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Wild relatives of genetically engineered crops can acquire transgenic traits such as herbicide resistance via spontaneous crop–wild hybridization. In agricultural weeds, resistance to herbicides is often a beneficial trait, but little is known about possible costs that could affect the persistence of this trait when herbicides are not used. We tested for costs associated with transgenic resistance to glufosinate when introgressed into weedy Brassica rapa. Crosses were made between transgenic B. napus and wild B. rapa from Denmark. F1 progeny were backcrossed to B. rapa and BC1 plants were selected for chromosome numbers similar to B. rapa. Further backcrossing resulted in a BC2 generation that was hemizygous for herbicide resistance. We quantified the reproductive success of 457 BC3 progeny representing six full‐sib families raised in growth rooms (plants were pollinated by captive bumblebees). Pollen fertility and seed production of BC3 plants were as great as those of B. rapa raised in the same growth rooms. Segregation for herbicide resistance in BC3 plants was 1:1 overall, but the frequency of resistant progeny was lower than expected in one family and higher than expected in another. There were no significant differences between transgenic and nontransgenic plants in survival or the number of seeds per plant, indicating that costs associated with the transgene are probably negligible. Results from this growth‐chamber study suggest that transgenic resistance to glufosinate is capable of introgressing into populations of B. rapa and persisting, even in the absence of selection due to herbicide application.

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Genetic diversity in the storage protein hordein encoded by two loci, Hor1 and Hor2, was analyzed electrophoretically in seeds from 123 individual plants of wild barley, Hordeum spontaneum, the progenitor of cultivated barley. The test was conducted in two topographically different 100 meter transects in Israel, each equally divided into basalt and terra rossa soil types. Altogether 15 Hor1 and 16 Hor2 phenotypes were detected; 7 phenotypes in Hor1 and 5 in Hor2 were common. Significant differentiation of both Hor1 and Hor2 phenotypes and their associations was found with soil type and topography. Likewise, significant correlations were found between hordein phenotypes and allozyme types detected in a previous study. Our results suggest that at least part of the hordein polymorphisms in wild barley is adaptive and selected by soil and topographic differences over very short distances.

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