Plant roots associate with a microbial community (rhizobiome) composed of a diversity of bacteria and fungi that can benefit plant health or have adverse effects. It is of agronomic interest to characterize rhizobiomes associated with healthy and diseased plants and identify microbes with beneficial effects on plant growth, development, and defense to soil pathogens. Taproot decline (TRD), caused by Xylaria sp., is recognized as an essential soil-borne disease of soybean challenging to control with devastating effects on yield. Therefore, there is a critical need to harness the biocontrol activities of the rhizobiome for controlling TRD. What remains lacking is knowledge on the composition of the rhizobiome of MS-cultivated soybean. Our group's preliminary studies demonstrate that a non-pathogenic strain of Fusarium oxysporum has a significant growth-enhancing and Xylaria-inhibitory effects in cotton and soybean.

Moreover, we initiated a comparative study to identify microorganisms associated with healthy soybean roots and quantify Xylaria's effects on rhizobiome composition. Our long-term goals are to discover and deploy management techniques that lead to improved soybean growth and higher yields. We aim to understand the diversity of rhizobiome microorganisms that cause specific phenotypes in soybeans, test rhizobiome isolates for beneficial activities, and utilize this knowledge to establish methods for improved growth and biological control of soil pathogens. At the completion of the proposed research, our expected research outcomes are to have characterized a library of microorganisms for biocontrol effects and to have designed a method for TRD control in the field. These results are expected to have a substantial positive impact because they will provide evidence and proof-of-principle for the future development of synthetic rhizobiomes for targeted use against soil pathogens, ultimately providing new opportunities to enhance crop production.

Objective 1: Identify rhizobiome microorganisms with inhibitory activity on Xylaria growth
Objective 2: Characterize the rhizobiome communities of the healthy and diseased soybean to quantify the impact of Xylaria infection on the composition and structure of soybean rhizobiome.
Objective 3: Evaluate the biocontrol activity of rhizobiome microorganisms against soybean taproot decline in the field.

1. Oral and poster presentations at regional and national conferences of the American Pathological Society (APS) and American Society of Plant Biologists (ASPB)
2. Journal publications at the completion of the project in APS and ASPB journals.
3. Ph.D. and Master Dissertations (electronically accessible through MSU Library), as well as the Executive Summary of the Theses and Dissertations.
4. We are posting research results and conclusions of the proposed study through the MSPB website (www.mssoy.org), MSUES website www.Mississippi-crops.com and MS LandMarks.

Taproot decline of soybean is widespread throughout MS. With the current understanding of the biological properties of the pathogen, Xylaria sp, we can now address the challenges of TRD management. An alternative disease management approach is to discover and deploy management techniques that lead to improved soybean growth and higher yields. We will characterize the diversity of rhizobiome microorganisms that cause specific phenotypes in soybeans, test rhizobiome isolates for beneficial activities, and utilize this knowledge to establish methods for the biological control of TRD. These results are expected to have a substantial positive impact on TRD management because they will provide evidence and proof-of-principle for the future development of synthetic rhizobiome communities for targeted use against Xylaria sp., ultimately providing new opportunities to enhance soybean production in MS by reducing TRD incidence.