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Professor Barbara Howlett
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Each year, Australia’s vital canola industry is threatened by the blackleg fungus, a wind-borne pathogen, which causes the most significant yield loss to canola crops worldwide.
To help predict and prevent disease outbreaks, scientists from the University of Melbourne and Marcroft Grains Pathology at Horsham have developed an extensive disease monitoring and management program funded by the Grains Research and Development Research Corporation.
Professor Barbara Howlett from the University of Melbourne's School of Botany leads this national project and said that although the blackleg fungus can never be eradicated,farmers can stay one step ahead of it.
Each variety of canola (cultivar) has been traditionally bred to incorporate different resistance genes that protect against infection from the fungus, like an internal defence system. But the blackleg fungus can evolve very quickly by gaining, losing or mutating genes at its sexual reproduction stage to overcome these disease resistance genes, allowing it to cause infection.
Professor Howlett said our program is taking a ‘genome to paddock approach’. With our colleagues from State Departments of Agriculture, we monitor the disease at 36 sites across Australia.
“After canola harvesting in November/December, we collect the disease-infested crop stubble, and analyse the fungus to identify disease-causing genes and their mechanism of action,” Prof Howlett added.
Dr Angela van de Wouw, a researcher in Professor Howlett’s lab has devised a clever high throughput method to measure the number of blackleg spores that can cause disease. She places blackleg-infested canola stubble into a wind tunnel that blows the fungal spores onto sticky tape. The genetic material from the fungus is then analysed.
If there is a large increase from the previous year in the frequency of blackleg spores that can cause disease, the team then advises farmers in the regions from where the stubble was collected to grow canola cultivars with different resistance genes.
“The risk of breakdown of blackleg resistance arises when the same cultivar is grown for several years in a row, giving the fungus enough time to adapt and work around canola's genetic defences,” Dr Van de Wouw said.
The researchers observed in late 2011 that although yields were not diminished,commonly grown canola cultivars in the Eyre Peninsula region had high levels of blackleg disease. This region had experienced $30 million in canola crop losses in 2003.
So the team produced a fact sheet for farmers warning them not to grow these cultivars, and recommending alternative cultivars to sow in the 2012 growing season. This advice was taken up widely by farmers and trial sites showed the’ banned’ cultivars suffered severe losses, but the recommended alternative cultivars did not. Calculations from subsequent harvests now show the recommendations saved farmers at least $18 million in crop losses.
Dr Steve Marcroft (a former PhD student of Professor Howlett) the Principal of Marcroft Grains Pathology, who leads the field work, said that farmers are able to make significant changes that help prevent disease outbreaks.
‘Apart from changing the cultivar grown, we have provided guidelines for farmers to implement disease monitoring programs by visually inspecting their crops aswell as planting new crops in a different paddock, at least 500 metres awayfrom last season’s crop.”
“It has also been very encouraging to work with seed retailers who have supported our recommendations to farmers on which cultivars to grow in the next season.”