Jo Luck

Impacts of global change on diseases of agricultural crops and forest trees

The fourth assessment report of the Intergovernmental Panel on Climate Change projects rising levels of greenhouse gas and global temperature. The well-known dependence of plant diseases on weather has long been exploited for predicting epidemics and to time applications of control measures for tactical disease management. Fingerprints of inter-annual climatic variation on pathogens have recently been shown in literature linking pathogen abundance to atmospheric composition. Past reviews have dealt with impacts of changing atmospheric composition and climate on diseases, regional or country-wide assessments of climate change impacts and impacts on specific disease/pathogen or pathogen groups. All agree on paucity of knowledge prompting a need to generate new empirical data on host‐pathogen biology under a changing climate. Focused on experimental research, the purpose of this review is to summarize published and unpublished studies on plant pathogens and diseases in free-air CO2 enrichment (FACE) facilities and open top chambers and other current non-FACE research to offer a summary of future research needs and opportunities. Critical review of recent literature on the influence of elevated CO2 and O3 on agriculture and forestry species forms a major part of the treatise. Summaries of unpublished or ongoing experimental research on plant pathogens from FACE studies are included as a catalogue of work in this neglected area. The catalogue and knowledge gaps are intended as a resource for workers initiating research in this area as well as the general scientific community grappling with the design and scope of next generation of FACE facilities.

Virus disease in wheat predicted to increase with a changing climate

Current atmospheric CO2 levels are about 400 μmol mol(-1) and are predicted to rise to 650 μmol mol(-1) later this century. Although the positive and negative impacts of CO2 on plants are well documented, little is known about interactions with pests and diseases. If disease severity increases under future environmental conditions, then it becomes imperative to understand the impacts of pathogens on crop production in order to minimize crop losses and maximize food production. Barley yellow dwarf virus (BYDV) adversely affects the yield and quality of economically important crops including wheat, barley and oats. It is transmitted by numerous aphid species and causes a serious disease of cereal crops worldwide. This study examined the effects of ambient (aCO2 ; 400 μmol mol(-1) ) and elevated CO2 (eCO2 ; 650 μmol mol(-1) ) on noninfected and BYDV-infected wheat. Using a RT-qPCR technique, we measured virus titre from aCO2 and eCO2 treatments. BYDV titre increased significantly by 36.8% in leaves of wheat grown under eCO2 conditions compared to aCO2 . Plant growth parameters including height, tiller number, leaf area and biomass were generally higher in plants exposed to higher CO2 levels but increased growth did not explain the increase in BYDV titre in these plants. High virus titre in plants has been shown to have a significant negative effect on plant yield and causes earlier and more pronounced symptom expression increasing the probability of virus spread by insects. The combination of these factors could negatively impact food production in Australia and worldwide under future climate conditions. This is the first quantitative evidence that BYDV titre increases in plants grown under elevated CO2 levels.

The effect of elevated temperature on Barley yellow dwarf virus-PAV in wheat

Barley yellow dwarf virus-PAV (BYDV-PAV) is associated with yellow dwarf disease, one of the most economically important diseases of cereals worldwide. In this study, the impact of current and future predicted temperatures for the Wimmera wheat growing district in Victoria, Australia on the titre of BYDV-PAV in wheat was investigated. Ten-day old wheat (Triticum aestivum, cv. Yitpi) seedlings were inoculated with BYDV-PAV and grown at ambient (5.0-16.1°C, night-day) or elevated (10.0-21.1°C, night-day) temperature treatments, simulating the current Wimmera average and future daily temperature cycles, respectively, during the wheat-growing season. Whole above-ground plant samples were collected from each temperature treatment at 0 (day of inoculation), 3, 6, 9, 12, 15, 18, 21 and 24 days after inoculation and the titre of BYDV-PAV was measured in each sample using a specific one-step multiplex normalised reverse transcription quantitative PCR (RT-qPCR) assay. Physical measurements, including plant height, dry weight and tiller number, were also taken at each sampling point. The titre of BYDV-PAV was significantly greater in plants grown in the elevated temperature treatment than in plants grown in the ambient treatment on days 6, 9 and 12. Plants grown at elevated temperature were significantly bigger and symptoms associated with BYDV-PAV were visible earlier than in plants grown at ambient temperature. These results may have important implications for the epidemiology of yellow dwarf disease under future climates in Australia.

Virus infection mediates the effects of elevated CO2 on plants and vectors.

Atmospheric carbon dioxide (CO2) concentration has increased significantly and is projected to double by 2100. To increase current food production levels, understanding how pests and diseases respond to future climate driven by increasing CO2 is imperative. We investigated the effects of elevated CO2 (eCO2) on the interactions among wheat (cv. Yitpi), Barley yellow dwarf virus and an important pest and virus vector, the bird cherry-oat aphid (Rhopalosiphum padi), by examining aphid life history, feeding behavior and plant physiology and biochemistry. Our results showed for the first time that virus infection can mediate effects of eCO2 on plants and pathogen vectors. Changes in plant N concentration influenced aphid life history and behavior, and N concentration was affected by virus infection under eCO2. We observed a reduction in aphid population size and increased feeding damage on noninfected plants under eCO2 but no changes to population and feeding on virus-infected plants irrespective of CO2 treatment. We expect potentially lower future aphid populations on noninfected plants but no change or increased aphid populations on virus-infected plants therefore subsequent virus spread. Our findings underscore the complexity of interactions between plants, insects and viruses under future climate with implications for plant disease epidemiology and crop production.

