Thanks to a technique known as genetic mapping, Cornell University scientists have for the first time located genetic factors that allow significant increases in yields of rice grown by poor farmers trying to produce crops in hardscrabble conditions.

The researchers' breakthrough has been to use genetic maps to identify regions of chromosomes containing genes that control traits such as grains per plant, disease resistance and earliness. These genes are identified in a wild ancestor of rice and then introgressed, or "spliced," into domesticated, popular varieties of rice. In this case, the genes were introduced into a variety of upland rice, widely grown in unfavorable conditions such as on mountain slopes. As a result, the yield of the domesticated rice has been increased.

"The ability to use modern molecular techniques to improve yield and disease resistance of varieties grown by poor farmers under adverse conditions is as important as using this technology in the high-production areas of the world," says Susan R. McCouch, Cornell assistant professor of plant breeding.

McCouch presented the results of this plant-breeding achievement today at the annual meeting of the American Association for the Advancement of Science. Her talk, "Molecular Breeding and Genetic Resources," was part of a panel discussion on "Accelerating Crop Evolution for Greater Production and Better Biodiversity Conservation."

McCouch noted that she and her colleague, Steven D. Tanksley, Cornell Liberty Hyde Bailey Professor of Plant Breeding, have been able to unlock the genetic potential of domesticated rice varieties. Looking specifically at rice and tomatoes, the two researchers systematically mapped the genes of those plants, looking for specific loci, or genes, known as quantitative trait locus, or QTLs, which could be used to boost production.

This follows Cornell research reported two years ago on introgressing high-yield production genes from wild rice varieties into domesticated varieties grown under favorable, bread-basket conditions as a way to improve yields.

"Our latest work shows that the strategy to boost yields in domesticated varieties from genes in wild varieties is likely to work with any existing variety," said McCouch. "Whatever the baseline is that we're working from, we have shown that we can expand our concept and detect improved production performance. And, at the same time, we can broaden the genetic base of these plants."

Agricultural practices of the past century, McCouch noted, have led researchers to be victims of their own success. Modern plant-breeding techniques, she said, have been successful in developing high-yielding rice and tomatoes, but the crossing and re-crossing of close plant relatives has resulted in a "genetic bottleneck." Paradoxically this could result in reducing plant production and render plants more vulnerable to pests and disease.

However, said McCouch, "the upland varieties of rice have very interesting genetics" that could be exploited by farmers far from the regions where they are adapted. In countries like Brazil, she noted, the less productive yet sturdy upland varieties of rice thrive on subsisdence farms in acidic soils and even in areas prone to disease. She said that these traits could be valuable elsewhere, particularly in Asian countries, where boosting rice production is critical to keeping up with the needs of burgeoning populations.