“Killer Joules”: spores of Bipolaris sorokiniana and fusarium species are susceptible to microwave radiation

Cereal production in Australia is severely impacted by diseases such as Fusarium crown rot (caused predominantly by Fusarium pseudograminearum) and common root rot (caused by Bipolaris sorokiniana). These diseases are particularly difficult to manage because inoculum can survive at least three years within cereal stubble, or four years in soil in the case of B. sorokiniana. Microwave radiation may be able to reduce or eliminate inoculum within stubble and soil. Several cereal pathogens have been previously shown to be susceptible to microwave radiation, but the energy requirements to achieve a significant decrease in pathogen populations were not defined. Laboratory based microwave dose-response experiments on conidia of B. sorokiniana and macroconidia of F. pseudograminearum and F. cerealis revealed that all three pathogens are susceptible to microwave radiation, with lethal dose (LD) thresholds estimated for each pathogen. Bipolaris sorokiniana conidia required 103.8 Jg− 1 and 236.6 Jg− 1 of microwave radiation energy for LD50 and LD99, respectively, whilst F. pseudograminearum required 78.4 Jg− 1 and 300.8 Jg− 1 and F. cerealis required 95.3 Jg− 1 and 152.7 Jg− 1 for LD50 and LD99, respectively. These results were derived from experiments whereby samples were microwaved for up to 10 s using a domestic 1100 W microwave oven. These timing and energy requirements serve as a starting point to define requirements for further development of microwave radiation treatments under field conditions

Is there a disease downside to stripper fronts? Harvest height implications for Fusarium crown rot management

Take home messages • Taller standing stubble allowed vertical progression of the Fusarium crown rot fungus within the stubble after harvest, whilst short stubble prevented further growth (i.e. vertical growth was limited to the height of the cut stubble). • Stripper fronts, which leave higher standing stubble, may increase stubble-borne disease inoculum after harvest of an infected crop, especially if wet fallow conditions are experienced. • In high-risk situations, such as an infected crop with high biomass, cutting the crop shorter at harvest will limit further inoculum development within the stubble after harvest (beyond the levels already present at harvest). • Cutting infected cereal stubble shorter prior to rotation with shorter-stature crops such as chickpea or lentils also prevents the dispersal of infected stubble when harvesting these shorter break crops

Stubble Olympics: the cereal pathogen 10cm sprint – growth patterns of fungi causing crown rot, common root rot and yellow leaf spot in post-harvest cereal stubble

Take home messages • Wetter is better (for cereal pathogens): moist conditions promoted growth of pathogenic fungi (Fusarium pseudograminearum, Bipolaris sorokiniana and Pyrenophora tritici-repentis) within post-harvest cereal stubble, meaning inoculum levels of crown rot, common root rot and yellow spot may increase if wet weather is experienced after harvest • Not all cereal stubble is created equally: some pathogens progressed further in oat than bread wheat stubble. Additionally, there are indications that the resistance ratings of varieties and crops do not reflect the extent of saprophytic growth post-harvest • Each cereal pathogen had a unique stubble-colonisation pattern: the crown rot fungus was the quickest to progress within all stubble types and the yellow spot pathogen was the slowest. This is likely to influence which pathogen dominates in following seasons if mixed infections have occurred in the same crop • Reducing cereal stubble biomass may limit the post-harvest progression of pathogenic fungi in stubble, thereby reducing the amount of inoculum carried forward. Options could include selection of low-biomass varieties, low harvest heights or cutting for hay, however field validation is required

Stubble trouble! Moisture, pathogen fitness and cereal type drive colonisation of cereal stubble by three fungal pathogens

Stubble-borne cereal diseases are a major constraint to production in Australia, with associated costs rising as a result of increased adoption of conservation agriculture systems. The fungal pathogens that cause these diseases can saprotrophically colonise retained cereal residues, which may further increase inoculum levels post-harvest. Hence, saprotrophic colonisation by the stubble-borne fungal pathogens Fusarium pseudograminearum, Pyrenophora tritici-repentis and Bipolaris sorokiniana were compared under a range of moisture conditions for stubble of six cereal varieties (two bread wheat, two barley, one durum wheat and one oat). Sterile cereal stubble was inoculated separately with two isolates of each pathogen and placed, standing, under constant relative humidity conditions (90, 92.5, 95, 97.5 and 100%) for 7 days at 25 °C. Stubble was then cultured in increments of 1 cm to determine the percentage colonisation height of each tiller. Fusarium pseudograminearum colonised farther within tillers, leaving a greater proportion of the standing stubble colonised compared with B. sorokiniana and P. tritici-repentis, suggesting F. pseudograminearum has higher saprotrophic fitness. Saprotrophic colonisation also increased with increasing relative humidity for all pathogens and varied by cereal type. Disease management strategies, such as reduced cereal harvest height, may limit saprotrophic colonisation and improve stubble-borne disease management in conservation agriculture systems

The secret life of crown rot: what happens after harvest?

