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Differentiation of Maize Genotypes for Aflatoxin Concentration in Developing Kernels¹

Maize (Zea mays L.) hybrids have been shown to differ in the amount of aflatoxin found in kernels at harvest. The objective of this study was to determine the optimum time for measuring aflatoxin in samples of grain during ear maturation and thus evaluate the efficiency of measuring genotype differences in aflatoxin accumulation at grain maturity. Ten-ear samples of two commercial hybrids were wound-inoculated in the field with spores of Aspergillus flavus Link ex Fr. at 20 days after full silk and were collected at 30,40,50, and 60 days post-silking from 10 replicates of each hybrid-sampling date combination in 1982, 1983, and 1984. Data were recorded for aflatoxin concentration in the grain, percentage of ears with visible A. flavus, and insect damage. Significant differences occurred for aflatoxin concentration among years and also between hybrids and among sampling dates within years. Each hybrid had a unique linear rate of aflatoxin accumulation during maturation as determined by the regression of the logarithm of aflatoxin amount on sampling date. The accumulation rates of individual hybrids were not different from year to year. The magnitude of hybrid differences for aflatoxin accumulation was largest on the final sampling date as was the statistical difference between hybrids as determined by Fratios. Ratings of hybrids for insect damage and the percentage of ears with visible A.flavus tended to be smaller for ears harvested on the later sampling dates. The practice of evaluating hybrids based on differences in aflatoxin concentration in grain near physiological maturity (about 8 weeks post-silking) seems justified, based on the results of this study.

Key Words: Corn • Zea mays L. • Aspergillus flavus Link ex Fr. • Mycotoxins • Time of sampling

² Research geneticist, USDATARS-IBPMRL, P.O. Box 748? Tifton, GA 31793; plant pathologist, Coastal Plain Exp. Stn., Tifton, GA 31 793; and research entomologist, USDA-ARS-IBPMRL, P.O. Box 748, Tifton, GA 31793.

Received for publication November 29, 1985.