Summary1. Hybridization seems possible for many crop species after pollen transfer from crops to wild relatives in the surrounding vegetation. Subsequent introgression of crop-specific traits into wild relatives could lead to invasive introgressants. This process has become a public concern following the introduction of genetically modified (GM) crops. Until now, few studies have used demographic vital rates to compare the performance of hybrids with their wild relatives. 2. We created second-generation (S 1 and BC 1 ) hybrids between the non-transgenic crop Lactuca sativa and its entirely cross-fertile wild relative Lactuca serriola . Seeds of parents and hybrids were individually sown in field plots at three different locations. Next to germination and survival, we measured a range of single fitness components and morphological traits. We also compared observed phenotypes to phenotypes theoretically expected, according to different inheritance scenarios. 3. Phenotypes of both hybrid classes resembled L. serriola closely, and more than theoretically expected. However, demographic vital rates, i.e. germination and survival of hybrids were much higher than in L. serriola. 4. Our results indicate that hybrids between crop and wild Lactuca are phenotypically indistinguishable from the wild relative and thus will largely remain unnoticed when they occur. However, these hybrids could potentially become invasive because of substantial differences in vital rates and seeds returned per seed sown. Synthesis and applications.A comparative study on single fitness components, such as seed production, alone would not have revealed the performance advantage of cropwild hybrids in Lactuca . Therefore, studying demographic vital rates of hybrids and back-crosses to test for long-term consequences of hybridization should be part of any risk assessment of GM crops. Demographic vital rates are also important for the development of predictive modelling tools that can be employed to test the individual-and population-level consequences of new-to-add traits.

BackgroundThe secondary genepool of our modern cultivated potato (Solanum tuberosum L.) consists of a large number of tuber-bearing wild Solanum species under Solanum section Petota. One of the major taxonomic problems in section Petota is that the series classification (as put forward by Hawkes) is problematic and the boundaries of some series are unclear. In addition, the classification has received only partial cladistic support in all molecular studies carried out to date.The aim of the present study is to describe the structure present in section Petota. When possible, at least 5 accessions from each available species and 5 individual plants per accession (totally approx. 5000 plants) were genotyped using over 200 AFLP markers. This resulted in the largest dataset ever constructed for Solanum section Petota. The data obtained are used to evaluate the 21 series hypothesis put forward by Hawkes and the 4 clade hypothesis of Spooner and co-workers.ResultsWe constructed a NJ tree for 4929 genotypes. For the other analyses, due to practical reasons, a condensed dataset was created consisting of one representative genotype from each available accession. We show a NJ jackknife and a MP jackknife tree. A large part of both trees consists of a polytomy. Some structure is still visible in both trees, supported by jackknife values above 69. We use these branches with >69 jackknife support in the NJ jackknife tree as a basis for informal species groups. The informal species groups recognized are: Mexican diploids, Acaulia, Iopetala, Longipedicellata, polyploid Conicibaccata, diploid Conicibaccata, Circaeifolia, diploid Piurana and tetraploid Piurana.ConclusionMost of the series that Hawkes and his predecessors designated can not be accepted as natural groups, based on our study. Neither do we find proof for the 4 clades proposed by Spooner and co-workers. A few species groups have high support and their inner structure displays also supported subdivisions, while a large part of the species cannot be structured at all. We believe that the lack of structure is not due to any methodological problem but represents the real biological situation within section Petota.

BackgroundThe taxonomy and systematic relationships among species of Solanum section Petota are complicated and the section seems overclassified. Many of the presumed (sub)species from South America are very similar and they are able to exchange genetic material. We applied a population genetic approach to evaluate support for subgroups within this material, using AFLP data. Our approach is based on the following assumptions: (i) accessions that may exchange genetic material can be analyzed as if they are part of one gene pool, and (ii) genetic differentiation among species is expected to be higher than within species.ResultsA dataset of 566 South-American accessions (encompassing 89 species and subspecies) was analyzed in two steps. First, with the program STRUCTURE 2.2 in an 'unsupervised' procedure, individual accessions were assigned to inferred clusters based on genetic similarity. The results showed that the South American members of section Petota could be arranged in 16 clusters of various size and composition. Next, the accessions within the clusters were grouped by maximizing the partitioning of genetic diversity among subgroups (i.e., maximizing Fst values) for all available individuals of the accessions (2767 genotypes). This two-step approach produced an optimal partitioning into 44 groups.Some of the species clustered as genetically distinct groups, either on their own, or combined with one or more other species. However, accessions of other species were distributed over more than one cluster, and did not form genetically distinct units.ConclusionsWe could not find any support for 43 species (almost half of our dataset). For 28 species some level of support could be found varying from good to weak. For 18 species no conclusions could be drawn as the number of accessions included in our dataset was too low. These molecular data should be combined with data from morphological surveys, with geographical distribution data, and with information from crossing experiments to identify natural units at the species level. However, the data do indicate which taxa or combinations of taxa are clearly supported by a distinct set of molecular marker data, leaving other taxa unsupported. Therefore, the approach taken provides a general method to evaluate the taxonomic system in any species complex for which molecular data are available.