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Postharvest Pathology and Mycotoxins

Determination of Resistance to Aflatoxin Production in Maize Kernels and Detection of Fungal Colonization Using an Aspergillus flavus Transformant Expressing Escherichia coli β-Glucuronidase. R. L. Brown, Southern Regional Research Center, U.S. Department of Agriculture, Agricultural Research Service, New Orleans, LA 70179; T. E. Cleveland(2), G. A. Payne(3), C. P. Woloshuk(4), K. W. Campbell(5), and D. G. White(6). (2)Southern Regional Research Center, U.S. Department of Agriculture, Agricultural Research Service, New Orleans, LA 70179; (3)Department of Plant Pathology, North Carolina State University, Raleigh 27965; (4)Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; (5)(6)Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 85:983-989. Accepted for publication 9 June 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1995. DOI: 10.1094/Phyto-85-983.

Thirty-one maize inbreds and the highly resistant GT-MAS:gk maize population were screened for resistance to aflatoxin production by Aspergillus 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. Certain genotypes, previously shown to be resistant in field trials, demonstrated resistance in the kernel-screening assay. Twenty-two genotypes had intact-kernel resistance that was comparable to GT-MAS:gk. A separate experiment was done to visualize fungal colonization of internal tissue in susceptible and resistant maize kernels and to further elucidate the relationship between fungal colonization and aflatoxin production. Five genotypes screened in the inbred evaluation, were inoculated with an A. flavus aflatoxin-producing strain containing the Escherichia coli β-d-glucuronidase (GUS) reporter gene linked to an A. flavus β-tubulin gene promoter. Histochemical staining of nonwounded and wounded kernels detected differences in GUS expression among genotypes, and there was a relationship between GUS expression and the amount of aflatoxin detected in kernels. Minimal GUS expression was related to low aflatoxin production in wounded kernels of two inbreds previously identified in field trials as having moderate-to-high levels of resistance to aflatoxin production. These results suggest that resistance to aflatoxin production is directly related to resistance to fungal colonization in certain genotypes.