Soil microbiome inhibits white mold in agricultural crops

Researchers at Curtin University have identified agricultural soils with a natural capacity to suppress Sclerotinia sclerotiorum, a fungus that causes white mold. The disease causes losses in extensive crops, such as canola and legumes. Their study showed the action of the soil microbiome against plant infection and against the germination of the pathogen's survival structures.

The research compared a suppressive soil with a nearby soil favorable to the disease. Scientists observed differences in the structure of the microbial communities. The suppressive soil showed a greater presence of biocontrol organisms, especially bacteria of the genera Bacillus and Streptomyces. These microorganisms acted as antagonists to the pathogen.

Samples collected

The work assessed Sclerotinia sclerotiorum in canola, in samples collected near Kojonup, Western Australia. Scientists used samples from a canola area with a history of disease suppression, from a neighboring area conducive to the disease, and from an area of ​​remnant vegetation. Collections took place in October 2022, at a depth of zero to ten centimeters.

In bioassays, canola seedlings grown in suppressive soil showed less disease progression. Metabarcoding data from ITS also detected a higher abundance of Sclerotinia sclerotiorum. In conductive soil, the rate was higher than in suppressive soil. Carpogenic sclerotia germination fell to 29,9 percent in suppressive soil. Conductive soil recorded 59 percent. Remaining vegetation soil recorded 75,7 percent.

Biological origin

The results also indicated a biological origin for the suppression. Heat treatment of the suppressive soil at eighty degrees Celsius for sixty minutes reduced its control capacity. Mixing the suppressive soil with a conductive soil reduced infections in seedlings. Mixing two conductive soils did not produce the same effect.

According to Viet-Cuong Han of the Centre for Crop and Disease Management, the study shows the soil as a living biological system. The researcher stated that the team identified a soil capable of preventing plant infection and inhibiting the germination of the fungus's survival structures.

Microbiome analysis

Microbiome analysis indicated Bacillus as a keystone taxon in suppressive soil. The genus had a relative abundance of 28,1 percent in this soil, compared to 20,3 percent in conductive soil and 0,4 percent in remnant vegetation soil. Suppressive soil also had a higher abundance of Neobacillus, Nitrososphaera, Candidatus Nitrocosmicus and Geodermatophilus.

Scientists also found a higher presence of fungal genera associated with biocontrol in suppressive soil, such as Trichoderma, Chaetomium, Humicola and Coniothyrium minitans. Among the bacteria and archaea, the phylum Firmicutes showed the greatest abundance in the suppressive soil.

Cultivation and antagonism assays confirmed a higher number of bacteria with biocontrol action. Species of Bacillus and Streptomyces. They reduced fungal growth and decreased disease in plant tests. The study also identified previously unreported bacteria from Western Australian soils that were effective against the fungus Sclerotinia sclerotiorum.

Chemical and physical properties

Chemical and physical properties were also associated with suppression. The data linked higher pH and lower carbon:nitrogen ratio with a greater capacity to suppress the pathogen. Suppressive soil was also associated with greater water retention capacity and higher total organic carbon in the study analyses.

For the researchers, the results create a basis for microbiome-guided management strategies. Agronomic practices focused on soil health, such as maintaining organic matter and reducing unnecessary disturbances, can favor microbial communities linked to natural suppression. The work also points to the future use of soil microorganisms as indicators and tools in the management of white mold and other soil diseases.

Further information can be found at doi.org/10.1016/j.apsoil.2025.106722