FUNDED BY SOYBEAN CHECKOFF DOLLARS  
 


Finding New Disease Resistance

  
 
 
by Wendy Feik Pinkerton

Today’s modern soybean has a limited genetic base—50 percent of the genes in U.S. soybeans are derived from three ancestral lines and 80 percent from just 13 ancestral lines.

A three-year checkoff-funded research program is focused on finding new genes that can improve soybean traits, and then employing these new genes in new germplasm.

Illinois and Iowa soybean farmers have a long-standing commitment to supporting soybean germplasm research as one way to improve soybean traits such as composition or disease resistance, and then provide the subsequent germplasm to breeders and farmers to use in their own fields. The checkoff-funded germplasm research program is just the latest project.

Disease Resistance, Developing Varieties
The Soybean Germplasm Research Initiative, as one genetic research program example, has already screened extensive germplasm resources at the University of Illinois (UI) to locate genes that demonstrate new sources of resistance.

The UI houses one of the largest collections of soybean lines in the world and include 18,000 soybean lines, 1,100 Glycines soja lines (a soybean cousin), and 900 wild perennial lines. UI researchers are studying current domestic soybean lines, Chinese germplasm and germplasm from perennial species to discover new genetic sources for disease resistance and other important agronomic traits.

The cooperative efforts of the Illinois Soybean Checkoff Board, the Iowa Soybean Promotion Board, the Iowa Agriculture and Home Economics Experiment Station, the Illinois Agricultual Experiment Station, and the USDA-Agricultural Research Service made possible the introduction of seeds from 500 lines of soybeans native to nine central provinces in the People’s Republic of China in the Spring of 1992. These lines mare maintained at the USDA’s Soybean Germplasm Collection, housed at the National Soybean Research Center (NSRC) on the University of Illinois Urbana-Champaign campus.

Since then, three additional exchanges have occurred and more over 3,000 new lines have been added to the collection. These lines originated from 26 Chinese provinces and account for more than half of all Chinese soybean lines in the USDA collection. The lines from China are primitive varieties that were developed and preserved by farmers in each province.

Because of the diverse environments from which the Chinese germplasm originates, there is potential for finding new sources of tolerance to environmental stresses such as too much or too little moisture. New genetic diversity for oil and protein quality and quantity are possible, as well.

Using Random Amplified Polymorphic DNA (RAPD) markers, Randall Nelson, USDA Agricultural Research Service (ARS) plant geneticist, measured the diversity of Chinese lines at the DNA level.
These data showed that Chinese germplasm is more genetically diverse than other Asian germplasm and that the ancestral lines of modern Chinese varieties are genetically different from the ancestral lines of U.S. varieties even though many of them come from the same regions of China.

At the UI, USDA ARS plant pathologists Glen Hartman and Greg Noel and UI plant geneticist Ted Hymowitz have screened more than 300 accession of Glycine tomentella, the wild Australian relative of today’s modern soybean. They have found that 50 percent of these germplasm accessions had high levels of resistance to the most common type of soybean cyst nematode in the Midwest.

Hymowitz also has crossed G. tomentella with a commercial soybean variety using traditional variety cross methods, not biotechnology, to transfer this resistance to soybeans. This work, according to Hartman, represents just a portion of the untapped resources in wild perennial relatives of soybeans.

In field and greenhouse trials, researchers are screening and finding new sources of resistance to several soybean diseases and pests. In these trials, researchers are evaluating lines for resistance to soybean cyst nematode (SCN), sudden death syndrome (SDS), stem canker, charcoal rot, brown stem rot (BSR), white mold, and bean pod mottle virus.

The best source of resistance are being used as parents and the resulting progeny are being evaluated. In 2002, researchers also have looked for indications of resistance to soybean aphids in several soybean varieties and have found some sources of resistance. Further field evaluation is the next step.

Like the BSR studies in the plant pathology managed research, the researchers are also evaluating plant introductions to identify resistance genes for phytophthora rot. They are testing both domestic and Chinese lines.

Identifying New Yield Genes
Profitability in the soybean industry is largely influenced by yields. Yield increases over the past 30 years have happened, in part, through improved genetics, but the rate of genetic gains using conventional breeding methods is pain-stakingly slow. And with increased com-petition from South America, the need for great production with lower production costs is as critical as ever.

Researchers are now com-bining conventional field trials with genetic mapping to identify and evaluate specific genetic lines that increase soybean yield while assuring disease resistance and ultimately lower input costs.

In six different locations, researchers tested genetic populations for yield, agronomic traits, and genetic markers in order to identify the specific genetics from exotic soybean varieties that increase yield.

Three genetic mapping populations were tested in 2001 and two additional populations were tested in 2002. Each population was developed from crosses between experimental lines derived from plant introductions and high yielding varieties or experimental lines. The populations were evaluated for agronomic performance, including yield and maturity. The lines also were tested with genetic markers.

Researchers were then able to analyze the field and market data together, allow them to identify locations of genes that control yield and other agronomic traits. To date, researchers have evaluated nearly 4,000 yield plots in this part of the germplasm initiative program.

While the ultimate results, in the form of new varieties, may be at least eight years from reaching farmers’ fields, researchers have identified the locations of genes from the exotic plant introductions that can increase yield. By developing elite varieties with these genes, Brian Diers, UI professor of soybean breeding and genetics, believes that the private and public sectors will be able to directly apply the results of today’s genetic research in the agricultural field is making amazing strides, thanks to advanced research techniques, agriculture’s needs and funding support. The Illinois Soybean Germplasm Research Initiative is just one example of the research and the focus aimed at improving soybean‘s disease resistance, boosting its yields in an economical approach and enhancing the bean’s composition to the ultimate benefit of the U.S. soybean farmer.

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