Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/1/2005
Publication Date: 12/1/2005
Citation: Windham, G.L., Williams, W.P., Buckley, P.M., Abbas, H.K., Hawkins, L.K. 2005. Techniques used to identify aflatoxin resistant corn. In: Abbas, Hamed K., editor. Aflatoxin and Food Safety. Boca Raton, FL: CRC Press. p. 407-421. Interpretive Summary: Aflatoxins are produced by the fungus Aspergillus flavus and are one of the most toxic compounds found in nature. These toxins are often found in corn grown in the Southeast and occasionally are found in corn grown in the Midwest. Grain contaminated with high levels of aflatoxin can not be transported out of state and may be labeled unusable. The most promising method for controlling aflatoxins is the development of corn lines which prevent 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 artificially inoculated because fungal infection varies from year to year. Development of inoculation techniques has played an important role in producing corn lines with resistance to aflatoxin. 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. Fungal isolates with unique colors, or that contain proteins that fluoresce under UV light, or that can be stained to produce a certain color have been used to study fungal movement and development in resistant corn 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: Aflatoxin was first recognized as a preharvest problem in corn in 1971. Since that time, researchers have conducted studies to identify corn with resistance to Aspergillus flavus and aflatoxin contamination. Since A. flavus infection of developing ears and aflatoxin contamination is sporadic from year to year, artificial inoculation techniques needed to be developed. Field inoculation techniques have been developed that 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 involve delivering A. flavus conidia on to kernels that have been mechanically damaged. The side-needle technique, which wounds two to three kernels, has been a very reliable inoculation technique. Inoculation techniques utilizing ear feeding insects to vector conidia have also been used in field studies. Laboratory evaluation techniques have been developed to confirm aflatoxin resistance identified in corn genotypes in the field. Aspergillus color mutants and transformants have been used in field and laboratory studies to identify resistant genotypes. Additional research needs to be conducted to develop an inoculation technique that will provide uniform infection in multiple environments.