Researchers making progress against aflatoxin

There have been some new developments regarding aflatoxin concerns for corn growers in the Gulf South.

In Arizona, researchers and cooperative Extension personnel have been evaluating an “atoxigenic” strain(s) of Aspergillus flavus, the fungal pathogen that causes aflatoxin.

According to Larry Antilla, director of the Arizona Cotton Research and Protection Council, “atoxigenic strains of A. flavus can be highly effective agents for limiting or preventing aflatoxin contamination in cottonseed. We have had very good success with it here in Arizona. We have seen reductions in aflatoxin occurrences over most of the acreage that the product has been tested.

“Positive effects on the aflatoxin content of the cotton crop as indicated by commercial analyses were widespread in 2001 and 2002. In Pinal County, prior to initiation of AF36 treatments, one farm had not produced clean cottonseed in 30 years. By the second year of treatments (2000), 14 of 17 fields (82 percent) tested below 20 ppb. In 2001, after a third year of AF36 applications, 86 percent of the fields were below 20 ppb.

“As a result, the grower was able to derive an economic advantage through the sale of clean seed.”

At the present time, this project is being done in conjunction with USDA under an Emergency Use Permit. Arizona agriculture personnel will be requesting full registration and label for the product this year.

In Arizona, what the researchers have been doing is inoculating sterilized wheat seed with the atoxigenic strain (AF36) and either flying it on at 10 pounds of seed per acre or using a ground rig such as a Gandy rig at layby in producer's fields. The seed is put directly on the soil surface, with no disturbance of the soil taking place.

“The way this atoxicigenic strain works is it essentially outcompetes the biotic A. flavus to where the toxic A. flavus can not do as much harm,” according to Steve Moore, a professor located at the Dean Lee Research Station in Alexandria, La., working on aflatoxin in Louisiana.

“Results generated in Mississippi over the last two years have been mixed,” according to Rick Mascagni, a professor located at the Northeast Research Station in St. Joseph, La. “I think the reason that there was more success the first year was that aflatoxin levels were higher than what we experienced in the Mid-South last year, thus leading to less of an impact with the product when compared to the first year of testing.

Hamed Abbas, a research plant pathologist, and colleague Robert Zablotowicz, a microbiologist, both scientists with the USDA-ARS located in Stoneville, Miss., are working with two “new” nontoxigenic isolates of A. flavus that Abbas has developed. K49 and CT3 have the potential to reduce aflatoxin concentrations.

“What we experience is very difficult testing conditions because of aflatoxin not being a chronic problem as it is in parts of Arizona and Texas. Here in Mississippi and Louisiana we do not get consistently high aflatoxin levels. Thus, more years of evaluation are required to fully ascertain the success of this biological control strategy.

Results from 2001 indicated that inoculation with the toxigenic isolate increased levels of aflatoxin in corn by 167 percent compared to the non-inoculated control. CT3 and K49 inoculation reduced aflatoxin levels in corn kernels by 86 percent and 60 percent, respectively.

In 2002, the nontoxigenic CT3 and K49 reduced aflatoxin levels 61 percent and 76 percent, respectively, but inoculation with the toxigenic isolate had little effect on aflatoxin.

In 2001, mixtures of toxigenic and nontoxigenic isolates had little effect on aflatoxin levels, but in 2002 inoculation with mixtures of K49 and CT3 reduced aflatoxin levels 68 percent and 37 percent respectively.

Results indicate that indigenous A. flavus nontoxigenic isolates have potential as biocontrol agents to reduce aflatoxin contamination in Mississippi Delta corn. The bottom line is that there is potential to reduce aflatoxin concentration with these isolates.”

LSU AgCenter personnel will be working cooperatively with researchers at Stoneville, Miss., to evaluate this material on corn production in Louisiana.

Steve Moore and Rick Mascagni are planning to conduct individual location studies with preliminary results which should be available sometime at the end of the summer. There is a limited amount of compound available which makes large scale testing not feasible at the present time.

These atoxigenic strains of A. flavus may have the potential to reduce aflatoxin concentrations to acceptable levels where blending with non contaminated corn would be more feasible. This would be another tool for producers to try to insure a less contaminated crop.

In addition to the development of these atoxigenic strains of A. flavus research is on-going towards the development of more aflatoxin-tolerant corn hybrids. This research combined with the atoxigenic strains of aflatoxin could possibly give producers the break that they need.

David Y. Lanclos is the soybean, corn and grain sorghum specialist at LSU AgCenter.

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