Moving Toward a Solution to Taproot Decline of Soybean

In late summer of 2014, the MSPB became aware of a new fungal malady that was affecting soybeans in fields throughout Mississippi. The presence of this new disease on a widescale basis in Mississippi was first noted by crop consultants, and their keen observations were responsible for the recognition that this was a potential problem that warranted immediate attention.

In response to this occurrence, the MSPB requested a proposal from MSU research and extension specialists and pathologists. MSU scientists Maria Tomaso-Peterson, Tom Allen, and Trent Irby subsequently submitted a research proposal titled “Identification and characterization of ‘mystery disease’ pathogen that is prevalent in Mississippi soybean fields in 2014". The proposed project was accepted and funded in Oct. 2014. Its objectives were to 1) identify the fungal pathogen associated with taproot decline [TRD (agreed-upon name of this new disease based on the appearance of root symptoms)], 2) assess pathogenicity of the recovered fungi, and 3) determine the potential yield loss associated with TRD. Prior to this action, the above scientists/specialists had already begun collecting plant samples from infected fields so they would have material to work with subsequent to the hoped-for funding. The project was extended through March 2016, at which time a report was received describing the progress to that point.

In April 2016, the MSPB funded a continuation of the above project, with the new title “Characterization of soybean taproot decline; a new disease in Mississippi soybean production fields”. The objectives of this project were to 1) confirm Xylaria sp. as the pathogen responsible for TRD, 2) characterize the life cycle of Xylaria sp. and the disease cycle of TRD, and 3) complete a phylogenetic analysis with isolates of Xylaria sp. collected from TRD throughout Mississippi soybean production fields. A product from this research is a publication titled “First description of the causal agent of taproot decline of soybean, an emerging disease in the southern United States” that appeared in Vol. 18, p. 35-40 of Plant Health Progress in 2017. This is the first report of a species of Xylaria causing disease in soybean.

In February 2017, the MSPB funded a continuation of this project, but with new objectives to 1) apply various laser scanning microscopy methods to study the colonization and infection process of the TRD pathogen, 2) identify the growth stage at which the soybean plant is most susceptible to infection by TRD, and 3) develop a screening method to determine host tolerance among soybean varieties to isolates of the TRD pathogen. The ultimate goal of this phase of the TRD project progression is to provide sufficient information to develop approaches to manage/mitigate this new disease.

The progress resulting from this series of projects is an example of how various members of the state’s consultant, extension, and research community worked together to identify a problem, propose and conduct a concerted effort to find its cause, and develop a solution. The MSPB is pleased that its funding provided/is providing the resources needed to initiate and continue this progression of projects that will provide a direct benefit to the producers who contribute to the soybean checkoff in Mississippi.

Composed by Larry G. Heatherly, July 2017, larryheatherly@bellsouth.net