University of Illinois researchers have identified 27 current soybean varieties with resistance to white mold. Maturity groups range from 1.5 to 3.2.
The scientists, who started with 250 varieties, have completed two years of screenings and evaluations.
"The most efficient means of controlling white mold is through the use of resistant varieties," points out Illinois plant pathologist Wayne Pedersen. Fungicides are not as practical.
On a scale of 0 to 9 - with 0 signifying the best resistance and 9 the least - nine varieties were rated zero in 1998. Six other varieties scored a one.
Three varieties were rated zero in both 1997 and 1998. Several others scored consistently low both years. But some varieties had considerably different ratings from one year to the other.
"Figures from year to year may vary due to weather conditions and environmental control," Pedersen explains.
The study was funded by the Illinois Soybean Checkoff Board. Board director Alan Puzey points out that this type of information would not be available without checkoff funds.
"Commercial companies are not likely to rank their products against other companies' products when it comes to disease resistance," he says.
In another study, involving primarily Chinese and Japanese germplasm, researchers have found potential sources of white mold resistance. The research is a joint effort of universities, USDA-ARS, Agriculture Canada and three seed companies, says University of Illinois soybean breeder Brian Diers.
"We started the evaluations in 1995 with 5,000 lines ranging from maturity groups 0 to III," Diers notes.
By 1998 the researchers narrowed the field to 50 lines.
"We tested those lines in 20 locations throughout north-central U.S. and Canada last summer and have found 20 lines that look quite promising," says Diers.
"Seed companies have already begun incorporating some of this material in experimental crosses."
Diers and Richard Allison at Michigan State University also are trying a genetic engineering route for developing white mold resistance in soybeans.
"The pathogen that causes white mold produces oxalic acid during infection of the plant," Diers points out. "The oxalic acid aids the fungus in spreading through the plant. If the pathogen does not produce oxalic acid, it cannot infect plants."
Allison took a gene from barley that breaks down oxalic acid and transferred it into soybean plants.
"The expression of this gene in the soybean could slow or stop the fungus from infecting soybean tissue," Diers explains.
Lab tests have been promising. The researchers will do field-testing this summer.