Project Methodology
Background
Soybean cyst nematode (SCN) is a persistent threat to growers throughout the state of Minnesota. Fields infested with SCN are lower yielding and more susceptible to other disease and pest pressures. Moreover, new SCN isolates increasingly overcome existing resistant varieties. Therefore, novel resistant cultivars are needed to control SCN and provide growers with greater yield stability. A primary objective of the University of Minnesota breeding program continues to be the development of northern-adapted soybeans with robust SCN resistance.
The research in this proposal will enhance SCN resistance in Minnesota germplasm by building on a long and successful record of traditional plant breeding and DNA marker-assisted selection. A robust and high-throughput marker lab helps to increase soybean profitability through better resistant varieties and disease management strategies. Our breeding and genetics work will also result in resistant “pre-breeding” germplasm that can be utilized by the broader public and private breeding communities.
This proposal specifically targets the use of novel sources of SCN resistance for future crosses and variety development. While novel resistance sources have been part of the program for years, this area of research and breeding work will continue to be expanded upon. For example, a series of promising breeding lines that originated from crosses made in 2010 with a new source of SCN resistance – PI 567516C – discovered by Co-PI Dr. Senyu Chen. Breeding lines originating from these crosses were advanced to regional trials and performed relatively well in those trials. The Soybean Breeding Program has expanded the use of these lines as parents to develop new germplasm, target progenies coming from these crosses for advancement, as well as search for better markers that can tag the novel alleles donated from these new sources. Dr. Senyu Chen is continuing his work in discovering new sources of SCN resistance. His laboratory is the only one at UMN with the expertise to phenotype for SCN resistance on a large scale. As co-investigators on this project, Drs. Chen and Lorenz will continue to work together to discover new sources and integrate them into the breeding program. The breeding program is also actively working with the Peking-source of resistance and released two new public Peking varieties in 2023. One of these Peking-type varieties, with strong resistance to the HG Type 2.5.7, is of relative maturity 0.8, making it relatively unique. We have licensed this to private companies for breeding.
Beyond discovery and development, soybean producers need reliable and unbiased information on SCN resistance and performance of currently available commercial and public soybean varieties. The UMN Soybean Variety Trials are conducted each year and consist of ~100 commercial and public varieties evaluated in common tests across four maturity zones in Minnesota. In addition to the yield trials, entered varieties are also tested for resistance to SCN race 3 using greenhouse bioassays. The cost of the greenhouse bioassay raises the entrance fee for the SCN trial to nearly twice that of the entrance fee for the normal variety trial. Because of this increased fee, seed companies have been reluctant to enter varieties into the SCN variety trial. Nevertheless, growers want an unbiased source of information about the SCN resistance of the varieties they are purchasing, and in the past the Council has funded the entrance of commercial varieties into the SCN test.
As interest in non-88788 SCN varieties increases, it is also important to provide unbiased information on the actual effectiveness of these sources to races that can overcome 88788. Dr. Greg Tylka at Iowa State University and Bruce Potter at the UMN Southwest Research and Outreach Center annually compile lists of all commercially available non-88788 SCN resistant soybean varieties. These lists, however, are simply based on claims of the seed companies and no verification of their actual resistance has been reported. We feel it is important to do the hard work and actually test these varieties for their resistance to multiple races of SCN. We successfully did this in past years (2021-23), and would like to repeat this activity in 2024-25. This report (link here) was written and posted online. We only listed the varieties confirmed to be resistant to a HG Type 2.5.7 isolate, but we did find commercial varieties claiming Peking resistance that in fact were not resistant, verifying the importance of this independent screening. We would like to continue this activity to help build a list of verified non-88788 type SCN varieties commercially available. Interest in this report is increasing as evidenced by the increased number of entries.
Approach
1. Continue to develop and deploy DNA markers for SCN resistance.
In 2024, we will continue SCN resistance breeding at roughly the same level of intensity as in past years. This will include at least 40 new crosses between parents with SCN resistance and other desirable traits, and in making the 2024 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 2024.
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 also start to make crosses with breeding lines with PI 90763 in the background, as a recent publication has identified an additional gene in this source that provides robust broad-spectrum resistance.
We will continue to advance non-88788 SCN resistant germplasm through the pipeline by routinely crossing to these sources and tracking inheritance of resistance 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.