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Yellow Spot of Wheat

Yellow spot is a fungal wheat disease caused by the necrotrophic pathogen Pyrenophora tritici-repentis (Ptr). It is a global problem, and results in severe economic damage. In Australia it is arguably the most costly disease to the wheat industry, with wheat yield losses due to yellow spot estimated at $212 million per annum with control measures estimated at $463 million per year (Murray and Brennan 2009).

Our goal is to help minimise the cost of this disease to growers, through the use of molecular techniques targeting the mechanisms of pathogenicity and by developing tools for breeders to produce more resistant varieties.

More about the Yellow Spot team:
◾We are a well-funded research group within the Centre for Crop and Disease Management with access to excellent facilities.
◾We are proud to be the first research team in the world to create a gene deletion strain of the tan/yellow spot pathogen.
◾We have recently launched a national campaign called Stop the Spot to promote widespread sample collection and help us develop tools for breeders.
◾We were selected as finalists for the 2014 Eureka Science Prize in Sustainable Agriculture.

Our research covers multiple areas and encompasses a broad range of techniques and skills. These include molecular biology/biochemistry, genetics, metabolomics, bioinformatics and field work. Examples of our ongoing projects include:

Discovery of necrotrophic fungal effectors
Ptr thrives on dead cells. It secretes necrotrophic effectors (host-selective toxins) in order to kill the wheat tissue upon which it feeds. The most well-known tan spot effector is ToxA, which is found in approximately 80% of Ptr isolates worldwide.

Our goal is to discover new effectors which contribute to the fungal infection process. We are using various approaches to tackle this, including genomics, proteomics, transcriptomics, metabolomics and genetic manipulation. Purified effectors can then be supplied to breeders to utilise in their wheat breeding programs. Currently, we supply Australian wheat breeders with approximately 30,000 doses of purified ToxA each year for germplasm screening. As a result, wheat varieties with improved resistance to yellow spot are adopted by growers. Our work is already saving growers an estimated $50 million p.a. in yield and $24 million in fungicide application as ToxA insensitive cultivars are adopted. These figures are expected to rise further as additional effector insensitive varieties are released.

Genetic analysis of disease resistance
Presently, the majority of wheat varieties grown in Australia are susceptible to yellow spot. Since resistant wheat varieties offer the only real long-term solution, our aim is to map wheat susceptibility genes. We are achieving this through QTL identification and the development of molecular markers, in order to breed out effector susceptibility.

Isolate diversity

Another area of interest to us is the extent of yellow spot isolate variation. We are assessing genetic diversity and determining virulence variation through disease assays. This will help to determine how the pathogen is evolving and enable us to be best placed to combat it.

A mature lesion of yellow spot on wheat

Fruiting bodies on wheat stubble