Giles Hardy

According to the Food and Agricultural Organization, more than 800 million people still suffer from hunger, yet one third of food produced (equivalent to $ 1 trillion USD in value) is either lost or wasted globally each year. Postharvest losses are considered a major component of food loss and waste in the food supply chain, from raw production (total harvest) to food consumed. Losses occur due to improper handling, storage, transport, preservation techniques and infection by microorganisms, and can reach up to 45% in fresh fruits and vegetables. Postharvest diseases, particularly of perishable food crops, are predominately caused by fungal pathogens. Management practices for controlling such pathogens include physical, chemical and biological methods in addition to newer technologies such as UV radiation, nano-technology and plasma treatments. Fungicides are the most common management option due to the consistency of results, however, there is increasing demand by consumers for less chemical use, and chemical-free produce can attract premium prices for growers. New technologies are required to reduce postharvest disease losses, without exposing consumers to hazardous chemical residues. This paper reports a novel, non-chemical method for treating postharvest diseases that shows much promise – cold plasma. Our experiments indicate that this method does not have any phytotoxic effects on avocado fruit, but can inhibit pathogens in vitro following an exposure time of 3 min.

Cold plasma (CP) has successfully been used for the decontamination of fresh produce from microorganisms, particularly bacteria that cause food safety issues. CP can be used to produce plasma activated water (PAW) which has been demonstrated to have excellent antimicrobial properties. This study investigated the in vitro efficacy of PAW against Colletotrichum alienum, an important postharvest pathogen of avocado. Three volumes of deionised water, 100, 500 and 1000 ml, were treated with CP to generate PAW100, PAW500 and PAW1000, respectively. A conidial suspension of C. alienum isolate WAC-13891 (1 x 106 conidia/ml) was then combined with each PAW in a 1:3 ratio (conidia:PAW) and the percentage of germinating conidia were counted after 12, 15, 18, 24 and 36 h of treatment. In addition to treating conidia with freshly prepared PAW, each PAW was also stored for 1, 3, 7 or 15 days (250 C in the dark) and the germination tests repeated. All three PAW significantly reduced conidia germination compared to the control, even after 15 days of storage. The effect of PAW100 on conidia ultrastructure showed a significant change in the cell wall, plasma membrane and cytoplasm compared to untreated conidia as observed by transmission electron microscopy. CP technology is now being investigated as an alternative, chemical-free treatment for controlling postharvest rots of avocado.

Forest die-offs associated with drought and heat have recently occurred across the globe, raising concern that associated changes in fuels and microclimate could link initial die-off disturbance to subsequent fire disturbance. Despite widespread concern, little empirical data exist. Following forest die-off in the Northern Jarrah Forest, southwestern Australia, we quantified fuel dynamics and associated microclimate for die-off and control plots. Sixteen months post-die-off, die-off plots had significantly elevated 1-hr fuels (11.8 vs. 9.8 tons ha-1) but not larger activity fuel classes (10-hr and 100-hr fuels). Due to stem mortality, die-off plots had significantly greater standing dead wood mass (100 vs. 10 tons ha-1), visible sky (hemispherical images analysis: 31% vs. 23%) and potential near-ground solar radiation input (measured as Direct Site Factor: 0.52 vs. 0.34). Supplemental, mid-summer microclimate measurements (temperature, relative humidity and wind speed) were combined with long-term climatic data and fuel load estimates to parameterize fire behaviour models. Fire spread rates were predicted to be 30% greater in die-off plots with relatively equal contributions from fuels and microclimate, highlighting need for operational consideration by fire managers. Our results underscore potential for drought-induced tree die-off to interact with subsequent fire under climate change.

Global changes in climate are increasingly affecting forested ecosystems in Australia and around the world. The most striking examples of these effects have been reported in relation to extreme climatic events, such as droughts and heatwaves. In response, dominant tree species have shown distinct periods of severe dieback and mortality, resulting in major changes in forest structure and composition. Less visible, but equally important, are changes in forests driven by gradual long-term changes in temperature and rainfall. These gradual climatic changes increase tree mortality rates, and decrease growth and health. The primary negative flow-on effects of these processes are the reduction in biodiversity as well as a decrease in the potential for long-term carbon uptake and storage in forest ecosystems. In Australia, the majority of work in relation to climate change processes and their effects on forested ecosystems has been focussing on extreme climatic events, primarily on droughts. There is, however, a real lack of studies looking at the effects of long-term climate trends and their effects on forest health. Several regions in Australia have progressively become drier and warmer over the last five decades and are projected to continue this trend. In these regions, such as the southwest of Western Australia, the aforementioned forest change processes have become more prominent in recent times. To effectively counter the changes, we have to better our understanding of where, when, and what kind of changes are likely to occur through long-term monitoring and research.

Mediterranean type forest ecosystems commonly experience an extended dry period during summer months. In recent decades many Mediterranean regions have experienced elevations in temperature and decreases in rainfall, which have led to large-scale forest die-off events. This has also recently occurred in the Northern Jarrah Forest (NJF) (Matusick et al. 2012) and was closely associated with increased infestations by borers. These borers caused severe damage to jarrah and marri trees and contributed to increased tree stress and tree mortality.

Blue-stain (Ophiostomatoid) fungi, which attack woody tissue, can be closely associated with bark beetles. These fungi have been found in Eucalyptus species, invading the sapwood (van Wyk et al 2007), and appear to be present in the jarrah forest of Western Australia.

In this study, the occurrence and relationships between borers and blue-stain fungi in jarrah forest under drought conditions, is being investigated.

