CADET AND JACINTO, two new rice varieties with a gene for improved cooked rice texture, entered commercial production in 2000, thanks to new technology that speeded their development.

Agricultural Research Service scientists at Beaumont, Texas, 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.

Here's how marker-assisted selection works. 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, or QTL's. Once QTL's are identified, the scientists conduct DNA tests on rice breeding lines to find out whether they have the desired QTL's.

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. For addition information go to the Web at: http://www.ars.usda.gov/is/AR/archive/dec00/rice1200.htm

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

Scientific contact: Anna M. McClung, ARS Rice Research Unit, Beaumont, Texas; phone 409-762-5221, fax 409-752-5720, a-mcclung@tamu.edu.