Chocolate Pod: Not So Sweet for Bean
Growers By Jan
Suszkiw August 11, 2009
New, virus-resistant snap beans could soon be on tap, thanks to
genetic sleuthing by Agricultural Research
Service (ARS) scientists in Prosser, Wash.
The target of their investigation, a strain of the clover yellow vein
virus, is the culprit behind chocolate pod, a disease that causes unsightly
defects on snap bean pods, ruining their marketability.
Soybean aphids transmit the virus while feeding on bean plants, but
spraying insecticide to prevent such feeding isn't always effective or
economically feasible. Incorporating genes for resistance into the crop offers
a better approach, according ARS plant pathologist
Toward that end, he and ARS geneticist
Miklas developed a polymerase chain reaction (PCR)-based test for detecting
the chocolate pod virus and distinguishing it from other bean pathogens.
They were able to do so by identifying the sequence of amino acids
that make up the virus' coat protein, explains Larsen, who, along with Miklas,
works in the ARS
and Forage Crops Research Laboratory at Prosser. The research was published
in the journal Plant
The test, which yields results in less than a day versus weeks by
traditional methods, has become a critical screening tool in the search for
resistant bean germplasm. Only one snap bean variety out of 63 the researchers
screened showed some resistance to chocolate pod.
Fortunately, a gene found in dry edible beans conferred stronger
resistance. Even better, the gene "coexists" with another, dubbed bc-3, which
confers resistance to other bean pathogens, including bean common mosaic virus
and bean yellow mosaic virus.
Larsen and Miklas plan on crossing the resistant dry beans with the
susceptible snap beans so that they, too, will reap the benefits of possessing
multiple virus-resistance genes. Commercial cultivars developed from such
crosses will be especially important for snap bean farmers in Wisconsin,
Michigan and other Great Lakes states, where the first outbreak of chocolate
pod occurred in 2001.
about this research in the August 2009 issue of Agricultural Research
ARS is the principal intramural scientific research agency of the
U.S. Department of