Summary1 Adaptation of plant populations to local environments has been shown in many species but local adaptation is not always apparent and spatial scales of differentiation are not well known. In a reciprocal transplant experiment we tested whether: (i) three widespread grassland species are locally adapted at a European scale; (ii) detection of local adaptation depends on competition with the local plant community; and (iii) local differentiation between neighbouring populations from contrasting habitats can be stronger than differentiation at a European scale. 2 Seeds of Holcus lanatus, Lotus corniculatus and Plantago lanceolata from a Swiss, Czech and UK population were sown in a reciprocal transplant experiment at fields that exhibit environmental conditions similar to the source sites. Seedling emergence, survival, growth and reproduction were recorded for two consecutive years. 3 The effect of competition was tested by comparing individuals in weeded monocultures with plants sown together with species from the local grassland community. To compare large-scale vs. small-scale differentiation, a neighbouring population from a contrasting habitat (wet-dry contrast) was compared with the 'home' and 'foreign' populations. 4 In P. lanceolata and H. lanatus, a significant home-site advantage was detected in fitnessrelated traits, thus indicating local adaptation. In L. corniculatus, an overall superiority of one provenance was found. 5 The detection of local adaptation depended on competition with the local plant community. In the absence of competition the home-site advantage was underestimated in P. lanceolata and overestimated in H. lanatus. 6 A significant population differentiation between contrasting local habitats was found. In some traits, this small-scale was greater than large-scale differentiation between countries. 7 Our results indicate that local adaptation in real plant communities cannot necessarily be predicted from plants grown in weeded monocultures and that tests on the relationship between fitness and geographical distance have to account for habitat-dependent small-scale differentiation. Considering the strong small-scale differentiation, a local provenance from a different habitat may not be the best choice in ecological restoration if distant populations from a more similar habitat are available.

Evolutionary theory suggests that divergent natural selection in heterogeneous environments can result in locally adapted plant genotypes. To understand local adaptation it is important to study the ecological factors responsible for divergent selection. At a continental scale, variation in climate can be important while at a local scale soil properties could also play a role. We designed an experiment aimed to disentangle the role of climate and (abiotic and biotic) soil properties in local adaptation of two common plant species. A grass (Holcus lanatus) and a legume (Lotus corniculatus), as well as their local soils, were reciprocally transplanted between three sites across an Atlantic-Continental gradient in Europe and grown in common gardens in either their home soil or foreign soils. Growth and reproductive traits were measured over two growing seasons. In both species, we found significant environmental and genetic effects on most of the growth and reproductive traits and a significant interaction between the two environmental effects of soil and climate. The grass species showed significant home site advantage in most of the fitness components, which indicated adaptation to climate. We found no indication that the grass was adapted to local soil conditions. The legume showed a significant home soil advantage for number of fruits only and thus a weak indication of adaptation to soil and no adaptation to climate. Our results show that the importance of climate and soil factors as drivers of local adaptation is species-dependent. This could be related to differences in interactions between plant species and soil biota.

Summary• Genetic differentiation among plant populations and adaptation to local environmental conditions are well documented. However, few studies have examined the potential contribution of plant antagonists, such as insect herbivores and pathogens, to the pattern of local adaptation.• Here, a reciprocal transplant experiment was set up at three sites across Europe using two common plant species, Holcus lanatus and Plantago lanceolata. The amount of damage by the main above-ground plant antagonists was measured: a rust fungus infecting Holcus and a specialist beetle feeding on Plantago, both in low-density monoculture plots and in competition with interspecific neighbours.• Strong genetic differentiation among provenances in the amount of damage by antagonists in both species was found. Local provenances of Holcus had significantly higher amounts of rust infection than foreign provenances, whereas local provenances of Plantago were significantly less damaged by the specialist beetle than the foreign provenances. The presence of surrounding vegetation affected the amount of damage but had little influence on the ranking of plant provenances.• The opposite pattern of population differentiation in resistance to local antagonists in the two species suggests that it will be difficult to predict the consequences of plant translocations for interactions with organisms of higher trophic levels.

A survey conducted in a seven-county region of eastern Oregon during the summers of 1998, 1999, and 2000 characterized the occurrence of jointed goatgrass × wheat hybrids and the features of weed infestations promoting hybridization. During the survey, 93 infested sites were visited with jointed goatgrass collected from 57 sites and hybrids collected from 45 sites. Thirteen collection sites were located in uncultivated areas. Observations of jointed goatgrass infestations in and around cropped fields suggested that jointed goatgrass successfully escapes control where weed populations persist in fencerows, access roads, scablands, draws, and roadsides. Most jointed goatgrass and hybrid populations were located in winter wheat fields but were also found in five spring grain fields. Of the 754 hybrid plants collected, 44% contained backcross seed. For all 3 yr, a 1% backcross hybrid seed–production rate was found. A parentage analysis of a subsample of the total hybrid collection showed that the majority were F1 hybrids and that jointed goatgrass was most often the female parent. This observational study has established that F1 hybrids are common in jointed goatgrass–infested wheat fields. Their capability for backcross seed production suggests the potential development of advanced backcross forms that resemble jointed goatgrass. The survey results offer valuable input for the risk assessment of gene flow potential between jointed goatgrass and herbicide-resistant wheat.

The ability of the weedy species jointed goatgrass (Aegilops cylindrica Host) to form seed‐bearing hybrids with wheat (Triticum aestivum L.) raises questions concerning the potential movement of herbicide‐resistance genes from commercial wheat cultivars into the weed population. As a preliminary step for future gene‐flow risk assessments, a study of jointed goatgrass × wheat hybrids collected from infested wheat fields in 1998 and 1999 was undertaken in Oregon. Jointed goatgrass accessions representing the range of variation in its worldwide distribution also were included in this study. The high molecular weight (HMW) glutenins, a group of wheat endosperm storage proteins, were used as genetic markers for characterizing this material. In the Oregon jointed goatgrass accessions, the seed protein analysis identified F1 hybrid seed that was formed at a rate of 0 to 8% on a per field basis. The HMW glutenin patterns in the backcross seed threshed from Oregon hybrids showed a higher proportion of seeds formed from pollination by wheat than by jointed goatgrass. Analysis of the roots for remains of the maternal seed or spikelet indicated that most hybrid plants were of the F1 generation and that either jointed goatgrass or wheat could be the female parent. These analyses suggested a hybridization dynamics in which jointed goatgrass serves as the predominant F1 female parent and wheat as the predominant backcross male parent. Development of introgressed jointed goatgrass forms carrying wheat genes would be dependent on the presence of a continuous hybrid zone located near or within a persistent jointed goatgrass population.