Increasing the Value of Soybean through Breeding for Improved Seed Protein Content and Optimizing Production Practice

The protein within the soybean seed provides much of the value of the commodity. Soybean produced in the North Central and Western portions of the United States experience lower seed protein compared to soybean grown in other parts of the country. Given the value of the grain is driven, in part, by protein content, producers and processors in this region are adversely affected. Increasing soybean seed protein content through breeding has shown to be effective, however, often at the cost of overall grain yield and oil content. To address this issue, the University of Minnesota soybean breeding program initiated a project to increase seed protein content through introgressing high seed protein alleles from the Glycine max plant introduction PI153296 into the Minnesota adapted cultivar 'Evans'. Through four generations of successive backcrossing, protein content was increased and yield was maintained. Although oil content was diminished, this combination of high protein and high yield within breeding lines is appealing within the target geography. QTL mapping was carried out to identify the genomic regions contributing to seed composition traits and yield. The primary driver of seed protein was found to derive from the previously reported QTL region on chromosome 20. Enabled through the genetic characterization of the USDA-GRIN soybean collection with the Soy50KSNP assay and previous genomic characterizations of this region, a comparison between recurrent parent and donor line indicate that the polymorphic segments in the region are contained to two of the five delineated haplotype blocks.;Additionally, much variation exists in the literature for soybean yield response to seed/plant density. One likely contributing factor to this variation is the discontinuity of experiments targeted at addressing this question across the soybean agronomic research community (e.g. research is generally carried out on a state by state basis). Other factors such as the environments and geographies evaluated, the specific cultivars studied, and the cultural practices implemented in the experiments also contribute to this variability. A driving force behind this report was to bring a group of soybean production specialists across the United States together to address this fundamental question of optimum plant density with an experimental design that was consistent across the entire range of environments sampled. We hypothesized that soybean yield response to plant population will differ depending on cultivar maturity and latitude and that adapted, full-season cultivars would require a reduced plant density to achieve maximum yield relative to short-season cultivars. To test our hypotheses, we evaluated soybean yield response to seeded density and harvested plant density for full-season and short-season cultivars across 59 environments distributed across the United States from 30.2° to 47.8° N. latitude. We observed that full-season cultivars yielded greater than shorter-season cultivars at 23 of the 25 environments that showed a significant yield difference (alpha = 0.05) for cultivar maturity. However, short-season cultivars can achieve comparable yields when seeded at higher densities compared to full-season cultivars. We observed more northerly locations to require greater plant densities to achieve 95% of asymptotic yield (Y95%) compared to southern environments.