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New Pinto Bean Lines Resist White Mold
September 18, 2006

Two pinto bean germplasm lines are now available for breeding varieties of the crop that will resist white mold, according to the USDAs Agricultural Research Service.

Caused by the fungus Sclerotinia sclerotiorum, white mold is an endemic disease affecting pinto and other dry edible bean crops throughout the
United States. Crop losses can be minimized with fungicides, careful irrigation, widely spaced rows and other measures. But the cornerstone defense is to plant a disease-resistant crop, according to Phil Miklas, a Prosser, Wash. ARS plant geneticist who led in the development of the new pinto bean lines, USPT-WM-1 and USPT-WM-2.

Under favorable conditions, the fungus mushroom stage will eject millions of infectious spores into the air, infecting nearby bean plants or riding the wind to wreak havoc elsewhere. Infected plants typically sport white, cottony tufts on their stems, leaves and pods, with severe outbreaks that can reduce yield and seed quality.

The new pinto lines owe their resistance to crosses made between Aztec, a semi-upright pinto bean, and ND88-106-4, an upright navy bean breeding line. Miklas developed, tested and evaluated the new pintos together with James Kelly at
Michigan State University in East Lansing, and Ken Grafton and Darrin Hauf, both with North Dakota State University in Fargo.

Besides white mold resistance, the new pintos offer high yield. For example, in field trials at a white mold nursery in
Michigan, USPT-WM-1 and USPT-WM-2 produced the second and third highest yields of 64 pinto beans tested. However, they did show susceptibility to race 53 of bean rust at a N.D. site, and were mildly susceptible to beet curly top virus.

ARS plant pathologist Marcial Pastor-Corrales inoculates bean plants with spores of the bean rust fungus.  Photo by Peggy Greb

New Pintos Resist Bean Diseases

Five new pinto bean lines released by the USDAs Agricultural Research Service have resistance to significant bean diseases.

The new lines, known as BelDakMi-RMR and numbered 19 to 23, are resistant to common bean rust, caused by the rust fungus Uromyces appendiculatus, and to the common mosaic and common mosaic necrosis viruses. These diseases reduce yield and crop quality and increase production costs.

Scientists at the Vegetable Laboratory, part of ARS Henry A. Wallace Beltsville (
Md.) Agricultural Research Center, bred the lines in collaboration with colleagues at North Dakota State and Michigan State universities.

Most commercial bean varieties contain two or fewer disease-resistance genes. The BelDakMi pintos have six resistance genes  more than any other known bean. Each contains four genes for resistance to U. appendiculatus, and two for resistance to bean common mosaic and bean common mosaic necrosis.

According to ARS plant geneticist Marcial Pastor-Corrales, who worked on the project, the pintos are resistant to every known strain of these variable pathogens.

Ken Grafton, dean of the NDSU College of Agriculture and before that, longtime bean breeder at NDSU, says these lines are germplasm lines that were developed to carry a number of resistance genes to rust, as well as having resistance to bean common mosaic virus.  He points out that they may or may not become commercially available, since they have not been evaluated for yield, resistance to other diseases, maturity, or quality.  Still, he says the lines do have tremendous potential to be used by breeders as parental lines in the development of better cultivars for this region. 

Geneticists Phil Miklas (left) and George Vandermark analyze results of quantative polymerase chain reaction assays used to rapidly genotype bean plants for disease resistance. Photo by Stephen Ausmus


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