The fungicide knocked back many fungi, but again, not Septoria. Mideros thinks the fungicide removed Septoria's competitors, allowing the pathogen to flourish.
The surprising result calls into question the common practice of yield-protective fungicide application.
"Based on previous research, we know when we spray a lot of fungicide, like every week, the symptoms of Septoria are kept in check and yield increases," Mideros says. "But that application frequency isn't feasible for farmers. This study is a closer approximation of what producers actually do, with one to three applications during the season.
"I'm not saying fungicide wouldn't increase yield in some fields. It might. But what I'm getting out of this study is that we don't know exactly what we're doing when we apply fungicides to protect yield. We need to learn a lot more about the unintended effects of chemical applications. We could be doing things more effectively if we had a better understanding of all the changes to the systems when we do a fungicide application."
Although the jury's still out on whether producers should shelve the fungicide when battling Septoria, the study provides an important look at how the soybean mycobiome interacts. The researchers identified a total of 3,342 distinct fungi on the three soybean lines they studied, some pathogenic, others beneficial, and still more whose effects on soybeans haven't been characterized.
Knowing what fungi are on each soybean line and how they interact could pave the way for future disease-fighting tools, such as biocontrol agents.
"One of the things we were trying to address with this analysis was to see which fungi are associated with each other. If we found patterns where one fungus seemed to have a suppressive effect on another, it could be used as a biocontrol agent. We did find some negative associations, but not many, and unfortunately, none with Septoria," Mideros says. "But there are several organisms that have a negative association with other fungi, so it's something we could follow up on.
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