Molecular Mapping of Three Recombined Versions of the Lr56/Yr38 Translocation in Wheat.

Molecular mapping of three recombined versions of the Lr56/Yr38 translocation in wheat

               

Mohamed Somo, Seyed Mostafa Pirseyedi, Xiwen Cai and Francois Marais

Department of plant Sciences, North Dakota State University, Fargo, ND 58108.

Leaf rust (caused by Puccinia triticina Erikss) may inflict significant yield losses in wheat. The use of resistance genes is the most economical and environmentally friendly way to combat the disease. A dwindling supply of new and effective resistance genes from within the primary gene pool of wheat has prompted geneticists to search for similar genes in the secondary and tertiary gene pools. The linked leaf rust and stripe rust (caused by Puccinia striiformis Westend) resistance genes Lr56/Yr38 were transferred from Aegilops sharonensis (Hackel) Maire et Weiler to common wheat chromosome 6A in an earlier study. A fairly big translocation occurred spontaneously during backcrossing of the primary and secondary hybrids to wheat. The full length translocation line (0352-4) showed strong resistance to prevalent isolates of South African, Australian, and Canadian, leaf and stripe rust races. Due to the size of the alien fragment, the line was not deployed in breeding programs. Following allosyndetic pairing induction in the absence of Ph1, three resistant recombinants with greatly reduced alien chromatin have been derived (Lr56-39, Lr56-157, and Lr56-175). The alien segments in the three recombinants are thought to be comparatively small and to occur between Xgwm427 and Xwmc59 on 6AL, yet this has not been confirmed. The present study employed previously mapped microsatellite markers and unmapped DArT loci in a continued attempt to physically map the recombinants and determine which has retained the least linkage drag. An F₂ population for each recombinant is also being employed to genetically map Lr56 with the use of single nucleotide polymorphism (SNP) markers. Finally, genomic in situ hybridization (GISH) is being done in order to confirm and compare the alien inserts. Eventually, an attempt will be made to construct integrated linkage and cytogenetic maps for the recombinant chromosomes in order to determine which will be the most useful for breeding purposes.