The soybeans grown today in Illinois are descended from Chinese varieties that were introduced into the U.S. between 1910 and 1930. Eight of those varieties contribute 75% of the genes in the current varieties grown here.
And, according to Randy Nelson, curator of the USDA Soybean Germplasm Collection at the University of Illinois, that narrow genetic base could well limit future progress to increase yields.
"In recent years, we have seen new diseases develop, such as sudden death syndrome and white mold," he says. "We also have found changes in the pathogen populations of other diseases, such as Phytophthora rot and soybean cyst nematode. Finding new genes for resistance to those diseases is critically important for health of soybean production in Illinois."
He notes that the maximum genetic diversity for any trait is most likely to occur in varieties from China because the soybean originated there.
"During the time that the soybean became a major crop in Illinois, we had no opportunity to exchange germplasm with China," Nelson says. "In 1992, the Illinois Soybean Checkoff Board, the Illinois Agricultural Experiment Station, and the USDA's Agricultural Research Service finally established a major germplasm exchange with the Chinese Ministry of Agriculture. Over the following eight years, this collaboration increased the number of Chinese varieties in our collection from 2,900 to nearly 6,100."
Those new additions came from 27 different provinces in China, representing all the soybean growing areas in the country. Prior to 1992, nearly 80% of the Chinese varieties in the collection came from only three provinces in northeast China, and many provinces were not represented at all.
"Extensive research supported by the United Soybean Board has now demonstrated the genetic uniqueness of those exotic Chinese varieties and the value of that diversity," Nelson says. "Improved resistance has been found for nearly all the diseases that have been evaluated."
For example, the highest known level of resistance to sudden death syndrome was found among those varieties, as well as new sources of resistance to soybean cyst nematode, white mold, brown stem rot, Phytophthora rot and leaf-feeding insects. Preliminary data also indicates that tolerance to drought may exist in varieties from the area adjacent to the Gobi Desert.
"Ongoing genetic research is aimed at determining how those new genes can be incorporated into the commercial varieties grown in Illinois and across the country," he says. "This exotic germplasm clearly has the potential to improve the yield of the varieties that growers in our state will use in the future."
During the last six years, 14 experimental lines have been released for use by universities and private companies to develop improved varieties.
"By making comparisons at the DNA level, we can estimate how closely soybean lines are related, even when we have no pedigree information," Nelson says. "Based on DNA similarities, the major ancestral lines of the U.S. varieties have been placed into six genetic groups. The new exotic parents represent nine genetic groups that are distinct from those contained in the major U.S. ancestral lines."
Nelson points out that the most recent releases from this research were evaluated at nine regional locations in 2001.
"One line derived from 25% exotic germplasm exceeded the yield of the best commercial variety by nearly 12% and was the highest yielding entry in the test," he says. "Another experimental line derived solely from the exotic Chinese lines equaled the yield of the best commercial variety we tested. Those results indicate that the use of this exotic germplasm from China has the potential to enhance disease resistance, increase yield and improve seed composition in the future."