ARS Releases Two Rice Varieties

December 28, 2000

Two new rice varieties containing a gene to improve cooked rice texture, Cadet and Jacinto, entered commercial production this year after a new technology from USDA's Agricultural Research Service speeded their development. ARS scientists at Beaumont, TX, and their colleagues at the Texas Agricultural Experiment Station, College Station, used the fast-paced biotechnological selection process--called marker-assisted selection--to locate desirable genes in noncommercial varieties and deploy them into the new varieties through conventional breeding.

For the marker-assisted selection to work, scientists first create maps of markers--DNA sequences in or near genes whose locations are known--and compare them with the occurrence of traits associated with improved market or agronomic qualities of rice varieties. If the markers and these traits appear together more often than would occur by chance, the locations of the genes for the improved trait are likely to be near the same chromosomal locations of the markers.

As is usually the case, multiple genes govern a single trait of economic importance. These genes' locations are called quantitative trait loci (QTLs). Once QTLs are identified, the scientists conduct DNA tests on rice breeding lines to find out whether they have the desired QTLs. If so, marker-assisted selection enables the researchers to put these traits into new-variety development programs much sooner than if they tried to identify plants with good genes through trial-and-error breeding experiments.

In just five years the scientists developed the new varieties. New variety development normally takes seven to 10 years. The new varieties, which produce rice low in amylose content, a carbohydrate in the grain, are adapted to southern U.S. and European growing regions.

Marker-assisted selection is expected to become more and more useful as scientists continue refining a map of the rice genome. An article about the research appears in the December issue of ARS' Agricultural Research magazine and on the web.