Story by Ann Y. Robinson
Farmers may soon plant soybean seeds coated with essential oils to prevent crop disease. The biobased pesticides could be cheaper, more effective and friendlier to the environment than most of today’s plant protection chemicals.
Iowa State University’s Leonor Leandro (’02 PhD plant pathology), professor of plant pathology, entomology and microbiology, leads a research group studying the fungal-fighting properties of plant essential oils and how they might be delivered to fields as biopesticides.
"These natural products have an 'oily' appearance and feel, but they are not lipids (fats)," Leandro says. "They are complex, organic compounds with various modes of action. That may be one of their superpowers – pests will likely be slow to develop resistance to them.”
Potent disease fighters
Leandro is pitting the oils against four common soybean diseases: sudden death syndrome (SDS), pythium damping-off, white mold and charcoal rot. Out of 16 plant oils being studied, cassia and cinnamon bark, both grown in Asia, have been the most potent antimicrobials. Even in minuscule amounts, cassia suppressed almost 100% growth of the pathogens that cause these diseases in lab studies and showed promising results in suppressing SDS when applied as a seed treatment in growth chamber studies.
“These results are incredibly exciting, but there is a lot of important work ahead to test effectiveness at the field scale,” Leandro says.
“We have known for a while that essential oils can inhibit some pathogens, which we’re confirming,” she says. “But can the oils be delivered in a way that’s practical and effective? How long will these volatile oils last in the environment? Could they be toxic to nontarget organisms, possibly even to the crop?”
Nanoparticle delivery addresses challenges
Nanoencapsulation – an innovative method of delivering the oil as a seed coating in biodegradable, time-release nanoparticles – could help address many of the potential challenges. This part of the research is led by Carmen Gomes, professor of mechanical engineering, and Cicero Pola, assistant professor of food science and human nutrition. They currently favor a biopolymer coating made from alginate, a gel-forming substance extracted from seaweed. Other materials being considered include chitosan, derived from shells of crustaceans and insects.
The lab and greenhouse tests of the encapsulated oils have gone very well, Leandro says.
“We believe this approach has significant potential to benefit soybean farmers – and may someday be transferable to fighting other diseases and crops,” she says. “We’re anxious to move ahead.”
Learn more about Leandro's research using essential oils to combat soybean disease.
Watch as Leandro explains essential oils' potential for soybean pathogen suppression.