New research has discovered some agricultural soils can naturally suppress one of Australia’s most damaging broadacre crop diseases
Researchers from Curtin University have found some soils can inhibit the infection and survival of the fungus responsible for Sclerotinia stem rot, a disease which causes significant yield losses in broadacre crops such as canola and pulses.
Lead author Viet-Cuong Han, from the Centre for Crop and Disease Management, says the study highlights the role of soil as a living biological system, rather than a passive growing medium.
“We identified a soil that naturally suppresses Sclerotinia sclerotiorum by preventing the fungus from infecting plants and by inhibiting germination of its survival structures in the soil,” Han says.
“In field conditions, by comparing a suppressive soil with a nearby disease-conducive soil, we found clear differences in microbial community structure.
“Suppressive soils were enriched with well-known naturally occurring biocontrol organisms, particularly bacteria from the genera Bacillus and Streptomyces.”
Han also says the microbes actively ‘antagonise’ the pathogen.
“This suppressive effect is driven by the soil microbiome – the community of microscopic organisms living in the soil – and under controlled and experimental conditions the effect can be expressed in soils that are normally conducive to disease, by inoculating the conducive soil with the microbiome from the suppressive soil,” he says.
Han adds the research showed Bacillus bacteria are central to disease-suppressing soils, while both Bacillus and Streptomyces help stop fungal growth and reduce disease in lab and plant tests.
“The study also identified bacteria from Western Australian soils that had not previously been shown to fight Sclerotinia sclerotiorum, suggesting that disease-suppressing soils could be a source of native microbes that may be helpful to control crop disease,” Han says.
“We also found certain soil properties were linked to disease suppression, with less acidic soils and those with lower carbon-to-nitrogen levels better able to suppress the pathogen.”
These findings open the door to future disease management strategies that work with soil biology rather than relying solely on chemical control.
“Agronomic practices that support soil health — such as maintaining soil organic matter and minimising unnecessary disturbance — may help support microbial communities associated with natural disease suppression,” Han says.
“Understanding which microbes are responsible, and how soil conditions influence them, brings us closer to managing disease through biology.
“Ultimately, this work supports the possible future use of soil microbes as indicators and tools for more sustainable management of Sclerotinia stem rot and other soil borne crop diseases.”
