis can be developed. Pot‐grown eucalypts of three species important to the Australian plantation industry were used for crown‐scale spectral (400–1000 nm) evaluations of vegetation indices as indicators of common symptoms of stress. When defoliation treatments (in E. globulus) or exposure to cold and nutrient deprivation (in E. pilularis) resulted in large differences in leaf cover, the red edge position and slope indices, two normalized difference vegetation indices (NDVIs), modified chlorophyll absorption ratio index 2 (MCARI2) or modified triangular vegetation index 2 (MTVI2) were most strongly correlated to leaf cover. However the NDVIs were significantly affected by soil background in a study with E. globulus. The percentage of red leaves resulting from stress treatment was most strongly correlated with the anthocyanin reflectance index (ARI) and red‐green index (RGI) in both E. grandis and E. pilularis, however the RGI was affected by background type in the E. globulus study while the ARI was not. Exposure to cold and nutrient deprivation led to marked changes in leaf cover for E. pilularis but not in E. grandis and a much more reduced level of chlorophyll in E. pilularis than is suspected in E. grandis. In E. globulus, defoliation from the upper crown was easier to detect with spectral data than from the lower crown. Results were generally comparable to studies of eucalypt crown condition from native forests.

Ganoderma and Amauroderma species associated with root-rot disease of Acacia mangium plantation trees in Indonesia and Malaysia

Fungal sporocarps and cultures associated with signs and symptoms of root-rot disease were collected from Acacia mangium and other tropical hardwood species. The collections were identified by either morphological characters and/or by phylogenetic analysis based on DNA sequences as Ganoderma philippii, G. mastoporum, G. aff. steyaertanum, G. australe and Amauroderma rugosum. Phylogenetic analysis unequivocally placed in the G. philippii clade four sequences amplified from A. mangium root and butt tissue showing clear signs of red root-rot disease (roots are covered by a red rhizomorphic skin). Whereas G. philippii was the most frequently encountered fungal species in A. mangium with red root-rot disease, this study indicates that other fungal species related to G. mastoporum may cause root-rot disease with very similar symptoms. An isolate (FRIM 138) that had caused red root-rot disease in artificial inoculations carried out before this study and was presumed to be G. philippii, is here determined to be closely related to G. mastoporum, G. cupreum and G. sinense. A Ganoderma species associated with a yellow-brown root-rot disease killing trees in an A. mangium plantation in Central Java, previously identified as G. lucidum, is shown by phylogenetic analysis to be closely related to G. steyaertanum, though some morphological characters vary from the original description of that species.

Consequences of resource limitation for recovery from repeated defoliation in Eucalyptus globulus Labilladière

Recovery following defoliation can be modified by co-occurring site resource limitations. The growth response of young Eucalyptus globulus saplings to two defoliation events was examined in an experimental plantation with combinations of low (-) or high (+) water (W) and nitrogen (N) resources. Artificial defoliation was applied at 3 and 9 months of age to remove ~40 and 55% of leaf area in the upper crown, respectively. At 18 months of age, height, stem diameter and leaf area were not significantly different between control and defoliated saplings, across all resource treatments. However, stem volume, bark volume and branch number were significantly increased in defoliated saplings, including a significant interaction with resource treatment. Total above-ground biomass of saplings in response to defoliation was significantly higher (almost double) than controls for the low water (N + W-) treatment only. Significantly increased foliar starch content (and a trend for increased soluble sugars) in the upper crown zone was found in the defoliated saplings of the N + W- treatment compared with the upper zone of control saplings. Foliar total non-structural carbohydrates were significantly correlated to stem biomass regardless of resource treatment or defoliation, and we suggest that foliar resources are most important for stem growth in E. globulus rather than stored carbon (C) from other tissues. After repeated defoliation and several months recovery, E. globulus saplings were generally not C limited in this study.

Solid-wood production from temperate eucalypt plantations: a Tasmanian case study

Since 1988, there has been a major focus in Tasmania on research for the management of temperate eucalypt plantations for solid wood. This coincided with the formal transfer of large areas of native forest that had previously been part of the production forest estate into reserves, a decision that triggered the establishment of eucalypt plantations for solid wood. This review summarises research on several key areas: silvicultural requirements for solid-wood production; wood properties of plantation-grown eucalypts and the influence of silviculture and genetics on these properties; factors influencing stem defect and decay; balancing silvicultural requirements with maintenance of tree vigour; and issues concerning wood processing and products. We conclude that there are still operational challenges to be confronted in the production of solid wood from plantations. If these can be overcome in the medium term, temperate plantation eucalypts have the potential to provide wood products that meet the requirements for appearance-grade material and that can compete in the same markets as wood from native forests. The bigger challenge at the national level will be to provide the log volumes of suitable material to meet the anticipated demand 25 to 30 years from now.

Polyphenols in Acacia mangium and Acacia auriculiformis heartwood with reference to heart rot susceptibility

The heartwood of Acacia mangium is vulnerable to heart rot and this is the first study to investigate the role of heartwood extractives in its susceptibility. Acacia auriculiformis was compared with A. mangium because it is rarely associated with heart rot. The heartwood extracts of both species were dominated by three flavonoids (2,3-trans-3,4′,7,8-tetrahydroxyflavanone, teracacidin, and 4′,7,8,-trihydroxyflavanone), which were purified and identified by nuclear magnetic resonance spectroscopy. The latter compound has not been previously reported in A. mangium and evidence for melacacidin is also newly reported. The mass spectrometric (MS) behavior of these compounds is given, for example teracacidin does not form molecular ions by either electrospray ionization or atmospheric-pressure chemical ionization. The nature of Acacia tannins was compared to quebracho tannin (composed of profisetinidins) using oxidative cleavage to enable MS detection but a negative reaction was obtained for both, which suggests the Acacia tannins may also be of the 5-deoxy proanthocyanidin type. The concentration of flavanones was less when A. mangium heartwood was decayed but the amount of proanthocyanidins was only slightly reduced and therefore these compounds may be more resistant to degradation by heart rot fungi. We found that the total phenol content of A. auriculiformis was about fivefold that of A. mangium, and, while preliminary, this provides evidence for a role played by phenolic extractives in heart rot resistance of these Acacia species.

