Assessing the efficiency of phenotypic and molecular genotype selection methods for complex traits in Soybean

Soybean [Glycine max (L.) Merrill] is an important source of protein and oil for both nutritional and industrial applications. Increasing seed yield and protein concentration is the main goal of many soybean breeders to meet market demands. Soybean breeders have occasionally succeeded in producing high yielding cultivars with increased protein content using conventional means despite the negative correlation that exists between these two traits. The efficiency of breeding for seed yield and protein concentration improvement in soybean could be increased using marker assisted selection (MAS) breeding strategies to select genotypes containing favorable alleles for faster cultivar development. The objective of this study was to identify quantitative trait loci (QTL) associated with seed yield, and separately, seed protein concentration and then compare phenotypic selection (PHE) and MAS approaches for seed yield and protein concentration improvement. Two hundred and eighty two F₅ derived recombinant inbred lines (RILs) were developed from a cross of Essex × Williams 82 and genotyped with 1586 single nucleotide polymorphism (SNP) markers. The population was divided by days to maturity (10 days) into three tests (early, mid and late) each with 94 genotypes, with one genotype overlapping in maturity in the mid and late tests. In 2009, the three tests, parents and checks were grown in a randomized complete block design (RCBD) in: Fayetteville, AR; Harrisburg, IL and, Knoxville, TN replicated three times, and evaluated for seed yield and protein concentration. Data were combined within each test across three locations and analyzed using the MIXED procedure of SAS to determine that there were significant genotypic differences among RILs. Composite interval mapping (CIM) detected nine seed yield and ten protein concentration QTL which may be good candidates for MAS as they were environmentally stable. Selections to compare PHE, and MAS for seed yield and protein concentration provided 8 replicated field tests in four relative maturity groups grown in a RCBD replicated three times in three locations in Tennessee, in 2010. We demonstrated that both MAS and PHE may be used to select quantitative traits; however, more studies are required to optimize MAS for quantitative trait improvement.