Genome size and complexity of the obligate fungal pathogen, Bremia lactucae

The size and organization of the genome of Bremia lactucae, a highly specialized fungal pathogen of lettuce, has been characterized using dot blot genomic reconstructions, reverse genomic blots, and genomic DNA reassociation kinetics. The haploid genome contains 5 × 10⁷ bp of DNA and 65% of the nuclear DNA is repeated. Low copy sequences are interspersed with repeated sequences in a short-period interspersion pattern. This pattern of genome organization is different to that described for other fungi. Although most fungi have been shown to contain some form of repetitive DNA other than the ribosomal repeat, the high percentage of repetitive DNA and the interspersion of low copy and repeated sequences are atypical of fungi characterized previously.