Submitted to: Mycoscience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/1998
Publication Date: N/A
Interpretive Summary: Aflatoxin contamination in corn requires destruction of the grain and is considered a major problem. One approach to overcome this problem is to breed plants resistant to the Aspergillus flavus, the fungus that produces the toxin. In a 25-year effort to identify corn varieties with resistance to aflatoxin, many plant pathologists have used the aflatoxin-producing strain Aspergillus flavus NRRL 3357 as pathogen inoculum in corn resistance trials. The present study shows that A. flavus from corn in Illinois is highly sensitive to beta-carotene, a natural aflatoxin-inhibitor in corn, while A. flavus isolates from molded raw peanuts, including NRRL 3357, are much less sensitive to beta-carotene. The study shows that potential resistance factors in corn may have been overlooked because NRRL 3357 is not representative of A. flavus from the Corn Belt. Furthermore, in regions where peanuts and corn are grown in the same fields, the corn crop is likely to become infected with greater numbers of these more potent aflatoxin-producing A. flavus strains. This information will be useful to scientists interested in breeding corn resistant to A. flavus.
Technical Abstract: Thirty-nine Aspergillus flavus genotypes (DNA fingerprinting) isolated from corn grown in a field near Kilbourne, IL, were evaluated for their sensitivity to beta-carotene (50 ug/ml) inhibition of aflatoxin B1 biosynthesis. Inhibition of aflatoxin was greater than 90% for 31 of the genotypes and >79% for 38 of the 39 genotypes. Five A. flavus genotypes isolated from molded raw peanuts, NRRL 3239, NRRL 3357, NRRL 6514, NRRL 6515 and NRRL 13135, produced greater quantities of aflatoxin than all 39 genotypes isolated from corn, and were less sensitive to beta-carotene inhibition. Aspergillus flavus NRRL 3357 is commonly used as inoculum in variety trials for aflatoxin resistance. Isolate identity and sensitivity to potential inhibitors in corn can be critical in assessing corn resistance to aflatoxin. A hypothesis is offered that the cultivation of peanuts contributes to the accumulation of A. flavus clonal populations in field soil that produce consistently elevated quantities of aflatoxins and are less sensitive to naturally occurring aflatoxin inhibitors (e.g. carotenes, xanthophylls, etc.). Furthermore, in rotations with peanuts, corn should become infected with greater numbers of these more potent aflatoxin-producing A. flavus strains.