Agronomic Performance and Seed Inorganic Phosphorus Stability of Low Phytate Soybean Line TN09-239
Wiggins, S. J., C. Smallwood, D. R. West, D. A. Kopsell, C. E. Sams, and V. R. Pantalone.  2018.  J. Am. Oil Chem. Soc., 95:787-796.

Phytate (myo-inositol-1,2,3,4,5,6-hexa-kisphosphate) in soybean [Glycine max (L.) Merr.] cannot be absorbed by livestock with monogastric digestive systems and thus is often excreted in their waste, contributing to agricultural runoff pollution and fresh water eutrophication. Phytate also binds nutritional minerals and can cause deficiencies in poultry (Gallus gallus domesticus) and swine (Sus domesticus).The use of the enzyme phytase is often employed to break the phytin salt bonds and allow for phosphorus (P) absorption, but is an added cost for animal producers. The high yielding line 5601T was backcrossed four times with low phytate mutant donor line CX1834-1-2 to develop the BC4 derived line TN09-239. Low phytate trait introgression was confirmed at both QTL cqPha-001 and cqPha-002 in the BC4 derived line TN09-239. The purpose of this study was to compare agronomic and seed quality traits in TN09-239 to the recurrent parent. Two field experiments were conducted. The first was a study at three TN locations for two years. The second was at 10 southern USA environments as entries in the 2010 USDA Uniform Preliminary V Soybean Test. In the first experiment, TN09-239 was significantly higher for inorganic P (Pi) (P<0.0001), with TN09-239 containing 1657.9 ng ÁL-1 compared with 5601T at 222.9 ng ÁL-1. TN09-239 was significantly lower for yield (P<0.05), with TN09-239 yielding 3151 kg ha-1 compared with the recurrent parent (3500 kg ha-1). The second experiment allowed us to assess potential differences in agronomic and seed quality traits, fatty and amino acid content, inorganic phosphorus (an indicator of phytate), and SCN races 2 and 3 susceptibility. Significant differences were observed between 5601T and TN09-239 for lodging, plant height, yield, and seed weight (P<0.05). No significant differences were observed for oil or protein, however significant differences were observed for fatty acid compositions, palmitic, stearic, oleic, linoleic, and linoleic acids (P<0.01, P<0.01, P<0.05, P<0.05, and P<0.001, respectively). Significant differences in amino acid compositions of crude protein were found for arginine, cysteine, leucine, and tryptophan (P<0.05, P<0.01, P<0.05, and P<0.001, respectively). 5601T and TN09-239 were also evaluated for stability across southern environments. For Pi a significant genotype by environment interaction was evident (P<0.01), and in a linear regression, 5601T was found to have a slope of zero (P>0.05) while TN09-239 had a slope significantly different from zero (P<0.0001). Although the low phytate trait and much of the recurrent parent genome have been captured, further backcrossing is necessary to recover the seed yield of 5601T and other traits desirable for southern U.S. producers.