PHYTIC ACID LEVELS IN SEEDS OF GLYCINE-MAX AND G-SOJA AS INFLUENCED BY PHOSPHORUS STATUS

Improvement in soybean [Glycine mar (L.) Merr.] nutritional quality may be achieved via a reduction in seed phytic acid P. To advance our knowledge of factors that determine seed phytic acid P levels, the relations between external P availability, leaf or shoot P, and seed P fractions (phytic acid and non-phytic acid P) were studied in soybean and G. soja (Sieb. & Zucc.) germplasm. Mean phytic acid P varied from 4.3 to 6.2 g P kg(-1) in mature seeds of 12 soybean cultivars grown under three field environments. Cultivars ranked similarly in each environment and 98% of the variation in phytic acid P was attributable to a positive, linear effect of available soil P. No significant variation was observed in seed non-phytic acid P. Similar results were obtained when selected soybean and G. soja lines were grown in sand watered with nutrient solutions containing P concentrations ranging from 2 to 50 mg L(-1). Leaf or shoot P concentrations and seed phytic acid P concentrations were positively correlated and in G. soja were nearly double those observed with indeterminate soybean cultivars. The higher leaf P and seed phytic acid P concentrations in G. soja as compared with indeterminate soybean lines were attributed to reduced P utilization efficiency defined as reduced biomass production per unit of total shoot P. These results indicate that essentially all variation in seed P is found as variation in phytic acid P, and that this variation is related to leaf P concentration in a complex manner determined by genotype and soil P availability.