The Australian canola industry has averaged 3.5 million tonnes each year over the past 5 years, with exports resulting in $1.6 billion annually. In addition to direct profits, canola is an essential part of the cropping system, providing significant yield benefits through the control of diseases and weeds for subsequent cereal crops. The main limitations to expansion and threats to the canola industry are from diseases, especially those caused by fungi. Fungal diseases such as blackleg and Sclerotinia Stem Rot (SSR), can cause significant yields losses to Australian growers.

The blackleg fungus (Leptosphaeria maculans) is a sexually reproducing pathogen that continuously overcomes resistance bred into cultivars and in recent years has developed fungicide resistance. The canola industry recognises that continual management of blackleg is required to sustain the canola industry. Annually blackleg disease is estimated to cause 10% yield loss, and epidemics such as 2003 on the Eyre Peninsula, have resulted in up to 90% yield losses. Recently, new symptoms have been detected for blackleg, termed upper canopy infection, which is causing an additional 20% in yield losses annually. Blackleg disease can be minimised through the use of cultural practices, such as avoidance of last year’s stubble, genetic resistance and fungicide controls.

The research we focus on is a three-pronged approach: genetic resistance, cultural practices and fungicide regimes. Our research also investigates the interactions between these approaches and provide knowledge across a wide range of environments, differing canola intensity and varying farming systems.

All research is carried out in collaboration with other agencies including the University of Melbourne, CSIRO, University of Western Australia, Department of Primary Industries and Regional Development (DPIRD), Australian breeding companies and chemical companies.

Genetic resistance to blackleg 

There are two types of resistance to blackleg: major gene (qualitative) and quantitative resistance. Major gene resistance occurs in a gene-for-gene manner whereby for each resistance genes in the plant there is a corresponding avirulence gene in the fungus. When effective, major gene resistance prevent the fungus from entering the plant, providing complete resistance. However, when cultivars with major gene resistance are grown widely, the fungal population can evolve, resulting in an increase in frequency of virulent isolates, and the major gene resistance can be overcome. This has happened twice in Australia on the Eyre Peninsula; the breakdown of sylvestris- resistance in 2003 and the breakdown of LepR1 resistance in 2012.

Quantitative resistance is much more poorly understood, as rather than providing complete protection it minimises the damage caused by the pathogen. This type of resistance is generally expressed in the crown or base of the plant.

Our research includes; 

• classification of all commercial cultivars into resistance groups based on their major gene complement (see the resources section for more information) 
• determining the overall blackleg rating of all commercial cultivars, which encompasses both major and quantitative resistance (see the resources section for more information) 
• monitoring fungal populations for changes in virulence and providing advice to industry regarding the effectiveness of resistance at a regional level (see the resources section for more information) 
• identification of avirulence and resistance genes and the development of associated molecular markers 
• developing tools for understanding the genetics of quantitative resistance 

Cultural practices for minimising blackleg 

Blackleg disease can be minimised using cultural practices such as isolation from last years stubble and rotation of different resistance genes in space and time. However, with increased canola production isolation from the previous year’s stubble is becoming more challenging. Furthermore, with improvements in technology, such as satellite-guided tractors, stubble management and retention have changed dramatically in the farming system. These changes have resulted in stubble being conserved for longer periods of time, with standing and lying stubble left in the paddock and breaking down at different rates.

Our research includes; 

• Determining the impact of standing versus lying stubble on spore production and spore release 
• Determining the impact of standing versus lying stubble of stubble load and stubble breakdown 
• Determining the impact of changes in spore release patterns on disease epidemiology. 

Fungicide use and fungicide resistance 

Fungicides have become an integral part of disease management for blackleg. Seed-dressings and fungicide-amended fertilizer are routinely used by most growers. In addition, foliar fungicide applications at the 4-10 leaf stage or the 30% bloom spray (see upper canopy infection section) are becoming more common in high-disease pressure years. Until recently, all fungicides belonged to the DMI class of fungicides, however, in the past few years SDHI and strobilurin fungicides have also been released. With the heavy use of fungicides, fungicide resistance is a potential problem for Australian growers.

Our research includes; 

• Developing recommendations on when to use foliar fungicides to gain an economic return 
• Screening for fungicide resistance to all commercially available fungicides 

Upper canopy infection 

Canola is now being sown earlier, and therefore flowering earlier, to prevent drought-stress due to poor rainfall during the spring. This earlier flowering time has resulted in crops flowering during July-August and therefore being exposed to ascospore showers. As a result, blackleg is now infecting the flowers, pods, upper stem and upper branches of the canola plants, collectively termed upper canopy infection.  

Our research includes; 

• Identifying fungicide strategies for minimising the impact of upper canopy infection 
• Identifying management strategies such as the use of genetic resistance, to minimise the impact of upper canopy infection 
• Developing phenotyping techniques for screening for potential resistance to upper canopy infection