Submitted to: Journal of Toxicology Toxins Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 6, 2003
Publication Date: September 1, 2003
Citation: WINDHAM, G.L., WILLIAMS, W.P., BUCKLEY, P.M., ABBAS, H.K. INOCULATION TECHNIQUES USED TO QUANTIFY AFLATOXIN RESISTANCE IN CORN. JOURNAL OF TOXICOLOGY TOXINS REVIEWS. 2003. V.22.P.313-325. Interpretive Summary: Aflatoxins are cancer causing toxins produced by the fungus, Aspergillus flavus, and may be found in corn kernels in developing ears in the field. Grain contaminated with high levels of aflatoxin can not be transported out of state and may be labeled unusable. Developing corn lines which resist the development of aflatoxin or limit growth of the fungus is the best control method. Corn genotypes evaluated for aflatoxin resistance in field studies must be inoculated with the fungus because aflatoxin levels fluctuate from year to year. Development of inoculation techniques has played an important role in producing corn lines with resistance to aflatoxin. A number of different inoculation techniques are used by researchers in the South and in the Corn Belt. Field inoculation techniques either wound developing kernels or leave the kernels intact. Some inoculation techniques simply apply fungal spores to silks once they emerge from the ear. Wounding techniques place fungal spores on to kernels that have been mechanically damaged. Insects have also been used to carry spores inside ears to infect kernels. Environmental conditions such as high temperature and drought stress may have an important role in the amount of fungal infection caused by different inoculation techniques. Corn lines can also be tested for resistance in laboratory studies. Fungi with unique colors or that can be stained to produce a certain color have been used to determine the resistance of certain lines. Although much progress has been made in the methods used to evaluate corn for aflatoxin resistance, inoculation techniques that are more efficient, less labor intensive, and less costly still need to be developed.
Technical Abstract: The development of Aspergillus flavus inoculation techniques has played an important part in developing corn (Zea mays L.) germplasm resistant to aflatoxin contamination. Corn genotypes evaluated for aflatoxin resistance in field studies must be artificially inoculated due to the sporadic nature of aflatoxin contamination from year to year. A number of different inoculation techniques are used by researchers in the South and Midwest. Field inoculation techniques either wound developing kernels or leave the kernels intact. Non-wounding techniques apply A. flavus conidia to exposed silks or silks inside the husks without damaging kernels. Wounding techniques deliver A. flavus conidia onto kernels that have been mechanically damaged. Inoculation techniques utilizing ear feeding insects to vector conidia have also been used in field studies. Environmental conditions such as ambient temperature and drought stress appear to have a significant impact on artificial inoculations. Laboratory evaluation techniques have been developed to confirm aflatoxin resistance identified in corn genotypes in the field. Color mutants and transformants of Aspergillus spp. have been used in field and laboratory studies to identify resistant genotypes. More efficient, less labor intensive, and less costly inoculation techniques need to be developed to aid in the production of aflatoxin resistant corn hybrids.