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Research Highlights

Research Highlights
Genetic Markers Improve Development of Chloride-Tolerant Soybean Varieties

By Laura Temple

Salts in irrigation water, soil types and soil drainage in Arkansas combine to make salt stress a challenge in many soybean fields. As the crop uses water, salt minerals build up in the soil and the plants themselves.

“Based on how soybeans handle salts, it appears that chloride is the main culprit behind this stress,” says Dr. Ken Korth, professor in the Department of Entomology and Plant Pathology for the University of Arkansas Division of Agriculture. “Farmers need soybean varieties that can tolerate chloride.”

Work in Korth’s lab measured how salt negatively impacts chloride-sensitive soybeans.

“Chloride stress reduces photosynthesis in soybeans,” he explains. “This physiological stress can occur well before visible signs appear. Eventually symptoms will mimic drought stress, and the plant dies.”

The rate of photosynthesis, as measured by CO2 exchange, differs significantly between chloride-sensitive (right) and chloride-tolerant (left) soybeans. Measurements were taken at the V1 stage from leaves showing no damage after 7 days of exposure to salt water. Source: Ken Korth, University of Arkansas – Division of Agriculture

Korth is working closely with the University of Arkansas Soybean Breeding Program to identify genes that help soybeans tolerate chloride. The Arkansas Soybean Promotion Board supports this research to provide farmers access to an improved selection of soybean varieties with chloride tolerance.

“The checkoff invests in research to keep soybean farmers on the leading edge,” says Doug Hartz, a professional farm manager based in Stuttgart and member of the Arkansas Soybean Promotion Board. “As a board, we fund practical independent research that addresses challenges we are seeing in producers’ fields to improve their operations.”

Exploring variability in chloride tolerance

Previous work identified a single gene, called GmSalt3, as the primary determiner of salt tolerance in soybeans. Its presence allows soybean roots to pump out, or exclude, chloride from the plant. These salt-tolerant lines are labeled “excluders.” Its absence means that soybean roots absorb chlorides, causing photosynthesis reduction and other damage. These salt-sensitive soybean lines are labeled “includers.”

However, ongoing research has found substantial variation in chloride tolerance within some soybean varieties and populations. Those lines are considered “mixed,” and Korth’s current work focuses on determining if other genes also influence chloride tolerance. Identifying markers for these genes would arm soybean breeders with additional knowledge and genetic material to develop chloride-tolerant varieties.

“It appears that other genes either create synergy with GmSalt3 to improve chloride tolerance, or they may interfere with its function, reducing tolerance,” Korth says. “We want to learn what genes or DNA segments contribute to chloride tolerance, because as minerals continue to build up in our fields over time, more tolerance is better.”

10-day time-lapse shows how “excluders” and “includers” typically respond to salt stress.
Source: Ken Korth, University of Arkansas – Division of Agriculture

To determine what other genetics may be involved in chloride tolerance, the Soybean Breeding Program crossed a known “excluder” with a known “includer” to create a variety of mixed seeds for Korth’s team to test. They grow out those seeds in the greenhouse, treating them with salt water and recording salt sensitivity results. Then they share the results with the breeding program. Mapping the genetics of specific crosses, correlated to chloride tolerance levels supports identification of quantitative trait locus (QTL), or specific regions on chromosomes where genes influence chloride tolerance are located. This allows breeders to see existing known markers and identify potential markers that can be associated with improved tolerance in the same genomic region.

“As our understanding of chloride tolerance in soybeans grows, so will our ability to provide better soybean varieties for farmers to choose from,” Korth says. “Farmers will be able to select the best-performing salt-tolerant varieties for the fields where they are most needed.”

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.