Strategies to prevent spread of Leptosphaeria maculans (phoma stem canker) onto oilseed rape crops in China.

Field experiments in Europe have shown that Chinese cultivars of winter oilseed rape (Brassica napus) are very susceptible to the pathogen Leptosphaeria maculans (cause of phoma stem canker). Climatic and agronomic conditions in China are suitable for L. maculans since the closely related but less damaging pathogen L. biglobosa occurs on the winter oilseed rape crops there.
Major gene resistance to L. maculans is not durable; when introduced into commercial oilseed rape cultivars it is rapidly rendered ineffective by changes in the pathogen population. The threat to Chinese oilseed rape production from L. maculans is illustrated by the way in which L. maculans has spread into other areas where previously only L. biglobosa was present, such as Canada and
Poland. Models have been developed to describe the spread (in space and time) of L. maculans across Canada, based on survey data collected over a 15-year period in Alberta province. These models have been used to estimate the potential spread of L. maculans across the oilseed rape growing areas of China. Short-term strategies to prevent occurrence of severe phoma stem canker epidemics in China include training of extension workers to recognise symptoms of the disease and use of PCR-based diagnostics to detect the pathogen on imported seed. Long-term strategies include the introduction of durable QTL-mediated resistance to L. maculans into Chinese oilseed rape cultivars as a component of an integrated disease management programme.