Control of phoma stem canker in oil rapeseed crops typically depends on cultivars resistant to L. Maculans, the virus that causes it. Recently, virus populations have overcome resistance, causing serious canker outbreaks in Australia and Europe. There is an urgent need to find sources of resistance to L. maculans. This book synthesizes studies in management of resistance genes control L. maculans, and will stimulate further research on this important model system.