CROP SCIENCE, VOL. 48, SEPTEMBER– OCTOBER 2008 1853 RESEARCH T he evolutionary consequences of gene fow between domesticated crops and their wild relatives are widely rec- ognized (Ellstrand et al., 1999; Jarvis and Hodgkin, 1999; Ell- strand, 2003, Lefèvre, 2004). From a conservation perspective, the consequences are frequently negative for wild relative spe- cies. Domestic alleles have been shown to impact ftness in wild populations (Ellstrand, 2003; Hails and Morley, 2005). Hoc et al. (2006) reported degeneration of hybrid progeny between Phaseolus vulgaris var. aborigineus and domesticated beans growing in Argentina. Introgression between wild and cultivated forms has also resulted in the development of highly aggressive weeds (Panetsos and Baker, 1967; de Wet and Harlan, 1975; Boudry et al., 1993). Hybridization with cultivated crops can also threaten wild relatives through outbreeding depression or genetic assimila- tion (Hails and Morley, 2005). For example, Oryza rufpogon ssp. formosana is considered nearly extinct due to hybridization with O. sativa (Oka 1992), and genetic erosion is predicted for common wild rice ( O. rufpogon) throughout China due to hybridization with domesticated rice (Song et al., 2005). Conserving Alfalfa Wild Relatives: Is Past Introgression with Russian Varieties Evident Today? Stephanie L. Greene,* Theodore J. Kisha, and Nikolai I. Dzyubenko ABSTRACT Central Asia, particularly Kazakhstan, supports a rich concentration of wild alfalfa (Medicago sativa L.) relatives. Because tetraploid wild alfalfa freely crosses with domesticated alfalfa, they are important genetic resources. When identifying in situ populations to conserve, contamination of wild populations with domesticated alleles is an important consideration. We evaluated population structure and introgression between six wild populations of M. sativa nothossp. varia collected in northwestern Kazakhstan and fve traditional Russian cultivars historically grown in the same region using two amplifed frag- ment length polymorphism primer pairs and six simple sequence repeat loci. We found no dif- ference between the Russian cultivars and wild populations for number of alleles or percentage polymorphic loci; however, gene diversity was less in the wild than in the cultivated populations. Cluster analysis and principle component analy- sis showed clear separation between wild and cultivated populations. Genetic differentiation among the cultivars was less than among the wild populations. Using a Bayesian approach, we found limited evidence of admixture among the wild and cultivated forms, although more admixture was evident in wild populations col- lected in less-remote areas. On the basis of marker data, we concluded that three of the six wild populations stood out as candidates for in situ conservation given their uniqueness and lack of admixture with cultivated forms. S.L. Greene, USDA-ARS, National Temperate Forage Legume Germ- plasm Resources Unit, 24106 N. Bunn Rd., Prosser, WA 99350; T. Kisha, USDA-ARS, Western Regional Plant Introduction Station, Johnson Hall, Room 59, Washington State Univ., Pullman, WA 99164; N. Dzyubenko, N.I. Vavilov Institute, 42, Bolshaya Morskaya Str., St. Petersburg, Russia, 196600. Received 5 Dec. 2007. *Corresponding author (stephanie.greene@ars.usda.gov). Abbreviations: AFLP, amplifed fragment length polymorphism; PCA, principle component analysis; PI, plant inventory; SSR, simple sequence repeat. Published in Crop Sci. 48:1853–1864 (2008). doi: 10.2135/cropsci2007.12.0668 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.