Discovery and molecular mapping of a new gene conferring resistance to stem rust, Sr53, derived from Aegilops geniculata and characterization of spontaneous translocation stocks with reduced alien chromatin.

This study reports the discovery and molecular mapping of a resistance gene effective against stem rust races RKQQC and TTKSK (Ug99) derived from Aegilops geniculata (2n = 4x = 28, U(g)U(g)M(g)M(g)). Two populations from the crosses TA5599 (T5DL-5M(g)L·5M(g)S)/TA3809 (ph1b mutant in Chinese Spring background) and TA5599/Lakin were developed and used for genetic mapping to identify markers linked to the resistance gene. Further molecular and cytogenetic characterization resulted in the identification of nine spontaneous recombinants with shortened Ae. geniculata segments. Three of the wheat-Ae. geniculata recombinants (U6154-124, U6154-128, and U6200-113) are interstitial translocations (T5DS·5DL-5M(g)L-5DL), with 20-30% proximal segments of 5M(g)L translocated to 5DL; the other six are recombinants (T5DL-5M(g)L·5M(g)S) have shortened segments of 5M(g)L with fraction lengths (FL) of 0.32-0.45 compared with FL 0.55 for the 5M(g)L segment in the original translocation donor, TA5599. Recombinants U6200-64, U6200-117, and U6154-124 carry the stem rust resistance gene Sr53 with the same infection type as TA5599, the resistance gene donor. All recombinants were confirmed to be genetically compensating on the basis of genomic in situ hybridization and molecular marker analysis with chromosome 5D- and 5M(g)-specific SSR/STS-PCR markers. These recombinants between wheat and Ae. geniculata will provide another source for wheat stem rust resistance breeding and for physical mapping of the resistance locus and crossover hot spots between wheat chromosome 5D and chromosome 5M(g)L of Ae. geniculata.