RAPD ANALYSIS OF 3 ALTERNARIA SPECIES PATHOGENIC TO CRUCIFERS

Genetic variation in Alternaria brassicae, A. brassicicola, and A. rap hani collected from geographically diverse regions of the world was st udied with RAPD and RFLP markers. Twenty 10-mer primers of arbitrary n ucleotide 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 geog raphically distinct regions could be broadly classified into four grou ps. Intra-regional variation between isolates was less apparent. Varia tion was, however, higher in A. brassicicola, as based on RAPD analysi s. Two isolates (from Canada and France) of A. raphani also showed var iability with different RAPD profiles generated by all five primers te sted. Five polymorphic, distinct RAPD products were used as hybridizat ion probes for RFLP analysis to detect inter- and intra-specific varia tion. Variation among A. brassicae, A. brassicicola, and A. raphani wa s evident. Non-radioactive probes were also used to hybridize with Sou thern blots of A. brassicae, A. brassicicola, Leptosphaeria maculans, Rhynchosporium secalis and Brassica juncea for the selection of A. bra ssicae-specific probe(s). Probe AbP3 specifically hybridized with rest riction digests of A. brassicae but not with those of A. brassicicola or other tested species. This probe should, therefore, be useful for d istinguishing between two important pathogens of crucifers, i.e. A. br assicae and A. brassicicola both in culture and infected tissues.