DNA Fingerprinting Analysis of Vegetative Compatibility Groups in Aspergillus flavus from a Peanut Field in Georgia

Aspergillus flavus Link:Fr. may infect seed of corn, cotton, peanut, and tree nuts and contaminate them with aflatoxins, which are potent hepatoxic, carcinogenic metabolites that pose a significant health hazard (3,4). Members of Aspergillus section Flavi are widespread in crop fields, particularly in subtropical to tropical latitudes (5,11,17,19). Population biologists seek to understand the genetic structure and diversity of A. flavus populations in crop fields and the distribution of relevant phenotypic characters (e.g., aflatoxin and cyclopiazonic acid production, enzyme production, sclerotium formation, pathogenicity or virulence, competitive ability, and so on) among genetically isolated clonal populations. Vegetative compatibility groupings (VCGs), based on complementation tests between nitrate-nonutilizing (nit) mutants, have been used to examine the genetic diversity of A. flavus populations in an Arizona cotton field (1,2), in a Georgia peanut field (7,8), and in samples of corn grown in Georgia (14). McAlpin and Mannarelli (12) developed what appeared to be a species-specific DNA probe, pAF28, that hybridized strongly only to strains of A. flavus and, based on the DNA fingerprints, was able to correctly distinguish the 22 VCGs among 29 strains of A. flavus reported by Papa (14). The pAF28 probe hybridized to multiple and distinct bands for DNA from different subspecies and cultivars of A. flavus (e.g., A. flavus subsp. flavus, A. flavus subsp. parasiticus (Speare) Kurtzman et al., A flavus subsp. flavus var. oryzae (Ahlburg) Kurtzman et al., and A. flavus subsp. parasiticus var. sojae (Sakaguchi and Yamada) Kurtzman et al.), but only a single band on a Southern blot with A. nomius Kurtzman et al. This probe subsequently has been used to characterize the genotypic diversity for populations of A. flavus subsp. flavus (20) and A. flavus subsp. parasiticus (13) isolated from a corn field in Illinois. In the present study, we examined the ability of DNA probe pAF28 to distinguish among 75 A. flavus strains, belonging to 44 VCGs, that were isolated from soil and peanut seed sampled from a peanut field in southwestern Georgia (7). This A. flavus population offers a rigorous test of the probe’s ability to distinguish A. flavus strains belonging to different VCGs and thus provides an independent measure of the genetic structure and diversity of the same A. flavus population. Three strains from Papa (14), representing VCGs 6, 14, and 17 detected by Horn and Greene (7), also were examined. It is also important to know if the pAF28 hybridization probe is capable of distinguishing strains representing other Aspergillus spp. in section Flavi: A. tamarii Kita, A. nomius Kurtzman et al., A. caelatus B. W. Horn (6), A. pseudotamarii Ito et al. (9), and A. bombycis Peterson et al. (15).