Soybean yield has been increased through high planting density, but investigating plant height and petiole traits to select for compact architecture, lodging resistance, and high yield varieties is an underexplored avenue to improve yield.  We compared the relationship between yield-related traits, lodging resistance, and petiole-associated phenotypes in the short petiole germplasm M657 with three control accessions over 2017-2018 in four locations of the Huang-Huai region.  The results showed M657 exhibited stable and high tolerance to high planting density and resistance to lodging, especially at the highest density (8×10⁵ plants ha^-1).  Regression analysis showed that shorter petiole length was significantly associated with increased lodging resistance.  Yield analysis showed that M657 achieved higher yields under higher densities, especially in the north Huang-Huai region.  There are markedly different responses to intra- and inter-row spacing designs among varieties in both lodging and yield related to location and density.  Lodging was positively correlated with planting density, plant height, petiole length, and number of effective branches, and negatively correlated with stem diameter, seed number per plant, and seed weight per plant.  The yield of soybean was increased by appropriately increasing planting density on the basis of current soybean varieties in the Huang-Huai region.  This study provides a valuable new germplasm resource for introgression of compact architecture traits amenable to high yield in high density planting systems and establishes a high-yield model of soybean in the Huang-Huai region.

Phenotypic screening of soybean germplasm suitable for high planting density is currently the most viable strategy to increase yield.  Previous studies have shown that soybean varieties with dwarf features and a short petiole often exhibit a compact plant architecture which could improve yield through increased planting density, although previously reported short petiole accessions were ultimately not usable for breeding in practice.  Here, we established a method to assess petiole length and identified an elite mutant line, M657, that exhibits high photosynthetic efficiency.  The agronomic traits of M657 were evaluated under field conditions, and appeared to be stable for short petiole across seven locations in northern, Huang–Huai, and southern China from 2017 to 2018.  Compared with the Jihuang 13 wild type, the mutant M657 was shorter in both petiole length and plant height, exhibited lower total area of leaf, seed weight per plant and 100-seed weight, but had an increased number of effective branches and the growth period was prolonged by 2–7 days.  Using M657 as a parental line for crosses with four other elite lines, we obtained four lines with desirable plant architecture and yield traits, thus demonstrating the feasibility of adopting M657 in breeding programs for soybean cultivars of high density and high yield.