Take home messages A preliminary survey of cereal stubble from 2017 showed that in the northern region (NSW and Qld) the crown rot fungus is commonly present from the crown up to 18 cm, with detection up to 33 cm within tillers at harvest. However, moist conditions can promote further growth of the crown rot fungus post-harvest in inoculated cereal stubble (increasing by almost 1 cm up from the crown per day at 100% humidity). Inoculum levels in post-harvest stubble are not static and may fluctuate as different weather patterns are experienced. Planting different bread wheat, durum wheat and barley varieties may not be useful for supressing inoculum growth in stubble after harvest. Reducing cereal stubble height may limit inoculum build-up in crown rot affected paddocks by restricting the capacity for further fungal growth post-harvest. This could also help reduce dispersal of infected residues when harvesting shorter break crops such as chickpea, but field validation of this management option is required

Microwave radiation reduces survival of Fusarium pseudograminearum in durum wheat stubble

Fusarium pseudograminearum (Fp) is a stubble-borne fungal pathogen which is the main causal species of the disease crown rot across the Australian wheat-belt. Microwave radiation may offer a rapid and chemical-free approach to reduce Fp inoculum levels in cereal residues. Crown and node sections of durum wheat stubble infected with Fp collected from an inoculated field experiment were microwaved using a conventional 1100 W microwave oven for 0, 15, 30, 60 and 120 s either embedded in moist soil or without soil. The survival of Fp after microwave radiation was assessed by culturing on 1/4 PDA plus novobiocin. Microwave radiation for 15, 30, 60 and 120 s without soil reduced recovery of Fp to an average of 69%, 46%, 30 and 19%, respectively, compared to the control (72%). Efficacy was improved by embedding stubble segments in moist soil, with recovery of Fp reduced to an average of 34%, 0%, 1 and 0% when microwaving for 15, 30, 60 and 120 s, respectively. Although microwave radiation significantly reduced the survival of Fp in durum wheat stubble in the laboratory, the practicality of this method for crown rot management under field conditions is yet to be established

“Killer Joules”: spores of Bipolaris sorokiniana and fusarium species are susceptible to microwave radiation

Cereal production in Australia is severely impacted by diseases such as Fusarium crown rot (caused predominantly by Fusarium pseudograminearum) and common root rot (caused by Bipolaris sorokiniana). These diseases are particularly difficult to manage because inoculum can survive at least three years within cereal stubble, or four years in soil in the case of B. sorokiniana. Microwave radiation may be able to reduce or eliminate inoculum within stubble and soil. Several cereal pathogens have been previously shown to be susceptible to microwave radiation, but the energy requirements to achieve a significant decrease in pathogen populations were not defined. Laboratory based microwave dose-response experiments on conidia of B. sorokiniana and macroconidia of F. pseudograminearum and F. cerealis revealed that all three pathogens are susceptible to microwave radiation, with lethal dose (LD) thresholds estimated for each pathogen. Bipolaris sorokiniana conidia required 103.8 Jg− 1 and 236.6 Jg− 1 of microwave radiation energy for LD50 and LD99, respectively, whilst F. pseudograminearum required 78.4 Jg− 1 and 300.8 Jg− 1 and F. cerealis required 95.3 Jg− 1 and 152.7 Jg− 1 for LD50 and LD99, respectively. These results were derived from experiments whereby samples were microwaved for up to 10 s using a domestic 1100 W microwave oven. These timing and energy requirements serve as a starting point to define requirements for further development of microwave radiation treatments under field conditions

Progressing stubble-borne disease management of winter cereals in the northern grain region of Australia - Dataset

