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Aflatoxin taking millions from peanut growers

Ron Smith dfp-ron.smith_.apres_.2.panel_.jpg
An APRES panel discussed aflatoxin via zoom during the annual meeting, held virtually July 14. Panelists are: Top, Johnny Cason, Renee Arias and Marshall Lamb; bottom: Tim Brenneman and Corley Holbrook..
Aflatoxin research must eliminate the start and stop approach that has not worked.

A Texas AgriLife Extension agronomist used to challenge producers to accept change. He said: "If you always do what you've always done, you'll always get what you've always got."

The peanut industry could adopt that advice as it wrestles with the devastating impact of aflatoxin contamination, which resulted in more than $117 million in losses to the 2019 Southeast peanut crop.

"That's $84 per acre," said Marshall Lamb, research leader and location coordinator of the USDA/ARS National Peanut Research Laboratory in Dawson, Ga.

Lamb was one of six speakers during an American Peanut Research and Education Society (APRES) aflatoxin panel discussion during the Society's 52nd annual meeting, held virtually July 14 as a result of the COVID-19 pandemic.

Lamb added that aflatoxin cost Southeast peanuts an average of $56.8 million a year from 2010 through 2019, a $41 per acre loss.

Since 1980, the industry experienced aflatoxin contaminated crops every 10 years, said Darlene Cowart, corporate director of food safety and quality for Birdsong Peanuts, Suffolk, Va.

"Since 2010, we have had six moderate to severe aflatoxin crops," Cowart said.

Lamb said aflatoxin contamination net losses from 1993 through 1996 averaged almost $26 million per year, $28.06 per acre. Those figures include some disaster relief options. Gross figures show annual losses totaling more than $52 million and $56.59 per acre.

"These estimates are not official," Lamb said, "and are very conservative."

Cowart said these losses occur in an era with evolved management, sampling and testing programs, "currently one of the best in the world." Yet the problem is no better.

"We haven’t improved at all," Lamb said. "If we account for changes in policy and old loss protections, we are actually worse."

He and Cowart agree that the industry must change to prevent "getting what they've always got."

"We must eliminate the start-stop approach we've used in the past," Lamb said.

Need new approach

He said the past trend has been to escalate research efforts when aflatoxin levels rise and then to back off when crops were cleaner.

"We have not succeeded with this approach. And we will not succeed if we continue this way. The 2019 crop is proof. We need a long-term, comprehensive, coordinated approach to eliminate aflatoxin in U.S. peanuts," Lamb said.

Other panelists weighed in on ongoing research efforts focused on managing aflatoxin contamination and reducing losses.

Diane Rowland, chair of the agronomy department and professor of crop physiology in the Institute of Food and Agricultural Sciences, University of Florida, Gainesville, said research under way considers identifying vulnerability points for aflatoxin.

"We need to find the weak links in the Aspergillus pathosystem," Rowland said. Research efforts include imaging technology — thermal and hyperspectral.

"We are using advanced sensing and advanced analytical approaches," Rowland said. "We hope to get to machine learning and perhaps eventually to artificial intelligence."

She said research efforts must be "transdisciplinary with researchers embedded into each other's programs. We have to conduct risk analysis across the entire peanut industry."

Vulnerability points include planting, harvesting, buying points, warehousing and shelling, Rowland said.

Old enemy

Tim Brenneman, University of Georgia plant pathologist, Tifton, says aflatoxin is "an old enemy that has learned some new tricks.

"Aspergillus is an old one that is suited to a changing climate," he said. "It is highly seed-borne and easily spread. It is rapidly adapting to some of the fungicides we now use. Fungicides are critical, but we need to find the weak links… and new approaches to control."

Brenneman said the pathogen presented a new challenge in 2020. In February the Georgia seed lab reported low germination and high levels of Aspergillus flavus in treated seed, but not in all seed lots.

He said the primary seed treatment, Dynasty, showed a high incidence of the pathogen. A relatively new one, Rancona, was more effective.

"The seed lab was swamped." he said, "In Georgia, we will see a shift in seed treatment in 2020 to Rancona."

He said pathogens developing resistance to fungicides is not new. "We've seen it before."

Rancona, he added, is not a silver bullet. "It did not solve all the stress issues. Other factors play a role." He referred to the disease triangle. Infection requires a host, a pathogen and the proper environment.

The 2019 environment favored A flavus late in the season, hot and dry.

Brenneman added that aflatoxin can be a threat not only to crops but also to human health. He said fungicides will remain important, but resistance will continue to be an issue, even with new ones coming on.

Varietal resistance

Varietal resistance is one option Corley Holbrook, USDA/ARS research leader for the Crop Genetics and Breeding Research Unit in Tifton, has been working on for some 30 years.

"Our objective is to develop screening technology to identify sources of resistance, then begin a breeding program.

"Do genetic variations exist?" He said screening looks for "moderate resistance. We did not expect complete resistance."

Holbrook said south Georgia trials show a correlation between drought tolerance and aflatoxin tolerance. "We've made progress with improved yield and drought tolerance. A few have aflatoxin tolerance."

The target, he said is preharvest aflatoxin contamination.

"It is possible, but far from easy," he said, "to breed peanut for reduced preharvest aflatoxin contamination (PAC).

"In Georgia, there seems to be an association between drought tolerance and PAC."

He said the aflatoxin "set" of cultivars contain several genotypes with good drought tolerance and/or reduced PAC.

"When feasible, drought tolerance and/or reduced PAC would be ideal traits for breeding with molecular markers. We've made progress."

RNA interference

Renee Arias, USDA/ARS plant pathology, University of Georgia, is looking deep into the peanut. She talked about research in advances in RNA interference technology.

“The purpose of RNA interference technology is to use a non-GMO delivery of RNA to the plant as a way to make the plant generate small interfering RNAs (siRNAs) to reach the peanut seed; thus, when the fungus Aspergillus invades the seeds, the siRNAs prevent the fungus from making aflatoxin (that is siRNAs can silence aflatoxin-biosynthesis genes inside the fungus).”

Arias reported progress in reducing the aflatoxin load in seed treated with the RNA interference process.

She noted other questions to be considered in ongoing research. "What is the effective delivery method and the number of applications? When should the application occur? How can we be sure to reach all the seeds in a lot?"

Other concerns include the minimum siRNA concentration necessary to prevent aflatoxins.

"And how long will it last in the seed after harvest?" she asked.

Infection factors

Cowart talked about factors that predispose peanuts to aflatoxin infection. Those include: seed variety, high temperatures (air and soil between 72 and 95 from 30 to 45 days before harvest), drought conditions 30 to 45 days before harvest, commingling dryland stressed acres and irrigated acres, short window from digging and harvesting, rain at harvest, high moisture, uneven drying (mechanical or natural), and damaged kernels due to insect or mechanical operations.

Management makes a difference, Cowart said. "Monitor the crop during the season and identify risk factors."

She said regional testing at harvest is important. "Segregate based on risk for storage. Electronic sorting is recommended for damaged kernels."

She also recommends finished lot tasting.

Aflatoxin management is "an industry problem," Cowart said. "Own it together. We have a lot of smart people in this industry."

Lamb said the magnitude of the issue can't be overestimated. "We lose more than the crop," he said. "We also risk losing customers. If we lose customers in Europe because of aflatoxin, it will take a long time to get them back.

"We have to have a short-, medium- and long-range research approach for aflatoxin research. And we cannot stop until we have won the battle."

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