Molecular characterization of the black Aspergillus isolates responsible for ochratoxin A contamination in grapes and wine in relation to taxonomy of Aspergillus section Nigri.

This work examines ochratoxigenic mycobiota in grapes by ap-PCR analysis sequence analysis of the ITS and IGS regions and ability to produce OTA. A comparison was also made with many reference strains of Aspergillus section Nigri. Based on ap-PCR profiles, derived from two microsatellite primers, three main groups were obtained by UPGMA cluster analysis corresponding to A. carbonarius, A. niger and A. tubingensis. The cophenetic correlation values corresponding to ap-PCR UPGMA analysis revealed a higher genetic variability in A. niger and A. tubingensis than in A. carbonarius. In addition, no genotypical differences could be established between OTA producers and nonproducers in all species analysed. Phylogenetic relationships inferred from ITS and IGS sequences are, mostly, congruent with earlier works. A. niger and A. tubingensis strains were closely related, but not identical, and they clustered into two distinct groups within the A. niger aggregate. Sequence analysis also showed genetic divergences between strains of A. foetidus and the rest of the Aspergillus section Nigri. Additionally, the phylogenetic analysis was consistent in separating a new group of ochratoxigenic strains, frequently isolated from grapes, named A. tubingensis-like. All strains of A. carbonarius analysed by sequence analysis had identical ITS and IGS sequences confirming the lack of significant genetic variability within this important ochratoxigenic species.