Soil Science Society of America (SSSA)

Method to differentiate open pollinated varieties of maize developed


Open pollinated varieties of maize are going to be easier to distinguish from each other, thanks to scientists at the International Maize and Wheat Improvement Center (CIMMYT) in Africa and Mexico. They have developed a new technique to differentiate the genes of one open pollinated variety from another, particularly important to African farmers, most of whom do not plant hybrid varieties. The results of the study were reported in the 2010 March/ April edition of Crop Science, published by the Crop Science Society of America.

Unlike hybrid varieties, seeds from open pollinated varieties can be replanted for several years without a loss of yield or other valuable traits. In sub-Saharan Africa, the benefits of replanting seeds outweighs the lower yields compared to hybrid varieties, because the low-cropping systems there do not rely on the fertilizer, irrigation, or pesticides that hybrids require. When farmer do purchase seed, they run the occasional risk of local suppliers adulterating seed bags with simple maize grain from local markets, and not even of the variety whose name appears on the label. Farmers who sow such mixed bags will have poor plant stands and inferior harvests, representing the loss not only of precious food grain but of their time, labor, and monetary investment. There are other causes of seed impurities, but the end result is that farmers have now way of knowing for sure if they have the seeds they need.
Hybrid maize varieties have identical genes in every plant, making it easy to use molecular techniques to fingerprint their genetic code. This is not easily done for open pollinated varieties. While individual plants may be uniform for certain traits, such as disease resistance, flowering time, or grain type, the remaining genes may contain different alleles, or versions of the gene.
Nonetheless, the frequencies of these alleles within each variety remain constant over generations or subsamples. Two plants from the same variety will show differences when fingerprinted using DNA markers, but those differences will be fewer than the differences between plants from distinct varieties. Thus, it is difficult but possible to distinguish open pollinated varieties at the molecular and statistical level.
The new fingerprinting method collects equal amounts of DNA from each variety and uses specialized software to calculate the allele frequencies within each group for up to 50 molecular genetic markers. The allele frequencies allow comparisons between two seed samples, and to determine if the differences between the two samples are greater than the differences within each sample; if so, the two samples are concluded not to be the same variety.
This fingerprinting method will allow government agencies, non-governmental organizations, breeders, seed companies, and others to conclusively identify each open pollinated variety and ensure that the correct seed of high yielding, locally adapted variety reach farmers, so that they may generate the highest yields possible in their fields.
The team of scientists was led by Peter Setimela and others at CIMMYT, and joined by researchers from USDA, and the Univerisdad de la Republica, Uruguay.

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