Farmersí hands are tied when it comes to managing soybean injury related to soil flooding and water-loving root rot diseases, but after several years of research at Ohio State University and the U.S. Department of Agriculture-Agricultural Research Service, some promising solutions are on the horizon.
To combat the yield impacts associated with standing water, disease development and poor soil structure during heavy rains and flooding situations, Ohio State University plant scientists are taking a three-pronged approach to improving soybean health: molecular plant breeding, transgenics and soil management.
Over the past three years, USDA-ARS and Ohio State plant scientist Tara VanToai and her colleagues with the University Missouri-Delta Center have been analyzing 196 soybean lines that carry the genes of a flood-tolerant Asian variety and a flood-prone variety. The goal is to identify molecular markers in lines that exhibit flood tolerance to aid in developing flood-tolerant soybean varieties by molecular plant breeding.
"Out of that work, we have identified a handful of lines, less than 10, that show sufficient flood tolerance - 60 percent to 70 percent tolerance in standing water after 10 days," said VanToai.
VanToai said that what makes those specific soybean lines flood-tolerant is their ability to form roots from the stem section near the soil surface, called adventitious roots, to give the plant more access to oxygen during times of flooding.
"As we expected, the lines segregated on a bell curve, with a few lines forming a few adventitious roots, a few forming a lot, and the majority somewhere in the middle," said VanToai. "What was interesting was that some lines developed adventitious roots as early as two days after the plant was exposed to standing water."
In addition, flood-tolerant lines also absorbed more oxygen through the development of channels in the roots. Known as aerenchyma, the channels allow the plant to transport oxygen to the deepest parts of the roots.
VanToai said that researchers are looking for the genes that support flood-tolerant expressions and trigger the development of adventitious roots and aerenchyma.
In other molecular marker research, Ohio Agricultural Research and Development Center 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 growing in flooded soil," said VanToai. "Our goal is to identify the genes that help protect against Phytopthora root rot and excessive water, so the plant is protected under flooded situations."
In another area of research, VanToai and her colleagues are studying flood tolerance in soybeans through transgenics. They found that an anti-aging gene inserted into about 150 soybean lines delayed senescence and enhanced grain yield. These lines will be tested for tolerance to flooding and drought.
Lastly, researchers are trying to counteract the symptoms of standing water and disease development by improving overall soil structure under saturated conditions.
"Flooding destroys the soil structure and increases heavy metals solubility in the soil which can be toxic to plants and make them more susceptible to flooding and disease injury," said VanToai.
Researchers are exploring gypsum as a soil amendment to improve soil structure and reduce the level of heavy metals found in saturated soils.
The series of research studies are being funded by USDA-ARS, USB North Central Region, USDA Foreign Agricultural Service, and OARDC SEEDS.