Ms Ashmita Lamichhane1, Dr Pippa Michael1, A/Prof. Sarita Bennett1
1Centre for Crop and Disease Management, Curtin University, Perth, Australia
Sclerotinia stem rot (SSR) is a serious disease of canola, causing significant yield loss in years when environmental conditions are conducive. It is caused by the necrotrophic plant pathogen Sclerotinia sclerotiorum, which has a predominately clonal population structure, although there are reports of outcrossing, potentially increasing the genetic diversity and environmental adaptability of the pathogen.
Sclerotia were collected from infected stems in eight canola and one lupin paddock across the WA grainbelt. Mycelial compatibility grouping (MCG) is a phenotypic marker used to characterise diversity in populations of S. sclerotiorum. Mycelial cultures from 40 sclerotia per paddock were tested against 12 reference MCG isolates, along with total number and weight of sclerotia from isolates of each MCG grouping.
More than a quarter of all tested isolates did not match any of the reference isolates. Isolate IX was the only isolate found in all three populations collected in 2018, and Isolate XII was the only isolate found in all four populations collected in 2019. These two isolates were also the most commonly recorded. Isolate IX was found to have high variability in total sclerotia produced, compared the other reference isolates, but had the lowest average sclerotia weight. There were significant differences in sclerotia number and average sclerotia weight between the 12 reference isolates.
The results show the extensive ecological diversity within and between S. sclerotiorum paddock populations, suggesting local adaptation to different environments across the south-western Australian grainbelt. Work is underway to characterise the unknown isolates collected as part of this study.