Pseudo-linkage or real-linkage of rust resistance genes in a wheat-Thinopyrum intermedium translocation line

We analysed the chromosomal structures of two wheat-Thinopyrum intermedium addition lines Z4 and Z5 and resolved the linkage relationship between the leaf rust and stripe rust resistance genes in Z4. Wheat addition lines Z4 and Z5 carrying rust resistance genes from Thinopyrum intermedium (JJJ^sJ^sStSt, 2n = 6x = 42) together with three wheat lines involved in the production of these addition lines were analysed by rust response, 90K SNP genotyping, and molecular cytogenetic analysis. Seedling leaf rust (LR) responses to five diverse pathotypes indicated that the LR resistance gene(s) was located in translocation chromosome T3DS-3AS.3AL-7StS common to Z4 and Z5. The stripe rust (YR) resistance gene(s) was located in translocation chromosome T3AL-7StS.7StL, which is unique to Z4, based on the seedling YR responses to four diverse pathotypes. Backcross and selfed populations involving the addition lines and various wheat cultivars were studied to understand the inheritance of the alien resistance genes. Although inheritance studies indicated genetic linkage, the alien genes for resistance to leaf rust (LR) and stripe rust (YR) in Z4 were present in different wheat-Th. intermedium translocation chromosomes. We found that LR and YR were in pseudo-linkage, rather than true linkage.