152 WWW.CROPS.ORG CROP SCIENCE, VOL. 58, JANUARY– FEBRUARY 2018 RESEARCH Published in Crop Sci. 58:152–158 (2018). doi: 10.2135/cropsci2017.05.0272 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. Leaf rust of wheat (Triticum aestivum L.), caused by Puccinia tri- ticina Eriks., is a common disease that occurs in most wheat growing regions of the world. In the United States, leaf rust causes annual losses in the spring and winter wheat regions (Kolmer et al., 2009). Soft red winter wheat cultivars are grown in the Ohio Valley and southeastern states. Leaf rust resistance is an important objective of wheat improvement programs in these areas, since susceptible cultivars can sufer losses of >20% given suitable conditions for leaf rust development (Caldwell et al., 1934). Many soft red winter wheat cultivars were derived from the cultivar ‘Mediterranean’ with Lr3a and the cultivar ‘Hussar’ with Lr11 (Soliman et al., 1964). These genes are present in many soft red winter wheat cultivars but are completely inefec- tive due to the high prevalence of leaf rust races with virulence to both genes. Other resistance genes in this wheat class include Lr1, Lr2a, and Lr10 originally from common hexaploid wheat, and Lr9, Lr14a, Lr18, and Lr26 derived from lower ploidy wheat relatives (Kolmer, 2003). Races of P. triticina with virulence to all of these genes have been found in the soft red winter wheat growing region (Kolmer and Hughes, 2015), most likely having been selected by cultivars with these genes. Adult Plant Leaf Rust Resistance Derived from the Soft Red Winter Wheat Cultivar ‘Caldwell’ Maps to Chromosome 3BS J. A. Kolmer,* S. Chao, G. Brown-Guedira, U. Bansal, and H. Bariana ABSTRACT ‘Caldwell’ is a US soft red winter wheat (Triti- cum aestivum L.) that has partial, adult plant resistance to the leaf rust pathogen Puc- cinia triticina Eriks. A line of ‘Thatcher*2/ Caldwell’ with adult plant resistance derived from Caldwell was crossed with ‘Thatcher’ to develop a population of recombinant inbred lines (RILs). The parents and RIL population were evaluated for segregation of leaf rust resistance in four feld tests. A genetic map of the RIL population was constructed using 90K single-nucleotide polymorphism (SNP) mark- ers with the Illumina Infnium iSelect 90K wheat bead array. Signifcant effects for reduction of leaf rust severity in all four tests were found for a quantitative trait locus on chromosome 3BS. Simple sequence repeat (SSR) markers linked to the adult plant resistance gene Lr74 and kompetitive allele specifc polymerase chain reaction (KASP) assay markers were added to the map on chromosome 3BS. Thatcher and the resistant Thatcher*2/Caldwell parent were negative for the presence of Sr2 on chromo- some 3BS based on the tightly linked marker csSr2. The SSR marker cfb5006 linked closely to Lr74 mapped the closest to the logarithm of odds peak for leaf rust resistance on chromo- some 3BS. The SNP and SSR markers on chro- mosome 3BS can be used to add Caldwell leaf rust resistance to wheat breeding germplasm. J.A. Kolmer, USDA, Cereal Disease Laboratory, St. Paul, MN 55108; S. Chao, USDA, Cereal Crops Research Unit, Fargo, ND 58102; G. Brown- Guedira, USDA, Plant Science Research Unit, Raleigh, NC 27695; U. Bansal and H. Bariana, The Univ. of Sydney, Plant Breeding Institute, Private Bag 4011, Narellan, NSW 2567, Cobbitty NSW 2570, Australia. Received 2 May 2017. Accepted 5 Sept. 2017. *Corresponding author (jim.kolmer@ars.usda.gov). Assigned to Associate Editor Shuyu Liu. Abbreviations: CAPS, cleavage amplifed polymorphism; IT, infection type; KASP, kompetitive allele specifc polymerase chain reaction; LOD, logarithm of odds; PCR, polymerase chain reaction; QTL, quantitative trait locus; RIL, recombinant inbred line; SNP, single- nucleotide polymorphism; SSR, simple sequence repeat; Tc, Thatcher. Published January 15, 2018