Invasion by Leptosphaeria maculans (phoma stem canker on brassicas): from genome to worldwide crop

Leptosphaeria maculans and L. biglobosa, which cause phoma stem canker disease, are related pathogens of brassicas that were originally considered as one species but occupy slightly different ecological niches and are now reproductively isolated. Globally, the invasion by the more damaging L. maculans into areas where only L. biglobosa was present occurred in North America in the 1980s and Eastern Europe in the 1990s, whereas there are still areas of the world, such as China, where only the less damaging pathogen L. biglobosa is present. The threat to Chinese oilseed rape production from L. maculans was assessed by using models developed to describe the spread (in space and time) of L. maculans across Alberta, Canada. In addition, the worldwide population of L. biglobosa is much more variable than that of L. maculans. Further evidence is provided by the massive invasion, dated 5-20 million years ago, of the genome of L. maculans by only a few repeated element families. 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 and exploitation of new genomic information about L. maculans and L. biglobosa as a component of an integrated disease management programme