Derivation and Characterization of Recombinants of the Lr54/Yr37 Translocation in Common Wheat

The wild relatives are an important source of new genes for the genetic improvement of wheat. Leaf and stripe rust resistance genes Lr54 and Yr37 occur on an Aegilops kotschyi-derived chromosomal translocation that had apparently replaced wheat chromosome arm 2DL. The alien chromatin also includes the locus of a gene for reduced plant height (H), which appears to be different from Rht8 on chromosome arm 2DS. The introgressed genes were mapped relative to homoeologous wheat marker loci following the induction of chromosome pairing in translocation heterozygotes that lacked the Ph1 locus. Ten recombined Lr54/Yr37 translocation chromosomes were derived and characterized with micro- satellite, AFLP and SCAR markers. The data suggested that there was significant homoeology between the full-length translocated segment and the wheat 2DL chromosome arm. The recombined translocations apparently resulted from single crossovers during which the distal end of the long arm of the translocation chromosome was replaced with wheat chroma- tin. Recombinant (Lr54/Yr37-74) retained the least alien chromatin and both resistance genes, yet had lost the reduced plant height gene. A polymorphic AFLP fragment was converted into a dominant SCAR marker to detect rec. #74. In addition three wheat microsatellite loci that map to the introgressed region provide a useful recessive marker system to detect Lr54/Yr37. The shortened translocation could be useful in breeding and may be used for continued, closer mapping of the resistance genes.