Selective Genotyping for Marker Assisted Selection Strategies for Soybean Yield Improvement.

Molecular markers have already played a major role in the genetic characterization and improvement of many crop species.  The location of major loci is now known for disease resistance, tolerance to abiotic stresses and quality traits.  However, although many quantitative trait loci (QTL) have been identified for quantitative traits, few previously reported QTLs have been confirmed in subsequent studies and even fewer reports have utilized them for marker assisted selection (MAS).  Most yield QTLs are population specific and the genetic variation found in the specific bi-parental population might not be shared in other genetic populations.  The major objective in breeding soybean is to develop cultivars with the potential for high seed yield.  Unfortunately, yield is also the most complex trait to characterize from both a phenotypic and genotypic perspective.  The objective of this study was to identify QTL associated with soybean seed yield in preliminary yield trials and evaluate their effective use for MAS in different environments.  To achieve this objective, 875 F­_6:9 recombinant inbred lines (RIL) from a population developed from a cross between two prominent ancestors of the North American soybean (Essex and Williams 82) were used.  The 875 RILs and check cultivars were divided into four groups based on maturity and each group was grown in Knoxville, TN and one other location of adaptability.  Each RIL was genotyped with >50,000 single nucleotide polymorphic markers (SNPs) of which 17,232 were polymorphic across the population.  Yield QTL were detected using single factor ANOVA and composite interval mapping (CIM).  Based on CIM, 23 yield QTLs were identified.  Twenty-one additional QTL were detected using single factor ANOVA.  Individually, these QTLs explained from 4.5 % to 11.9% of the phenotypic variation for yield.  QTLs were identified on all 20 chromosomes and five of the 44 QTLs have not been previously reported.  Some of these new loci maybe attractive candidate regions for further understanding the genetic basis of soybean yield.  This study provides new information concerning yield QTL in soybean and may offer important insights into marker assisted selection (MAS).