Over 500 soybean lines planted in nearly 4,000 plots will be evaluated in Ohio this season for potential resistance to soybean rust.

Ohio State University's Soybean Breeding Program has joined a nationwide effort to identify resistance to the disease, which growers, plant pathologists, agronomists, specialists and industry representatives have been preparing for all season. So far, thankfully, its bark has been worse than its bite, with reported sightings in only two states.

"Our fungicide program is only going to be a short-term solution to manage soybean rust," said Anne Dorrance, an Ohio State plant pathologist with the Ohio Agricultural Research and Development Center, and Ohio's leading soybean rust researcher. "If we are looking at managing the disease on this many soybean acres, then we are going to need host resistance."

Ohio State, partnering with the Ohio Soybean Council, is following on the heels of the U.S. Department of Agriculture, which evaluated commercial soybean varieties from an Illinois performance test and found that a small proportion of plant lines appeared to carry slow-rusting resistance.

"We put everything in the ground, including the kitchen sink," said Steve St. Martin, an Ohio State OARDC soybean breeder. "If there is indication that some commercial varieties are showing some difference, then there is a chance that perhaps the varieties we are testing will show some resistance as well." Evaluations include 132 exotic lines, mainly from Asia, 156 early maturing breeding lines and 300 late maturing lines, including soybean varieties developed by Ohio State and already released for industry use.

Slow-rust resistance refers to a process of slowing down the development and spread of the disease so that fewer spores develop per leaf and there is a longer time period between infection, potentially decreasing fungicide applications or eliminating fungicide treatments completely.

"We don't want an 'R' gene like we have with Phytophthora because soybean rust changes much faster than Phytophthora does. With Phytophthora resistance genes, they work very fast. The fungus is killed as soon as the spores germinate the plant," said Dorrance. "Soybean rust has more life cycles per season than Phytophthora and, therefore, has a higher mutation rate. So we want a slow rusting partial resistance so it just slows the whole thing down. The rust will penetrate the plant and begin to grow, but it just doesn't seem to take a foothold."

The soybean varieties chosen for the evaluation are being planted later in the plots (beginning this month) to take advantage of soybean rust arriving late in fields, if it shows in Ohio at all.

"We want to make sure that we have plant material to work with come September," said Dorrance. "If soybean rust hits Ohio, and hits the OARDC Western and Northwestern research branches (where the varieties are being tested), we'll have results this year."

The project is a one-time study, part of a series of experiments funded through a $100,000 grant from soybean check-off dollars.

Date: 7/21/05