Soybean Disease Worries

Study Finds Soybean Seeds Carry Fungal Pathogens

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Before soybean seeds even hit the ground, they may carry fungal species capable of causing soybean diseases, according to new research from Kansas State University. (DTN photo by Pamela Smith)

ROCKVILLE, Md. (DTN) -- You couldn't see them, but there may have been some unwelcome passengers in the bags of soybean seed you planted this spring.

A recent study from Kansas State University found that soybean seed samples collected across Kansas contained fungi capable of producing soybean diseases, such as the Fusarium species.

Some of those fungal strains found in the seeds were especially ominous, noted Kansas State University plant pathologist Chris Little, who oversaw the research.

"We've found that some isolates of the Fusarium species commonly found in soybean seeds are resistant to commonly used fungicide active ingredients," Little told DTN.

The finding raises concerns about the role that widespread fungicide seed treatments may play in the development of fungicide resistance, Little noted.

FUNGAL STOWAWAYS

Led by graduate student Rodrigo Pedrozo, the Kansas State research team pulled more than 400 samples of soybean seed from soybean fields in 11 locations around Kansas from 2010 to 2012.

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In the laboratory, the seeds revealed a surprising amount of fungal stowaways. In particular, Fusarium species were present in the internal seed tissues of 100% of the samples, and some of those strains were capable of causing soybean diseases.

"We did not determine how the fungi got into the seed," Little said. "It is possible that these fungi, which are present in soil and crop debris, are introduced into the flower and pod during development, [but] this is not known."

Nor can the researchers be sure that the amount of fungal pathogens within the seed could cause problems.

"The question is not only if the pathogen is present in the seed, but is it there at a high enough level to actually become a pathogen when the seed is planted," Little said. "In other words, can it cross the threshold from being a harmless resident of the seed 'mycobiome' to being a pathogen that causes seedling damage?"

THE QUESTION OF RESISTANCE

At least some of the Fusarium species found in the soybean seeds proved resistant to common fungicides.

"For example, 20% of the Kansas isolates of Fusarium proliferatum that we've tested, another common soybean seedborne fungal pathogen, are resistant to fludioxonil at some level," Little said. Fludioxonil is a common fungicide included in many seed treatment packages.

Fungicide use has risen dramatically in the past decade, both in foliar applications and seed treatments, which are applied to the majority of all corn and soybean seed planted in the U.S.

The fact that fungal pathogens might be present before a treated seed even hits the ground raises the specter of large-scale selection for fungicide resistance, Little said.

"[Just as] the overuse of antibiotics in clinical settings has increased the prevalence of resistant bacterial strains, the overuse of seed treatment fungicides may change the proportion of fungicide-resistant seedborne pathogens in the mycobiome over time," he explained.

You can read more about Little and Pedrozo's research, which was funded by the United Soybean Board and the North Central Soybean Research program, here: http://bit.ly/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

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Emily Unglesbee