Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/2004
Publication Date: 1/1/2005
Citation: Williams, W.P., Windham, G.L., Buckley, P.M., Perkins, J.M. 2005. Southwestern corn borer damage and aflatoxin accumulation in conventional and transgenic corn hybrids. Field Crops Research. 91:329-336. Interpretive Summary: Aflatoxin contamination is a major obstacle to profitable corn production in the South. Aflatoxin is produced by the fungus Aspergillus flavus and is toxic to livestock and causes cancer in humans. Heat and drought stress during the growing season increases the likelihood of aflatoxin accumulation in the grain. Damage from ear feeding insects, such as the southwestern corn borer, also causes an increase in aflatoxin. In this investigation, 10 pairs of corn hybrids consisting of one conventional hybrid and the same hybrids transformed with an insecticidal gene from Bacillus thuringiensis (Bt) were evaluated for damage by southwestern corn borer and aflatoxin contamination. The developing ears were either inoculated with A. flavus, infested with southwestern corn borer, or both. When infested with southwestern corn borer, ears of the Bt hybrids sustained less damage than those of the conventional hybrids. Aflatoxin contamination was significantly higher in the conventional hybrids as well. When ears were wounded during inoculation with A. flavus, aflatoxin contamination was high in both Bt and conventional hybrids. Growing Bt hybrids rather than conventional corn hybrids in areas where southwestern corn borer levels are high should be effective in reducing both feeding on the ears and aflatoxin contamination.
Technical Abstract: Southwestern corn borer, Diatraea grandiosella Dyar, is a major pest of corn, Zea mays, L., in the southern United States. In addition to the direct yield losses caused by southwestern corn borer, larval feeding on developing ears provides a site for fungi to enter the ear. Aspergillus flavus infection and the subsequent accumulation of aflatoxin in corn grain are major limitations to profitable corn production in the southern United States. This investigation was conducted to determine the effect of southwestern corn borer feeding on aflatoxin accumulation and to determine the effectiveness of transgenic corn hybrids expressing the delta endotoxin insecticidal (Cry delta Ab) proteins isolated from Bacillus thuringiensis (Bt) in reducing aflatoxin accumulation. The effects of kernel-wounding and nonwounding A. flavus inoculation techniques and southwestern corn borer infestation on aflatoxin accumulation in 10 pairs of conventional (nonBt) and transgenic (Bt) corn hybrids were investigated in a two-year study. Both (nonBt) and (Bt) hybrids exhibited high levels of aflatoxin accumulation when inoculated with a kernel-wounding technique. When inoculated with a non-wounding technique and infested with southwestern corn borer, aflatoxin accumulation was significantly higher in nonBt than Bt hybrids. Aflatoxin accumulation was also significantly higher for nonBt hybrids inoculated with A. flavus and infested with southwestern corn borer than for hybrids that were only inoculated with A. flavus. The results of this investigation indicate that these Bt hybrids should be effective in reducing aflatoxin contamination in areas where high southwestern corn borer infestations occur. The reduced levels of aflatoxin accumulation associated with Bt hybrids are likely a consequence of reduced insect damage rather than resistance to A. flavus infection or aflatoxin accumulation per se.