Crop diseases in the GRDC Northern Region cost growers at least $400 million p.a. As growers rely on tighter margins more than ever, effective disease management is a must. With current global and climate change, pathogens affecting crops are changing requiring new management methods to be developed and made available. The project’s research was conducted in several levels, from basic pathogen identification, host range and host-pathogen interaction, novel methods of disease management, to insect-vector investigation and yield loss caused by disease.
The project found that the Fusarium species associated with Fusarium wilt in mungbean are capable of surviving in the asymptomatic roots of other crops, including barley, chickpea, cotton, soybean, and to a lesser extent sorghum. It was also demonstrated that plant growth and pod production was reduced when the Fusarium wilt pathogens infected mungbean when the root lesion nematode, Pratylenchus thornei was also present.
Evidence was provided to show that phytoplasma infection in peanut is a causal agent for symptoms typical of peanut kernel shrivel (PKS), and demonstrated that the leafhopper Orosius orientalis is a vector of the most commonly found phytoplasma species in grain legumes, Ca. P. aurantifolia.
A strong relationship existed between the incidence of charcoal rot and percent lodging, supporting the notion that charcoal rot is one of the causative agent in lodging of sorghum. Low levels of Macrophomina load results to low level of charcoal rot and consequently low level of damage. Variation in the pathogen densities between pre-sowing and pre-harvest soil samples is influenced by location and environmental factors. Rainfall and location were shown to influence lodging rate, and some varieties of sorghum may be less susceptible to charcoal rot than others. While this study has provided useful information, it has highlighted the need for further data collection to be able to develop a reliable disease risk categories based on PREDICTA®B test results and its associated yield loss.
Several indigenous Trichoderma strains have displayed the ability to inhibit mycelial growth of M. phaseolina in vitro. However, in vivo, only one Trichoderma strain showed potential to minimise charcoal rot development as seed treatment. The commercially available Trichoderma-based products evaluated as seed treatment were not able to minimise the sorghum charcoal rot disease. The in vitro bioassay demonstrated the mycelial growth inhibiting ability of different fungicides at varying rates. However, when applied as seed treatment, the fungicides were not able to minimise the charcoal rot infection in sorghum, which can be attributed to the short post-infection activity of the systemic fungicides evaluated. Most Trichoderma strains evaluated for biocontrol mechanisms displayed the antibiosis ability by lytic enzymes, but not as host resistance inducer. Further studies are needed to include other biocontrol mechanisms tests to identify the Trichoderma strains that can potentially be used for biocontrol.
No significant difference among the different M. phaseolina inoculum densities in their ability to cause charcoal rot disease was observed in the 'sick soil method' of inoculation. The 'toothpick method' of inoculation guarantees consistent infection and more disease, while the 'sick soil method' is comparable to natural infections taking place under natural outdoor conditions. However, the inconsistency of the 'sick soil method' in causing infection needs to be addressed. The existence of interactions among the host, pathogen and environmental conditions highlights the need for additional studies to improve the reproducibility of these methods.
In vitro, 30°C is the optimum temperature for growth of most northern region M. phaseolina strains, with some growing well at 40°C and at 15°C mycelial growth is significantly affected. The use of species-specific primers to identify M. phaseolina have shown that they can be used for the selective and specific identification that is rapid, easy, accurate and cost-effective.
The project’s research allowed for a wide range of effective tools and recommendations to be developed. The tools were not just for growers and agronomists, but also for breeding programs, which will benefit growers and other researchers in the future. This provides both immediate and long-term benefits that will provide lasting impact.