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Newly approved fungus may help clean up cotton

A fungus discovered by an Agricultural Research Service scientist crowds out its relatives, steals their food and space — and could prove to be an important ally to farmers across Arizona and Texas.

Known simply as AF36, the naturally occurring fungus crowds out harmful fungi that can contaminate crops, a burden costing the U.S. cotton industry up to $10 million annually.

ARS scientist Peter J. Cotty discovered this “atoxigenic” strain of fungus and used it to invent a biocontrol strategy for fighting fungal toxins that may spoil some crops. Now, after 11 years of studies and field tests on more than 80,000 acres, AF36 has received approval from the U.S. Environmental Protection Agency for use on cotton throughout Arizona and Texas.

Aflatoxin is a toxic compound produced by some strains of the fungus Aspergillus flavus that may occur on cottonseed, corn and peanuts. Cottonseed is the main feed of dairy cows, so a safe milk supply relies on “clean” cottonseed. Because toxins may be transferred to milk, the U.S. Food and Drug Administration maintains a stringent 20-parts-per-billion limit on aflatoxin in cottonseed. Anything more renders the cottonseed unmarketable.

Cotty, a plant pathologist at ARS' Southern Regional Research Center in New Orleans, La., developed a strategy to aid farmers: alter fungi in fields so that they don't produce aflatoxins. It was a simple-sounding solution, but one requiring an expert knowledge of fungi and 17 years of lab and field studies.

Fungi compete with one another for limited space and nutrients to survive. Playing on this biological fact, Cotty seeded affected fields with the AF36 strain he discovered in Arizona, essentially pitting this benign strain of A. flavus against toxin-producing ones.

The good news: In the field tests, AF36 reduced toxic strains by up to 90 percent.

The real advantage of AF36, however, lies in its delivery. Wheat seed, colonized with the beneficial strain, is distributed on top of the soil after the last cultivation. With a ready food supply of wheat, AF36 gets a step ahead of other fungi.

ARS joined with the Arizona Cotton Research and Protection Council to develop a commercial process for producing and delivering atoxigenic formulations.

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