ARS | Publication request: Aspergillus flavus biomass in maize estimated by quantitative real-time polymerase chain reaction is strongly correlated with aflatoxin concentration

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 12, 2009
Publication Date: November 1, 2009
Citation: Mideros, S.X., Windham, G.L., Williams, W.P., Nelson, R.J. 2009. Aspergillus flavus Biomass in Maize Estimated by Quantitative Real-Time Polymerase Chain Reaction is Strongly Correlated with Aflatoxin Concentration. Plant Disease. 93:1163-1170.

Interpretive Summary: The accumulation of aflatoxin in corn grain is a major food and feed safety problem. Grain contaminated with aflatoxin is markedly reduced in value. Aflatoxin is produced by the fungus Aspergillus flavus, and corn grown in the South is especially vulnerable to high levels of aflatoxin accumulation. Growing corn hybrids with resistance to A. flavus infection and the subsequent accumulation of aflatoxin is widely considered the best way to reduce losses to aflatoxin in corn. Germplasm with resistance to aflatoxin accumulation has been identified; however, corn hybrids with high levels of resistance to aflatoxin accumulation are not yet available commercially. Accurately quantifying resistance to A. flavus infection and aflatoxin accumulation are critical to the development of resistant corn hybrids. The current investigation was undertaken to evaluate the effectiveness of a new method for quantifying A. flavus in grain samples. Quantitative real-time polymerase chain reaction (qPCR) was used to quantify A. flavus in grain samples that were also analyzed for aflatoxin. The correlation between the two traits was generally good, but evaluating both characteristics should help in identifying and determining the roles of genes associated with reduced levels of aflatoxin. By quantifying both A. flavus and aflatoxin, it should be possible to determine the function of genes associated with resistance. This will enhance efforts to develop commercial hybrids with resistance to aflatoxin contamination.

Technical Abstract: Aspergillus flavus causes Aspergillus ear rot of maize and produces aflatoxins. There are published assertions that resistance to aflatoxin accumulation and pathogen colonization are distinct traits in maize. However, the levels of colonization are difficult to characterize for a pathogen such as A. flavus. For this reason, we developed and validated quantitative real-time PCR (qPCR) assays to estimate fungal biomass in maize tissues. In order to study their relation, fungal biomass and aflatoxin levels were measured in a set of hybrids that were field-inoculated in a conducive environment in Mississippi. These plant materials were part of breeding efforts for development of resistance to A. flavus and carry known sources of resistance among their progenitors. The hybrids were mainly early tropical and non-stiff stalk genotypes adapted to the local conditions. Our results show an unexpectedly high correlation between fungal load and aflatoxin levels in ground maize kernels. Our qPCR methodology could have a direct impact on breeding programs that aim to identify lines with resistance to aflatoxin accumulation, and set the stage for future studies on the genetic dissection of aflatoxin-related traits.