The cross incompatibility allele GA-1S was incorporated into white corn parent lines T175 and T177, and yellow corn parent lines T274 and T276. This genetic system will allow seedsmen or farmers to produce hybrids which cannot be cross pollinated by corn that does not have the GA-1S allele. None of the currently available commercial field corn hybrids have GA-1S. This will prevent adventitious presence of GMO DNA in fields planted to non-GMO corn varieties, which occurs when pollen from GMO varieties is wind-blown into nearby non-GMO fields.
1. Genetically convert yellow and white parent corn lines to cross-sterility, so they cannot be pollinated by GMO varieties.
2. Produce hybrid seed from lines developed in objective one, and test hybrids on farms of organic corn producers.
Transgenic crop varieties, commonly referred to as GMO’s (Genetically Modified Organisms), are prohibited from use in certified organic production. However, organic growers planting non-GMO corn varieties cannot control the varieties grown by nearby farmers, who may choose a GMO corn variety. Approximately 80% of commercial field corn seed sold in the U.S. each year is transgenic. A single GMO corn plant commonly produces more than two million pollen grains, which may be carried more than one-half mile by wind. This long distance cross-pollination can result in “adventitious presence” or GMO contamination of the grain of non-GMO varieties. GMO contamination of organically grown corn results in loss of market value for the organic farmer. A genetic “factor” (allele) was identified in corn as early as 1926 (1) that prevented fertilization by pollen that does not carry this factor. Thomas (2) presented a method to transfer this cross-sterility factor to popcorn in 1955. Corn breeding has been an ongoing project of The University of Tennessee for 90 years, and many parent corn lines have been developed (3,4). We obtained genetic stocks that possess the cross-sterility gene Ga1-S (Ga for gametophyte factor, 1-S identifies the specific allele), and used the method given by Thomas to breed the gene into white and yellow grained public hybrids. All of the commercial dent or field corn hybrids marketed in the U.S. carry the allele ga1-S (recessive form of the gene), which is inactive on the silks of Ga1-S plants. The grain produced on Ga1-S hybrids will be the result of pollination by plants that have the Ga1-S gene. Grain on Ga1-S hybrids grown in the same field as non-Ga1-S GMO hybrids will be free of GMO DNA.
1. Schwartz, Drew. 1950. The analysis of a case of cross-sterility in maize. Proc Natl Acad Sci. 36(12): 719–724.
2. Thomas, Walter I. 1955. Transferring the GaS factor for dent-incompatibility to dent-compatible lines of popcorn. Agron. Journal 47:440-441.
3. West, D. R., D. R. Kincer, F.L. Allen, and M.A. Thompson. 2006. Registration of T175 parental line of maize. Crop Sci. 46:2733.
4. West, D. R., D. R. Kincer, and C. R. Graves. 2001. Registration of T173 parental line of maize. Crop Sci. 41:1375.
Tennessee elite corn lines T175, T177, T274, and T276 (recurrent parents) were crossed to corn lines obtained from the National Plant Germplasm System (NPGS) with the cross sterility allele GA-1S. Once the first cross was made, the following generations were backcrossed to the recurrent parent. This method required that individual plants from a segregating population be self-pollinated and test-crossed to a GA-1S tester to identify plants that had the GA-1S allele. Crosses that produced seed on the GA-1S tester were positive for the GA-1S allele and, in the next generation, progeny of these plants were backcrossed to the recurrent parent line. In order to complete the project within a 3 year time restriction, a winter nursery was utilized to allow two generations per year. The project timeline was as follows:
Year 1: Summer nursery, Knoxville, TN. Cross GA-1S lines to elite Tennessee lines.
Year 1: Winter nursery, Homestead, FL. Backcross GA-1S x TN line to recurrent parent.
Year 2: Summer nursery, Knoxville, TN. Self-pollinate and cross individual plants to GA-1S tester. Harvest selfed seed from plants that produced seed when crossed to the tester.
Year2: Winter nursery, Homestead, FL. Backcross selected plants to recurrent parent.
Year 3: Summer nursery, Knoxville, TN. Self-pollinate and cross individual plants to GA-1S tester. Harvest selfed seed from plants that produced seed when crossed to the tester.
Year 3: Winter nursery, Homestead, FL. Backcross selected plants to recurrent parent.
Year 4: Summer Nursery, Knoxville, TN. Cross pollinate individual plants in segregating population by varieties with colored grain, then self-pollinate the same plants the following day. Harvest seed from plants that have no colored grain. The harvested plants with no colored grain are homozygous for the GA-1S allele and have 93.75 % of the germplasm of the recurrent parent.
In year 4 we identified plants from each elite Tennessee line that were homozygous for GA-1S. Three experimental GA-1S lines from each recurrent parent were selected. These lines will be used to produce experimental hybrids for evaluation, allowing us to select the best lines for use by farmers and seedsmen wishing to produce hybrid seed. The best F1 hybrid identified in yield trials will be intermated to produce F2 seed. The F2 seed will be used to produce a synthetic or open-pollinated variety. This synthetic variety can be grown by producers who want to save seed from one crop to plant next year’s crop, but do not have the capability to produce hybrid seed.
Four parent corn lines have been developed that have the cross-sterility allele: T175GA-1S, T177GA-1S, T274GA-1S, and T276GA-1S. These lines are the product of three backcrosses, and thus are expected to have 93.75 % of the germplasm of the recurrent parent. Following the third backcross, lines homozygous for the GA-1S allele were identified by pollinating individual plants in a segregating population with pollen from a line with colored grain. These plants were self-pollinated the following day. Plants that produced no colored grain were selected at harvest as homozygous for the GA-1S allele. Experimental hybrids will be produced in the 2015 Knoxville, TN nursery for testing in yield trials in 2016. Data from the 2016 yield trials will be used select the best hybrids for production by farmers and seedsmen. We will also increase seed of each of the parental lines in order to make this germplasm available to all who wish to produce their own GMO resistant corn seed.
Educational & Outreach Activities
Seed of experimental GMO resistant hybrids and synthetic varieties are being produced in small quantities in 2015. These varieties will be evaluated in 2016 and additional seed will be produced. We will have sufficient quantities of seed to place limited amounts in farmer’s fields in 2017.
Production of hybrid or synthetic varieties of corn that have the cross sterility allele will reduce the incidence of adventitious presence of GMO DNA in non-GMO corn fields. This will prevent economic loss to organic and other producers who target the non-GMO corn market.
The timeline of this project required 6 growing seasons to develop GMO resistant corn lines. The products of this research have not yet been available to farmers.
Areas needing additional study
This project will continue unfunded for an additional three years. During this time we will produce and test GMO resistant corn hybrids and synthetic varieties. We will increase seed of the best performing parent lines of hybrids and develop synthetic varieties by intermating F1 plants. Seed of these parent lines and synthetics will be available to farmers producing corn for the non-GMO market.