The rich taste and smooth texture of walnuts make this versatile tree nut an American favorite. Now, Agricultural Research Service (ARS) scientists and their University of California-Davis colleagues have embarked upon a 4-year study to uncover new clues to this venerable tree's little-known genetic makeup.

The researchers want to develop what are known as "genetic markers" that would help tree breeders pinpoint prized walnut seedlings. These sought-after trees would boast about a half-dozen traits valued highly by those who grow--and those who eat--walnuts.

The traits range from the plumpness of the kernel to the time of year the tree comes into leaf, a feature useful for avoiding frost damage and some diseases.

The tell-tale markers that ARS Geneticist Mallikarjuna Aradhya and colleagues are creating are known as "SNPs," short for "single nucleotide polymorphisms." Ideally, walnut breeders would be able to use these markers to identify superstars while the trees of interest are still very young. That's a time-saving advantage when breeding English walnut. This popular tree takes several years to begin bearing marketable nuts--a long wait for breeders anxious to determine which candidate trees are the best.

According to Aradhya, the collaboration will also yield several different kinds of genetic maps. In all, the venture is expected to provide the most comprehensive picture ever offered of walnut's mostly mysterious genetics.

More than 600 trees are being grown especially for the research, which is sponsored by the Walnut Marketing Board, the university, and ARS, a scientific research agency of the U.S. Department of Agriculture.

The markers will be invaluable for profiling the genetic makeup of the more than 1,600 walnut trees in the nation's official walnut collection in Davis, Calif. Aradhya is the geneticist for this collection of wild and domesticated walnuts, officially known as the ARS National Clonal Germplasm Repository for Tree Fruit and Nut Crops and Grapes.