Reproduced from Crop Science. Published by Crop Science Society of America. All copyrights reserved. CROP SCIENCE, VOL. 47, MAY– JUNE 2007 951 RESEARCH U pland cotton ( Gossypium hirsutum L.), one of the most eco- nomically important crops in the world, provides raw material for the textile and oil industry. In the USA in 2004, the estimated total cotton yield loss due to diseases was 10.93% (Blasingame and Patel, 2005). Among various cotton diseases, the southern root-knot nematode (RKN), Meloidogyne incognita (Kofoid and White) Chit- wood race 3, has become a widespread, destructive pest throughout the Cotton Belt (Kirkpatrick and Rothrock, 2001). The nematode forms galls or ‘knots’ on the roots of cotton, and limits the abil- ity of plants to uptake and transport water and nutrients (Bridge, 1992). Nematode infection also may increase the susceptibility to Fusarium wilt (Minton and Minton, 1966). Yield losses in cotton attributed to RKN damage in 2004 across the U. S. Cotton Belt were 545 728 bales, about 2.49% (highest among cotton diseases) of the total U. S. cotton production (Blasingame and Patel, 2005). Use of resistant cultivars is considered to be an efective, eco- nomic, and environmentally sustainable strategy for managing RKN. Identiication of Molecular Markers Associated with Root-Knot Nematode Resistance in Upland Cotton Chen Niu, Doug J. Hinchlife, Roy G. Cantrell, Congli Wang, Philip A. Roberts, and Jinfa Zhang* ABSTRACT Cotton breeding for resistance to root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] is hindered by the lack of convenient and reliable screening methods for resistant plants. The identiication of molecular markers closely linked to RKN resistance will facilitate the development of RKN resistant cul- tivars through marker-assisted selection (MAS). Our objective was to identify and develop new DNA markers that are associated with RKN resistance in cotton. Using three pairs of near- isogenic (NIL) resistant (R) and susceptible (S) lines, two AFLP markers, two RAPD mark- ers, and three RGA markers were identiied to be polymorphic between the NIL-R and NIL-S lines. One RAPD marker was converted into a sequence-tagged site (STS) marker. In an F 2 population of ‘ST 474’ × ‘Auburn 634 RNR’, the two RAPD markers and the STS marker were mapped to the same linkage group containing several markers that were previously reported to be linked with the RKN resistance gene rkn1 on chromosome 11 in ‘Acala NemX’. All these markers were found to be associated with a major RKN resistance gene, presumably Mi 2 in the resistant line Auburn 634 RNR, suggest- ing that rkn1 and Mi 2 are either allelic or closely linked. In addition, no susceptible recombi- nants were found in a resistance screen of 200 F 2 plants from the cross Acala NemX × Auburn 634 RNR. The utility of the two RAPD markers and the converted STS marker were evaluated using 23 R and 8 S germplasm lines. The RAPD and STS markers, along with other previously reported markers associated with RKN resis- tance will be useful in germplasm screening, MAS for RKN resistance, and map-based clon- ing for RKN resistance genes. C. Niu and J. Zhang, Dep. of Plant and Environ. Sci., Box 30003, New Mexico State Univ., Las Cruces, NM 88003; D.J. Hinchlife, USDA- ARS, Southern Regional Research Center, 1100 Robert E. Lee Blvd., New Orleans, LA 70124; R.G. Cantrell, Cotton Incorporated, 6399 Weston Pkwy., Cary, NC 27513; C. Wang and P.A. Roberts, Dep. of Nematology, Univ. of California, Riverside, CA 92521-0415. Received 31 July 2006. *Corresponding author (jinzhang@nmsu.edu). Abbreviations: AFLP, ampli ied fragment length polymorphism; CAP, cleaved ampli ied polymorphism; MAS, marker-assisted selec- tion; NIL, near isogenic line; RAPD, random ampli ied polymorphic DNA; RGA, resistance gene analogue; RKN, root-knot nematode; SSR, simple sequence repeat; STS, sequence-tagged site. Published in Crop Sci. 47:951–960 (2007). doi: 10.2135/cropsci2006.07.0499 © 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. Published online May 31, 2007 Published online May 31, 2007