Mediterranean biomes represent five biodiversity hotspots worldwide and cover just 2% of the Earth's land area; however, they support 20% of the Earth's known plant diversity. The Jarrah forest of South West, Western Australia, represents one of these valuable biomes. Documented climate change in Western Australia shows 35 years of consistently less rainfall and higher temperatures, with an extreme drought event in 2011 resulting in mortality of 1.7% or 19,000 ha of Northern Jarrah forest. To assess drought impact on vegetation of the Northern Jarrah forest, sites were chosen with a steep gradient from areas of canopy collapse to healthy forest. This provided an opportunity to assess the forest vegetation across an ecotone using space for time substitution. Our objectives were: 1) to determine factors affecting drought /heatwave induced vegetation mortality and 2) to assess differences in species response to this event. Results from this study show mortality of species occurs in zones on sites of drought induced canopy collapse in the Northern Jarrah Forest. Midstorey mortality is determined by soil depth. Results, indicate a complex interaction between plants with differing root functional traits and soil depth, determines the collapse response in an extreme drought event. There is an ongoing shift in the species composition and structure of the forest in and around areas of drought induced canopy collapse. We anticipate the use of presence /absence of midstorey, as a proxy for soil depth, and stand composition to predict areas of forest likely to collapse in the future.

Marri (Corymbia calophylla) is an iconic and keystone forest tree in Western Australia. A canker disease caused by the fungus Quambalaria coyrecup has devastated many marri stands. Disease incidence is higher in remnant stands that border cleared land such as road edges and farmland where there is greater anthropogenic disturbance, such as fertiliser, pesticide and herbicide use, and the introduction of plant pathogens. The progression of the decline strongly suggests a breakdown in the ability of the trees to maintain nutrient balance and we hypothesize that mycorrhizal fungi play a role in this process. The aim of this project was to examine the mycorrhizal species associated with marri and how these communities differ between intact and anthropogenically disturbed forest sites and whether pesticide use, changes in soil nutrition and/or soilborne pathogens are responsible for changes in communities of mycorrhizal fungi and hence canker disease incidence and severity. Seventeen sites were surveyed. Each site consisted of a disturbance gradient. Soil was collected from each transect and tested for nutrient composition, mycorrhizal composition and pathogens. Preliminary results demonstrate differences in soil nutrition between the disturbed transect and all intact forest transects. In addition, there are differences among the communities of fungi between the disturbed and intact forest transects. Disturbed transects show a higher proportion of pathogenic fungi particularly Phytophthora species, than in intact forest transects. Currently, the presence of pesticides and herbicides across the transects are being examined to determine their role in marri decline.

Corymbia calophylla (Marri) is an endemic tree in the forests of South-Western Australia. This iconic, keystone species is being threatened by soil-borne oomycete (Phytophthora spp.) root pathogens and an aerial fungal canker pathogen (Quambalaria coyrecup) that are causing widespread mortalities. Phytophthora is often isolated from the rhizosphere of dying marri and it is hypothesized that Phytophthora root infection compromise marri to attack by other pathogens, such as this canker pathogen. The aim of this study was to investigate if the spectral absorption features of the photosynthetic components in the leaves of marri could be used as an indicator of stress caused Phytophthora species. For this purpose, non-destructive spectral measurements were conducted using a handheld hyperspectral sensor (ASD FieldSpec portable spectroradiometer). Isolates of Phytophthora cinnamomi and P. multivora were used to infect the roots of marri seedlings in a glasshouse pathogen nicity trial. Weekly spectral measurements were taken during the course of this experiment. These measurements were correlated with measurements of above-and below-ground biomass at the completion of the experiment. Seedlings inoculated with P. cinnamomi displayed decreased values in root volume, a belowground biomass indicator. The value s of the Red Edge Normalized Difference Vegetation Index (Red Edge NDVI), a narrow-band greenness vegetation index which makes use of the absorption features in the red and near-infrared regions of the electromagnetic spectrum, was also decreased. In contrast, the root volumes for seedlings inoculated with P. multivora displayed increased values. These values were mirrored by the increased values for the Red Edge NDVI for these seedlings. This study suggests that spectral measurements done with a hyperspectral sensor may provide early-warning signs of root pathogen stress in marri. Future work would include analyzing the time-series component of the weekly spectral measurements, investigating the change in the photochemical components in the leaves over time. Current studies are examining spectral indices and disease development with dual inoculations with Phytophthora species and the canker pathogen Quambalaria coyrecup.

An outbreak of the native Eucalyptus longhorned borer (Phoracantha semipunctata, Coleoptera: Cerambycidae) coincided with a severe drought-induced dieback event in the Northern Jarrah Forest of southwestern Australia in 2010-2011. Although the behaviour of P. semipunctata is well known where it is exotic, little is known about its ecology in its native habitats within Australia. Intensive whole-tree sampling was used to investigate population levels, host preference, and within-tree infestation patterns in Eucalyptus marginata and Corymbia calophylla trees during the outbreak. The density of oviposition sites was similar between host tree species, whereas infestation levels were significantly greater in marri compared to jarrah, including 20% more larval galleries per oviposition site and 46% more emergence holes/m2. Larval damage in sapwood was extensive (mean of 48%) in both species. Significant positive correlations were found between density of oviposition sites, larval galleries, and emergence holes with stem diameter. This study is the first to establish the association between drought and outbreak levels of P. semipunctata in southwestern Australia, raising questions about the future impact of P. semipunctata with continued climate change in this region. It is also first to describe the within-tree distribution of the beetle in susceptible hosts in its native environment in Australia.