Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/1999
Publication Date: N/A
Interpretive Summary: Aflatoxin contamination of corn is a major problem for growers in the southern United States and can also be a problem for growers in the Midwest. Aflatoxin is a cancer-causing toxin produced by the fungus, Aspergillus flavus. Corn containing low levels of aflatoxin can not be shipped out of the state and may be unsuitable for livestock feed. Insect damage to developing corn ears may increase the levels of aflatoxin in the grain at harvest. The effect of the southwestern corn borer, an important pest of corn, on aflatoxin contamination has not been determined. Studies were conducted in the field at Mississippi State University to determine the effect of the southwestern corn borer (SWCB) on aflatoxin levels in corn grain. Aflatoxin levels were highest when plants were treated with both SWCB and the fungus when compared to plants treated with either SWCB or the fungus alone. However, a number of factors needed to be considered to demonstrate this dramatic increase in aflatoxin levels caused by SWCB. Methods used to apply SWCB and the fungus, site of placement of these pests on the plant, and timing of the insect and fungus application were all critical to demonstrating increased aflatoxin levels due to SWCB. Hybrids resistant to the fungus and a Bt hybrid had high levels due to SWCB and the fungus were both present. These studies demonstrate the need to develop corn hybrid with resistance to both the fungus and insects to control aflatoxin contamination.
Technical Abstract: Field studies were conducted to determine effect of southwestern corn borer (SWCB) on Aspergillus flavus kernel infection and aflatoxin accumulation in maize hybrids. When A. flavus conidia and SWCB neonate were applied to commercial hybrids, aflatoxin contamination and A. flavus kernel infection were highest in plants treated with both the fungus and the insect. In another study, the effect of SWCB on aflatoxin contamination and A. flavus kernel infection in hybrids resistant and susceptible to A. flavus was determined. When SWCB was combined with A. flavus, aflatoxin levels and kernel infection were dramatically higher than hybrids inoculated with A. flavus alone regardless if hybrids were resistant or susceptible to A. flavus. The interaction of A. flavus and SWCB was also determined on hybrids resistant and susceptible to A. flavus on a commercial hybrid with and without the Bacillus thuringiensis (Bt) toxin. Although insect damage ratings were lowest on the Bt hybrid, alfatoxin contamination in this hybrid was not different (P=0.05) from the other hybrids. These studies indicate that SWCB can substantially increase aflatoxin levels when combined with A. flavus. However, inoculation/infestation techniques, placement of the fungus and the insect, and timing of inoculation and infestation are all critical in demonstrating a synergistic relationship between A. flavus and SWCB on maize.