Validation of Quantitative Trait Loci Conditioning Seed Phytate and Protein Concentration in Soybean [Glycine max (L.) Merrill]

The concentration of phytate, a mixed cation salt of phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate), is an important consideration when analyzing grain for livestock feed rations. A discovery that SSR marker Satt237 and Satt561 are associated with quantitative trait loci (QTL) for phytate content in soybean [Glycine max (L.) Merr] has been made recently. The objectives of this study were to 1) confirm those QTL in independent segregating soybean populations, 2) compare the effectiveness of marker assisted selection (MAS) or dual MAS and phenotypic selection for seed phytate and protein concentration in soybean, and 3) assess the agronomic and seed quality traits of low phytate soybean in a recombinant inbred line (RIL) population. Satt237 and Satt561 were found to be significantly associated with QTL for seed phytate (p <.0001). Satt237 was considered a major QTL (R² > 0.10) governing the low phytate trait, and Satt561 was considered a minor QTL (R² < 0.10) in two RIL populations (5601T x Cx1834-1-2 and S97-1688 x Cx1834-1-2). Although MAS selection with either or both SSR markers was effective in lowering the mean phytate levels in the selected progeny groups, phenotypic selection was found to be more cost efficient and effective in lowering mean phytate levels. This study found four QTL significantly associated with SSR markers for seed protein concentration in the RIL population of Danbaekkong x Cx1834-1-2. Markers Satt429 and Satt239 were found to be minor loci controlling protein concentration (R² = 5.2 % and 7.1 %), respectively. Markers Satt441 and Satt561 were found to be major loci controlling protein concentration (R² = 10.1 % and 14.5 %), respectively. This study also found five QTL significantly associated with inorganic phosphorus (Pi) seed concentration in that population. Markers Satt385, Sattt239, Satt441, and Satt561 were all found to be major loci controlling Pi seed concentration (R² = 21.2 %, 23.1 %, 24.6 %, and 11.8 %), respectively. Marker Satt231 was found to be a minor locus controlling Pi seed concentration (R² = 5.1 %). Dual marker assisted selection for seed protein and phytate concentration is not recommended in the Danbaekkong x Cx1834-1-2 population because of the inability of molecular data to predict the superior phenotype (low phytate high protein) for both trains simultaneously. The heritability estimate for Pi was high (h² = 0.92), which indicates that selecting RIL with varying Pi phenotypes is readily accomplished in the 5601T x Cx1834-1-2 population. We found low correlations between seed Pi concentration and maturity, height, lodging, seed yield, and seed protein and oil concentration (r=0.07, 0.26, 0.09, 0.05, 0.18, and 0.17, respectively). A sufficiently large population size will overcome these weak correlations and readily enable breeders to select superior progeny in RIL populations targeting the development of low phytate seed. RIL 56Cx-332 had the highest Pi concentration (3122 μg g^-1), a moderate seed yield (79% of check cultivar ‘5002T’), and favorable protein and oil concentrations of 442 g kg^-1 and 180 g kg^-1, respectively. The RIL 56Cx-318 was the highest yielding low phytate line in this population. This line had normal protein and oil concentrations, and a seed yield of 2976 kg ha^-1 (91% of check cultivar ‘5601T’). These data indicate that breeding with lines low in phytate concentration should not have major detrimental effects on seed yield and other agronomic and seed quality traits, but population size must be adequate for selection techniques to identify superior progeny which combine desirable traits.