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A gene encoding a cyanide hydratase was cloned from an aggressive isolate of Leptosphaeria maculans, the fungus which causes blackleg disease of oilseed Brassica spp. This enzyme catalyses the breakdown of hydrogen cyanide to a less toxic compound, formamide. The predicted amino acid sequence of cyanide hydratase in L. maculans is 77% and 82% identical to cyanide hydratases from two other ascomycetes, Gloeocercospora sorghi and Fusarium lateritium, respectively. The gene is present as a single copy in the L. maculans genome, in both aggressive and non-aggressive isolates, although there is a restriction fragment length polymorphism between these two isolate groups for this gene. The cyanide hydratase promoter contains four putative target sites for GATA transcription factors, proteins that regulate nitrogen metabolism and other processes. Transcription of cyanide hydratase in an aggressive L. maculans isolate is induced strongly by potassium cyanide. Transcription of the gene is detectable in cotyledons of Brassica juncea and B. napus during infection . L. maculans can utilise the reaction product, formamide, as a sole source of nitrogen. [ABSTRACT FROM AUTHOR]

Volatiles released from glucosinolates (predominantly 2-propenyl glucosinolate) in tissues of Brassica juncea and Wasabi japonica are toxic to the blackleg fungus, Leptosphaeria maculans, in vitro. However, there is no relationship between blackleg resistance (in stems or cotyledons) and the level of 2-propenyl glucosinolate in seed or shoot tissue of B. juncea. A representative isolate from each of two classes of Australian isolates of L. maculans was tested: those which cause stem cankers on both B. napus and B. juncea (e.g. isolate MI), and those which cause stem cankers on B. napus but not on B. juncea (e.g, isolate C13). Even in lines of B. juncea in which levels of 2-propenyl glucosinolate were as low as those in B. napus, isolate C13 was still unable to cause stem cankers. This suggests that either 2-propenyl glucosinolate does not play a major role in blackleg disease resistance, or that isolates of L. maculans able to attack B. juncea can detoxify or evade the toxic effects of hydrolysis products from this glucosinolate. [ABSTRACT FROM AUTHOR]

Pulsed field gel electrophoresis can determine karyotypes (chromosome size and number) of fungi that cannot be studied using cytological methods, 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 analysis. Pulsed field gel electrophoresis has revealed that many fungal plant pathogens have highly variable genomes, even within individual species and that novel-sized chromosomes can be produced in some fungi during meiosis. It can also be exploited to demonstrate the presence of dispensable (B-type) chromosomes in fungi and it is a valuable tool in taxonomic studies for distinguishing between morphologically similar fungi. Pulsed field gel electrophoresis can be used to characterise complex 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. [ABSTRACT FROM AUTHOR]