Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/1999
Publication Date: N/A
Interpretive Summary: Aflatoxins produced by the fungus Aspergillus flavus, and found on corn at harvest, are recognized as potent hepatotoxins and carcinogens causing mortality or reducing the productivity of farm animals. The corn industry's first defense against aflatoxin is the black light test for bright greenish yellow fluorescent (BGYF) kernels. However, it is difficult to predict aflatoxin levels based on the percentage of BGYF kernels in grain sampled. To investigate this problem, we measured the ability of a natural population of the aflatoxin-producing fungus to produce BGYF kernels and aflatoxin. The study identifies sources of natural variation in aflatoxin levels in infected corn kernels which will better enable the corn industry to interpret the significance of BGYF counts for a specific region and corn hybrid.
Technical Abstract: Nineteen strains of Aspergillus flavus, including 14 genotypes (DNA fingerprinting), isolated from corn grown near Kilbourne, IL, were evaluated for their ability to produce BGYF kernels and aflatoxins in a commercial corn hybrid (Pioneer 3394) grown at the same location. Tooth-pick wound-inoculations were performed with each A. flavus strain on ten or more corn ears in the late milk to early-dough stage of maturity (21 days following mid-silk). At harvest, the 20 kernels nearest each wound-site were segregated into three categories: wound-inoculated kernels, non-wounded BGYF kernels, all other non-wounded kernels. Sample weights of wound-inoculated kernels averaged 0.6% (range = 0.4%-3%) while sample weights of BGYF kernels averaged 5% (range = 1.5%-11.5%). Aflatoxin levels among 11 samples of wound-inoculated kernels varied sixteen fold (mean = 10,500 ppb; range = 1,060 ppb-17,200 ppb) while related samples of non-wounded bright greenish yellow fluorescent (BGYF) kernels varied seventy-three fold (mean = 1,100 ppb; range = 52 ppb-3,800 ppb). Greater sensitivity to kernel 'resistance factors' may explain why some A. flavus genotypes (e.g. GT#02, NRRL 27676; GT#38 NRRL 26477, etc.) showed a proportionately greater suppression in aflatoxin following infection of the germ and endosperm. Removal of both the aflatoxin-contaminated wound-inoculated kernels and non-wounded BGYF kernels afforded grain samples with a mean aflatoxin value of 2 ppb (range = ND-14 ppb).