A total of seventeen isolates of Aspergillus flavus from maize were collected from different agro-ecological zones of Tamil Nadu, India. The isolates were tested for their ability to produce aflatoxin B1 (AFB1) in vitro by indirect competitive enzyme-linked immunosorbent assay (ELISA). The amount of AFB1 produced by the isolates of A. flavus ranged from 1.9 to 206.6 ng/ml. Among the various isolates of A. flavus, the isolate AFM46 produced the highest amount of AFB1. DNA was extracted from A. flavus isolates and their molecular variability was investigated by using restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified internal transcribed spacer (ITS) regions of ribosomal DNA. PCR amplification with ITS1 and ITS4 primers resulted in the amplification of a product of approximately 600 bp. Digestion of the PCR products with the restriction enzymes EcoRI, HaeIII and TaqI produced fragments of different sizes. Analysis of the genetic coefficient matrix derived from the scores of RFLP profiles showed that minimum and maximum per cent similarities among the tested A. flavus strains ranged from 0 to 88%. Cluster analysis using the unweighted pair-group method with arithmetic average (UPGMA) clearly separated the isolates into five groups (group I–V) confirming the genetic diversity among the A. flavus isolates from maize.
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