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Corn+Soybean Digest

Endless Search For New Varieties

The tenacious ability of insects and diseases to replicate and change rapidly poses big problems not only for producers, but also for the plant pathologists and breeders who earn their keep combating them.

So when a breakthrough comes along, there's always good reason to take heed.

The most recent breakthrough can be found at the University of Illinois (U of I) where — after nearly three years of screening and testing — a team of researchers identified and mapped a single gene that provides soybean aphid resistance.

The gene came from Dowling, a Group VIII variety that was originally released by Texas A&M in 1978.

“The source of the resistance in Dowling can be traced back to Asia,” says Glenn Hartman, plant pathologist with USDA's Agricultural Research Service (ARS) at U of I.

Because aphid resistance comes from a single gene, Hartman says getting it into commercial types should move quickly, provided public and private seed industries adopt the licensed methods and technology.

“A simple, back-crossing breeding program should get this resistant gene into commercial types within three to four years,” he says.

The resistance source has been field tested, and so far the results confirm that aphid resistance is “very good,” according to Brian Diers, U of I plant breeder.

“We're making crosses with commercial varieties adapted to the northern U.S., so ultimately producers will likely see new, aphid resistant lines in the Group II-IV range within a few years,” he says.

The cost savings to producers will be tremendous, says Hartman, who points out spraying for aphids cost $15-25/acre or more in 2003. More than 1 million acres were treated in Illinois alone, he says.

Diers and Hartman also say that such discoveries wouldn't be possible if it weren't for the USDA/ARS Soybean Germplasm collection overseen by Randall Nelson, a USDA/ARS scientist at the U of I. The collection now holds more than 16,000 germplasm accessions — many from Asia and China.

“No matter what the disease or pest, it usually takes about two to three years to screen the entire germplasm bank in hopes of finding sources of resistance that may be useful for further screening and testing,” says Hartman.

Hartman, Diers and other researchers at U of I are also screening and testing parent materials for use in developing resistance to other diseases and pests, such as soybean cyst nematode (SCN), soybean rust and some select viruses.

Soybean Cyst Nematode: While SCN resistant varieties now exist, most resistant varieties in the northern U.S. have resistance genes only from Plant Identification No. (PI) 88788. Further screening and testing is being done with other resistance sources, too, according to Diers. Hartwig is a source many breeders are using because it gives broader SCN resistance than PI 88788. Incorporating resistance from this source into high-yielding northern varieties has been difficult, however.

Soybean Rust: Backed by funding from the United Soybean Board, USDA/ARS scientists are extensively conducting screenings of the USDA germplasm bank at Ft. Detrick, based in Frederick, MD. “It's a highly secure military facility, and it's the only place in the U.S. where containment is available and screenings for soybean rust resistance can be done,” says Hartman.

Soybean Mosaic and Tobacco Streak Viruses: Based on screenings of the USDA's germplasm collection at U of I, Hartman says he may have found a new source of resistance to these two viruses. He says screening and testing efforts will continue.

Phytophthora Root Rot: A new, single gene has been identified for resistance to Phytophthora root rot, as well as genes which contribute to partial resistance, says Anne Dorrance, plant pathologist at the Ohio Agricultural Research and Development Center, based in Wooster. “This finding comes at a good time because Phytophthora is slowly adapting to current soybean resistant genes,” she says.

In 2002, Ohio State University released the single, new gene to the industry in adapted germplasm combined with both resistant and partial resistant genes.

Producers may likely see commercial introductions of high- yielding lines of soybeans with this new, resistant gene to Phytophthora as early as 2007.

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