Most veteran peanut farmers in the Southeast will remember the devastating spread of tomato spotted wilt virus (TSWV) in the 1990s. Yields suffered with the spread of the disease and the value of Georgia’s crop was reduced more than 10 percent. Nearly every variety grown back then was susceptible to the virus and a flood of cultivars were developed to incorporate resistance.
But TSWV is hardly the only disease researchers and growers are affected by. White mold, leaf spot, root knot nematodes and many others can also impact crop quality. As breeders are developing new cultivars, it’s useful to know the resistance or susceptibility levels so that growers can modify their disease management programs. However, many breeding programs can’t afford their own plant pathologists for that evaluation.
One research program at the University of Georgia quantifies and evaluates the levels of disease resistance of runner peanut cultivars currently grown in the Southeast, as well as advanced lines from breeders’ programs that are being considered for release. Led by Dr. Tim Brenneman, department of plant pathology at the UGA Tifton campus, the program offers “any breeder, public or private, the opportunity to send germplasm they wish to have evaluated. The information we generate is useful to the breeders in knowing the strengths and weaknesses of potential cultivars. The data is also critical in assigning point values in the Peanut RX disease risk index to new cultivars as they are released, as well as to help plan their fungicide programs to get the most economical control.”
Difference in leaf spot susceptibility of two genotypes. Image: Tim Brenneman
Brenneman believes that one of the most significant contributions of the program was “the development of the inoculation methods in the field to actually quantify disease resistance, particularly to white mold. White mold is arguably number one of the biggest disease problems we have with peanuts and also one of the hardest to control because it grows underground very easily. Even though we have good fungicides, the difficulty of getting those fungicides to the target can make it hard to control it. When it gets underground and starts going it can really cause a lot of loss.”
“The methodologies we developed in this project where we fumigate fields and then inoculate individual plants by hand under natural conditions, has really been the best way to get consistent, accurate phenotypic data on these peanut lines. That type of information has been really critical to breeders like Dr. Corley Holbrook with USDA, who works with collaborators like Dr. Peggy Ozias-Akins and Dr. Josh Clevenger to identify and understand the genes for resistance.”
That understanding is also useful to private breeders like Dr. Kim Moore of ACI Seeds. “Since we're small, we don't have access to all of the technology that is available to the university breeding programs,” said Moore. “But through the work that Tim Brenneman has done in testing lines, we've learned a lot about our new lines that we could never have known about the levels of disease resistance for specific diseases. Dr. Brenneman's program has been instrumental in getting that information to us. And we actually have found that we had a whole lot better disease resistance than we even thought.”
When disease resistance information comes from a university and not a commercial company, Moore says, growers see the information as more credible. “When we can present third-party data that’s from a researcher at the University of Georgia, it gives us a lot more clout with the growers.”
“I think the way the breeding technology and the understanding of the peanut genome identifying markers for resistance, high oleic oil chemistry and many other traits will continue to revolutionize the industry," said Brenneman. "It’s the most exciting arena in the whole peanut industry right now. I think we're just seeing the tip of the iceberg with some of these developments.”
Thinking back to the 1990s, “if it wasn't for the new varieties coming from the breeding programs, it would have been a disaster for the industry,” said Moore. “Having diversity of genetics in production is the safety net of the industry.” The more we can understand about the resistance and susceptibility of current and future cultivars through programs like Dr. Brenneman’s at UGA, the better protected the industry will be.
Header image: Research plots showing an overview of the test prior to harvest. Courtesy of Tim Brenneman.