Lactuca sativa (lettuce) is susceptible to Bremia lactucae (downy mildew). In cultivated and wild Lactuca species, Dm genes have been identified that confer race-specific resistance. However, these genes were soon rendered ineffective by adaptation of the pathogen. Lactuca saligna (wild lettuce) is resistant to all downy mildew races and can be considered as a non-host. Therefore, L. saligna might be an alternative source for a more-durable resistance to downy mildew in lettuce. In order to analyze this resistance, we have developed an F2 population based on a resistant L. saligna × susceptible L. sativa cross. This F2 population was fingerprinted with AFLP markers and tested for resistance to two Bremia races NL14 and NL16. The F2 population showed a wide and continuous range of resistance levels from completely resistant to completely susceptible. By comparison of disease tests, we observed a quantitative resistance against both Bremia races as well as a race-specific resistance to Bremia race NL16 and not to NL14. QTL mapping revealed a qualitative gene (R39) involved in the race-specific resistance and three QTLs (RBQ1, RBQ2 and RBQ3) involved in the quantitative resistance. The qualitative gene R39 is a dominant gene that gives nearly complete resistance to race NL16 in L. saligna CGN 5271 and therefore it showed features similar to Dm genes. The three QTLs explained 51% of the quantitative resistance against NL14, which indicated that probably only the major QTLs have been detected in this F2 population. The perspectives for breeding for durable resistance are discussed.
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Jeuken, .M., Lindhout, .P. Lactuca saligna, a non-host for lettuce downy mildew (Bremia lactucae), harbors a new race-specific Dm gene and three QTLs for resistance. Theor Appl Genet 105, 384–391 (2002). https://doi.org/10.1007/s00122-002-0943-z
- Non-host resistance Lactuca saligna Lettuce Downy mildew QTL mapping