Reduction in Aflatoxin Content of Maize by Atoxigenic St rains of Aspergillus flavus
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چکیده
In field plot experiments, an atoxigenic strain of Aspergillus flavus interfered with preharvest aflatoxin contamination of corn when applied either simultaneously with or one day prior to a toxigenic strain. The atoxigenic strain reduced preharvest aflatoxin contamination 80 to 95%. The atoxigenic strain was also effective in reducing postharvest aflatoxin contamination caused by both an introduckd toxigenic strain and by strains resident on the kernels. The results suggest that atoxigenic strains of A.flavus may have potential use as biological control agents directed at reducing both preharvest and postharvest aflatoxin contamination of corn. Aflatoxins, toxic metabolites of the fungi Aspergillus jlavus Link: Fr. and A. parasiticus Speare, are potent carcinogens which pose serious health hazards to humans and domestic animals because they frequently contaminate agricultural commodities (4,8). Corn grown in the southeastern United States is more frequently colonized by high populations of A. flavus than corn grown in the Midwest, where most U.S. corn is grown (19). However, the drought of 1988 created favorable conditions for A. j7avus in the Midwest, and the Wall Street Journal (February 23, 1989) reported one-third of the crop tested in Iowa and Illinois contained dangerous levels of aflatoxin. This, according to the article, caused greatly increased concern in the U.S. corn industry. Biological control of several plant diseases has been demonstrated by utilizing certain strains of the causal organism (12,14,15,20). Strains of A. flavus that do not produce aflatoxins have been selected from fungal populations in cotton and corn fields (6,17). In greenhouse tests, atoxigenic strains of A.flavus significantly reduced production of aflatoxin B, in cottonseed coinoculated during development with toxigenic strains (7). When atoxigenic strains were introduced into wounded cotton bolls one day prior to the toxigenic strain, even greater control of aflatoxin was obtained (7). This study provided useful information but was camed out in a controlled environment. In the field, where A. j7avus first associates with the crop, greater biological and environmental complexities exist. Also, it is not known if atoxigenic strains influence contamination of harvested crops which already possess complex microflora and may be previously infected with A. f laws (10). In the present study, an atoxigenic strain, previously identified and shown effective in greenhouse tests on cottonseed, was tested for efficacy on corn under field and storage conditions. A preliminary presentation of these studies has been made (3). MATERIALS AND METHODS F~rngal strains and growth conditions Strains of A. flavus utilized in this study were isolated from agricultural soil and cottonseed in Arizona (6,7). Strain 13 produced large quantities of aflatoxins both in culture and in developing cottonseed. while strain 36 did not produce detectable levels (<I0 nglg) (6). Cultures were grown at 30°C in the dark on a 5% V-8 juice, 2% agar medium. Plugs (3 mm in diameter) of sporulating cultures were stored at 8OC on a long-term basis in Cdram vials containing 5 ml of distilled water (5.6). Conidia from 7to10-d-old cultures suspended in deionized water served as inocula
منابع مشابه
Evaluation of atoxigenic isolates of Aspergillus flavus as potential biocontrol agents for aflatoxin in maize.
Aflatoxin contamination resulting from maize infection by Aspergillus flavus is both an economic and a public health concern. Therefore, strategies for controlling aflatoxin contamination in maize are being investigated. The abilities of eleven naturally occurring atoxigenic isolates in Nigeria to reduce aflatoxin contamination in maize were evaluated in grain competition experiments and in fie...
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