Genome-wide association analysis is a powerful approach to identify the causal genetic polymorphisms underlying complex traits. In this study, we evaluated a population of 191 soybean landraces in five environments to detect molecular markers associated with soybean yield and its components using 1,536 single-nucleotide polymorphisms (SNPs) and 209 haplotypes. The analysis revealed that abundant phenotypic and genetic diversity existed in the studied population. This soybean population could be divided into two subpopulations and no or weak relatedness was detected between pair-wise landraces. The level of intra-chromosomal linkage disequilibrium was about 500 kb. Genome-wide association analysis based on the unified mixed model identified 19 SNPs and 5 haplotypes associated with soybean yield and yield components in three or more environments. Nine markers were found co-associated with two or more traits. Many markers were located in or close to previously reported quantitative trait loci mapped by linkage analysis. The SNPs and haplotypes identified in this study will help to further understand the genetic basis of soybean yield and its components, and may facilitate future high-yield breeding by marker-assisted selection in soybean.

Phosphorus deficiency is a primary constraint to soybean productivity in acid and calcareous soils. Our aim was to map quantitative trait loci (QTL) controlling phosphorus deficiency tolerance using 152 recombinant inbred lines derived from a cross between the P stress tolerant variety Nannong94-156 and the P stress sensitive variety Bogao.

Salt stress is an important factor affecting the growth and development of soybean. The inheritance and expression of traits associated with salt tolerance during the seedling stage are complex. The present study was conducted to identify quantitative trait loci (QTLs) associated with salt tolerance during seedling growth in soybean. Field and greenhouse experiments were conducted to evaluate 184 recombinant inbred lines (RILs) derived from a cross between Kefeng No. 1 and Nannong1138-2 for salt tolerance and QTLs that are associated with salt tolerance. The molecular map of this RIL population, covering 2625.9 cM of the genome, converged into 24 linkage groups and consisted of 221 SSR markers and 1 disease-resistant gene (Rsc-7). QTL mapping was conducted using WinQTLCart. Eight putative QTLs significantly associated with salt tolerance were identified. One QTL was identified both in field and greenhouse experiments. In the field, salt tolerance was assessed (tolerance rating, TR) visually on a 0 (death) to 5 (unaffected by salt stress) scale. Three QTLs were detected on two linkage groups explaining 7.1–19.7% of the total phenotypic variance for salt tolerance. In the greenhouse, plant survival days (PSD) and percentage of plant survival (PPS) under salt stress were measured. Six QTLs were detected on six linkage groups, and explained 7.8–19.2% of total phenotypic variation for salt tolerance. A major QTL was identified between markers Sat_164 and Sat_358 on linkage group G in both the field and greenhouse. This QTL qppsN.1 was identified in the same location as a salt tolerance QTL previously reported in soybean. The detection of new QTLs will provide important information for marker-assisted selection (MAS) and further genetic studies on salt tolerance in soybean.

Water soluble protein content (SPC) plays an important role in the functional efficacy of protein in food products. Therefore, for the identification of quantitative trait loci (QTL) associated with SPC, 212 F(2:9) lines of the recombinant inbred line (RIL) population derived from the cross of ZDD09454 × Yudou12 were grown along with the parents, in six different environments (location × year) to determine inheritance and map solubility-related genes. A linkage map comprising of 301 SSR markers covering 3,576.81 cM was constructed in the RIL population. Seed SPC was quantified with a macro-Kjeldahl procedure in samples collected over multiple years from three locations (Nantong in 2007 and 2008, Zhengzhou in 2007 and 2008, and Xinxiang in 2008 and 2009). SPC demonstrated transgressive segregation, indicating a complementary genetic structure between the parents. Eleven putative QTL were associated with SPC explaining 4.5-18.2 % of the observed phenotypic variation across the 6 year/location environments. Among these, two QTL (qsp8-4, qsp8-5) near GMENOD2B and Sat_215 showed an association with SPC in multiple environments, suggesting that they were key QTL related to protein solubility. The QTL × environment interaction demonstrated the complex genetic mechanism of SPC. These SPC-associated QTL and linked markers in soybean will provide important information that can be utilized by breeders to improve the functional quality of soybean varieties.

Low phosphorus (P) stress limits soybean production. A population of 152 recombinant inbred lines (RILs) derived from a cross between ÔBogaoÕ (P sensitive variety) and ÔNannong 94-156Õ (P tolerant variety) and 248 markers were used to map quantitative trait loci (QTLs) for low-P tolerance. Two pot culture trials were conducted and low-P tolerance evaluated using flower and pod abscission rate under low P and normal P. Conditional QTLs and epistasis for tolerance to low P were also analysed. A conditional QTL (near Satt274) on linkage group D1b+W was identified which conferred low-P tolerance epistatic effects and coincided with previously discovered QTLs. An additive QTL, qFARLPG-07, for flower abscission rate under low P was detected with a LOD score of 7.79 and explained 32.3% of phenotypic variation. It was detected at the same interval of the corresponding QTL for other traits across years. This region coincided with two conditional QTLs (cqFARLPG-07 and cqPARLPG-07), from the P-tolerant parent ÔNannong 94-156Õ related to low-P tolerance. These results will provide a basis for further fine mapping and eventual cloning of the P-efficiency genes in soybean.