Just how much more can breeders squeeze out of the soybean? We know the soybean is wholesome, full of protein, omega-3 fatty acids and isoflavones. Soybeans also fit an array of food and industrial uses. It's a tough legume that holds its own in a range of climatic conditions.
All this has been accomplished, however, with just a small slice of the soybean's genetic potential. Two processes of selection narrowed our soybean genetic base. When the soybean was domesticated in China about 5,000 years ago, those first breeders selected only a few of the many wild soybean plants growing around them. Then, soybeans grown in North America descended from just a handful of varieties brought here by plant hunters throughout the past century or so.
From the gene up. Plant breeders always knew wild soybeans in China offered tremendous genetic potential. In 1907, Bill Morse, who worked for USDA's Office of Forage-Crop Investigations, went to Asia and brought 4,500 cultivars to the U.S. Most of the samples were discarded or lost due to poor facilities.
USDA's Soybean Germplasm Collection at the University of Illinois still contains many strains, though. That's tantalizing to any researcher wanting to sample the genetic soybean base.
Xingyou Gu, a South Dakota State University plant science professor, is plumbing the genetic depths, looking for wild soybean plants that may improve domestic varieties. He grows dozens of wild lines in his plots in Brookings, S.D., hoping to find a wild gene that provides resistance to iron deficiency chlorosis, a common problem in high-pH soils in the Midwest. Plants affected by it turn pale green or yellow because they lack the iron to make chlorophyll.
Gu got 196 wild lines from the Soybean Germplasm Collection, began growing them in 2006 and is crossing them with cultivated varieties.
"The major limit with soybean is genetic diversity. It has a very narrow genetic background. That limits soybeans' growth area, [creating the danger of] new exotic diseases and also presenting a challenge for value-added traits. Eighty percent or more of the soybean genes were lost in domestication. Wild soybean is the source for new traits,” Gu says.
Samuel Bowen, a sailor imprisoned in China for four years, learned about soybeans there and slipped some out of the country. Starting in 1766, he grew them in what's now Savannah, Ga., and had a thriving business exporting soy sauce to England until the Revolutionary War halted trade. Soybeans first came to the Midwest in 1851, when Benjamin Franklin Edwards grew them in his Alton, Ill., garden.
The potential help from wild soybean genes could be far-reaching. Gu says some wild plants have aphid or rust resistance or natural drought tolerance. Others produce as many as seven or eight pods at each node, compared to three or four pods for typical domestic soybean varieties.
Once these traits are identified, breeders can insert them into new varieties using genetic markers and gene mapping techniques.
"We need to identify the genetic response to specific conditions. It will take generations of crossing the lines to solve this issue. We can advance our knowledge greatly,” Gu says.
In parts of China, soybeans are literally everywhere. You might not recognize them, though. Many are viny plants, running along the ground, with few pods. From a farmer's stance, wild soybeans are far from ideal. Most have indeterminate growth habits and produce small, often black, seeds.
"Wild soybeans survive in the environment without human care. Most scientists do not get a chance to look at this sort of uniqueness,” Gu says.
Gu says he understands U.S. farmers' drive to increase profitability. He grew up on a small Chinese farm and farmed for seven years himself before attending college. "Farmers contribute a lot of good things to the world. My goal is to help them,” Gu says.