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Winzeler Tanksley 1989), the ml-o resistance locus in barley (Hinze et al. Wenzel e.g., the Tm-2a viral resistance gene in tomato (Young and G. This approach has given tightly linked RFLP markers for several important disease resistance genes, Communicated by G.
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Near-isogenic lines (NILs) differing in a specific trait have been successfully used to isolate genetic markers for the gene determining that trait. However, it has been proposed that the latter may be useful in the characterization of introgressed single chromosome segments. 1992, 1993), RAPD Key words Leaf rust 9 RAPD 9 RFLP 9 Triticum aes- markers have been found to be of limited use in the constructivum 9 Triticum spelta tion of linkage maps in wheat (Devos and Gale 1992). While genetic maps based on RFLP markers are known for several chromosomes (Chao et al. 1990) have been used as molecular markers in wheat. 1980) and random amplified polymorphic DNA (RAPD) (Williams et al. Both restriction fragment length polymorphism (RFLP) (Botstein et al. In order to determine the presence of Lr9 in a complex genetic background of other leaf rust resistance genes a genetic marker for Lr9 is needed. Therefore, its presence, in combination with other resistance genes, is desirable in new cultivars to be released. In addition, no undesirable traits have been associated with the leaf rust resistance of Aegilops umbellulata (Soliman et al. In several European countries, including Switzerland, no virulence has yet been detected for this gene (Denissen and van der Putten 1991 Poinso and Ollivier 1988 von Kr6cher et al. 1992) for example, the Lr9 resistance gene, localized on the long arm of chromosome 6B (Sears 1961), was translocated into wheat from Aegilops umbellulata (Sears 1956). Many of these resistance genes were introgressed from wild relatives of wheat by wide crosses (Baum et al. Specific resistance genes are known and have been used to breed resistant varieties. Leaf rust is one of the most important diseases of wheat. All three PCR markers detected the Lr9 gene in independently derived breeding lines and varieties, thus proving their general applicability in wheat breeding programs. As this marker maps to the distal part of the long arm of chromosome 6B of wheat, Lr9 and the other DNA markers also map to the distal region of 6BL. A second RFLP marker (PSR546) was closely linked (8 _+2.4 cM) to the Lr9 gene and the other four DNA markers. All three polymorphisms detected by the PCR (polymerase chain reaction) and one RFLP marker (cMWG684) showed complete linkage to the Lr9 gene in 156 and 133 plants analyzed, respectively. A cross between a resistant NIL and the spelt (Triticum spelta) variety 'Oberkulmer' was made, and F 2 plants were analyzed for genetic linkage. Thus, these primers define a sequence-tagged site that is specific for the translocated fragment carrying the Lr9 gene. Specific primers were synthesized, and after amplification only resistant lines showed an amplified product. One of these polymorphic bands was cloned and sequenced. Out of 395 RAPD primers tested, three showed polymorphisms between NILs, i.e., an additional band was found in resistant lines. RAPD (random amplified polymorphic DNA) primers as well as RFLP (restriction fragment length polymorphism) markers were used. Identification and localization of molecular markers linked to the Lr9 leaf rust resistance gene of wheatĪbstract Near-isogenic lines (NILs) for the leaf rust resistance gene Lr9 were screened for polymorphisms at the molecular level.