Soybean yield has traditionally 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 option for further improving yield.We compared the relationships between yield-related traits,lodging resistance,and petioleassociated phenotypes in the short petiole germplasm M657 with three control accessions during 2017–2018 in four locations in the Huang–Huai region,China.The results showed that M657 exhibited stable and high tolerance to high planting density and resistance to lodging,especially at the highest density(8×105 plants ha–1).The regression analysis indicated that a shorter petiole length was significantly associated with increased lodging resistance.The yield analysis showed that M657 achieved higher yields under higher densities,especially in the northern part of the Huang–Huai region.Among the varieties,there were markedly different responses to intra-and inter-row spacing designs with respect to both lodging and yield that were related to location and density.Lodging was positively correlated with planting density,plant height,petiole length,and number of effective branches,but negatively correlated with stem diameter,seed number per plant,and seed weight per plant.The yield of soybean was increased by appropriately increasing the planting density on the basis of the current soybean varieties in the Huang–Huai region.This study provides a valuable new germplasm resource for the introgression of compact architecture traits that are amenable to providing a high yield in high density planting systems,and it establishes a high-yield model of soybean in the Huang–Huai region.
Stem growth habit is an important agronomic trait in soybean and is subject to artificial selection. This study aimed to provide a theory for genotypic selection of stem growth habit for breeding purposes by analyzing the alleles of Gm Tfl1 gene in Chinese soybean varieties and establishing a database of Gm Tfl1 variation. Using knowledge of insertion and deletion(Indel) in the non-coding region and four single-nucleotide polymorphisms(SNPs) in the coding sequences of the Gm Tfl1 gene, four CAPS and one Indel markers were developed and used to test 1120 Chinese soybean varieties. We found that the dominant Gm Tfl1 allele was prevalent in accessions from the Northern ecoregion, whereas the recessive allele, Gmtfl1, was more common in the Southern ecoregion, and the proportions of Gm Tfl1 and recessive alleles were respectively 40.1% and 59.9% in the Huang-Huai ecoregion. The proportion of Gm Tfl1 decreased and that of Gmtfl1 increased, gradually from north to south. Allele Gm Tfl1-a was present in higher proportions in the Huang-Huai spring, Huang-Huai summer, and Northern spring sub-ecoregions than that in the other sub-ecoregions. Gm Tfl1-b was common in the Northeast spring, Northern spring and Southern summer sub-ecoregions. Gmtfl1-ta was found mainly in the Huang-Huai spring,Huang-Huai summer and Southern spring sub-ecoregions. The Gmtfl1-ab allele was distributed in all six soybean sub-ecoregions. The Gmtfl1-bb allele was distributed mainly in the Huang-Huai spring and summer and Southern spring and summer sub-ecoregions,but the Gmtfl1-tb allele was detected only in the Huang-Huai summer sub-ecoregion. The distributions of Gm Tfl1 and Gmtfl1 have shown no large changes in nearly 60 years of breeding, but the frequency of the recessive genotype Gmtfl1 has shown a rising trend in the last 20 years. This study provides a theoretical foundation for breeding new soybean varieties for different ecoregions.
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.
