Effect of Population Size on Genome-Wide Association Study of Agronomic Traits in Soybean

Soybean is increasingly becoming one of the main oilseeds crops in Kazakhstan, with a major growing area in the south-eastern part of the country. The comparative assessment of small-size (108) and medium-size (276 accessions) collections of soybean originated from five regions of the world was made in field trials in Almaty region (south-east of Kazakhstan). The full collection was genotyped using the Illumina iSelect 6K SNP (single nucleotide polymorphism) array that allowed observation of 4651 polymorphic SNPs. The genome-wide association study (GWAS) was conducted using the following six important agronomic traits: flowering time, seed maturation time, plant height, number of fertile nodes, number of seeds per node, and thousand seed weight. In total, GWAS using TASSEL package identified 56 stable QTNs (quantitative trait nucleotdies) for all the studied traits, including 42 QTNs detected using the medium-size collection. It was shown that the medium-size population, in comparison with the small-size population, was preferable for the detection of significant associations. A comparative analysis of the data with previously published results suggested that 36 of the stable 56 QTNs were presumably novel associations. The revealed QTNs can be used in the molecular breeding projects for soybean yield improvement.