Adjusting fertilizer to create low-phytate crops

29.nov.06
ARS News Service via Agnet

Giving too much phosphorus to wheat and barley plants has been shown to raise the amount stored as phytate, rather than as more digestible forms of phosphorus. This finding is important for two reasons: Livestock that are fed high-phytate grains excrete more phosphorus in their manure, which can pollute water. Also, phosphorus is a finite resource that could be irreplaceable once it has been thoroughly mined--which could happen in the next 25 years.
Agricultural Research Service (ARS) geneticist Edward J. Souza and colleagues at the University of Idaho Research and Extension Center in Aberdeen--David Bowen, Mary J. Guttieri and Karen M. Peterson--made the discovery. Souza, formerly at the University of Idaho, is now research leader of the ARS Soft Wheat Quality Research Unit in Wooster, Ohio. Guttieri is now with the Ohio Agricultural Research and Development Center in Wooster, and Bowen is now with Pioneer Hi-Bred International, Inc., Johnston, Iowa.

The researchers found that soil phosphorus levels may affect grain phytate levels as much as plant breeding can, offering two complementary solutions to the nutritional and environmental problems caused by high phytate levels in grains. Besides being more environmentally sound, getting the application rate for phosphorus fertilizers just right might improve the nutrients delivered by grain crops such as wheat and barley.

Not only is the phosphorus in low-phytate grain crops more digestible by people, but low-phytate grains free up minerals essential to human nutrition: zinc, manganese and iron.


ARS plant geneticist Victor Raboy, in Aberdeen, is a co-author of a paper on phosphorus development in barley seeds--one of four papers by Souza, Guttieri and Peterson in the November-December 2006 issue of Crop Science Journal. Raboy pioneered development of low-phytate corn, rice and barley. His patented work also led to low-phytate soybeans.

A summary paper is available online.


Agronomic Performance of Low Phytic Acid Wheat
M. J. Guttieri, K. M. Peterson and E. J. Souza,*

Low phytic acid (LPA) genotypes of wheat (Triticum aestivum L.) improve the nutritional quality of wheat by reducing the concentration of phytic acid (PA) in the aleurone layer, thus reducing the chelation of nutritionally important minerals and improving the bioavailability of phosphorus. Field studies were conducted at Aberdeen and Tetonia, ID, in 2003 and 2004 to evaluate the effects of the LPA genotype on the agronomic performance of wheat. These studies included wild-type (WT) and LPA genotypes in hard red spring, hard white spring, and soft white spring wheat genetic backgrounds. In the hard red spring genetic background, LPA genotypes had delayed development and reduced grain yield (8–25%) in the high yield environment, in part due to reduced kernel size (up to 3 mg kernel–1). In the hard white spring genetic background, differences in crop development and grain yield were not observed; however, in the high yield environment LPA genotypes produced smaller kernels (2.0–2.4 mg kernel–1). In the soft white spring genetic background, LPA genotypes developed earlier, but the grain yield of LPA genotypes was reduced 20 to 24% in the high yield environment. However, LPA kernels, on average, were heavier and larger in diameter than WT kernels. The absence of consistent effects of the LPA genotype across the three genetic backgrounds suggests that deleterious effects of the LPA genotype may be mitigated by plant breeding.

Abbreviations: HIP, high inorganic phosphorus • LPA, low phytic acid • PA, phytic acid • PAP, phytic acid phosphorus • WT, wild-type

Published in Crop Sci 46:2623-2629 (2006)
DOI: 10.2135/cropsci2006.01.0008
a Univ. of Idaho Research and Extension Center, P.O. Box 870, Aberdeen, ID 83210
b 105A Williams Hall, OARDC, 1680 Madison Ave., Wooster, OH 44691

Phosphorus Fractions in Developing Seeds of Four Low Phytate Barley (Hordeum vulgare L.) Genotypes
David E. Bowen, Mary J. Guttieri, Karen Peterson, Kevin Peterson, Victor Raboy and Edward J. Souza,*

Low phytic acid (lpa) crops have reductions in the amount of seed phytic acid (myo-inositol hexakisphosphate, InsP6) and increases in inorganic phosphorus (Pi) with little change to the amount of total seed P. In this study, four barley lpa genotypes (lpa1–2, lpa2–1, lpa3–1, and M955), backcross wild-type (wt) sib-selections, and original parental line ‘Harrington’ were grown in the field over 2 yr. Developing seed was harvested once a week for 3 wk and then again at physiological maturity, and the seeds assayed for levels of total P, Pi, and phytic acid P. Total phosphorus concentration showed no consistent differences between the lpa genotypes and Harrington. Inorganic P declined during development in the wt genotypes; however in lpa genotypes, inorganic P declined during the first few weeks of development, and then increased from 24 d to maturity. Phytic acid concentration increased steadily during development for the wt lines and barley lpa1–1 and lpa2–1, although the increase was much slower in the lpa lines. The lpa3–1 and M955 had very little InsP6 accumulation until later in development, with little to no increase in the amount of phytic acid in mature seed of M955 compared to the developing seeds of lpa3–1. This information is useful in understanding timing of phosphorus accumulation in seeds, as well as the nature of the low phytic acid mutation in seed development.

Abbreviations: DAA, days after anthesis • InsP6, myo-inositol hexakisphosphate • lpa, low phytic acid • P, phosphorus • Pi, inorganic phosphorus • PA, phytic acid • wt, wild-type

Published in Crop Sci 46:2468-2473 (2006)
DOI: 10.2135/cropsci2005.12.0459

Pioneer Hybrid Int'l., 7200 NW 62nd Ave., Johnston, IA 50131
Univ. of Idaho, P.O. Box 870, Aberdeen, ID 83210
USDA-ARS, 1691 S. 2700 W. Aberdeen, ID 83210
former Professor, University of Idaho, current address: USDA-ARS, 1680 Madison Ave, Wooster, OH 44691