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

Corn genotypes evaluated for aflatoxin resistance in field studies must be artificially inoculated with Aspergillus flavus due to the sporadic nature of aflatoxin contamination from year to year. We compared a spray inoculation technique 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 loam soil were more prone to drought stress and had higher levels of aflatoxin contamination than those grown in a silty clay loam soil with a high water-holding capacity. 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 silty clay loam, maximum daily temperatures during the 14-day period following inoculation were positively correlated with aflatoxin contamination. Cumulative rainfall during periods of 14 to 28 days and 21 to 42 days following inoculation was negatively correlated with aflatoxin contamination. In the 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. Our results also demonstrated that temperature and moisture stress prior to inoculations may have a significant effect on aflatoxin contamination.