Research Highlights

Determining Organisms that Affect Soybean Seed Quality and Fungicide Efficacy

By Barb Baylor Anderson

Phomopsis seed decay, along with pod and stem blight caused by the Phomopsis/Diaporthe complex, are some of the most damaging diseases affecting soybean seed quality today. The complex causes more losses than any other fungal pathogens worldwide and are particularly harmful in the Mid-South, where farmers have increasingly adopted an early production system.

“Soybean seed quality has become a growing concern, and overhead irrigation and rainfed environments can produce an increase in Phomopsis sp. infection in seed,” says Tessie Wilkerson, Mississippi State University Delta Research and Extension Center assistant research professor and principal investigator for the Mississippi Soybean Promotion Board research. “Seed infection is more severe with early maturing cultivars, when harvest is delayed and when environmental conditions continue to be warm and humid during late season and harvest.”  

Symptoms of disease include shriveled, elongated soybean seeds which appear chalky and have reduced germination and emergence, says Wilkerson. Many variables contribute to post-harvest grain quality, including pathogen and insect damage, grain color, seed size, splits and test weight, and farmers know all can contribute to dockage at the grain elevator. 

Current management strategy includes crop rotation with non-hosts, tillage, fungicide application during pod-fill and limited resistant cultivars. However, information about efficacy of fungicide application and cultivar resistance in commercial soybeans is limited. Wilkerson is exploring what, if any, other organisms contribute to seed quality reduction. She is evaluating whether it is a single pathogen or relationship between one or more pathogens and management methods. 

“The objective is to provide a thorough understanding of the causes of reduced soybean seed quality and potential management options to prevent losses,” she says. “To date, we have isolated several fungi off seed. We are still working on identifying which contribute to a reduction in quality. We know Phomopsis is a player, but I believe there could be others.”

Wilkerson also is early in her research studies to learn about pathogen entry, including from the red banded stink bug. Although increased damage has been previously documented with stink bug feeding, the goal is to determine if there is an increase of fungi colonizing the seed when the red banded are more prevalent. Additionally, she is conducting fungicide sensitivity assays to determine the sensitivity of fungi isolated off seed to several classes of fungicides. 

“I suspect there is resistance among the fungi, but we will see,” she says. “I will still need to figure out how to get chemical to the right spot, seed, pod, leaf or stem to provide protection.”

Another field season in 2021 will allow Wilkerson to look at soybean breeder lines as well to determine which have exhibited any resistance to seed damage. 

“I think at this point, selection of commercial varieties with known tolerance to damage as found in the Mississippi State University Official Variety Trial data, is key for farmers along with scheduling planting and harvest to ensure beans won’t be at risk at remaining in the field after maturity and susceptible to inclement weather which promotes increased damage,” she says.

Published: May 3, 2021