Fungal species can help control major soybean pest

Experts have identified a fungal species that has the potential to control the soybean cyst nematode (SCN), a pest that devastates soybean crops worldwide. The presence of the fungus Funneliformis mosseae was found to reduce the number of juvenile nematodes by more than half.

The SCN is a parasitic roundworm that attacks the roots of soybean plants and sucks out the nutrients. In the United States alone, these pests cause annual yield losses of more than $1 billion.

Glen Hartman is a researcher for the Department of Agriculture at the University of Illinois at Urbana-Champaign. 

“Soybean cyst nematodes survive in the soil as eggs in cysts,” said Hartman. “The eggs hatch at the start of the growing season, and the juveniles penetrate root tissue and migrate into the plant’s vascular system. The females find a feeding site and stay there for the rest of their lives. They take nutrients away from the soybean plant, which reduces plant productivity.”

In previous studies, scientists have determined that fungi which form symbiotic relationships with plants can influence parasitic nematodes like SCN. According to Hartman, the effectiveness of using these “arbuscular mycorrhizal fungi” varies from study to study, so growers are reluctant to embrace the fungi as a method of control.

“In this study, we focused on five different species of arbuscular mycorrhizal fungi to see if they differed in their ability to protect soybeans against SCN,” said study author and graduate student Michelle Pawlowski.

The researchers used greenhouse experiments to introduce young soybean plants to fungi and SCN. The study revealed that five different fungal species were successful in reducing the number of SCN cysts in the soybean roots. 

The most effective fungus was Funneliformis mosseae. Soybean plants introduced to F. mosseae were found to accumulate an average of 10 cysts per plant. By comparison, soybean plants that were not inoculated with fungi developed at least 75 cysts. Hartman explained that each cyst may contain hundreds of nematode eggs.

“We found that as early as seven days after inoculation, roots that were inoculated with F. mosseae were colonized with significantly fewer nematode juveniles,” said Pawlowski.

“To see if this interaction and suppression might occur even earlier, we incubated SCN eggs in sterile water alone, with fungal spores or with exudates of the fungal spores. These exudates are microbes and molecules secreted by the spores.”

According to Pawlowski, the research demonstrates that the fungal spores and their exudates undermine nematode egg hatching. “If we can find out what function or compound from the fungi is suppressing egg hatching, that could potentially be a useful nematicide.”

The study is published in the journal Plant Disease.

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By Chrissy Sexton, Earth.com Staff Writer