Scientists develop new approaches to fighting bacterial diseases in corn, dry beans

Date:12-21-2010

Certain bacterial diseases in corn and dry edible beans have re-emerged in recent years, sending University of Nebraska–Lincoln scientists in search of new solutions.

In the case of corn, it’s Goss’ bacterial wilt and blight of corn that is again causing problems for producers. For dry edible beans, it’s bean wilt that’s an issue again. Research so far seems to indicate that the fight against Goss’ wilt will be easier than the one against bean wilt.

Goss’ bacterial wilt – Clavibacter michiganensis ssp. nebraskensis — first was found in Nebraska corn 40 years ago, said Institute of Agriculture and Natural Resources plant pathologist Anne Vidaver (photo). After resistance was discovered in corn germplasm, the disease became much less common. But it has reared its head again in the last three years, cutting yields in some fields up to 40% as it spreads across the United States and Canada.

Yield losses of 40% or more also have been seen in dry edible bean fields hit by bean wilt (Curtobacterium flaccumfaciens pv. flaccumfaciens), Vidaver said. In addition, the disease can affect seed quality and phytosanitary certification for export.

Scientists including Vidaver have been trying to determine what’s changed to increase the incidence of these two diseases, exploring the possibility of changes in the germplasm as well as the potential that it’s being transmitted through seed.

"Our primary question was whether there had been substantial changes in the pathogen, overcoming resistance,” Vidaver said. “Tools used for examining this question centered on the genetics of the pathogen, whether there were substantial changes in the genomic structure over the years that might indicate that the newer isolates were different from those originally isolated.”

Researchers compared more than 100 isolates, going back 40 years to the present and representing strains collected from all previously known states, to determine similarities and differences.

"The results are strikingly different between the two pathogens,” Vidaver said.

Analyses show little difference over the years in the corn pathogen, suggesting it is quite stable and that using a single or a few strains in breeding programs should be successful in obtaining resistance to Goss’ wilt.

"In contrast, the bean pathogen is very heterogeneous, with no clear patterns emerging over the years or geographic location,” Vidaver said.
 
Vidaver noted that the bean pathogen originally was isolated about 50 years earlier than the corn pathogen. The bean wilt bacterium’s ability to evolve “may simply reflect more opportunity to mutate and/or exchange genetic material than with the corn pathogen, or that the origins, perhaps from contaminated seed, reflect diversity in sites of origin.

"The results also mean that breeders must use multiple strains of the bean pathogen to test for resistance in their germplasm,” the IANR scientist said of the research, funded by the university’s Agricultural Research Division, Nebraska Department of Agriculture and Nebraska Dry Bean Commission.

Obtaining resistance in dry beans to the diversity of strains will be more challenging than for breeders working with corn, said Vidaver.

This research – which also includes UNL scientists Irina Agarkova, Robert Harveson, Tamra Jackson and Patricia Lambrecht – will continue without Vidaver, who retired in July after a 44-year career at UNL.

Her career has been marked by many firsts: first woman department head in the Institute of Agriculture and Natural Resources; first married woman hired to a tenure track in IANR; first woman department head in plant pathology worldwide; first woman to direct UNL’s Center for Biotechnology; first married woman with children to be named president of the American Phytopathological Society; and the first (and only) woman to serve as chief scientist for the United States Department of Agriculture.

Vidaver, who escaped the Nazis from her native Austria during World War II, also has made a number of scientific discoveries, including a rare purple-pigment producing bean wilt bacterium; a Gram-positive bacterium that causes Goss’ bacterial wilt and blight of corn; an unusual pathogen that causes blight of milkweed; and the tracking of beneficial bacteria associated with plants.

Source: CropWatch