Breakdown of Major Gene Resistance to Blackleg

The Australian canola industry has minimised losses due to blackleg by sowing varieties with polygenic resistance. In 2000, the first canola cultivar incorporating a major gene for blackleg resistance was released onto the Australian market. The major gene was introgressed from Brassica rapa subsp. sylvestris and provided almost complete immunity to infection and thus cultivars with this resistance source were widely adopted by growers. In 2003 these cultivars had yield losses of up to 90% in some regions, whilst cultivars with polygenic resistance were unaffected. Both the speed and widespread nature of the resistance breakdown suggested that isolates able to attack sylvestris-derived cultivars have always been in the population but due to selection pressure from a major resistance gene are now present at a high frequency. This is supported by our findings that isolates cultured 20 years ago can cause stem cankers on these cultivars. To develop effective disease management and for breeders to keep up with changes in blackleg populations, it is important to understand how the fungus overcomes resistance and to develop strategies for deploying different resistance genes into Australian canola cultivars. This project aims to

This project will be pursued in collaboration with Thierry Rouxel and Mylene Balesdent, INRA, Versailles, France who have characterized an avirulence gene of L.maculans corresponding to LmR1 resistance gene of Brassica napus.