Autor(es):
Rodrigues, P. 
; Venâncio, Armando ; Kozakiewicz, Z. ; Lima, Nelson
Data: 2009
Identificador Persistente: http://hdl.handle.net/1822/11244
Origem: RepositóriUM - Universidade do Minho
Assunto(s): Aspergillus; Section flavi; Aflatoxins; Cyclopiazonic acid
Descrição
A polyphasic approach consisting of morphological, chemical and molecular characterization was applied to
31 isolates of Aspergillus Section Flavi originating from Portuguese almonds, with the aim of characterizing
and identifying aflatoxigenic and non-aflatoxigenic strains. On the basis of morphological characters (mainly
colony color on Czapek-Dox agar and conidia morphology), we found two distinct groups among the
population under study: 18 isolates (58%) had dark-green colonies and rough conidia, and were classified as
Aspergillus parasiticus; the remaining 13 isolates (42%) had yellow-green colonies and smooth to finely rough
globose conidia, and were classified as Aspergillus flavus. Chemical characterization involved the screening of
the isolates for aflatoxins B (AFB) and G (AFG), and also for cyclopiazonic acid (CPA), by HPLC with
fluorescence and UV detection, respectively. All A. parasiticus isolates were strong AFB and AFG producers,
but no CPA production was detected, showing a consistent mycotoxigenic pattern. The A. flavus isolates
showed to be more diversified, with 77% being atoxigenic, whereas 15% produced CPA and low levels of AFB
and 8% produced the 3 groups of mycotoxins. Aflatoxin production was also screened on Coconut Agar
Medium (CAM), and the results were consistent with the HPLC analysis. Sclerotia production showed no
correlation to aflatoxigenicity.
Molecularly, two genes of the aflatoxin biosynthetic pathway, aflD (=nor1) and aflQ (=ord1=ordA) were
tested for presence and expression (by PCR and RT-PCR, respectively). The presence of both genes did not
correlate with aflatoxigenicity. aflD expression was not considered a good marker for differentiating
aflatoxigenic from non-aflatoxigenic isolates, but aflQ showed a good correlation between expression and
aflatoxin-production ability.
