Research Highlights

Research Highlights
Increasing Genetic Diversity, Yield and Protein of U.S. Commercial Soybean Germplasm

Seed quality of experimental line DS25-1 compared with a commercial check.

By George Graef, University of Nebraska-Lincoln

The ability to improve soybean qualities by breeding new varieties depends upon sufficient genetic diversity. The U.S. soybean commercial germplasm currently contains just 17 accessions that contribute nearly 90% of the genes. With 45,000 soybean accessions available in world collections, and more than 22,000 in the USDA Soybean Germplasm Collection, making intelligent choices about which soybean plant introductions (PIs) will best contribute to enhancing yield and compositional quality is crucial. In addition, strategies and germplasm that will complement and enhance commercial breeding efforts for the long term must both be developed. Besides limitations on increasing yield, the narrow genetic base of soybean affects potential improvements in seed composition and other traits.

The general negative correlation between yield and seed protein concentration resulted in a protein decrease of about 2 percentage points over the last 85 years of breeding, with associated increases in seed oil concentration and yield. Unless breeders refocus efforts on protein concentration and overall balance of soybean seed composition, this decrease in seed protein concentration will likely continue, to the point where U.S. soybean is at a disadvantage in the global marketplace.

It is not sufficient to increase seed protein concentration alone without considering the correlated changes that occur to seed oil, soluble carbohydrates and other traits. Soybean processors expect 10 to 12 pounds of oil per bushel of soybean, and need to produce a soybean meal with 48% protein (47.5% to 48.5% to allow for measurement error). However, there is a wider range of soybean seed protein and oil concentrations that will result in the desired products. Therefore, estimates of seed protein, oil and carbohydrate concentrations must be considered, as well as processed yield of seed oil and 48% protein meal per bushel.

This comprehensive and coordinated $524,867 program includes applied development efforts to transfer genetically diverse, high-yielding lines with an improved nutritional bundle to commercial partners. It includes basic research to identify genes and gene functions related to seed composition, and especially to high protein.

Figure 1. Seed protein and oil concentration values that will produce a 48% protein meal (shaded tan area). Processed oil yields of 10 and 12 pounds per bushel are shown by the dashed horizontal lines (From Brum, et al., 2005). Historical USA averages are shown in black circles for 1986-2004. The red star shows the USA 2004 average. Filled circles show Diversity Protein Tests averages for 2016 (green), 2017 (blue) and 2018 (purple). In 2017, a low-protein year overall, the high-yield checks in the USDA URT MGII, III and IV are shown in yellow circles — none made a 48% protein meal. The average of entries in the 2018 Diversity Protein Tests (purple circle) have greater value compared with the USA 2003, 2004 and long-term averages, producing at least a 48% protein meal, with higher yield and higher oil percentage. That’s progress!

This project had four major objectives.

  1. Use novel PI accessions from the USDA Soybean Germplasm Collection for yield improvement to develop and release soybean lines with significantly increased genetic diversity, greater productivity, higher seed protein concentration and improved nutrition bundle. Industry partners are involved for wide-area cooperative evaluation throughout Maturity Groups 0, I, II, III, IV and V.
  2. Identify and characterize candidate genes for the large-effect quantitative trait loci (QTLs) on Chr 15 and Chr 20, to evaluate the effects of gene candidates in different genetic backgrounds in greenhouse and field environments. Analyze the genetically diverse germplasm developed by all cooperators for allele status at the Chr 15 and Chr 20 QTLs.
  3. Characterize protein composition, amino acid profiles and soluble carbohydrate composition of seeds from developed high-protein, high-yield lines from diverse G. max accessions and of selected experimental extreme high-protein lines from long-term selection programs.
  4. Increase genetic diversity, seed composition and seed quality in the early-planting soybean production system (ESPS) in southern U.S. production areas.

This project will broaden the genetic base of U.S. soybean to allow sustained, long-term improvements in both yield and quality by encouraging the active introgression of novel soybean germplasm into soybean variety development programs. Because many of these diverse soybean accessions held by the Collection are not adapted to the U.S., and have not been improved upon by modern breeding, a large portion of the material resulting from these crosses is currently not suitable for modern production. Through screening and selection, breeding lines with high value in both yield and quality can be identified. After these germplasm enhancement activities, a critical action will be to share this germplasm with the seed industry through germplasm exchange and cooperative testing programs. This public-private sector partnership will advance long-term diversification of the breeding germplasm of U.S. soybean, and ultimately help deliver ever higher-yielding varieties with enhanced seed composition profiles.

The project is well on its way to success. The 2019 Diversity Cooperative Tests included 340 candidate varieties tested at 20 unique sites spread across seven states. Through cooperative testing with the university, USDA and industry partners, several new breeding lines in all maturity groups were identified that are superior both in terms of yield and expected meal protein relative. Some of these breeding lines are entered into USDA Uniform Soybean Tests, and have shown superior yield and composition compared with the high-yield checks in those tests. Significant progress has been made for improved yield and seed quality in the South, with high-yielding lines similar to commercial checks and a 75% reduction in monetary losses from seed quality issues.

This work has already led to new high-yielding, high-protein breeding lines that collectively include 72 new soybean accessions in their pedigrees, representing a four-fold increase in the number of accessions underlying the U.S. soybean genetic base. These new lines are being transferred to commercial companies with material transfer agreements. In the long term, these efforts are crucial and will continue to expand the genetic base of elite U.S. soybean, allowing for sustained, long-term success and profitability for U.S. soybean producers far into the future. Continued partnership with the seed industry through cooperative testing and germplasm exchange will remain a cornerstone of this project.

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.