Using a systems approach to investigate the efficacy of a disease rating system for Sclerotinia stem rot in canola

Sclerotinia stem rot (SSR), caused by the necrotrophic fungus Sclerotinia sclerotiorum, is a major, but unpredictable disease of canola in Australia. However, there is no disease rating system for current canola varieties. Over the last four years the most common varieties of canola grown in Western Australia were assessed in the field using natural disease occurrence, and in glasshouse experiments using manual inoculations, to determine their susceptibility to SSR. The results highlighted the complexity and unpredictable nature of SSR with infection levels and varietal response varying depending on seasonal conditions and time of infection, despite limited levels of genetic resistance to SSR in current varieties. It is suggested that a disease rating system should not be based purely on inseason plant infection, but should also include potential for future infections through the contribution of sclerotia from infected plants to the system.