COLUMBUS, Ohio -- Little can be done to prevent soybean injury due to flooding, but the future is bright for farmers to grow varieties tolerant to the effects of standing water.
Ohio State University researchers, collaborating with the University of Missouri-Delta Center, are studying the effects of flooding on soybean lines in the hopes of identifying tolerance genes that can be bred into existing susceptible varieties. After one year of research, results look promising.
"Things so far look good," said Tara VanToai, an Ohio State University plant scientist with the U.S. Department of Agriculture-Agricultural Research Service. "We can tell just by looking at the soybean lines which ones are exhibiting flood tolerance."
VanToai and her colleagues are analyzing 220 soybean lines that carry the genes of a tolerant Asian variety and a flood-prone variety. The lines, grown in Missouri and at the Ohio Agricultural Research and Development Center in Wooster, Ohio, are being evaluated for yield, plant height, leaf greenness, and level of survival after fields are flooded.
"We flood the fields until the plants start to show symptoms. Then we quantify the tolerance of each line under those field conditions," said VanToai. "Our hope is that when we compare the data between Wooster and Missouri, we find lines grown in both locations that are flood tolerant."
The research, partly funded by USDA-ARS, stemmed from earlier work conducted by VanToai that found that carbon dioxide buildup in flooded fields is a major cause of injury and death to soybean plants.
"It was previously suspected that lack of oxygen was the main problem with damaged or dying soybeans associated with flooding. But what we found was that, although lack of oxygen played a small part, carbon dioxide build-up was the biggest factor," said VanToai. "Carbon dioxide is toxic to plants, causing them to turn yellow, become stunted and drop leaves, resulting in yield reductions, and, in some cases, death."
Researchers discovered that soybean plants adapt to low or no oxygen by producing additional roots and modifying the stem to help transport oxygen from the shoot to the roots. Soybeans, however, are susceptible to carbon dioxide. The carbon dioxide concentration of non-flooded soybean fields is about 1 percent, but increases to 30 to 35 percent after two weeks of flooding. Soybeans growing under that situation face yield reductions as high as 60 percent.
"Based on these findings, we were very interested in improving the tolerance of soybeans to flooding, from the standpoint of saying, ‘Well, if beans lose 60 percent of their yields after seven days of flooding, then varieties we develop that lose only 20 percent of their yields would help farmers.'"
Identifying varieties tolerant to carbon dioxide levels in flooded fields or prolonged standing water is only a piece of soybean research puzzle. Researchers also recognize the importance of identifying varieties that exhibit resistance to diseases associated with flooded soil, such as Phytophthora root rot.
OARDC plant pathologist Anne Dorrance is collaborating with VanToai to identify the genes of flood-tolerance and Phytophthora resistance that can be used to develop future varieties.
"The cross research is very exciting because it is helping us better understand the relationship between flooding and diseases, and what it takes to keep soybean plants alive and grow in flooded soil," said VanToai.
Other researchers collaborating on the project include Rouf Mian, an OARDC researcher with USDA-ARS, and Grover Shannon and Henry Nguyen of the University of Missouri.
The soybean is Ohio's No. 1 field crop commodity, generating over $1 billion to the agricultural industry, according to the Ohio Department of Agriculture. Soybeans are grown in Ohio for a wide variety of uses -- from grain to food to renewable energy production.