Summary:
Farmers have raised concerns that test weight is on a long-term decline. In the early 1900s the test weight of soybean was standardized as 60lbs/bu, and it is still the standard today. According to the U.S. Soybean Quality Annual Report, based on a four-year average from 2017-2020, the actual test weight of the crop is now only 56.7lbs/bu. Determining what factors impact test weight and how to obtain a test weight of 60lbs/bu in soybean is the premise of this project. Since lower test weight means fewer beans in a given volume, lower test weight decreases processing efficiency for crushers and can lead to inferior animal feed quality. With test weight on a slow decline and one region of the U.S. already averaging 54.7lbs/bu, it is urgent to address this issue. Research on increasing test weight may also be tied to seed composition traits, e.g., protein and oil contents. The goal of this research is to identify management and genetic factors that can reverse the decline in test weight. We will determine the impact of increased test weight on seed protein and oil contents, nutritional quality and develop breeding strategies which will simultaneously incorporate improved test weight and optimum protein and oil contents into high yielding varieties.
Accomplishments:
1) Multiple lines were identified that yielded >97% of the commercial checks and had a stable and high-test weight (~58lb/bu). 2) New advanced elite lines were evaluated for yield, agronomic traits, seed composition, seed size, and test weight to determine the relation of test weight to seed size, seed quality, protein and oil content, sucrose concentration, amino acid content and yield. The DNA from these lines have been extracted and are being genotyped using SoySNP6k Infinium chips to understand the genomic regions controlling the test weight. 3) A GWAS analysis identified five genomic regions for test weight. Four genomic regions were found for seed size, all with small effects. One region for test weight overlapped with seed size, indicating seed size influences test weight. 4) Another GWAS was used to identify one SNP each for seed size, oil, and protein content that demonstrated a significant association with test weight in multiple years. In total, we found 13 QTL regions for seed index, 9 QTL regions for oil content, and 15 QTL regions for protein content that were associated with the trait in multiple environments in the current study or found in at least one environment in the current study and in other publications. Data analysis is ongoing to identify other seed characteristics outside of protein and oil, that have an impact on test weight. 5) To better understand the relationship of test weight with genetic differences between varieties and environment data collected from >100 lines (MG IV-VIII) grown across >30 locations for two years were analyzed and reported as the TW Data Set (TWDS). 6) The results of the TWDS revealed a significant negative correlation between TW and seed size (MGs V-VII), and TW and oil (MG V -VI) was observed but was impacted by environment. 7) Environment was shown to have a larger impact on TW than genetic effect in all MGs, but more significant in earlier MGs (IV-V). 8) The relationship between TW and protein was inconsistent across MGs, which further suggests environment has an effect on test weight. 9) Preliminary results infer there was a significant interaction between variety and harvest time for MG IV and no significant interaction between variety and harvest date in MG V. 10) Multiple breeding populations are being advanced with high test weight, which are expected to produce >500 new breeding lines that will be grown in progeny rows for selection in 2024. 11) A manuscript was submitted to a peer reviewed journal for publication. 12) Results were presented at field days and scientific meetings to show our work to local farmers, researchers and industry personnel.