Soybean plants that survived China's 1991 "flood of the century" could hold the key to the development of flood-tolerant soybeans for U.S. growers.

Tara VanToai, a plant physiologist with the USDA-ARS Soil Drainage Research Center in Columbus, OH, is working to identify genes in those Chinese plants that may aid in flood tolerance.

VanToai's discovery would be a godsend for U.S. growers, who lose thousands of dollars in yield to flooding each year. It's estimated that flooding for as little as two days may reduce soybean yields by 25%, depending on variety, soil type and growth stage.

The flood-tolerant genes in the Chinese soybeans may be related to the presence of aerenchyma. Aerenchyma is tissue with air passages that enable roots of plants - rice, for example - to grow underwater. In aquatic plants, the corky tissue aids gas exchange and buoyancy.

Instead of a root packed with an organized array of cells, roots with aerenchyma are spongy, with large holes formed by cells either pulling apart or disintegrating. The holes run longitudinally through the roots. They enable flooded roots to snorkel air from above-water plant parts. Aerenchyma tissue is also found in eastern gamagrass and vetiver grass.

VanToai grew soybeans with aerenchyma in an artificially flooded field in Columbus. The plants, offspring of plants that survived China's flood, thrived - despite being partially submerged the entire season, beginning two weeks after the seedlings sprouted.

In a project sponsored by the United Soybean Board (USB), VanToai is working with 10 other scientists across the country to breed new varieties of flood- tolerant soybeans. They hope to release a variety in about four years.

The researchers have screened 230 soybean lines for DNA markers linked to flooding tolerance and have identified several. The flood-tolerant lines are being used as donor parents in crosses to produce flood-tolerant cultivars.

"The goal of our research program is to produce a high-yielding, flood-tolerant soybean variety," points out VanToai. "Our strategies to achieve this goal include the use of molecular plant breeding and genetic transformation."

VanToai interestingly notes that support for her research grew dramatically after floods devastated the Midwest in '93 and the South in '94.

Other key findings of the USB-funded research include the following:

Field flooding injuries are likely caused by the buildup of carbon dioxide in flooded soils, which is 50 times higher than in non-flooded soils.

Flooding inhibits nitrogen fixation more than growth.