Strategies to increase durability of host resistance for effective control of phoma stem canker on oilseed rape

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Phoma stem canker, caused by the fungal pathogen Leptosphaeria maculans, is a damaging disease on oilseed rape in the UK, causing annual yield losses > £100M despite use of fungicides costing £20M. With recent loss of the most effective fungicides (e.g. Punch C) through EU legislation and predicted global warming, potential yield losses will increase. Use of host resistance to control this disease is becoming ever more important. However, new sources of resistance are often rendered ineffective due to pathogen population changes. The aims of this project are to monitor the emergence of new virulent races of L. maculans and to develop new control strategies to increase durability of host resistance. To maintain effectiveness of cultivar resistance against L. maculans, this project will use molecular technology to investigate the differences between different regions in distribution of virulent races of L. maculans in populations assessed from spore samples and from crop plant samples. Results will be used to guide deployment of cultivars with suitable resistance for the region where the corresponding avirulent pathogen races are predominant. Resistance against L. maculans relies on major resistance (R) gene-mediated qualitative resistance and minor gene-mediated quantitative resistance. The fungus L. maculans has high evolutionary potential to overcome host resistance. Resistance can be rendered ineffective in 2-3 years due to L. maculans population changes from avirulent to virulent. This project will investigate the molecular events leading to virulent mutations in L. maculans by exploiting new genomic information about L. maculans. Modelling work shows that the range and severity of phoma stem canker will increase under predicted global warming. To investigate the effects of environmental factors (e.g. temperature) on operation of different R genes for resistance against L. maculans, severity of phoma stem canker on cultivars with different R genes will be assessed in field experiments in different regions (i.e. different environments) and in controlled environment experiments at different temperatures. Recent work showed that R gene-mediated resistance against L. maculans (an apoplastic pathogen) operates by recognition of pathogen effectors through receptor-like proteins (RLPs). The sequences of R genes stable at increased temperatures and the genome sequences of host Brassica napus and its related species B. rapa and B. oleracea will be used to identify candidate R genes coding for RLPs. New knowledge obtained from this project will be used to develop strategies to improve control of phoma stem canker by using effective cultivar resistance. Improved control of this disease will benefit growers by reducing yield losses. It will also address the challenge of food security. The environment will also benefit from reduced use of fungicides.