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brad-haire-farm-press-peanut-june-ga-2018.JPG Brad Haire
Leaf spot resistance would allow peanut growers, as a part of a continued systems approach to disease management, to reduce fungicide applications during a season.

Decades, new technology put leaf spot-resistant peanut within reach now

Peanut breeders continue to improve the cultivated U.S. peanut with some cultivars already resistant or near-resistant to diseases.

It's been called the 'low-hanging fruit," but it took decades of people pushing down on the limb and a recent technological advancement to put a viable peanut variety with leaf spot resistance within the reach of farmers.

One person leaning hard on the limb now is Corley Holbrook. On March 20, he sat in his lab in Tifton, Ga., somewhat isolated, going over data and working on plans for his peanut breeding program this year, which at that moment had a small problem caused by a big thing.

(EDITOR'S NOTE: It starts in a farmer's field, but the U.S. peanut industry is vast, reaching across the country and beyond. This is the second installment of Farm Press 2020 peanut series sponsored by AMVAC "Going off the farm," which will look at some of the key activities, initiatives and people working on behalf of the Southeast peanut industry.)

The longtime USDA peanut breeder's Plan A to get peanut seed back from the USDA winter nursery in Puerto Rico wasn't going to work. The island was all but shut down due to the ever-growing COVID-19 pandemic. A small snag for him, he said, compared to the problems the pandemic was causing worldwide.

Peanut breeders continue to improve the cultivated U.S. peanut with some cultivars already resistant or near-resistant to diseases such as the tomato spotted wilt virus and to nematodes, or cultivars developed with other characteristics the industry wants to handle and consumers want to use.

Early Leaf Spot

Leaf spot resistance would allow peanut growers, as a part of a continued systems approach to disease management, to reduce fungicide applications during a season, at least reduce the need for fungicides specific to leaf spot control.

Holbrook said some wild species of peanuts are naturally almost immune to leafspot. For years peanut breeders through conventional crossing and backcrossing methods worked to transfer the desirable genetics of those wild species to cultivated varieties. The work done by these peanut breeders starting decades ago cleared the path to leaf spot resistance today, he said, particularly the work of Dan Gorbet, retired University of Florida peanut breeder. In 1984, Gorbet and the UF peanut breeding program released Southern Runner, a cross between Florunner and a plant introduction line with leaf spot resistance, and became the first variety with any leaf spot resistance and what later would show some moderate tomato spotted wilt virus resistance: a milestone for peanut breeding.

Conventional breeding has brought the peanut industry a long way over the years, but it's now getting a shot in the arm. The fiver-year-long, industry-supported initiative to map the peanut genome successfully completed its work and released the information last year. The genomic map along with marker-assisted selection now lets breeders better understand which genes contribute directly to the desired trait.

Genomic Toolbox

But conventional breeders like Holbrook need help to unlock the genomic toolbox. Holbrook didn't have to go far to incorporate the advancement into his work. It's right down the road. Peggy Ozias-Akins is a world-renowned professor in the University of Georgia College of Environmental and Agricultural Sciences and director of UGA’s Institute of Plant Breeding, Genetics and Genomics, and she's a Tifton, Ga., native.

The process is complex with high-tech techniques and equipment, but at the basic level, Holbrook annually gives Ozias-Akins' lab 150 bags containing 100 seeds each. Her laboratory experts are able to slice a small piece of each seed without damaging its vitality, grind the slice, run the DNA and look for the genes specific to leaf spot resistance and return to Holbrook a bag or bags containing seed he knows contain leaf spot resistance. He can then grow those seed out in research plots in Tifton and in Puerto Rico, greatly increasing the speed and accuracy of his conventional breeding program.

A leaf spot resistant cultivar is coming, Holbrook said, either the trait will be introduced into an existing cultivar or come in a completely new cultivar or both, but it's coming.

"Of course, there's no sure things in life, but this is a pretty sure thing that we're going to be successful and we don't know if it's going to be two years out or four years out or what. But eventually in the short term, there's going to be something very promising coming out," Holbrook said.

Marker-assisted Breeding

Steve Brown is the executive director of the Peanut Research Foundation, the group that spearheaded the peanut genome project and the one that rides herd on its projects now.

Brown said the Ozias-Akins Holbrook collaboration may be the best example of how marker-assisted breeding is being used in a real breeding program, "but all U.S. peanut breeders are successfully using marker-assisted breeding to some extent and many genomic scientists are providing critical support for those programs. Each growing region is prioritizing the traits most important to their growers, so each breeder has their own focus.  Diseases other than leafspot such as white mold, sclerotinia and tomato spotted wilt are being addressed, too."

Drought tolerance is also a part of most U.S. peanut breeding programs, Brown said, along with identifying genes and markers for traits such as seed size and fatty acid content. 

"Aflatoxin resistance and flavor conservation is being addressed with research trying to understand complex mechanisms and possible genetic controls, not really breeding programs yet.   There are challenges and costs associated with shifting from conventional breeding to marker-assisted breeding programs and each breeder is addressing those challenges," Brown said.

Brown said agriculture is moving to marker-assisted breeding, gene editing and GMO technologies and that new genomic technologies will change agriculture for the better. 

"Of course, in peanut we have chosen to avoid controversial GMO technologies, even though science continues to confirm the safety of GMO crops. There may be some initial resistance to gene editing as well, but successes in human medicine as well as agriculture will make these concerns fade away with time.

"We may very well shift toward more gene editing technologies in future peanut breeding, but the industry will be our guide as to when and how extensively we move in that direction. These technologies are complex and hard for the consumer to understand, but increasing demand for more, safe, nutritious food will inevitably drive us to use advanced breeding technologies," Brown said.

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