It’s not fun when a fungus contaminates crops. But safe native fungi show promise in the fight against toxic fungal contamination.
The fungus Aspergillus flavus can infect several crops including corn. Some varieties or strains of A. flavus produce aflatoxins. Aflatoxin contamination costs U.S. farmers billions of dollars every year. Worse, aflatoxins are harmful for humans and animals.
To reduce aflatoxin contamination of crops, farmers use safe commercial strains of A. flavus. Those biocontrol strains don’t produce aflatoxins. When applied to crops, the biocontrol strains out-compete the harmful aflatoxin-producing fungi. That reliably reduces levels of aflatoxins in the harvest, transport and storage stages.
But commercial strains may not be the only answer. A new study shows that using safe native strains of A. flavus can be as effective, or even more effective, than commercial strains.
Using native A. flavus strains could have many advantages. Native strains may be better adapted to the soil type and weather conditions. Therefore they may perform better in the field compared to non-native strains.
Using commercial strains can have some disadvantages. They usually need to be reapplied each year, at a cost of $20 per acre. Also the application must be done aerially or manually. That can deter farmers from using commercial strains.
Native strains, on the other hand, occur naturally in growing areas. They may be more persistent in the soil and not need to be reapplied every year. My colleagues and I tested native strains of A. flavus that produce no or depressed levels of aflatoxin. We also tested commercial strains. Both reduced crop aflatoxin levels.
Corn for human consumption can have maximum aflatoxin levels of 20 parts per billion, per U.S. Food and Drug Administration regulation. Untreated crops had aflatoxin levels greater than 35 parts per billion. Native and commercial strains reduced aflatoxin levels to less than 10 parts per billion.
Unexpectedly the study also showed that certain combinations of native strains are more effective than commercial strains in reducing aflatoxin levels. That’s because the combinations take advantage of fungal biology. Their mating types are compatible, allowing them to reproduce and sustain their population.
When the researchers applied native strains of compatible mating types to the test plots, aflatoxin levels were reduced to less than 2 parts per billion in some cases. That was a better outcome than any commercial strain. Our results suggest that using native strains could lead to sustained reductions of aflatoxin levels. Using native strains could be cost-effective for farmers through the long term.
Although the study was conducted in North Carolina, we anticipate the approach can work in other areas. A preliminary experiment in Texas also showed that paired native strains reduced aflatoxin levels more efficiently compared to a single commercial strain. We need to continue testing this approach in cornfields across different states. We also need to monitor aflatoxin levels through several growing seasons.
Future field trials may include testing current commercial strains plus a compatible mating-partner strain. Different combinations of native strains may also be tested. I’m optimistic the approach can go beyond aflatoxin. Fungal toxins pose a continual threat to food safety. Our approach can potentially be applied to other toxin-producing fungi as well.
Read more about the research in “Agronomy Journal.” The work was supported by the Agriculture and Food Research Initiative Competitive Grants Program grant no. 2013-68004-20359 from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.