Genetic variation in Alternaria brassicae, A.
brassicicola, and A. raphani collected from geographically
diverse regions of the world was
studied with RAPD and RFLP markers. Twenty 10-mer primers of arbitrary
nucleotide sequences were tested for amplification of
genomic DNA of A. brassicae using PCR. Of these, five primers
amplified the genomic DNA from 20 A. brassicae isolates and
produced reproducible RAPD profiles. UPGMA analysis of RAPD data showed
that isolates collected from geographically distinct
regions could be broadly classified into four groups. Intra-regional
variation between isolates was less apparent. Variation was,
however, higher in A. brassicicola, as based on RAPD analysis.
Two isolates (from Canada and France) of A. raphani also showed
variability with different RAPD profiles generated by all five primers
tested. Five polymorphic, distinct RAPD products were used as
hybridization probes for RFLP analysis to detect inter- and
intra-specific variation. Variation among A. brassicae, A.
brassicicola, and A. raphani was evident. Non-radioactive
probes were also used to hybridize with Southern blots of A.
brassicae, A. brassicicola,
Leptosphaeria maculans, Rhynchosporium secalis and
Brassica juncea for the selection of A. brassicae-specific
probe(s). Probe AbP3 specifically hybridized with restriction digests of
A. brassicae but not with those of A. brassicicola or
tested species. This probe
should, therefore, be useful for distinguishing between two important
pathogens of crucifers, i.e. A. brassicae and A. brassicicola
in culture and infected tissues.