APPLICATION OF PULSED-FIELD GEL-ELECTROPHORESIS TO THE STUDY OF GENOMES OF FUNGAL PATHOGENS OF PLANTS

Pulsed field gel electrophoresis can determine karyotypes (chromosome size and number) of fungi that cannot be studied using cytological met hods, due to their chromosomes failing to condense or being too small to visualise. This technique allows genome size and genetic maps to be developed for fungi that are not amenable to classical linkage analys is. Pulsed field gel electrophoresis has revealed that many fungal pla nt pathogens have highly variable genomes, even within individual spec ies and that novel-sized chromosomes can be produced in some fungi dur ing meiosis. It can also be exploited to demonstrate the presence of d ispensable (B-type) chromosomes in fungi and it is a valuable tool in taxonomic studies for distinguishing between morphologically similar f ungi. Pulsed field gel electrophoresis can be used to characterise com plex loci, such as those controlling host-specific toxin production in Cochliobolus species. The application of this technique to Australian isolates of Leptosphaeria maculans, which causes blackleg disease of canola (Brassica napus), is discussed.