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Aflatoxin Program Objectives

Atoxigenic Strain Technology for Aflatoxin Management in Cotton

Summary

Aflatoxin contamination of cottonseed and other commodities such as corn, pistachios, almonds and figs has, for decades, created a major negative impact on agriculture in Arizona and other southwestern and western states. In order to ensure a healthy food supply in the United States, crops cannot enter select markets if contamination exceeds regulatory limits. Widespread aflatoxin contamination results in sizable annual revenue losses to each of these industries each year.

For years, technology utilizing atoxigenic strains of the common fungus Aspergillus flavus, has reduced the aflatoxin producing potential of fungal communities in both pilot scale field tests and area wide commercial program settings. A commercial scale grower owned manufacturing facility has enabled the production of atoxigenic strains to keep pace with expanding demand. Laboratories at the manufacturing facility assist in the extensive array of analyses necessary to evaluate both the development and implementation of the program as well as its potential for expansion to other crops.

Technical Review

Aflatoxins are a group of toxic, carcinogenic fungal metabolites produced by specific isolates of Aspergillus flavus. Concern for human and animal health has led to the establishment of regulatory limitations on the quantity of aflatoxins permitted in foods and feeds throughout the world. Aflatoxin contamination creates serious problems for the United States cottonseed industry. This is due to the ability of dairy cattle to readily transmit aflatoxins from feed to milk in slightly modified form. In order to ensure a healthy food supply in the United States, laws prohibit the aflatoxin content of milk from exceeding 0.5 ppb. To ensure this level, cottonseed fed to dairy cattle is mandated to contain less than 20ppb. Overseas, aflatoxin controls are frequently more stringent than in the U.S. Thus, aflatoxin content can limit export of commodities and aflatoxin regulations can serve as non-tariff barriers to trade. The desert southwest and particularly Arizona is at a serious disadvantage in this area due to aflatoxin.

The fungal isolate AF36 is an atoxigenic member of the species Aspergillus flavus that has been shown to have the ability to competitively exclude aflatoxin-producing fungi and thereby reduce aflatoxin contamination of cottonseed. In greenhouse, field-plot, and commercial field tests, the efficacy of Aspergillus flavus AF36 has repeatedly been demonstrated. Results to date suggest that applications of AF36 reduce the average aflatoxin producing potential of fungal communities within both the treated and nearby fields. Treatments also have been shown to cause long-term reductions in the average aflatoxin producing potential of fungi in treated fields and in so doing provide the opportunity to reduce contamination throughout entire treatment areas over the long run. Evaluating the extent to which such reductions can be economically achieved is a major emphasis of the current work.

Data covering more than seven years of intensive field studies exists which supports the use of atoxigenic strains of Aspergillus flavus to reduce aflatoxin contamination. The application of this bio-control management strategy in both full field and area wide management settings strongly suggests that this technology will be capable of producing long term reductions in the quantity of aflatoxins that the fungi in an area are capable of producing. However, as stated above, this needs to be tested and agronomic procedures to optimize are-wide programs are needed. Efforts to develop area-wide management programs based on atoxigenic strain technology have been undertaken since 1999 with total cumulative statewide acres treated exceeding 105,000. Despite this level of use, many questions still demand resolution for atoxigenic strain technology to meet its potential of being a reliable tool for area-wide aflatoxin management programs.

Based on analysis of the data, the assumption is that utilization of atoxigenic strain technology in a large scale or area wide setting would significantly increase the level of program effectiveness over time. This is true for two principal reasons: 1) tests have shown that AF36 applications have influences beyond treated fields and 2) increased levels of AF36 in field soils tend to persist from one season or cropping cycle to the next, thereby resulting in a cumulative increase in the atoxigenic strain. These phenomena may very well result in a cost benefit ratio, which would be economically attractive to Arizona cotton producers.

Relevance Statement

The sale of cottonseed for dairy and feedlot cattle represents a key element in the agricultural economy of Arizona. The closing of the State’s last cottonseed oil mill in 1998 resulted in the elimination of a critical outlet for seed with high aflatoxin levels. The annual value of Arizona cottonseed exceeds $38 million. Losses due to high aflatoxin levels often are calculated at more than $9 million. This represents a significant loss to the State’s cotton producers. Prior to the introduction of atoxigenic strain technology no effective aflatoxin management tools existed. Data collected and analyzed from five years of area-wide commercial evaluation of this unique biological control system have validated the benefits of the technology. From a manufacturing standpoint, refinements in processing technique coupled with equipment modifications continue to improve and standardize the AF36 program.

Facilities and Equipment

The Arizona Cotton Research & Protection Council has two fully equipped laboratories; one for manufacturing and quality control of atoxigenic strain inoculum and one for conducting soil, crop and air sample fungal evaluation.

Field sampling activities necessary to generate soil, crop and air samples for fungal analyses are organized through six district supervisors working out of five field offices geographically located throughout Arizona’s cotton grower regions.