In the soil beneath Australian broadacre farms, invisible allies are mounting a defense against one of the country's most costly crop diseases. Researchers at Curtin University have discovered that certain agricultural soils naturally suppress Sclerotinia sclerotiorum, the fungus behind Sclerotinia stem rot, a disease that devastates high-value crops like canola and pulses by causing significant yield losses.
The finding, published in Applied Soil Ecology, challenges the way farmers think about soil—not as inert dirt but as a living biological system teeming with microscopic organisms that can actively protect crops. Dr. Viet-Cuong Han, lead author from the Centre for Crop and Disease Management, and his team identified soils that prevent the fungus from infecting plants and block the germination of its survival structures, essentially choking off the disease before it can take hold.
What makes these soils special is their microbial makeup. When researchers compared suppressive soils with nearby disease-prone soils, they found stark differences in microbial community structure. The protective soils were enriched with naturally occurring biocontrol organisms, particularly bacteria from the genera Bacillus and Streptomyces. These microbes actively antagonize the pathogen, standing guard against infection. In controlled experiments, inoculating normally disease-prone soil with microbes from suppressive soil transferred that protective effect, proving the suppressive power comes from the soil microbiome itself.
Bacillus bacteria emerged as central players in disease suppression, while both Bacillus and Streptomyces reduced fungal growth and disease severity in lab and plant tests. The research even identified previously unknown bacteria from Western Australian soils that fight Sclerotinia sclerotiorum, suggesting these native microbes could become tools for natural disease control. Interestingly, soil chemistry also matters: less acidic soils and those with lower carbon-to-nitrogen ratios proved better at suppressing the pathogen.
"This research shows that soil microbial communities can play a crucial role in limiting disease prevalence," said Professor Sarita Bennett, deputy head of the School of Molecular and Life Sciences. As Sclerotinia stem rot becomes increasingly prevalent in Australian agricultural systems, the economic stakes have never higher.
What sets this work apart is its practical implications. Rather than relying solely on chemical controls, these findings suggest farmers can harness soil biology itself as a defense system. Dr. Han notes that agronomic practices supporting soil health—maintaining organic matter and minimizing unnecessary disturbance—may foster the microbial communities that naturally suppress disease. Understanding which microbes drive suppression and how soil conditions influence them brings sustainable disease management within reach.
The research opens the door to a future where soil microbes serve not just as disease fighters but as biological indicators, helping farmers monitor and optimize soil health. This represents a shift toward working with nature's own systems rather than against them, offering Australian broadacre industries a path to more resilient, sustainable crop protection.