Fine Mapping of the SCN Resistance Locus rhg 1 - b from PI 88788

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the most economically damaging soybean [Glycine max (L.) Merr.] pest in the USA and genetic resistance is a key component for its control. Although SCN resistance is quantitative, the rhg1 locus on chromosome 18 (formerly known as Linkage Group G) confers a high level of resistance. The objective of this study was to fi ne-map the rhg1-b allele that is derived from plant introduction (PI) 88788. F2 and F3 plants and F3:4 lines from crosses between SCN resistant and susceptible genotypes were tested with genetic markers to identify recombination events close to rhg1-b. Lines developed from these recombinant plants were then tested for resistance to the SCN isolate PA3, which originally had an HG type 0 phenotype, and with genetic markers. Analysis of lines carrying key recombination events positioned rhg1-b between the simple sequence repeat (SSR) markers BARCSOYSSR_18_0090 and BARCSOYSSR_18_0094. This places rhg1-b to a 67-kb region of the ‘Williams 82’ genome sequence. The receptor-like kinase gene that has been previously identifi ed as a candidate for the ‘Peking’-derived SCN resistant rhg1 gene is adjacent to, but outside of, the rhg1-b interval defi ned in the present study. SOYBEAN CYST NEMATODE is the pest that causes the most damage to soybean in the USA (Wrather and Koenning, 2006). Th e fi rst report of SCN in the USA was in North Carolina during 1954 (Winstead et al., 1955). Since that time, SCN has spread throughout most soybean producing states (Niblack et al., 2008). Th e USDA-ARS soybean germplasm collection has been screened to identify sources of SCN resistance and at least 118 soybean PIs with SCN resistance were identifi ed (Arelli et al., 2000). Although these resistance sources are available to breeders, PI 88788 is the predominant resistance source for most commercially utilized SCN resistant cultivars in the northern USA. In a summary of soybean cultivars available for planting in Illinois during 2008, PI 88788 was the only SCN resistance source for 94% of the cultivars listed in maturity groups II through IV (Shier, 2008). Th e genetic basis of SCN resistance was fi rst studied through classical genetic experiments. Th e inheritance of SCN resistance from the SCN resistance source Peking fi ts a three recessive gene model, and the three genes were named rhg1, rhg2, and rhg3 (Caldwell et al., 1960). A later study showed that Peking carried a fourth resistance gene designated Rhg4 that conferred dominant resistance and this gene mapped near the i locus (Matson and Williams, 1965). An additional dominant gene designated Rhg5 was later identifi ed from PI 88788 (Rao-Arelli, 1994). Many genes and quantitative trait loci (QTL) controlling SCN resistance have been mapped, and the results from these eff orts were reviewed by Concibido Published in The Plant Genome 3:81–89. Published 30 Sept. 2010. doi: 10.3835/plantgenome2010.02.0001 © Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA An open-access publication 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. M. Kim and B.W. Diers, Dep. of Crop Sciences, Univ. of Illinois, Urbana, IL 61801; D.L. Hyten, USDA-ARS, Soybean Genomics and Improvement Lab., Beltsville, MD 20705; A. Bent, Dep. of Plant Pathology, Univ. of Wisconsin, Madison, WI 53706. Received 10 Feb. 2010. *Corresponding author ([email protected]). Abbreviations: FI, female index; INDEL, insertion-deletion; LRR, leucine-rich repeat; QTL, quantitative trait locus (loci); SCN, soybean cyst nematode; SNP, single nucleotide polymorphism; SSR, simple sequence repeat; STS, sequence tagged site.