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serriola showed a balanced pattern, the pathogen population from L. Here we report that Bremia lactucae on Lactuca sativa is not homogeneous but emerged from several host shifts from Lactuca serriola and that Bremia accessions from both species are not forming distinct genepools. Bremia belongs to the genera of downy mildews with pyriform haustoria, which feature highly variable ITS-repeats that can be used as high-resolution markers for population genetics studies.
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In the first case, searching for resistance in prickly lettuce is straightforward, in the second case it would rather be futile. Consequently, it seems important to investigate the population genetic relationships of wild prickly lettuce and cultivated lettuce, in order to determine, if the Bremia lineages infecting these hosts are distinct or intermingled. serriola, but often a fast overcoming of the resistance in the crop by new downy mildew races was observed. Many of the Dm resistance genes in cultivated lettuce were crossbred from L. lactucae is restricted to cultivated Lactuca sativa and its wild progenitor Lactuca serriola. Long time it was thought to infect various members of the Asteraceae but recent phylogenetic investigations revealed that B. Bremia lactucae is a devastating pathogen causing heavy yield losses in lettuce production worldwide.