A Sclerotinia disease assay for screening flowering canola plants in controlled environments

Sclerotinia sclerotiorum is an important fungal pathogen of canola, for which limited host resistance or tolerance has been identified. Several robust seedling-based S. sclerotiorum disease assays have been developed for germplasm screening, but there is no non-destructive, reliable and routine assay for screening mature, flowering canola plants at the developmental stage when disease symptoms are predominant under field conditions. Disease measurements from field trials are the most informative, but such trials are time consuming and require screening across multiple locations and years to take into account variable disease expression due to different pathogen inoculum levels and environmental factors. We developed a disease assay for screening mature canola plants under controlled environment conditions that ensures consistency in disease results between experiments. The method involves applying petals, dipped in a broth containing S. sclerotiorum mycelia, to the leaves of canola plants at the 10-30% bloom stage. The inoculated plants are then housed in a chamber wrapped in plastic sheeting until assessment, and kept well-watered to ensure high humidity (> 70% relative humidity) and temperature conditions (> 10 A degrees C) which favour disease development. The method is an effective disease assay for measuring the foliar effects of S. sclerotiorum with leaf lesion formation developing in > 94% of inoculated plants. Within 21 days, in 64-68% of cases these leaf lesions developed into stem lesions and associated sclerotia.