Discovering Soybean Plants Resistant to Aphids and a New Aphid

FOR IMMEDIATE RELEASE
September 24, 2009

Aphids have become a problem for soybean growers in most years. This year only a small number of fields had high enough aphid numbers to treat with insecticides, but even in a year with low numbers, some reduction in yield may be taking place.

Next year farmers in the Midwest may be growing a new variety of soybeans developed by University of Illinois researchers that has resistance to soybean aphids. However, in addition to the resistant plants, U of I researchers also discovered a new soybean aphid which is not controlled by this resistance.

Soybean aphids made their first appearance in North America in the summer of 2000, resulting in tremendous crop losses for farmers. U of I researchers began immediately searching for a variety of soybean that is resistant to the new pest.

Dowling and Jackson were the first two resistant varieties to be identified. "We have the U. S. Soybean Germplasm collection here at Illinois. It houses about 18,000 different accessions," said Glen Hartman, soybean plant pathologist with the USDA and U of I. "We didn't screen all 18,000, but we went through a small set of 4,000 to 5,000 and that's where Jackson and Dowling came from. We knew they were resistant, but we had to do the crossings and look at the inheritance patterns to figure out whether the resistance was because of a single gene or multiple genes."

With additional screening, a third soybean resistant to aphids was found --a Japanese variety known as PI 200538. "After we mapped the genes from these sources, we discovered that Jackson and Dowling had genes mapping to the same place on a chromosome and the PI had a gene mapping to a different place. This means that Jackson and Dowling likely have the same resistance gene and PI 200538 has a different gene we can use in breeding."

Diers said that both Jackson and Dowling originated in the southern United States, so neither could be grown to seed in the Midwest. They used traditional breeding techniques together with marker-assisted selection to quickly breed the resistance genes into varieties that are adapted to the Midwest.

The first aphid-resistant variety developed and released by the University of Illinois is Round-up Ready, and the second is a conventional, non-Round-up Ready variety. Diers says "we believe that the aphid resistance in a conventional background will be especially helpful to organic soybean producers because currently if they have aphids in their fields, they don't have any practical method of control because they cannot spray insecticides. I've been contacted by some organic growers in northern Iowa and southern Minnesota who are ready to give up growing organic soybeans because aphids have caused such large losses."

Diers said that resistant varieties can save farmers money and help the environment. "Farmers have been controlling soybean aphids by spraying insecticides. If we can deploy resistance, this could reduce the use of these insecticides, which will have many environmental benefits."

The message to farmers is that there are going to be varieties with soybean aphid resistance available. "The tests we've done have shown that we have less aphid reproduction on these resistant lines than on susceptible lines," Diers said. "But so far the resistance isn't a magic bullet. You can't grow these aphid-resistant varieties and not scout for aphids because there may be aphids in your fields that can defeat the resistance."

The other unknown is how adaptable aphids will be to these new varieties. "Our hope is that we can combine these two genes and get more durable resistance," Diers said. "We hope that we can develop a plant with a number of resistance genes so that if any one of them breaks down, the plant would still be resistant."

This research was supported by funding from the United Soybean Board and the Illinois Soybean Association. "Without funding from these organizations, our research on aphid resistance and the development of aphid-resistant varieties would not have been possible," says Diers.

The work appeared in the following journals: Soybean Aphid Resistance Genes in the Soybean Cultivars Dowling and Jackson Map to Linkage Group M was published in a 2007 issue of Mol Breeding. Discovery of Soybean Aphid Biotypes was published in the May-June 2008 issue of Crop Science. Inheritance of Resistance to the Soybean Aphid in Soybean PI 200538 was published in the July-August 2009 issue of Crop Science. Funding was provided by the United Soybean Board and the Illinois Soybean Association. Yan Li, Curtis B. Hill, Shawn R. Carlson, Ki-Seung Kim, M.A. Rouf Mian, and Laura Crull contributed to the research.