As cover crops become more adopted through Illinois soybean fields, it is essential to investigate how SCN populations respond to cover crops species and varieties. The objectives of this project are to, investigate the impact of cover crop species and varieties on SCN populations under field conditions, use metagenomics to study further how cover crops may potentially affect SCN populations and provide information regarding SCN management to Illinois soybean growers.

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the major plant-parasitic nematode in US soybean production. SCN causes losses of up to 60% in susceptible cultivars, and often losses of up to 30% occur without showing noticeable aboveground symptoms. SCN has been consistently listed as the number one pathogen causing yield losses to Illinois farmers over the past decades.

In Illinois, SCN is present in more than 80% of the fields and every county. SCN demonstrates the ability to survive in fields for years without growing soybean. Therefore, once SCN is identified in an area, management practices that maintain populations under the damage threshold will help farmers maximize yield and profitability.

A large fraction of the genetic resistance available in commercial varieties is currently derived from the same source (PI-88788), which has already led to the selection of SCN populations able to reproduce on these varieties. Management practices such as crop rotation and cover crops may help manage these resistant populations and all the benefits to soil health and erosion control.

Growers integrate cover crops in soybean production systems to reduce soil degradation and improve soil chemical, physical and biological properties. As cover crops become more adopted through Illinois soybean fields, it is essential to investigate how SCN populations respond to cover crop species and varieties across different Illinois locations. Looking into SCN populations in the long-term research field will also better simulate growing conditions experienced by Illinois growers.

The objectives of this project are to i) investigate the impact of cover crop species and varieties on SCN populations under field conditions; ii) use metagenomics to study further how cover crops may potentially affect SCN populations; iii) provide information regarding SCN management to Illinois soybean growers.

Proposed methods/tactics:

1 - Field selection: Cover crop trials established across Illinois will be selected for this study. Information on field history, experimental design, and availability was collected from over 15 projects across Illinois. Fields with a minimum of three replicates and a non-cover crop check will be selected for potential use. The population densities of SCN will be determined at all locations. The researchers will use these densities to select 5 locations for repeated sampling in this project.

2 - Soil Sampling: Soil samples will be collected at four-time points: 1- in Fall 2022, at cover crop planting; 2- at soybean planting in April/May 2023; 3- at mid soybean season in August 2023; 4- after soybean harvest in September/October 2023. Ten to twelve soil cores 15.24 cm (about 6 inches) deep from each experimental plot will be collected from each time point.

3 - SCN Counts and Data Analysis: The number of SCN cysts and eggs will be assessed from each soil sample using standard SCN counting methods. Samples will be shipped to the University of Illinois Plant Clinic for SCN counts. All soil samples collected will be stored appropriately for future metagenomics studies.

4 - Metagenomics analysis: Selected field locations with contrasting differences in SCN egg densities between cover crops will be selected for a metagenomic study. This approach will allow us to identify potential mechanisms of SCN suppression and how specific cover crops affect the soil.

We previously used metagenomics to investigate the suppression mechanisms of SCN by wheat. A similar metagenomics pipeline will be used for this study.

Project outcomes: One outcome is a summary of most (if not all) cover crop research projects that are being managed via universities and funding agencies in the state of IL. This will be a resource that will be continuously updated and will benefit researchers and ISA. A second outcome will be the determination of how various cover crops and their production strategies will impact SCN and the microbial communities in these fields.

Communications plan: We will work closely with ISA to catalog cover crop resources in Illinois and promote the research findings. We will also disseminate the results through conference presentations, journal articles, and releases to the farming industry and consultants.

In Illinois, SCN is present in more than 80% of the fields and every county. SCN demonstrates the ability to survive in fields for years without growing soybean. Therefore, once SCN is identified in an area, management practices that maintain populations under the damage threshold will help farmers maximize yield and profitability.