Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2006
Publication Date: 4/25/2006
Citation: Bregitzer, P.P., Raboy, V. 2006. Effects of four independent low-phytate mutations on barley (hordeum vulgare l.) agronomic performance. Crop Science. 46:1318-1322. Interpretive Summary: The phosphorus in cereal grains such as barley, and other food crops like soybeans, is mostly stored as a compound , phytate, that is not digestible by non-ruminant animals (such as pigs, poultry, and fish). Consumption of normal cereals grains results in the excretion in the manure of the phosphorus contained in phytate. To achieve optimal animal growth, producers must supplement their rations with phosphorus, which adds to their costs of production. Furthermore, the excreted phosphorus is associated with significant environmental costs, as phosphorus is a major factor in many instances of water pollution. One solution that addresses both these problems is to develop grain that has reduced phytate and elevated available phosphorus. This has been accomplished for barley, wheat, rice, corn, and soybean, and the challenge is now to develop low phytate cultivars that perform well in commercial agriculture. This report documents the results of studying the grain yield and quality characteristics of barley lines containing four different types genes that increase phosphorus available and reduce phytate. Three of the four types showed good performance under low-stress, irrigated conditions. One of the types also showed good performance under higher-stress, non-irrigated conditions, and it appears that this type will be able to compete with standard barley cultivars in the marketplace. Thus, for barley, the development of commercially-competitive low-phytate cultivars is an achievable goal.
Technical Abstract: The seed phosphorus storage compound phytic acid (myo-inositol-1,2,3,4,5,6-heakisphosphate) is poorly utilized by non-ruminants such as poultry, swine and fish. Low Phytate (LP) cultivars of several crops, in which some of the phytic acid is converted into available inorganic P, are in development and their utility will be enhanced by agronomic performance that is competitive with standard cultivars and hybrids. To study the agronomic performance of LP types derived from mutagenized populations of 'Harrington' barley (Hordeum vulgare L.), sets sib lines that are homozygous wild-type (WT), or homozygous for one of four independent low phytic acid mutations (lpa1-1, lpa2-1, lpa3-1 and M 955), were developed via backcrosses to Harrington. Their agronomic performance, and that of Harrington, was evaluated in two types of production environments; irrigated and dryland. In both environments, the WT sib lines performed similarly to the Harrington parent, suggesting that the major variable in these experiments was the presence or absence of the LP alleles. Under irrigation, yields of lpa1-1, lpa2-1 and lpa3-1, mutants with relatively moderate reductions in phytic acid, were not significantly different than that of wild-type isoline controls, but yields of M 955, a mutant with a more extreme phytic acid reduction, was reduced by approximately 13%. In the more stressful dryland environments reductions in yield were more pronounced, and all mutants except for lpa1-1 yielded significantly less than that of their WT sib lines. Similar trends were noted for test weight and percentage plump kernels. Lines homozygous for the lpa1-1 mutation, which appears to be aleurone specific, performed nearly equivalently to their WT sibs and Harrington. These results indicate that one component of yield loss in LP types is due to reduced stress tolerance, and illustrate a strategy to avoid this source of yield loss: the use of genotypes where the desirable effect is limited to a target tissue, in this case the aleurone layer.