DETERMINATION OF RESISTANCE TO AFLATOXIN PRODUCTION IN MAIZE KERNELS AND DETECTION OF FUNGAL COLONIZATION USING AN ASPERGILLUS-FLAVUS TRANSFORMANT EXPRESSING ESCHERICHIA-COLI BETA-GLUCURONIDASE

Thirty-one maize inbreds and the highly resistant GT-MAS:gk maize popu lation were screened for resistance to aflatoxin production by Aspergi llus flavus using a kernel-screening laboratory assay. Intact kernels from each line were evaluated in three trials. Significant differences among genotypes for resistance to aflatoxin production were found. Ce rtain genotypes, previously shown to be resistant in field trials, dem onstrated resistance in the kernel-screening assay. Twenty-two genotyp es had intact-kernel resistance that was comparable to GT-MAS:gk. A se parate experiment was done to visualize fungal colonization of interna l tissue in susceptible and resistant maize kernels and to further elu cidate the relationship between fungal colonization and aflatoxin prod uction. Five genotypes screened in the inbred evaluation, were inocula ted with an A. flavus aflatoxin-producing strain containing the Escher ichia coli beta-D-glucuronidase (GUS) reporter gene linked to an A. fl avus beta-tubulin gene promoter. Histochemical staining of nonwounded and wounded kernels detected differences in GUS expression among genot ypes, and there was a relationship between GUS expression and the amou nt of aflatoxin detected in kernels. Minimal GUS expression was relate d to low aflatoxin production in wounded kernels of two inbreds previo usly identified in field trials as having moderate-to-high levels of r esistance to aflatoxin production. These results suggest that resistan ce to aflatoxin production is directly related to resistance to fungal colonization in certain genotypes.