RAPD analysis of genetic diversity among the isolates of Aspergillus flavus from different hosts and locations

Aflatoxin contamination is a major problem in maize, groundnut, chillies, cotton and tree nuts. These aflatoxins are low molecular weight toxic and carcinogenic secondary metabolites produced by Aspergillus flavus, A. parasiticus and A. nomius. In the present study, a total of 11 isolates of A. flavus isolated from groundnut, maize and chilli collected from different locations of Tamil Nadu, India were tested for their ability to produce aflatoxin B1 (AFB1) in vitro by indirect competitive enzyme-linked immunosorbent assay. The results show that the isolates vary in their level of toxin production. The amount of AFB1 produced by the toxigenic isolates of A. flavus ranged from 6.6 to 108.1 ng ml^-1. Among the various isolates of A. flavus, the isolate VKR produced the highest amount (108.1 ng ml^-1) of AFB1. The isolates viz. CBE1, CBE2, BSR1, BSR3 and BSR4 were found to be non-toxigenic. The genetic variability among these isolates was assessed by Random amplified polymorphic DNA (RAPD) analysis. DNA fragments of between 0.15 and 3.0 kb were obtained using 13 random primers, and each isolate differed in the size and number of PCR products indicating considerable polymorphism. Cluster analysis using Unweighted Pair Group Method with Arithmetic Mean clearly separated the isolates into four main clusters confirming the genetic diversity among the isolates of A. flavus. Both toxigenic and non-toxigenic isolates were intermingled in these four groups, indicating that no relationship exists between RAPD profile and the production of aflatoxin by A. flavus.