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Pathogen Resistance

Lactuca serriola can be affected by lettuce downy mildew, one of the most serious diseases of lettuce. To withstand this, L. serriola has shown resistance to the plant pathogen Bremia lactucae, the cause of the disease. Resistance is characterized either as an R-factor or a Dm gene. Nine of the dominant genes that confer resistance are Dml, Dm, Dm3, Dm6, Dml4, Dml5, DmlO, Dm5/8, Dm10, Dm4, Dm7, Dm11, and Dm13. These genes are mapped in four linkage groups, which describe their locations. L. serriola and B. lactucae have a gene-for-gene relationship, meaning that each resistance gene in the plant is associated with a specific gene in the pathogen, with avirulence being dominant to virulence. These genes have been analyzed using molecular markers. Combinations of these genes can respond to multiple isolates of Bremia lactucae. Testing for the presence of new resistance factors is conducted by screening samples of L. serriola with various isolates of B. lactucae. In a study comparing samples of Lactuca serriola from Israel and California, it was found that only six out of fifty-one haplotypes overlapped, showing the diversity between populations. Genetic diversity is considered a resource for lettuce breeding. There is especially high diversity within the Mediterranean area and Southwest Asia, but L. serriola has established populations on all continents and has the most widespread distribution compared to other Lactuca species. Part of the wide variation among L. serriola in Israel can be attributed to the diversity of the environment, which includes distinct climates and soil varieties. Knowledge about genetic resources in Lactuca serriola is useful for lettuce breeding, allowing breeders to effectively respond to the pathogen and predict changes. This is especially applicable because L. serriola is the wild progenitor of cultivated lettuce (Lactuca sativa). In addition, these resources are necessary as new strains of the pathogen

continually emerge.