Botanical Files on Lettuce (Lactuca sativa). On the chance for gene flow between wild and cultivated Lettuce (Lactuca sativa L. including L. serriola L., Compositae) and the generalized implications for risk-assessments on genetically modified plants

In Botanical Files, a study of the real chances for gene flow from cultivated plants to the wild a system of dispersal codes (Dpdf) was introduced (see text box Dpdf).³7 They are indications of already occurring gene flow from cultivated plants to the wild flora, as can be deduced from herbarium collections and florisdc archives. These codes apply to the Netherlands only. One of the crops of which the real chances for gene flow could not be determined, because of uncertainties regarding the relationship between the cultivated plant and its wild relatives, is Lettuce (Lactuca sativa L.). Its relationship with the wild L. serriola L. is accepted to be very close, but the species are considered to be distinguishable. In a field trial, using 350 specimens from 67 genetically different populations, the distinction between the two species proved to depend largely on character states usually connected to domestication, like absence or presence of prickles, retention of achenes, leaf texture and colour. The consequences are that both wild and cultivated lettuce must be considered to belong to the same species. The finding of some ‘domesticated’ character states in ‘wild’ lettuces indicates an already ongoing gene flow between cultivated lettuce and the wild flora, and the Dp(jf-code is adapted accordingly, indicating a substantial chance for gene flow from cultivated lettuce to its wild relative in the Netherlands. If the scope of Dispersal codes as in Botanical Files is extended to Europe, European Dpdf-codes are needed. In this report a model is proposed using a plant geographical division of Europe into six vegetational regions. For each species six Dpdf-codes, summarizing the chances for gene flow to each of the regions, should be developed. For the major part of the species this can be done using the information already present in national herbarium collections.