A ‘genome to paddock approach’ to
controlling blackleg of canola
Dr Angela Van de Wouw
Angela Van de Wouw
School of Botany, the University of Melbourne and
Marcroft Grains Pathology, Horsham
Wed, 1 May
Forgan Smith Building #1, UQ St Lucia
Room E303 (see map below)
Time: 12 midday
Dr Angela Van de Wouw obtained her PhD in genetics from the University of Melbourne in 2005. Since graduating she has been based at the School of Botany, the University of Melbourne working with Professor Barbara Howlett looking at control strategies for blackleg disease of canola. Her research is funded through the Grains Research and Development Corporation.
Brassica napus (canola) cultivars and isolates of the blackleg fungus, Leptosphaeria maculans interact in a ‘gene for gene’ manner whereby plant resistance (R) genes are complementary to pathogen avirulence (Avr) genes. Avirulence genes encode proteins that belong to a class of pathogen molecules known as effectors, which includes small secreted proteins that play a role in disease. Leptosphaeria maculans undergoes sexual recombination prolifically and populations can rapidly adapt to selection pressures imposed by the host, such as exposure to resistance conferred by single or major genes. This situation increases the frequency of virulent isolates and can cause resistance to break down. Accordingly resistance can be ‘overcome’ within a few years of release of a variety. For example, in 2003 after two seasons of extensive sowing, blackleg resistance of particular varieties broke down in the Eyre Peninsula, South Australia, causing 90% yield losses and withdrawal of these varieties from sale. This provided a unique opportunity to look at changes in the fungus during extreme selection pressure and determine strategies to control this disease.
In glasshouse and field trials we have shown that sowing canola cultivars with different complements of resistance genes in subsequent years (rotation of resistance genes) minimises disease pressure. This is because the frequency of virulence alleles of avirulence genes corresponding to particular resistance genes decreases. In 2012 we used this information to avert a breakdown of disease resistance in the Eyre Peninsula by advising farmers to change the canola varieties that they had sown for the previous two years. By switching varieties, not only have local farmers saved $18 million in yield losses, but seed companies have been able to sell these varieties in other canola-growing regions, where resistance breakdown was not predicted. This is a ‘win-win’ situation for farmers and seed companies.
With the completion of the genome sequence of L. maculans we now have a better understanding of how this fungus evolves so quickly. The avirulence genes of the fungus are embedded in gene-poor, repeat rich regions allowing them to be easily mutated, lost or gained. We have shown that this genomic environment and exposure to resistance genes in B. napus can affect evolution of the linked avirulence genes which has strong implications for management strategies such as ‘rotation of resistance’. Using this ‘genome to paddock’ approach we are developing management strategies for farmers to control this devastating disease and to avoid breakdown of resistance.