"The Rpp1 and Rpp3 resistance genes were found to be more effective in the United States, whereas the Rpp2 and Rpp4 genes were found to be more effective in South America," Walker said. "Nearly all of the soybean accessions that were found to be resistant to soybean rust in the United States were originally collected from southern Japan, northern Vietnam, or the island of Java (Indonesia)."
This suggests that the Brazil populations of soybean rust aren't the ancestors of the rust brought into the United States, he said. Many believed an October 2004 hurricane brought the spores from Central America or northern South America across the Gulf into the southern United States.
"It's possible it happened that way, but it seems less likely now," Walker said. "It's still a mystery how these spores got into the United States. Regardless, the soybean germplasm accessions that are resistant in South America are not necessarily resistant in the United States."
These discoveries have allowed soybean breeders to develop improved breeding lines that combine the resistance of Asian germplasm accessions with the higher yields and important agronomic traits of North American cultivars, Walker said. These lines are now being tested in the United States but are not in the public sector yet.
"It's difficult to transfer useful genes from Asian soybean types because the useful genes are often genetically linked to genes that cause problems with yield such as shattering, lodging and other undesirable traits," he said. "I
|Contact: Jennifer Shike|
University of Illinois College of Agricultural, Consumer and Environmental Sciences