Effect of Aspergillus flavus inoculation methods and environmental conditions on aflatoxin accumulation in corn hybrids

Authors: Windham, Gary; Williams, William; Hawkins, Leigh; Brooks, Thomas

Submitted to: Toxin Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2008
Publication Date: 12/1/2008
Citation: Windham, G.L., Williams, W.P., Hawkins, L.K., Brooks, T.D. 2009. Effect of Aspergillus flavus inoculation methods and environmental conditions on aflatoxin accumulation in corn hybrids. Toxin Reviews. 28:70-78.

Interpretive Summary: Aflatoxin contamination caused by the fungus Aspergillus flavus is a chronic problem in corn in the southeastern United States. Corn genotypes are commonly evaluated for aflatoxin in the field for resistance by inoculating developing ears with the fungus. Spraying Aspergillus flavus spores on silks on the ears simulates what happens naturally, but this technique is often inconsistent in producing suitable levels of aflatoxin. Our study was conducted to compare the spray inoculation technique with a wounding type inoculation technique and natural infection in two soil types. The wounding technique (where 2-3 kernels were wounded during inoculation) produced higher levels of aflatoixn contamination than either the spray or natural infection in both soil types. The spray technique produced higher levels of aflatoxin in a sandy soil compared to a clay soil. High temperatures and rainfall after inoculations were found to be associated with aflatoxin levels in corn grown in the clay soil. In the sandy soil, high temperatures and rainfall before inoculation were found to be important to aflatoxin contamination. The spray technique is useful in certain types of aflatoxin evaluations and should be most successful when conducted on sandy soils that will expose the plants to severe drought stress.

Technical Abstract: An Aspergillus flavus spray inoculation technique was compared with the side-needle technique and natural infection for inducing aflatoxin contamination in commercial corn hybrids in two soil types from 2000 to 2006. Hybrids inoculated using the side-needle technique consistently had high levels of aflatoxin contamination. Hybrids inoculated with the spray technique and grown in a soil more prone to drought stress (a Myatt loam) had higher levels of aflatoxin contamination than when grown in a soil with a high water-holding capacity (a Leeper silty clay loam). The association of maximum daily temperatures and cumulative rainfall during nine periods before or after A. flavus inoculation with aflatoxin contamination was determined. In the Leeper silty clay loam, maximum daily temperatures during the 14 day period following inoculation were positively correlated with aflatoxin contamination. Cumulative rainfall during period 14 to 28 days and 21 to 42 days following inoculation was negatively correlated with aflatoxin contamination. In the Myatt loam, maximum daily temperatures before and after inoculation were positively correlated with aflatoxin contamination. Also, cumulative rainfall during a period 21 to 42 days before inoculation was negatively correlated with aflatoxin contamination. We found that the spray technique induced higher levels of aflatoxin in the Myatt loam which has a high sand content. Our results also demonstrated that temperature and moisture stress prior to inoculations may have a significant effect on aflatoxin contamination.