Molecular mapping of leaf rust resistance gene Rph5 in barley

can be easily identified and transferred into appropriate germplasm (Parlevliet, 1976). To date, 16 major raceLeaf rust caused by Puccinia hordei G. Otth is an important disease specific genes (designated as Rph1 to Rph16) for leaf of barley (Hordeum vulgare L.) in many regions of the world. Yield losses up to 32% have been reported in susceptible cultivars. The rust resistance have been identified (Franckowiak et al., Rph5 gene confers resistance to the most prevalent races (8 and 30) 1997; Ivandic et al., 1998). of barley leaf rust in the USA. Therefore, the molecular mapping of Development of disease resistant barley cultivars has Rph5 is of great interest. The objectives of this study were to map been the most efficient way to control leaf rust (Mathre, Rph5 and identify closely linked molecular markers. Genetic studies 1997; Zillinsky, 1983). The pyramiding of multiple Rph were performed by analysis of 93 and 91 F2 plants derived from the genes is expected to increase the durability of leaf rust crosses ‘Bowman’ (rph5) ‘Magnif 102’ (Rph5) and ‘Moore’ (rph5) resistance in cultivars. Although virulence for Rph5 is Virginia 92-42-46 (Rph5), respectively. Bulk segregant analysis (BSA) widely prevalent in Europe (Parlevliet, 1976) and South using amplified fragment length polymorphism (AFLP), restriction America (Brodny and Rivadeneira, 1996; Fetch et al., fragment length polymorphism (RFLP), and simple sequence repeat 1998), it has not been identified in North America. Thus, (SSR) markers was conducted. Linkage analysis positioned the Rph5 locus to the extreme telomeric region of the short arm of barley Rph5 could be used to protect barley cultivars from leaf chromosome 3H at 0.2 centimorgans (cM) proximal to RFLP marker rust damage in North America. However, a more sound VT1 and 0.5 cM distal from RFLP marker C970 in the Bowman gene deployment strategy would be to use this gene in Magnif 102 population. Map positions and the relative order of the combination with other effective genes such as Rph3 markers were confirmed in the Moore Virginia 92-42-46 population. and Rph9 (Brooks et al., 2000). RFLP analysis of the near isogenic line (NIL) Magnif 102/*8Bowman, Most of the known barley leaf rust resistance genes the susceptible recurrent parent Bowman, and Rph5 donor Magnif have been described and mapped by means of morpho102, confirmed the close linkage of the markers VT1, BCD907, and logical characters, biochemical markers, and cytogenetic CDO549 to Rph5. Results from this study will be useful for markerstocks (Table 1). However, so far only five Rph genes assisted selection and gene pyramiding in programs breeding for leaf have been mapped by means of molecular markers. Two rust resistance and provide the basis for physical mapping and further cloning activities. alleles at the Rph9 locus, Rph9.i and Rph9.z (formerly designated as Rph12), were located on chromosome 5H using RFLP and sequence tagged site (STS) markers (Borovkova et al., 1997, 1998). STS and cleaved ampliL rust caused by P. hordei is generally considered fied polymorphic sequence (CAPS) markers were emthe most important rust disease of barley on a ployed to map Rph16 onto barley chromosome 2H worldwide basis. Severe yield losses have been observed (Ivandic et al., 1998). Recently, Rph7 was mapped onto in Australia (31%) (Coterill et al., 1992) and Europe the short arm of chromosome 3H by means of RFLP (17–31%) (King and Polley, 1976). In the USA, a 32% markers (Brunner et al., 2000; Graner et al., 2000). Fiyield reduction was reported for susceptible cultivars nally, Rph6 has been mapped onto chromosome 3HS under epidemic conditions in Virginia (Griffey et al., (Steffenson, unpublished). The precise chromosomal 1994). position of Rph5 is not known, although the gene was Clifford (1985) listed two types of resistance against assigned to chromosome 3H by trisomic analysis (Tan, P. hordei in barley: partial resistance and race-specific 1978; Tuleen and McDaniel, 1971). Thus, the objectives resistance. Partial resistance is controlled by several to of this study were to map Rph5 by means of molecular many genes and is generally considered more durable markers and develop closely linked markers for markerthan the race-specific resistance (Qi et al., 2000; Kichassisted selection. erer et al., 2000). However, the quantitative expression of this trait and complex genetics make this type of resistance more difficult to use in breeding programs. MATERIALS AND METHODS Race-specific resistance is usually governed by single Genetic Materials dominant genes. Although race-specific leaf rust resistance genes have not provided durable protection, they Two F2 populations derived from crosses Bowman (PI 483237) Magnif 102 (PI 337140) and Moore (CI 7251) Virginia 92-42-46 (hereafter, referred to as BM and MV popuJ.A. Mammadov, R.M. Biyashev, C.A. Griffey and M.A. Saghai Marlations, respectively) and consisting of 93 and 91 individuals, oof, Crop & Soil Environmental Sciences Dep., Virginia Tech, Blacksrespectively, were used for molecular mapping. Magnif 102 burg, VA 24061; J.C. Zwonitzer, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401; B.J. Steffenson, Dep. of Plant Pathology, Univ. of Minnesota, St. Paul, MN 55108Abbreviations: AFLP, amplified fragment length polymorphism; 6030; Y. Jin, Plant Science Dep., South Dakota State Univ., Brookings, BSA, bulk segregant analysis; CAPS, cleaved amplified polymorphic SD 57007. Received 12 Aug. 2001. *Corresponding author (smaroof@ sequence; cM, centimorgan; NIL, near isogenic line; RFLP, restriction vt.edu). fragment length polymorphism; SSR, simple sequence repeat; STS, sequenced tagged site. Published in Crop Sci. 43:388–393 (2003).