Comparison of Two Inoculation Methods for Evaluating Maize for Resistance toAspergillus flavusInfection and Aflatoxin Accumulation

W Paul Williams,J Erik Mylroie,Michael N Alpe,Gary L Windham,Seval Ozkan

doi:10.1155/2013/972316

W Paul Williams, J Erik Mylroie + Show 3 more

Open Access

https://doi.org/10.1155/2013/972316

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Abstract

Aflatoxin, the most potent carcinogen found in nature, is produced by the fungusAspergillus flavusand occurs naturally in maize,Zea maysL. Growing maize hybrids with genetic resistance to aflatoxin contamination are generally considered a highly desirable way to reduce losses to aflatoxin. Developing resistant hybrids requires reliable inoculation methods for screening maize germplasm for resistance toA. flavusinfection and aflatoxin accumulation. The side-needle technique is a widely used inoculation technique: anA. flavusconidial suspension is injected underneath the husks into the side of the ear. This wounds the ear and limits expression of resistance associated with husk coverage, pericarp thickness, and seed coat integrity. In this investigation, the side-needle technique was compared with a second inoculation method that involved dispensing wheat kernels infected withA. flavusinto plant whorls at 35 and 49 days after planting. Results showed that although the side-needle technique produced higher levels of aflatoxin accumulation, differences inA. flavusbiomass produced by the two inoculation techniques were not significant. Both inoculation techniques were effective in differentiating resistant and susceptible single cross hybrids irrespective of the use ofA. flavusinfection or aflatoxin accumulation as a basis to define resistance.

Highlights

Aflatoxin is produced by the fungus Aspergillus flavus and occurs naturally in maize, Zea mays L
The A. flavus/maize ratio was lowest for the three hybrids that had the lowest levels of aflatoxin accumulation with both inoculation methods. These results indicate that selection for a lower A. flavus/maize ratio should be effective in selecting and developing maize germplasm with resistance to aflatoxin accumulation
Inoculation of plants with A. flavus infected wheat was effective in identifying maize genotypes with resistance to aflatoxin accumulation

Summary

Introduction

Aflatoxin is produced by the fungus Aspergillus flavus and occurs naturally in maize, Zea mays L. The most potent carcinogen found in nature, is toxic to both humans and animals [1,2,3]. S. Food and Drug Administration restricts the sale of grain with aflatoxin levels exceeding 20 ng/g [2]. Aflatoxin was first recognized as a major problem for maize production in the southeastern United States in the 1970s. In 1977, over 90% of maize was contaminated with aflatoxin, and aflatoxin levels exceeded 20 ng/g in 90% of samples evaluated in Georgia [11, 12]. An increase in the use of maize as a substrate for ethanol production further exacerbates losses from aflatoxin contamination: concentration of aflatoxin in distillers’ dry grain during fermentation represents a serious impediment to its use in animal feeds [16, 17]. Identification and release of maize germplasm with high levels of resistance to A. flavus infection and aflatoxin

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