Soybean test weight in relation to genotype, environment, and genotype x environment interaction in the Southern United States

Test weight (TW) is a unit of bulk density that is influenced by several factors, including both genetics and environment. A subset of the trials in the Uniform Soybean Tests-Southern States was used to correlate seed composition traits of oil and protein percentages, and seed weight (SW) with TW to investigate the interaction of these traits in multi-environments for four different maturity group (MG) tests. The results indicate that environment (location and year combination) had a larger impact on TW than genetic effect in all MG tests. This difference was greater in the earlier MGs, compared to MG VI and MG VII. In all tests across four MGs, the genotype interaction with environment effect was significant, but practically was not as important as genotype or environment effects. Significant negative correlations between TW and SW (MG V, VI, and VII tests), and TW and oil (MG V and VI tests) were observed but not consistent in all environments within these tests. TW and protein correlations were inconsistent with a negative relationship in MG V but a positive relationship in MG VII. As anticipated, the inconsistencies in the relationships across MGs for TW and seed composition traits suggest that selection strategies for improving TW will differ across soybean breeding programs. In the future, a similar study using a diverse panel of cultivars that do not change from year to year may shed more light on the influence of seed composition and environmental conditions on TW. Soybean test weights are heritable. Test weight and seed trait correlations differ across maturity groups. Test weight values across Uniform Soybean Test-Southern States were lower than the standard 60 lb bu-1.