Soybean cyst nematode (SCN) is a persistent threat to growers throughout Minnesota. Fields infested with SCN are more susceptible to other disease, pest, and environmental stresses. Moreover, some parts of Minnesota have seen a breakdown in varietal resistance, with the appearance of new SCN races capable of overcoming the widely grown 88788 source of resistance. Developing new germplasm with alternative forms of resistance to combat resistance breakdown for long-term success is an important function of the public sector breeding efforts. With this in mind, our overall objective is to advance the development of SCN-resistant soybean varieties as well as provide accurate and unbiased sources of information on the resistance of commercial soybean varieties. Our specific aims are to: 1) Enhance the efficiency and efficacy of breeding for SCN resistance through the deployment of DNA markers linked to major genes conferring SCN resistance; 2) Advance new sources of SCN resistance and expand the use of these new sources for crossing in the breeding program; 3) Conduct SCN bioassays on commercial varieties entering the 2020 UMN Variety Trials, as well as all non-88788 commercial SCN varieties available to Minnesota growers.

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

Details of the ongoing activities at the University of Minnesota can be found in the quarterly reports. As a summary, some metrics that describe our accomplishments towards breeding SCN resistant varieties and germplasm include:
1) 15 new crosses made in 2020 that specifically target incorporation of 88788-type rhg1 SCN resistance (the number of crosses is actually much lower than we normally make as a result of the COVID restrictions in 2020).
2) 2064 F4 plants were genotyped for rhg1, and 928 of these plants were selected and harvested. The remaining families will be genotyped in the plant rows next year. This year we made a big step forward and transitioned from genotyping F4:5 families after F4 plant harvest to genotyping F4 plants directly. We are working to increase the efficiency of this and hopefully can genotype twice as many plants next year.
3) 1144 new SCN breeding lines were grown in plant rows; 310 breeding lines carrying 88788-type resistance were tested in preliminary yield trials in MGs ranging from late 00 to late I.
4) 125 breeding lines carrying 88788-type resistance were tested in advanced yield trials.
5) 20 breeding lines carrying 88788-type resistance were tested in the first year of regional trials.
6) 18 varieties were tested in advanced regional trials for their second, third or fourth year.
7) Breeder’s seed was created for two new SCN resistant varieties, and release decisions are awaiting 2020 yield data summaries.
8) 15 SCN-resistant varieties were released in the form of invention disclosures and seed transferred to two different private companies. Licensing and crossing rights pending negotiation.
9) One new variety with SCN – MN1901CN – was publicly released by the UMN Variety Review Committee in December of 2019.

Objective 2. Advance and expand new sources of SCN resistance

Regarding breeding with novel sources of SCN resistance, our program continues to aggressively create new breeding populations from which we plan on deriving breeding lines. In summary, we made 6 new crosses involving a novel SCN resistance source in 2020. Regarding breeding lines, our pipeline is progressing nicely. In 2020, we planted 1337 new breeding lines into plant rows that descended from crosses involving a new source of SCN resistance. Of these 1337 plant rows, 587 were selected based on visual characteristics. We also advanced 17 F4 populations and 11 F2 populations involving novel SCN sources.

An exciting development this year is the yield performance of a new advanced UMN breeding line with Peking-type SCN resistance, M13-250056. This variety has performed well in yield trials and continued to do so in 2020 based on preliminary test results. Below are the results from the 2019 regional trials. Note that this line has resistance to HG Type 2.5.7 whereas all others do not.




Objective 3. Conduct SCN testing on commercial varieties entered into the UMN Variety Trials.

Twenty-nine commercial and public varieties were entered into the 2020 UMN SCN Variety Trials. These varieties were screened for SCN resistance using a greenhouse bioassay as described in the proposal. Results have been summarized and published at www.soybeans.umn.edu. This year all varieties were verified to be resistant to race 3 SCN.

Another thing we committed to in 2020-21 was to screen all commercially available non-88788 varieties using a bioassay with races 3 and 14. We have identified a list of these varieties and are in the process of acquiring seeds from seed companies for the screening. We expect the screening to occur early in 2021.

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

View uploaded report

The research contained within this proposal addresses three areas targeted by the Production Action Team’s mission statement: (1) Plant breeding and genetics; (2) Molecular breeding and functional genomics; (3) Soybean cyst nematode (SCN). The work we propose aims to increase soybean yield and profit potential by providing growers with a broader range of variety options with stable or enhanced yield even in fields infested by SCN. To increase the utility of our work, we are introducing novel sources of resistance into Minnesota soybeans, combining SCN resistance with other marketable traits, and making our germplasm available to the broader community to catalyze additional variety development for the future benefit of Minnesota growers. We will also provide an unbiased source of information on the SCN resistance of commercially available varieties. This is particularly important for the non-88788 varieties, which have not been verified in this way before.