Abiotic conditions governing the myceliogenic germination of Sclerotinia sclerotiorum allowing the basal infection of Brassica napus

Sclerotinia sclerotiorum is the causal pathogen of sclerotinia stem rot (SSR) in canola, causing significant yield losses in this crop globally, when conditions are favourable. The pathogen can cause disease symptoms on canola through ascospore infection from carpogenically germinated sclerotia or by basal infection from myceliogenically germinated sclerotia. While infection through carpogenic germination in canola is the main mode of infection and well-studied, little is known about myceliogenic germination of sclerotia and subsequent basal infection of canola. This review describes the lifecycle of S. sclerotiorum on canola and presents an overview of the current knowledge of the factors that influence myceliogenic germination. These include factors such as sclerotium maturity, rind melanisation, temperature and moisture or a combination of these factors. Subsequently, the most likely avenues of S. sclerotiorum-based basal infection in canola are discussed and compared to basal infection in other host crops. We conclude that myceliogenic germination can be promoted by incubation of sclerotia at extreme temperatures followed by exposure to moisture. Future research to determine the prevalence of myceliogenic germination and subsequent basal infection of canola in the field is required.