| Résumé | A 5,238-bp repetitive DNA element from a highly virulent isolate of Leptosphaeria maculanss had been cloned and sequenced. The element is present in approximately 80 copies per haploid genome and hybridizes to every chrosequence is composed of 66% A + T and has numerous, very short, direct and inverted repeats. No RNA complementary to the element was detected in log phase cultures, and no open reading frames of significant length are present in the sequence. It has no structural similarity to other repetitive elements or significant homology to database sequences. We have designated the element LMR1. Southern blot hybridization indicated that the element is present in all isolated of L. maculans that are highly virulent to Brassica napus and B. rapa. The general structure of the element was conserved among isolates of different mating type, pathogenicity group, and geographic origin, as determined by both Southern blot analysis and primerdirected DNA amplification. LMR1 did not hybridize to DNA from weakly virulent strains of L. maculans, with the exception of one isolate. Phylogenetic analyses of restriction fragment length polygenetic analyses of restriction fragment length polymorphism and rDNA sequence indicated that e highly virulent and weakly virulent straing of L. maculans are not monophyletic. Therefore, the presence of the LMR1 element in a weakly virulent isolate may indicate that a rare transfer event has occurred. Surprisingly, the weakly virulent isolate that contains LMR1 is more pathogenic on B. napus and B. juncea that a similar isolate that lacks the element. |
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