Case Studies on Food Production, Policy and Trade

The purpose of this book is to critically examine food security issues in Australia, a country that is often assumed to be food secure. Australia, although a substantial producer of agricultural products, currently has many citizens suffering food insecurity (Temple 2008) and a growing number with diet-related health problems (AIHW 2010). Governments see diet issues as important social and economic problems because: Many diet-related chronic diseases … are the major cause of death and disability among Australians. Poor nutrition is responsible for around 16% of the total burden of disease and is implicated in more than 56% of all deaths in Australia (NHMRC 2011a p7). In addition to health-related food insecurities, a range of other pressures impact increasingly on the cost of food as well as its production. For example, globalization exposes food supply systems in Australia to rising resource prices as world demand increases. Australia’s agricultural production is not immune to the negative aspects of climate change. Indeed Garnaut maintains that Australian agricultural and resource industries are likely to be affected profoundly by climate change and the global response to it (Garnaut 2010 p9). Economic and population growth, changing attitudes to biodiversity conservation, and the pressure of climate change on native biodiversity (Lindenmayer et al. 2010), also have implications for food security by increasing competition for resources, such as land and water (Alston and Whittenbury 2011; Carey et al. 2011). Consequently, the food production status of Australia will change and food security, including dietary issues, is likely to become increasingly important for Australians. In order to contextualize Australia’s food security challenges, and how a more sustainable, resilient and equitable food system might be created, we need an appreciation of global food security issues.

The specificity of PCR-based protocols for detection of Erwinia amylovora

An evaluation of seven published conventional PCR protocols used for the detection of Erwinia amylovora has shown that six out of the seven protocols tested were not specific for all strains of E. amylovora. A collection of 40 genetically diverse strains of E. amylovora and 55 geographically diverse bacteria that are closely related or share the same ecological niche as E. amylovora were used to test the seven PCR protocols. All bacteria were tested for virulence by inoculation of immature pear fruit and for cultural characteristics on selective media. Only one PCR protocol, Taylor et al. (2001), was specific for all strains of E. amylovora and was able to differentiate E. amylovora from all other bacteria tested. Diagnostic laboratories may need to review their testing procedures in light of these findings.

The influence of increasing temperature and CO2 on Fusarium crown rot susceptibility of wheat genotypes at key growth stages

Despite recent reports advancing our understanding of climate change on plant diseases, uncertainty remains concerning how host and pathogen interactions are changed by increases in atmospheric carbon-dioxide (CO2) and temperature. This study has observed crown rot inoculated and non-inoculated plants in three glasshouse environments comprising ambient CO2 with ambient temperature (E1), elevated CO2 with ambient temperature (E2) and elevated CO2 with warm temperatures (E3). The proportion of crown rot infected tillers (incidence), length of stem browning (severity) and biomass of Fusarium pseudograminearum in 16 wheat genotypes was destructively assessed at node development, anthesis, soft dough and crop maturity. Mean incidence, severity and Fusarium biomass was greater in E2, and all three measurements increased at a faster rate across plant development stages; E1 showed the lowest mean incidence and severity. Incidence and severity at each development stage was dependent on the environment each genotype was grown. The influence of genotype on Fusarium biomass at each development stage however was not seen to be dependent on environment. Irrespective of genotype plants with greater severity or relative Fusarium biomass showed lower plant dry weight at crop maturity in all environments with exception to E3, where CR severity did not exert a cost to plant dry weight. These results may allude to plant maturity and temperature-dependent resistance as effective mechanisms in building resistance to crown rot. Regardless of temperature, if crown rot symptoms and Fusarium biomass are to increase at elevated CO2 there is potential for a loss in crop production capability while boosting inoculum in crop stubble.

The effect of elevated CO2 and virus infection on the primary metabolism of wheat

Atmospheric CO2 concentrations are predicted to double by the end of this century. Although the effects of CO2 fertilisation in crop systems have been well studied, little is known about the specific interactions among plants, pests and pathogens under a changing climate. This growth chamber study focuses on the interactions among Barley yellow dwarf virus (BYDV), its aphid vector (Rhopalosiphum padi) and wheat (Triticum aestivum L. cv. Yitpi) under ambient (aCO2; 400µmolmol-1) or elevated (eCO2; 650µmolmol-1) CO2 concentrations. eCO2 increased the tiller number and biomass of uninoculated plants and advanced the yellowing symptoms of infected plants. Total foliar C content (percentage of the total DW) increased with eCO2 and with sham inoculation (exposed to early herbivory), whereas total N content decreased with eCO2. Liquid chromatography-mass spectrometry approaches were used to quantify the products of primary plant metabolism. eCO2 significantly increased sugars (fructose, mannitol and trehalose), irrespective of disease status, whereas virus infection significantly increased the amino acids essential to aphid diet (histidine, lysine, phenylalanine and tryptophan) irrespective of CO2 concentration. Citric acid was reduced by both eCO2 and virus infection. Both the potential positive and negative biochemical impacts on wheat, aphid and BYDV interactions are discussed.