Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2006
Publication Date: 8/22/2007
Citation: Israel, D.W., Kwanyuen, P., Burton, J.W., Walker, D.R. 2007. Response of low seed phytic acid soybeans to increases in external P supply. Crop Sci. 47: 2036-2046. Interpretive Summary: This study demonstrated that the low seed phytic acid trait of soybean is stable across external P concentrations ranging from deficient to excessive levels. This means that the trait will be stable when soybeans are grown on soils with a wide range in P availabilities. These results also corroborated previous genetic studies that have demonstrated the low phytic acid trait is conditioned by two recessive genes. The study also provided information that will help us design experiments to determine which steps in the phytic acid biosynthetic pathway are altered by these two recessive genes. Protein and oil concentrations were the same in low and normal phytic acid lines which means the balance between oil and protein synthesis has not been altered in low phytic acid lines. These results support continued development of low phytic acid cultivars for use by soybean and animal producers.
Technical Abstract: Commercial development of soybean (Glycine max L. Merr.) varieties with low seed phytic acid concentrations will depend on both the stability of the trait when grown in soils with a wide range of phosphorus (P) availabilities, and on the impact of genetically altered P composition on protein and oil concentrations in the seed. The objectives of this study were to evaluate the impact of deficient to excessive levels of external P supply on phytic acid-P, phosphate-P and cellular-P concentrations in seed of normal and low phytic acid lines derived from CX1834-1-2, and the effect of altered seed P composition on the balance between protein and oil synthesis in the seed. Soybean lines homozygous recessive (pha/pha) at one of two loci with genes that condition the low seed phytic acid trait exhibited the same response to increasing external P supply (> 3 fold increase) as their normal phytic acid parent, ‘Prichard’ (Pha/Pha). This supports the conclusion from previous inheritance and mapping studies that the low seed phytic acid trait in CX1834-1-2 is controlled by two independent recessive genes. The seed phytic acid concentration in the low phytic acid line (G03PHY-443) was less than 1 mg phytic acid-P g-1 dry wt from deficient to excessive levels of external P supply. Seed phosphate-P concentrations for this line increased from 0.8 to 4.0 mg g-1 dry wt compared to an increase from 0.2 to 0.6 mg g-1 dry wt for the normal phytic acid lines with increasing P supply. This indicates that the low phytic acid trait should be highly expressed when these lines are grown in soils with a wide range of P availabilities. Increasing the external P supply decreased total protein concentrations and increased oil concentrations in seed of both normal and low seed phytic acid lines. However, these parameters did not differ significantly in normal compared to low phytic acid lines. Thus, although seed of the low phytic acid line had much higher phosphate-P concentrations than seed of the normal lines, the balance between protein and oil synthesis was not altered. The proportion of palmitic acid in the oil was 5 to 16% higher and the proportion of oleic acid in the oil was 9% lower for low phytic acid line compared to normal phytic acid lines. Collectively, these results support continued development of cultivars with low seed phytic acid concentrations and economical yield levels.