A Reliable Field-Inoculation Method for Identifying Aflatoxin-Resistant Maize

Abstract

Aflatoxin accumulation in maize (Zea mays L.), caused by Aspergillus flavus, is a serious and chronic problem in the southeastern United States. Identification and development of resistant germplasm are crucial for developing aflatoxin-resistant hybrids. However, a lack of a reliable field-inoculation method is a significant impediment to maize breeders’ success. Previously available inoculation methods resulted in extremely high coefficients of variation for aflatoxin. We evaluated four non-injury inoculation methods at five inoculation dates for studying concentration of aflatoxin in contaminated maize kernels. Needle-in-silk channel (NSC) method involved injection of A. flavus conidial suspension into an ear through silk channel with a syringe; toothpick-in-silk channel (TSC) involved insertion of a Czapek medium-covered, conidia-laden toothpick in silk channel of an ear; toothpick-under-husk (TUH) was similar to TSC, except that Czapek-covered, conidia-laden toothpick was placed on the surface of kernels by making an incision in the husk in the middle of an ear; and bag inoculation (BAG) involved placement on an ear of an inoculation bag (a shoot bag) at the bottom of which was placed 5 mL Czapek medium that was covered with A. flavus conidia. The toothpick-under-husk inoculation method was judged most reliable for evaluating aflatoxin concentration differences, as indicated by a substantially reduced coefficient of variation (CV = 20.6%).