Well, the answer is simple, and is the same way weed seeds also survive for years in the soil. Thanks to new CCDM research, we can now confirm that sclerotia have adapted to Australian grainbelt paddock conditions, allowing us to adjust recommendations for more effective disease management.
In a recently published paper, our team looked at the conditions needed to “precondition” sclerotia in the non-cropping season (ie. over summer) to become ready to germinate and produce apothecia (the little pink mushrooms that produce the ascospores) when the rains come.
Researcher Dr Pippa Michael said by treating local sclerotia from Western Australia (WA) with temperatures ranging from 4°C to 50°C, the team could test whether the globally reported preconditioning temperature treatment of 4°C was necessary to ensure maximum apothecia production in Australia.
“Interestingly, what we found in WA was the reverse – hot temperatures of 50°C were needed, and were in fact a prerequisite, for maximum apothecia production – while cool precondition temperatures of 4°C caused very little germination of apothecia,” she said.
“We can now see that sclerotia have adapted in the same way a weed or pasture species have adapted to our conditions; instead of responding to chilling as it would during a winter fallow in a northern hemisphere cool temperate climate, they respond to hot temperatures during a summer fallow in a southern hemisphere warm temperate climate.”
According to co-researcher Associate Professor Sarita Bennett, this finding is essential, as it means researchers can now refine predictions of disease behaviour, leading to more accurately informed management strategies for growers.
“We’re now really getting to know this fungal pathogen and how adaptable it is to our conditions – it wasn’t long ago this pathogen was a big question mark, but slowly we are piecing together how it works and how we can manage it,” Sarita said.She said with no resistant canola varieties currently available, growers rely on cultural and chemical methods as the main strategies for management of sclerotinia stem rot.
“But cultural practices are also coming under pressure, with a tightening of canola rotations as well as a decline in stubble burning under no-till farming systems, leading to a build-up of sclerotia that can survive up to eight years in the soil,” she said.
“Time is of the essence with this disease, we need to find new ways to help farmers manage it.”
How did they do it?
The team collected sclerotia from five wheatbelt canola paddocks, located in Greenough, Beverley, Toodyay and two in Kojonup. The sclerotia were then preconditioned at temperatures of 4°C, 20°C, 35°C, field and 50°C for durations of 30, 60 and 120 days.
When the team conditioned sclerotia for 60 days at 50°C, on average 70% of sclerotia germinated producing apothecia, as opposed to less than 40% at 4°C (see graph below).
“Sclerotia preconditioned at 4°C had lower germination than our control, indicating chilling is not a requirement for these WA isolates,” Pippa said.
“However, when we preconditioned sclerotia at 50°C, we had the highest proportion of sclerotia germination.”
About the team
Pippa is a WA local who grew up on a farm and has a PhD on agro-ecology of marshmallow weed. She started with Curtin as a research fellow in 2007 working on weed ecology before moving to CCDM in 2016 focusing on sclerotinia stem rot on canola and weed diseases.
Sarita has a background in pasture science and has been with the CCDM since 2015. Here, Sarita works together with Pippa on sclerotinia stem rot research, looking to improve options for farmers to reduce the impact of this disease. Sarita balances her canola disease and management research with her role as Discipline Lead for Curtin University’s Agriculture and Food and Agribusiness Course Coordinator.
To read the full paper, Impact of Preconditioning Temperature and Duration Period on Carpogenic Germination of Diverse Sclerotinia sclerotiorum Populations in Southwestern Australia, click here