Physical mapping of the barley stem rust resistance gene rpg4
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ORIGINAL PAPER
A. Druka á D. Kudrna á F. Han á A. Kilian B. Steenson á D. Frisch á J. Tomkins R. Wing á A. Kleinhofs
Physical mapping of the barley stem rust resistance gene rpg4 Received: 5 May 2000 / Accepted: 22 June 2000 / Published online: 9 August 2000 Ó Springer-Verlag 2000
Abstract The barley stem rust resistance gene rpg4 was physically and genetically localized on two overlapping BAC clones covering an estimated 300-kb region of the long arm of barley chromosome 7(5H). Initially, our target was mapped within a 6.0-cM region between the previously described ¯anking markers MWG740 and ABG391. This region was then saturated by integrating new markers from several existing barley and rice maps and by using BAC libraries of barley cv. Morex and rice cv. Nipponbare. Physical/genetic distances in the vicinity of rpg4 were found to be 1.0 Mb/cM, which is lower than the average for barley (4 Mb/cM) and lower than that determined by translocation breakpoint mapping (1.8 Mb/cM). Synteny at high resolution levels has been established between the region of barley chromosome 7(5H) containing the rpg4 locus and the subtelomeric region of rice chromosome 3 between markers S16474 and E10757. This 1.7-cM segment of the rice genome was covered by two overlapping BAC clones, about Communicated by R. G. Herrmann A. Druka á D. Kudrna á F. Han1 á A. Kleinhofs (&) Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164, USA E-mail: [email protected] Fax: +1-509-3358674 A. Kilian Center for the Application of Molecular Biology to International Agriculture, GPO Box 3200, Canberra ACT 2601, Australia B. Steenson Department of Plant Pathology, North Dakota State University, P.O. Box 5012, Fargo, ND 581055012, USA D. Frisch á J. Tomkins á R. Wing Genomics Institute, Clemson University, 100 Jordan Hall, Clemson, SC 29634, USA A. Kleinhofs School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA Present address: Pioneer Hi-Bred International, Inc., 7300 NW 62nd Ave., Johnston, IA 50131 USA
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250 kb of total length. In barley the markers S16474 and E10757 genetically delimit rpg4, lying 0.6 cM distal and 0.4 cM proximal to the locus, respectively. Key words Map-based cloning á Resistance genes á Barley genome á Stem rust
Introduction The barley stem rust resistance gene rpg4 confers resistance to Puccinia graminis f. sp. tritici pathotype Pgt-QCC (Jin et al. 1994b). This pathotype appeared relatively recently in the Midwestern USA, and was able to break down stem rust resistance provided by another resistance gene, Rpg1 (Roelfs at al. 1991). The Rpg1 gene has provided durable resistance to stem rust in barley since its discovery in 1937. In anticipation of a Pgt-QCC epidemic, mapping, isolation and characterization of rpg4 became an important pre-requisite for ecient development of barley cultivars resistant to Pgt-QCC via molecular breeding or transgene technology. Once isolated, rpg4 may also become a useful tool for isolation of other barley and wheat rust resistance genes u
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