Incidence of fumonisin B2 production within Aspergillus section nigri populations isolated from california raisins

Abstract

Fungi belonging to Aspergillus section Nigri occur frequently and in high populations on grapes. Species within this section include Aspergillus niger, A. tubingensis, and A. carbonarius, and they are potential sources for mycotoxins including ochratoxin A and fumonisin B2 (FB2) in grapes and grape products. Aspergillus section Nigri strains were isolated from California raisins to examine the frequency and extent of FB2 production. Of 392 strains isolated, 197 strains were identified as A. niger, 131 of which produced FB2. These strains produced from 1.2 to 27 μg/ml FB2 in culture. PCR amplification of fum1 and fum19 gene fragments showed that all FB2-producing strains and nearly all nonproducing strains of A. niger contain these genes. An additional 175 strains were identified as A. tubingensis, none of which produced FB2. PCR with fum1 and fum19 primers amplified gene fragments of 14 and 25% of A. tubingensis strains, respectively, suggesting that putative orthologs of A. niger fumonisin biosynthetic genes might occur in A. tubingensis. These results indicate that FB2 production is common among field isolates of A. niger and suggest that the potential for FB2 contamination of California raisins should be addressed further.