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Pathology and Mycotoxins

Aflatoxin B₁ and G₁ Production in Developing Zea mays Kernels from Mixed Inocula of Aspergillus flavus and A. parasiticus. O. H. Calvert, Professor of Plant Pathology, University of Missouri Agricultural Experiment Station, Columbia, MO 65201; E. B. Lillehoj(2), W. F. Kwolek(3), and M. S. Zuber(4). (2)(3)Research Microbiologist, and Biometrician, Northern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL 61604; (4)Formerly Supervisory Research Agronomist, Cereal Genetics Research Unit, U.S. Department of Agriculture, retired and now Professor of Agronomy, University of Missouri Agricultural Experiment Station, Columbia, MO 65201. Phytopathology 68:501-506. Accepted for publication 8 August 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-501.

Yields of aflatoxin B₁ for various fungal conidial proportions used as inocula (0/100% A. flavus only, 25/75, 50/50, 75/25, and 100/0% A. parasiticus only) were relatively constant for all inoculation treatments. But the yields of aflatoxin G₁, produced only by A. parasiticus in the mixed inocula showed marked, significant decreases from that produced by A. parasiticus alone. Ratios calculated from the aflatoxin G₁ and B₁ produced, remained relatively constant for each inoculum regardless of the inoculation treatment, but G₁/B₁ ratios for each treatment decreased significantly as the proportion of A. flavus conidia in the inocula increased. Production of aflatoxin G₁ and B₁ was significantly greater in the thin- than in the thick-pericarp hybrid. The highest amounts of aflatoxin G₁ and B₁ were observed when the husks of the ears were pulled back and the kernels either razor- or pinboard-injured before inoculation. The lowest amounts were observed for the widely-used hypodermic-syringe method. The results suggest that A. parasiticus in mixtures is significantly limited from developing fully by A. flavus in competing for the same corn substrate. This may help explain why A. flavus routinely is found present in naturally aflatoxin-contaminated corn and A. parasiticus only rarely.