Eucalyptus obliqua seedling growth in organic vs. mineral soil horizons

Eucalyptus obliqua, the most widespread timber tree in Tasmania, is a pioneer after fire which can eliminate the organic layer of forest soil, exposing the underlying mineral soil. We compared seedling growth, mycorrhiza formation, and mineral nutrient limitation in organic layer vs. mineral soil. We grew E. obliqua seedlings separately in pots of organic layer and mineral soil in a glasshouse. Additional treatments of organic soil only, involved fully crossed methyl-bromide fumigation and fertilization. Fertilization comprised chelated iron for 121 days after transplant (DAT) followed by soluble phosphorus. At 357 DAT, whole plant dry weight was three times greater in ambient organic than in mineral soil. In organic soil, fumigation halved ectomycorrhiza abundance and reduced seedling growth at 149 DAT, but by 357 DAT when negative effects of fumigation on seedling growth had disappeared, neither fumigation nor fertilization affected mycorrhiza abundance. Iron fertilization diminished seedling growth, but subsequent phosphorus fertilization improved it. E. obliqua seedlings grow much better in organic layer soil than in mineral soil, although phosphorus remains limiting. The prevalent forestry practice of burning to mineral soil after timber harvest exposes a poor growth medium likely only partially compensated by fire-induced mineral soil alterations.

The role of strigolactones and ethylene in disease caused by Pythium irregulare

Plant hormones play key roles in defence against pathogen attack. Recent work has begun to extend this role to encompass not just the traditional disease/stress hormones, such as ethylene, but also growth-promoting hormones. Strigolactones (SLs) are the most recently defined group of plant hormones with important roles in plant-microbe interactions, as well as aspects of plant growth and development, although the knowledge of their role in plant-pathogen interactions is extremely limited. The oomycete Pythium irregulare is a poorly controlled pathogen of many crops. Previous work has indicated an important role for ethylene in defence against this oomycete. We examined the role of ethylene and SLs in response to this pathogen in pea (Pisum sativum L.) at the molecular and whole-plant levels using a set of well-characterized hormone mutants, including an ethylene-insensitive ein2 mutant and SL-deficient and insensitive mutants. We identified a key role for ethylene signalling in specific cell types that reduces pathogen invasion, extending the work carried out in other species. However, we found no evidence that SL biosynthesis or response influences the interaction of pea with P. irregulare or that synthetic SL influences the growth or hyphal branching of the oomycete in vitro. Future work should seek to extend our understanding of the role of SLs in other plant interactions, including with other fungal, bacterial and viral pathogens, nematodes and insect pests.

Characterizing eucalypt leaf phenology and stress with spectral analysis

Detection of stress with remote sensing in any vegetation type relies on development of methods that highlight properties associated with stress which are discernable from background variation, such as phenological changes. Therefore the nature (and timing) of phenological foliar change needs to be systematically compared to foliar stress symptoms with physical, biochemical and optical analyses. Two such case studies with eucalypt species are presented here, including Eucalyptus globulus and Eucalyptus pilularis. Studies with both eucalypt species have shown that different leaf ages can be associated with alterations in pigments and properties that are as pronounced as those occurring for well-developed stress responses (potassium deficiency for E. globulus and low nutrient and cold exposure in E. pilularis). Chlorophyll, carotenoid and anthocyanin content were analysed, as well as specific leaf area and water content. Significant differences between leaf ages were detected for many of these leaf pigments and properties, but the significant differences between healthy and stressed leaves were usually of greater magnitude. Only carotenoid content was not significantly different with leaf age for E. globulus, but was significantly different with potassium-deficiency. This is a basis to further investigate the potential of carotenoids to discern stressed leaves from phenological changes. Preliminary data shown here provides a background for ongoing spectral research on this theme for eucalyptus.

Poppy Crop Height and Capsule Volume Estimation from a Single UAS Flight

The objective of this study was to estimate poppy plant height and capsule volume with remote sensing using an Unmanned Aircraft System (UAS). Data were obtained from field measurements and UAS flights over two poppy crops at Cambridge and Cressy in Tasmania. Imagery acquired from the UAS was used to produce dense point clouds using structure from motion (SfM) and multi-view stereopsis (MVS) techniques. Dense point clouds were used to generate a digital surface model (DSM) and orthophoto mosaic. An RGB index was derived from the orthophoto to extract the bare ground spaces. This bare ground space mask was used to filter the points on the ground, and a digital terrain model (DTM) was interpolated from these points. Plant height values were estimated by subtracting the DSM and DTM to generate a Crop Height Model (CHM). UAS-derived plant height (PH) and field measured PH in Cambridge were strongly correlated with R2 values ranging from 0.93 to 0.97 for Transect 1 and Transect 2, respectively, while at Cressy results from a single flight provided R2 of 0.97. Therefore, the proposed method can be considered an important step towards crop surface model (CSM) generation from a single UAS flight in situations where a bare ground DTM is unavailable. High correlations were found between UAS-derived PH and poppy capsule volume (CV) at capsule formation stage (R2 0.74), with relative error of 19.62%. Results illustrate that plant height can be reliably estimated for poppy crops based on a single UAS flight and can be used to predict opium capsule volume at capsule formation stage.