Hybridization and introgression between crops and wild relatives may have
important evolutionary and ecological consequences such as gene swamping or
increased invasiveness. In the present study, we investigated hybridization
under field conditions between crop lettuce (Lactuca sativa) and its wild relative prickly
lettuce (L. serriola), two cross-compatible, predominantly autogamous and insect
pollinated species. In 2003 and 2004, we estimated the rates of
hybridization between L. sativa and L. serriola in close-to-reality field experiments carried
out in two locations of Northern Switzerland. Seeds set by the experimental
wild plants were collected and sown (44 352 in 2003 and 252 345 in 2004).
Progeny was screened morphologically for detecting natural hybrids. Prior to
the experiment, specific RAPD markers were used to confirm that
morphological characters were reliable for hybrid identification.
Hybridization occurred up to the maximal distance tested (40 m), and
hybridization rates varied between 0 to 26%, decreasing with distance.
More than 80% of the wild plants produced at least one hybrid (incidence
of hybridization, IH) at 0 m and 1 m. It equaled 4 to 5% at 40 m. In
sympatric crop-wild populations, cross-pollination between cultivated
lettuce and its wild relative has to be seen as the rule rather than the
exception for short distances.