"We may never see a really drought-tolerant soybean variety, but we know we can add genes to adapted varieties that will increase yields by a few bushels per acre until mild to moderate drought stress, and that could be economically important to a dryland producer."

Dr. Clay Sneller recently gave this assessment of what he believes can be accomplished in the University of Arkansas soybean breeding program to improve drought tolerance. The work is supported by grants from the Arkansas Soybean Promotion Board and the United Soybean Board.

Dryland soybean producers are already using tactics such as reduced tillage to preserve soil moisture, and they're spreading the drought risk by varying planting dates and using varieties from a range of maturity groups.

Like a cautious coach, Sneller doesn't want to raise expectations too high, but he says progress is being made in the effort to assemble a "gene team" that can help plants fight off drought effects. Potentially valuable genetic traits include aluminum tolerance, fibrous rooting and nitrogen fixation under drought stress, he said.

The use of molecular markers to tag the genes that control aluminum tolerance has made it possible in recent years to identify plants that possess the trait.

Sneller said the crossing of aluminum tolerant plants with high-yielding varieties is giving promising results. Some of the early generation progeny of the crosses are showing both a high level of aluminum tolerance and high yield potential.

Aluminum tolerance is important because an estimated 800,000 acres in Arkansas have a combination of high aluminum content and high acidity--a hostile environment for soybean roots.

Roots that can tolerate high aluminum levels grow more vigorously in such soils and can reach reserves of moisture deeper in the soil, Sneller said.

Another trait that could improve drought tolerance is a fibrous root system, which may extract more water from a given volume of soil than a conventional root system, Sneller said. The plant introduction, PI416.937, has a high level of aluminum tolerance as well as a fibrous root system.

The method used to tag genes for aluminum tolerance, which was developed at the University of Georgia, is now being developed for fibrous roots, Sneller said. When that is accomplished, selection for fibrous roots will be added to the program.

The old Jackson soybean variety has genes that allow it to continue fixing nitrogen under drought stress for a longer period than other varieties. Crosses of Jackson and high-yielding varieties have yielded promising results for possibly adding this trait to the drought-tolerance gene team, Sneller said.