Summary• This study reconstructs the phylogeography of Aegilops geniculata, an allotetraploid relative of wheat, to discuss the impact of past climate changes and recent human activities (e.g. the early expansion of agriculture) on the genetic diversity of ruderal plant species.• We combined chloroplast DNA (cpDNA) sequencing, analysed using statistical parsimony network, with nonhierarchical K-means clustering of amplified fragment length polymorphism (AFLP) genotyping, to unravel patterns of genetic structure across the native range of Ae. geniculata. The AFLP dataset was further explored by measurement of the regional genetic diversity and the detection of isolation by distance patterns.• Both cpDNA and AFLP suggest an eastern Mediterranean origin of Ae. geniculata. Two lineages have spread independently over northern and southern Mediterranean areas. Northern populations show low genetic diversity but strong phylogeographical structure among the main peninsulas, indicating a major influence of glacial cycles. By contrast, low genetic structuring and a high genetic diversity are detected in southern Mediterranean populations. Finally, we highlight human-mediated dispersal resulting in substantial introgression between resident and migrant populations.• We have shown that the evolutionary trajectories of ruderal plants can be similar to those of wild species, but are interfered by human activities, promoting range expansions through increased long-distance dispersal and the creation of suitable habitats.

In order to estimate the potential of gene flow between wheat (Triticum aestivum L.) and jointed goatgrass (Aegilops cylindrica Host.), we carried out mixed pollinations in experimental and natural conditions. A set of species-specific RAPD (random amplified polymorphic DNA) and microsatellite markers were used to detect the presence of parental markers in the progeny of the plants used in these experiments. No hybrids were found within the offsprings of the plants used for the greenhouse experiments, while 85 Ae. cylindrica×T. aestivum hybrids were found within 2400 analyzed F 1 plants resulting from the field pollinations. The hybridization rates for individuals of different populations of the wild species differed considerably: 1% for two populations known for more than 90 years versus 7% for a newly discovered population. Most of the hybrids were completely sterile, but five of them produced 13 seeds (BC 1 ) by backcross with Ae. cylindrica. Twelve seeds germinated and generated viable and partly fertile plants. About 25% of the wheat specific RAPD markers were found in the BC 1 plants, indicating that introgression of wheat DNA into Ae. cylindrica is possible. In addition, one microsatellite marker, known to be situated on the D genome (a genome shared by both species), was also found in the BC 1 plants.

Gene flow between domesticated species and their wild relatives is receiving growing attention. This study addressed introgression between wheat and natural populations of its wild relatives (Aegilops species). The sampling included 472 individuals, collected from 32 Mediterranean populations of three widespread Aegilops species (Aegilops geniculata, Ae. neglecta and Ae. triuncialis) and compared wheat field borders to areas isolated from agriculture. Individuals were characterized with amplified fragment length polymorphism fingerprinting, analysed through two computational approaches (i.e. Bayesian estimations of admixture and fuzzy clustering), and sequences marking wheat-specific insertions of transposable elements. With this combined approach, we detected substantial gene flow between wheat and Aegilops species. Specifically, Ae. neglecta and Ae. triuncialis showed significantly more admixed individuals close to wheat fields than in locations isolated from agriculture. In contrast, little evidence of gene flow was found in Ae. geniculata. Our results indicated that reproductive barriers have been regularly bypassed during the long history of sympatry between wheat and Aegilops.

The closest wild relatives of maize, Zea mays ssp. mays are various Zea taxa known as "teosinte." Hybrids between maize and the teosinte taxon, Zea mays ssp. mexicana, often occur when the 2 are sympatric in Mexico. Measuring the spontaneous hybridization rate of the 2 taxa would shed light on the mechanisms contributing to the evolution and persistence of these hybrid swarms. We conducted a series of field experiments in Riverside, CA, to measure the natural hybridization rates between maize and 2 teosinte taxa, Z. m. ssp. mexicana and Zea mays ssp. parviglumis. We planted teosinte within and near maize plantations. Hybrids were identified by progeny testing for a maize-specific herbicide resistance allele and a teosinte-specific allozyme allele. Hybridity was confirmed by growing putative hybrid progeny to maturity to evaluate whether they had the characteristic morphology of maize x teosinte hybrids. We found that maize and Z. m. ssp. mexicana naturally hybridize at a low rate (<1%), whereas Z. m. ssp. parviglumis hybridizes with the crop at a high rate (>>50%).