Quantitative Trait Locus Mapping for Protein Content in Soybean Using Two Genetically Connected Populations.

Protein and oil content are the primary seed quality traits for which soybeans (Glycine max (L.) Merr.) are grown.  Soybean seed accounts for the majority of the world vegetable protein market.  This demand is the impetus for breeders to incorporate the high protein trait into soybean breeding programs.  The objective of this study was to identify major quantitative trait loci (QTL) associated with protein content in soybean seed using two genetically connected populations, QTL1 and QTL2.  QTL1 consisted of 277 F4-derived, via true single seed decent, recombinant inbred lines (RILs) from a cross between a low protein content cultivar, NCRoy (42.1% dry weight basis), and a high protein content cultivar, Prolina (46.1%); QTL2 consisted of 270 F4-dervied RILs from a cross between NCRoy and a high protein content germplasm line, NC106 (50.4%).  Both populations were grown in a sets-within-replication desgin in two replications at two North Carolina locations during the summers of 2008 and 2009.  Protein content analysis was completed on subsamples of harvested seed using a near infrared (NIR) transmittance instrument.  Genotypic data was collected on each population: QTL1 was evaluated with 89 simple sequence repeat (SSR) and 50 single nucleotide polymorphism (SNP) markers; QTL2 was evaluated with 93 SSR and 46 SNP markers, as well as with the 1536 SNP markers of the Illumina Golden Gate technology.  Single-factor ANOVA was initially completed to identify markers linked to potentially significant QTL.  Candidate QTL were later confirmed by composite interval mapping and multiple interval mapping.  Furthermore, the connected nature of these two populations via the maternal line allowed for composite interval QTL mapping with MCQTL.  Results of this study will be applied in a marker assisted selection breeding program in order to introduce the high protein trait into soybean germplasm.