Occurrence of aflatoxins and fumonisins in preharvest maize from south-western Nigeria.

A survey was conducted on the incidence of fungi, and the natural occurrence of aflatoxins and fumonisins in preharvest maize from fields in south-western Nigeria. Mycological examinations revealed the predominance of F. verticillioides (Zea mays) (syn. F. moniliforme), occurring in 89.3% of samples with a mean kernel infection of 49.4%, while Aspergillus flavus was isolated from 65% of samples having a mean kernel infection of 6.8%. Aflatoxin B1 was detected in 18.4% of samples with a mean of 22 micrograms kg-1, while aflatoxins B2, G1 and G2 were present in 7.8, 2.9 and 1% of the samples with mean levels of 10, 8 and 7 micrograms kg-1, respectively, in contaminated samples. Total aflatoxins ranged from 3 to 138 micrograms kg-1 in positive samples, with a mean of 28 micrograms kg-1. Fumonsin B1 was the predominant toxin detected in terms of frequency (78.6% of samples) and quantity (concentration range 70-1780 micrograms kg-1, mean = 495 micrograms kg-1). Fumonisin B2 was detected in 68 samples (66%) with a mean of 114 micrograms kg-1. Fifteen samples were contaminated with both aflatoxins and fumonisins.