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(American Journal of Botany. 2009;96:498-506.) doi: 10.3732/ajb.0800054 © 2009 Botanical Society of America, Inc.

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Can feral weeds evolve from cultivated radish (Raphanus sativus, Brassicaceae)?¹

² Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, Ohio 43210 USA

ABSTRACT

Cultivated plants that cannot survive on their own often have maladaptive domestication traits. Unharvested crop seeds may generate feral populations, at times causing serious weed problems, but little is known about the evolution of ferality. We explored the potential for cultivated radish, Raphanus sativus, to become feral, given that closely related taxa (e.g., R. raphanistrum and crop–wild hybrids) are well-documented weeds. First, we measured the population growth of five experimental, cultivated, self-seeding radish populations in Michigan, USA, for three generations. Three late-flowering populations went extinct, and two others apparently hybridized with local R. raphanistrum. A common garden experiment showed that the two surviving populations had earlier flowering, smaller root diameters, and greater individual fecundity than did nonhybridized populations. We also used artificial selection to measure the evolutionary potential for earlier flowering. After two generations of strong selection, two of three lineages flowered earlier and produced more seeds than control lineages, but insufficient genetic variation prevented dramatic evolution of crop phenotypes. In summary, it seems unlikely that radishes could spontaneously become feral in our study area without gene flow from R. raphanistrum. Applying these approaches to other cultivated species may provide a better understanding of mechanisms promoting the evolution of feral weeds.

Key Words: Brassicaceae • fecundity • ferality • Michigan • naturalized • population dynamics • Raphanus sativus • selection experiments • United States • volunteers

Received for publication 12 February 2008. Accepted for publication 13 October 2008.

FOOTNOTES

¹ Thanks to K. Mercer, P. Sweeney, Y. Teklu, M. Reagon, S. Su, J. Gao, D. Campbell, and C. Ridley for comments on this manuscript; the Ginop, Reimann, Sterzik, Jarman, and Romanik families for sharing their farmland; Harris-Moran, Ohio for generously donating seed; J. Leonard, the staff of UMBS, N. Marsh, and T. Waite for help with the experiments; and our many student researchers for their hard work. USDA grant 2002-03715, UMBS and The Nature Conservancy fellowships, and NSF grant 0508615 supported this work.

³ Author for correspondence (e-mail: lgc{at}rice.edu); Department of Ecology and Evolutionary Biology, Rice University, 6100 Main St., Houston, Texas, 77005, USA; phone: 713-348-3054; fax: 713-348-5232

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