Research Highlights

Research Highlights
Genetics Help Soybeans Withstand Flooding, Waterlogged Soils

The research team submerged soybeans in 4 to 6 inches of water at the R1 growth stage for seven days. They flooded another set of plots for seven days at the V4 growth stage, as well. Photo: Ben Fallen, USDA and North Carolina State University

By Laura Temple

As the colloquial saying goes, when it rains, it pours. Farmers know where local fields are prone to flooding or complete saturation following a pouring rain. 

“Flooding can be as detrimental as drought to soybean yield, causing losses of 25% or more,” says Ben Fallen, research geneticist for the USDA-Agricultural Research Service in North Carolina. “Both standing water and waterlogged soils can reduce nitrogen fixation in soybean roots, cause chlorosis and necrosis of leaves, stunt plant growth and more.”

As a soybean breeder, Fallen works out of the Soybean Nitrogen Fixation Research Unit based in Raleigh, North Carolina. Building on work originally started by Tommy Carter, he has been identifying genetics that help soybeans tolerate flooding and saturated soils. The North Carolina Soybean Producers Association invests checkoff dollars in his work, and he also collaborates with breeders in Arkansas, Missouri and Louisiana with soy checkoff support from the United Soybean Board.

After flooding, the team assigned visual scores to evaluate the severity of flood stress. This picture shows visual scores of 2 for slight yellowing on the left, 8 for severe chlorosis and plant death in the center, and 6 for extensive yellowing and defoliation on the right. Photo: Ben Fallen, USDA and North Carolina State University

“North Carolina is subject to hurricanes and dramatic weather events that cause flooding or saturate soils completely,” he explains. “This breeding research focuses on cultivars in Maturity Groups 5 through 7 adapted for regional conditions.”

He believes improving genetic diversity in soybeans is key to addressing challenges. Fallen notes that most U.S. soybean varieties can be traced to about 35 parental lines, though the soybean germplasm collection contains more than 20,000 lines. He works with wild soybeans to find advantageous traits that can be bred into commercial varieties.

Testing for Flood Tolerance

As Fallen identifies plant introductions, or PIs, from wild soybeans that show promise for flood tolerance, he tests them in the field. He uses the flood-tolerant PIs to develop progeny, which is then compared to the original PI to see how traits for these conditions carry over. He conducts these screenings at the Tidewater Research Station located near Plymouth, North Carolina.

“The research location has a high water table, flat topography and high organic matter,” he explains. “Plus, the area often gets rain, even when most of the state is dry. It’s ideal for flood trials. I suspect that over time, breeding efforts here have inadvertently selected for genetics that tolerate excess water.”

The research center team builds berms around each test, which are flooded independently. They normally induce flooding either during vegetative growth at V4, or at R1, as reproductive growth starts. In both cases, the fields remain flooded until the plants start showing visible signs of stress, usually between seven and 10 days. 

The team visually rates each cultivar for damage using a scale that ranges from healthy (0) to dead (9). They take ratings both one week and two weeks after releasing the flood. They also capture plot yields and compare them to the same set of cultivars grown under non-flooded conditions.

“We evaluate flooding at growth stages separately to identify PIs that handle those conditions anytime, since we can’t predict when flooding will happen,” Fallen says. “But they also need to yield well if it doesn’t flood.”

Releasing Promising Germplasm

Three of the breeding lines identified in Fallen’s trials performed well. They all had high yields compared to the check and test mean in both flooded and non-flooded conditions. 

“One of those lines, N11-352, will be the first germplasm released from this program with flood tolerance,” he reports. “It is an MG 6 line that has high yield potential and an elevated oil content, as well as flood tolerance.”

His data shows that it yielded about 8 bushels per acre more than the check and test mean under flooding conditions. Without flooding, it yielded about 98% of the check and test mean. 

He expects to receive final approval for release sometime in the fall of 2023. The germplasm will then be available for use by breeding programs — public or private — to incorporate into their soybean varieties. 

This is likely just the first in a pipeline of flood-tolerant germplasm that will come from this breeding program. Fallen also plans to examine PI performance in persistent waterlogged soils, as those conditions are becoming more common for regional farmers.

Meet the Principal Investigator of this research: Ben Fallen

Published: Jan 22, 2024