Bremia Lettuce

This present invention relates to novel Lactuca sativa plants resistant to Bremia. It also relates to methods of producing these plants and their seeds. This invention further relates to markers and their use in marker assisted breeding and for identifying the Bremia resistance trait.

Downy mildew is a fungal disease caused by the fungus Bremia lactucae . It occurs worldwide and represents a great problem for both the yield and quality of cultivated lettuce ( Lactuca sativa ). This fungus can infect the lettuce plant at any stage of growth, after which the first symptoms of downy mildew become visible as chlorotic yellow spots on the leaf surface. Within 24-48 hours a white fluffy fungus growth becomes visible on the lower leaf surface as an indication of spore formation. During the infection the spots of lesions become increasingly larger and more chlorotic until the leaves turn completely brown.

New Bremia physios occur relatively frequently through mutation of the virulence genes during spore formation preceding the propagation of B. Iactucae .  Due to the high variability of the pathogen, which is attributed to the occurrence of frequent mutations in the avirulence genes, the race-specific resistance mediated by the various resistance genes is usually rapidly broken by newly emerging races or physios of the Bremia pathogen.

This present invention addresses this problem by providing a Lactuca sativa plant which is resistant to Bremia lactucae infestation and thus protected from damage caused by this pathogen. The provision of Bremia resistant lettuce plants is an environmentally friendly alternative to the use of pesticides and may increase the efficiency of biological control options and contribute to successful integrated pest management programs.

The technical problem is solved by the provision of the embodiments characterized in the claims. Moreover, it was found that the linkage between genes responsible for undesired, morphological changes in the plant and the gene responsible for the resistance to Bremia lactucae as present in the wild type source material, is broken and thus no longer present in the Lactuca sativa plant according to this invention.

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