Stubble-borne diseases are a major constraint to wheat and barley production in the northern grain region (NGR) of Australia, with associated incidence and severity rising due to increased adoption of conservation agriculture. The fungal pathogens that cause these diseases can colonise retained cereal stubble (saprotrophic colonisation), which may further increase inoculum levels after harvest. As such, we set out to understand what drives saprotrophic colonisation of the pathogens which cause Fusarium crown rot (Fusarium pseudograminearum), common root rot (Bipolaris sorokiniana) and yellow leaf spot (Pyrenophora tritici-repentis) and investigate new field management options for reducing inoculum carry-over into subsequent seasons. This was done using a controlled relative humidity (RH) experiment, a glasshouse experiment, two three-year field experiments, and two laboratory-based microwave radiation experiments. In the RH experiment, Fusarium pseudograminearum showed an increased relative saprotrophic fitness, colonising 20 to 42% more stubble length over a 7-day period at 100% RH compared with B. sorokiniana and P. tritici-repentis, respectively. Saprotrophic colonisation by all three pathogens in sterile post-harvest stubble was also significantly faster under higher moisture conditions of 97.5 % RH and above and was largely unaffected by cereal crop type or level of genetic resistance. Further glasshouse experimentation with F. pseudograminearum confirmed that crop selection may limit pathogen colonisation in-crop (in oat) but not saprotrophic colonisation post-harvest. After plant senescence, F. pseudograminearum colonised up to 23.5 cm higher in the main tiller of highly resistant wheat germplasm LRC2012-122 compared with the most susceptible wheat cv. Kittyhawk. These findings confirmed that crop selection remains a useful tool to limit Fusarium crown rot symptoms but cannot be used to manage saprotrophic colonisation in post-harvest stubble. Two new management strategies were therefore investigated to control or reduce inoculum in post-harvest stubble. Lowering the cereal harvest height of a durum wheat crop infected with F. pseudograminearum effectively restricted saprotrophic colonisation of post-harvest stubble by 61 to 70% at two field sites in the NGR. In the shorter-term, harvest height modification could therefore be developed as a useful integrated disease management strategy to improve stubble-borne disease management in the NGR. In the longer-term, using microwave radiation to kill stubble-borne pathogens appears promising to remove pathogens from cereal stubble in situ whilst retaining the associated benefits of stubble retention. For instance, reduction of pathogens B. sorokiniana, F. pseudograminearum and F. cerealis in solution required 150 to 300 Jg-1 of microwave energy to eliminate 99% of pathogen populations. Heating of wheat and barley stubble using microwave radiation also appears effective, particularly at lower microwave frequencies (_MHz) and higher stubble moisture (30-100% moisture by weight). These findings have been important to improve our understanding of saprotrophic phase of the stubble-borne disease cycle whilst also offering several new directions for stubble-borne disease management. Ultimately, future management strategies need to consider the role of inoculum production in both the pathogenic and saprotrophic phases to better control stubble-borne cereal diseases in the NGR. Datasets included:Chapter 2 data set - Colonisation of sterile stubble (1 durum wheat, 1 oat, 2 wheat and 2 barley varieties) inoculated with 6 cereal pathogens (2 isolates each of Fusarium pseudograminearum, Fusarium cerealis and Bipolaris sorokiniana) and incubated at 90, 92.5, 95, 97.5 and 100% relative humidity.Chapter 3 data set - Stem colonisation, disease symptoms and pathogen biomass of cereal cultivars (1 durum wheat, 1 oat, 5 wheat and 3 barley) inoculated with Fusarium pseudograminearum and assessed at 4 sampling times (GS32, GS61, GS90 and post-harvest).Chapter 4 data set - Field experiments (Breeza site) - Data collected during 3-year field experiments to assess crown rot inoculum at different harvest heights and stubble management strategies using stubble from an infected durum crop through a chickpea break crop, with assessment of disease incidence and severity in a final wheat crop at Breeza, NSW across the 2019, 20 and 21 growing seasons.Chapter 4 data set - Field experiments (Narrabri site) - Data collected during 3-year field experiments to assess crown rot inoculum at different harvest heights and stubble management strategies using stubble from an infected durum crop through a chickpea break crop, with assessment of disease incidence and severity in a final wheat crop at Narrabri, NSW across the 2019, 20 and 21 growing seasons.Chapter 5 data set - Laboratory based microwave dose-response experiments on conidia of B. sorokiniana and macroconidia of F. pseudograminearum and F. cerealis whereby 10 ml spore solutions were microwaved for up to 10 seconds using a domestic 1100 W microwave oven. bytes Chapter 6 data set - Dielectric properties of cereal stubble infected with Bipolaris sorokiniana, Fusarium pseudograminearum and Pyrenophora teres in the microwave frequency range - characterising stubble to explain differences in dielectric responses.Chapter 6 data set - The dielectric properties of wheat and barley stubble with different pathogen loads (Fusarium pseudograminearum, Bipolaris sorokiniana and Pyrenophora tritici-repentis) were investigated at 10%, 15%, 30% and 100% moisture content using an open-ended coaxial probe in a spectral band covering three important industrial, scientific and medical (ISM) frequencies (915, 2450 and 5800 MHz)Chapter 6 data set - Raw data output files for dielectric properties of cereal stubble infected with Bipolaris sorokiniana, Fusarium pseudograminearum and Pyrenophora teres in the microwave frequency range

Is there a disease downside to stripper fronts? Harvest height implications for Fusarium crown rot management

Take home messages • Taller standing stubble allowed vertical progression of the Fusarium crown rot fungus within the stubble after harvest, whilst short stubble prevented further growth (i.e. vertical growth was limited to the height of the cut stubble). • Stripper fronts, which leave higher standing stubble, may increase stubble-borne disease inoculum after harvest of an infected crop, especially if wet fallow conditions are experienced. • In high-risk situations, such as an infected crop with high biomass, cutting the crop shorter at harvest will limit further inoculum development within the stubble after harvest (beyond the levels already present at harvest). • Cutting infected cereal stubble shorter prior to rotation with shorter-stature crops such as chickpea or lentils also prevents the dispersal of infected stubble when harvesting these shorter break crops