Reduction in Aflatoxin Content of Maize by Atoxigenic Strains of Aspergillus flavus

Abstract

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. flaws (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 conditionsStrains 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 ...

Influence of the Host Contact Sequence on the Outcome of Competition among Aspergillus flavus Isolates during Host Tissue Invasion

“…When pathogen exclusion relies on competition for a niche (i.e., physical space or a specific nutrient source), both inoculum density and timing of application influence efficacy (5,28,42). Reductions in crop aflatoxin content, for example, are significantly greater when the biocontrol A. flavus is applied to the crop 24 h prior to an aflatoxin producer than with simultaneous inoculation of atoxigenic and aflatoxin-producing isolates (6,8,11).…”

Aflatoxins Biochemistry and Molecular Biology - Biotechnological Approaches for Control in Crops

“…Additionally, this biocontrol agent was also tested for www.intechopen.com control of aflatoxin in corn (Cotty, 1996). When corn ears were either co-inoculated with AF36 and a toxigenic strain of A. flavus or inoculated with AF36 at 24 h prior to inoculation with the toxigenic strain, subsequent aflatoxins concentrations were significantly reduced, compared to inoculation with the toxigenic strain alone (Brown et al, 1991). Also have been demonstrated that other strains of A. flavus and A. parasiticus are capable of reduce aflatoxin contamination in crops; as is case of A. flavus NRRL 21882, a naturally occurring strain isolated from a peanut in Georgia in 1991, that has been used in diverse studies where has been verified its efficacy for reducing contamination in the field.…”

Current Maize Production, Postharvest Losses and the Risk of Mycotoxins Contamination in Tanzania

“…As cited by Magan and Aldred (2007) pre-harvest factors are critical for effective post-harvest prevention of mycotoxins from contaminated maize entering the food supply chain. Several strategies have been investigated to manage, prevent, and reduce mycotoxins contamination in crops include biological, chemical and cultural control practices (Cleveland et al, 2003;Kabak et al, 2006;Strosnider et al, 2006;Wu and Khlangwiset, 2010;Yin et al, 2008;Dorner, 2004;1991a;Wagacha and Muthomi, 2008;Magan and Aldred, 2007).…”

“…Atoxigenic applications rely upon the ability of atoxigenic strains to competitively exclude toxigenic strains from infecting the crop (Cleveland et al, 2003;Wu and Khlangwiset, 2010;Strosnider et al, 2006). Atoxigenic fungal strains include application of competitive nontoxigenic strains of A. flavus and/or A. parasiticus (Dorner, 2004;Yin et al, 2008;Brown et al, 1991a), AF36 (cottonseed), Afla-Guard TM (groundnuts) and AflaSafe TM (maize) (Wu and Khlangwiset, 2010;http://www.aatf-africa.org). A detailed review of biocontrol of mycotoxins can be found on Cleveland et al (2003).…”