Certain bacterial diseases in corn and dry edible beans have re-emerged in recent years, sending University of Nebraska 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 no-tillers. 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 first was found in Nebraska corn 40 years ago, says Institute of Agriculture and Natural Resources plant pathologist Anne Vidaver. After resistance was discovered in corn germplasm, the disease became much less common. But it has reared its head again in the last 3 years, cutting yields in some fields up to 40% as it spreads across the U.S. and Canada.
Yield losses of 40% or more also have been seen in dry edible bean fields hit by bean wilt, Vidaver adds. 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 says. “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 says.
Analyses show little difference over the years in the corn pathogen, suggesting it's 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 says. “The results also mean that breeders must use multiple strains of the bean pathogen to test for resistance in their germplasm."
Vidaver notes 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.
Obtaining resistance in dry beans to the diversity of strains will be more challenging than for breeders working with corn, Vidaver says.