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Thinopyrum intermedium translocations derived from the wheat (Triticum aestivum L.) substitution line P-29 were previously characterized by RFLP. We have further analyzed these lines and additional related germplasm with publicly available STS and SSRs. Primers which showed a polymorphism between wheat and P-29, were tested in all recombinant and nulli-tetrasomic lines confirming their position on chromosome 7D. The resulting 7D/7E chromosome maps appeared as a mosaic of wheat and Th. intermedium chromatin sections. To verify the composition of the translocation lines suggested by the RFLP-PCR map, F(2) progeny of two crosses (CS/216-1 and CS/260-1) were analyzed with molecular markers. Both populations gave an unexpectedly diverse number of recombinant individuals, suggesting that interstitial translocations occur more frequently than previously thought. This analysis also showed that there is a wide range in the number and position of the interstitial translocations within a given line such as the mosaic chromosome in recombinant line 260-1/CS-26, which has four Th. intermedium chromosome segments. Phenotypic data of the two populations suggested the presence of one gene which we have called Bdv3 to differentiate it from the previously reported orthologous gene Bdv2. Using the PCR-based molecular markers identified in this study, 5 out of 12 elite lines that showed good yields and no YDV symptoms contained Th. intermedium chromatin. Due to the multiple components involved in the YDV disease complex, combining selection for YDV resistance with the molecular markers and maps identified in this study will increase the efficiency of introgressing Th. intermedium chromatin containing YDV resistance or other beneficial traits into elite wheat germplasm.

Rusts and barley yellow dwarf virus (BYDV) are among the main diseases affecting wheat production world wide for which wild relatives have been the source of a number of translocations carrying resistance genes. Nevertheless, along with desirable traits, alien translocations often carry deleterious genes. We have generated recombinants in a bread wheat background between two alien translocations: TC5, ex-Thinopyrum (Th) intermedium, carrying BYDV resistance gene Bdv2; and T4m, ex-Th. ponticum, carrying rust resistance genes Lr19 and Sr25. Because both these translocations are on the wheat chromosome arm 7DL, homoeologous recombination was attempted in the double hemizygote (TC5/T4m) in a background homozygous for the ph1b mutation. The identification of recombinants was facilitated by the use of newly developed molecular markers for each of the alien genomes represented in the two translocations and by studying derived F(2), F(3) and doubled haploid populations. The occurrence of recombination was confirmed with molecular markers and bioassays on families of testcrosses between putative recombinants and bread wheat, and in F(2) populations derived from the testcrosses. As a consequence it has been possible to derive a genetic map of markers and resistance genes on these previously fixed alien linkage blocks. We have obtained fertile progeny carrying new tri-genomic recombinant chromosomes. Furthermore we have demonstrated that some of the recombinants carried resistance genes Lr19 and Bdv2 yet lacked the self-elimination trait associated with shortened T4 segments. We have also shown that the recombinant translocations are fixed and stable once removed from the influence of the ph1b. The molecular markers developed in this study will facilitate selection of individuals carrying recombinant Th. intermedium-Th. ponticum translocations (Pontin series) in breeding programs.