Gene Flow between Gossypium hirsutum L. and Gossypium barbadense L. is Asymmetric

As both Pima cotton (Gossypium barbadense L.) and Acala (Upland; G. hirsutum L.) are grown in the southwestern United States, understanding gene fl ow within and among these species is important to maintain genetic purity. In small scale and commercial fi elds, gene fl ow decreased exponentially from 1.44% at 1 m to less than 0.50% at 10 m in Acala cotton. Corresponding values for Pima cotton were 0.19% at 3 m and 0% at 10 m or beyond. When interspecies outcrossing occurred, Pima cotton was preferentially pollinated by Acala cotton. Gene fl ow was nondetectable in 7.5 m borders. Asymmetric pollination between Acala and Pima cotton was also observed in samples collected in borders located 6 m from the pollen source with no detectable gene fl ow beyond 7.5 m. At a given distance, in commercial scale Pima fi elds, gene fl ow was tenfold less than reported in Acala fi elds with gene fl ow not exceeding 0.43% beyond 10 m. No gene fl ow was detected beyond 800 m (0.5 mile). This study indicates that isolation distances can be shorter in Pima cotton than in Acala cotton to maintain the same level of genetic purity. Comparison with historical evidence suggests that there has been a shift in the relative gene fl ow among species in modern cultivars of Pima cotton. A.E. Van Deynze and K.J. Bradford, Seed Biotechnology Center, One Shields Ave., Univ. of California, Davis, CA 95616. R.B. Hutmacher, Dep. of Plant Sciences, Univ. of California, Davis, CA and Shafter Research and Extension Center, Shafter, CA, 93263. This research was funded by a grant from the California Crop Improvement Association and by Cotton Incorporated, 6399 Weston Parkway, Cary, North Carolina 27513. Received 18 Apr. 2010. *Corresponding author ([email protected]). Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; RR, Roundup-Ready. Published in Crop Sci. 51:298–305 (2011). doi: 10.2135/cropsci2010.04.0213 Freely available online through the author-supported open-access option. Published online 25 Oct. 2010. © Crop Science Society of America | 5585 Guilford 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.