1. Continue to develop and deploy DNA markers for SCN resistance.

In 2021, we will continue SCN resistance breeding at roughly the same level of intensity as in past years. This will include at least 50 new crosses between parents with SCN resistance and other desirable traits, and in making the 2021 crosses, we will specifically emphasize parents carrying novel resistance sources distinct from PI 88788.
In addition to variety breeding, we will continue to pursue “parent building” because some of the novel resistant parents are simply too exotic to be used directly in variety development. As a result, we hope to create semi-adapted SCN resistant lines that are stable and promising – and in this way – useful for subsequent crosses by us and other breeding programs.
Based on crosses made in earlier years, we will examine lines that reach the F4 generation for the presence of target SCN resistance genes through the use of proven DNA marker technology. Plants that are selected will be planted into “plant rows” where agronomic traits and yield begin to be systematically screened. We expect to screen approximately 4000 F4 plants using DNA markers. As we have in the past, we will continue to increase the efficiency of this screen. In 2020, we moved to single-plant screening using a more efficient marker assay. Will continue to build upon this advancement in 2021.

2. Advance and expand new sources of SCN resistance

Nearly all resistance sources carry the major gene Rhg1 – though different resistant parents carry different versions of this critical gene. PI 88788 is by far the most common source of one version of this resistance gene. Our current DNA marker technology successfully differentiates these different versions of the Rhg1 gene from one another. At the same time, an exciting novel resistance source, PI 567516C, carries a second SCN resistance gene on a separate chromosome and we have previously created a DNA marker system to follow the inheritance of this second important gene.

We will continue to advance non-88788 SCN resistant germplasm through the pipeline by routinely crossing to these sources and tracking the resistant using molecular markers in the breeding pipeline. Once the best performing breeding lines are advanced to regional trials, they will be screened for resistance to HG Type 2.5.7, the type of SCN that typically breaks down the 88788 source of resistance.

3. Conduct SCN testing on commercial varieties in UMN Variety Trials.

Each year the UMN Soybean Breeding Program conducts the MN Statewide Variety Trials (soybeans.umn.edu). This year we will test all newly entered commercial soybean varieties for resistance. Last year only 29 commercial varieties were entered into the regional trails, but years past suggests this number can range from 29 to 100. We will budget for screening 50 entries and fill entries from other tests if necessary. Bioassays are conducted using an HG Type 0 (Race 3) SCN population. Each container is inoculated with 4000 SCN eggs. Female index values are scored after 30 days. Results from these trials are reported in the Soybean Field Crop Trials Results published by the Minnesota Ag Experiment Station and provide an unbiased source of information allowing growers to evaluate the level of SCN resistance in their varieties.

As last year, we will work with Bruce Potter to identify all non-88788 SCN varieties currently on the market and test them with a bioassay using multiple SCN races to determine whether these varieties truly have broad resistance. We will obtain seed from as many of these varieties as we can and bioassay them using SCN races 3 (HG Type 0) and race 1 (HG Type 2.5.7). Results will be made available on www.soybeans.umn.edu as well as through MinnLine.

Update:
Soybean cyst nematode is the number one pest of soybean, causing large yield reductions wherever it is present in the soil. By far and away the best tool for ameliorating yield losses from SCN is to plant soybean varieties with genetic resistance. Development of varieties with strong resistance is not an easy task as SCN resistance screening is expensive and laborious. It is even possible that commercially available varieties claiming to have SCN resistance do not in fact have such resistance, or the resistance is only moderate. On top of all this, the most commonly deployed source of resistance – 88788-type resistance – has been in use for several decades. Reports of resistance breakdown have become increasingly common in Minnesota, and it is expected the situation will become rapidly worse. New sources of resistance are needed to sustain soybean production.

The research conducted as part of this proposal addresses all three of the above-mentioned issues. Firstly, this project funds the deployment of molecular markers that assist in the selection of SCN resistance. Each year, the UMN Soybean Breeding program screens 3000 – 5000 breeding line candidates for resistance, thus greatly enriching the probability an advanced variety has SCN resistance. During 2021, we made sure that all breeding crosses made contained SCN resistance, a scenario made possible only through these molecular markers. We are also converting many food-type varieties to having SCN resistance, and are having some success: one new natto cultivars with SCN resistance is on the foundation seed increase stage and has been sent out to several potential commercial partners for evaluation. Another SCN-resistant natto breeding line is in its final stages of field evaluation. Overall, the deployment of these methods made possible by this project has made it much more likely for released and licensed lines to have SCN resistance.

An important component to the UMN Variety Trials partially made possibly by this project is the screening of commercial and public varieties for SCN resistance using a greenhouse bioassay. This was again conducted in 2021 by screening 22 commercially available varieties. Of these 22, all were indeed resistant or moderately resistant except for one, which was found to be moderately susceptible. This result, and those in the past, highlight the need to independently screen commercial varieties for resistance to important pests such as SCN so growers are ensured they are getting what they are paying for. Results of this test are posted at soybeans.umn.edu. This past year we expanded this activity to testing non-88788 varieties for their resistance to other races that overcome the 88788-type of resistance. In 2021, we were able to secure seed of just 13 varieties. Of these varieties, eight were resistant to race 1, but four were found to be susceptible. This is important information for growers as they make variety selections for their farms. The report was published and can be found here: https://blog-crop-news.extension.umn.edu/2021/09/soybean-varieties-with-non-88788-scn.html. We are repeating during the summer of 2022. We requested several more non-88788 source SCN resistant commercial soybean varieties near the end of this grant period, and are currently working on completing the agreements for seed transfer. Any new cultivars found to be resistant will be added to the published list.

The incorporation of new sources of resistance into elite varieties adapted to Minnesota is an ongoing long-term process. Nevertheless, it is an important endeavor to help assure that such varieties exist in the future. We have continued to make new breeding populations with new sources of SCN resistance, which will be important sources of new varieties in the future. During the last year of funding, we make breeder’s seed of two new public Peking-type varieties with good resistance to evolving populations of SCN. Foundation seed is being produced in 2022, and seed has been sent to potential commercial partners for licensing. One variety is a 0.8 RM, which will be useful for northwestern MN as very few non-88788 SCN resistant varieties are commercially available. We only know of one or two

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