Research Provides Hope for Improving Drought Tolerance

by Howell M. Medders
Science Editor- Print Media

Good progress has been made in increasing soybean drought tolerance, says University of Arkansas researcher Dr. Larry Purcell.

The obvious solution to drought stress - just add water is not an option on some 2 million acres of soybeans planted each year in Arkansas that are not irrigated for various reasons. Even irrigated fields may receive too little water as farmers try to hold down production costs or schedule irrigation of other crops ahead of their soybeans during dry spells.

Soybean drought tolerance research by Purcell, a crop physiologist, and Dr. Clay Sneller, a soybean breeder and geneticist, is funded in part by the United Soybean Board and the Arkansas Soybean Promotion Board.

A long-term goal is to ldentify genes that will make soybean plants less susceptible to drought stress and then to add those genes to otherwise adapted, high-yielding varieties.

The United Soybean Board project includes researchers in Ohio and Georgia who are working on a genetic engineering approach to adding genes associated with drought tolerance from other species to soybeans.

In Arkansas, Purcell is studying the plant's physiology for clues to existing soybean genes that can be used in the conventional breeding program conducted by Sneller to enhance drought tolerance.

The genetic engineers in Ohio and Georgia have isolated genes that may increase drought tolerance and then placed them in soybeans, but they haven't been able to regenerate transgenic plants.

Purcell, meanwhile, is pleased with the progress of the physiol ogy research in Arkansas.

'We started with no way to select for drought tolerance as a genetic trait," he said. "Now we can screen plants in the green house for nitrogen fixation in response to drought stress."

Experiments have shown that a key plant response to drought stress is a decline in nitrogen fixation - the process by which soybean plants take in nitrogen from the air.

"Nitrogen fixation is more sensitive to drought than many other processes, and it repre sents a weak link in the plant's response to drought," Purcell said.

The Jackson variety was identified as somewhat drought tolerant based on its ability to continue fixing atmospheric nitrogen during a drought for a longer period than other soybean varieties or genotypes.

Jackson, a low-yielder, was crossed with the high-yielding KS4895. The cross might eventually produce an adapted variety with more drought tolerance than is currently available to farmers.

Even if it doesn't, it will provide germplasm for further study of the physiological mechanisms of the plant's response to drought, Purcell said.

"The more we can learn about the mechanisms of the plant's response to drought stress, the better our chances of finding | something we can use to our advantage," he said.

Researchers are also working to document the effects of different rates and application timings of nitrogen fertilizer on drought stressed plants. A preliminary field study indicates that applica tion of nitrogen fertilizer may improve drought tolerance.

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