Breeding Maize with Increased Methionine Content for Organic Farming in the USA.

For poultry, the sulfur-containing amino acid methionine is commonly regarded as being the first limiting amino acid for overall health and egg production. To meet the nutritional needs of their birds, organic poultry producers routinely supplement their rations with synthetic methionine. However, the USDA has ruled that synthetic methionine will be banned from organic poultry diets after October 2008. US organic layer and egg production tripled between 2000 and 2003 and then quadrupled between 2003 and 2006. A ban on synthetic methionine could limit organic poultry production in the USA or make it more expensive. Our team has been breeding corn with increased methionine content using different, naturally occurring genetic systems in both hard and soft endosperm corns, and testing them on organic farms. Hard endosperm corn developed by the University of Minnesota accumulates methionine-rich delta-zein proteins in the endosperm. USDA/ARS scientists bred hard endosperm inbreds from crosses made between Latin American corn and commercial inbreds. Routine screening of these hard-kernelled inbreds has identified some with high methionine content. Furthermore, USDA and Iowa State University researchers increased methionine content of grain of two populations by recurrent selection. The floury-2 allele makes the endosperm of corn kernels soft while increasing the overall protein and the methionine and lysine content of the protein. Michael Fields Agricultural Institute has been breeding floury-2 into higher yielding cultivars. They have also bred lines and populations with high methionine grain from high oil corn cultivars. Analyses showed high contents of methionine, cysteine, lysine, and protein in grain of high methionine cultivars. Experiments in 2007 with the cultivars mentioned at single sites in Iowa, Minnesota, and Wisconsin, suggest a range in yield potential for different high methionine hybrids. The floury-2 hybrids had the highest overall protein quality but the lowest yields relative to hybrid checks.