Molecular dissection of Secale africanum chromosome 6R(afr) in wheat enabled localization of genes for resistance to powdery mildew and stripe rust

BACKGROUND: Introgression of chromatin from Secale species into common wheat has for decades been a successful strategy for controlling the wheat diseases. The wild Secale species, Secale africanum Stapf., is a valuable source for resistance to foliar disease of wheat. A wheat-S. africanum chromosome 6R(afr) substitution line displayed resistance to both powdery mildew and stripe rust at the adult-plant stage. RESULTS: Wheat-S. africanum chromosome 6R(afr) deletion and translocation lines were produced and identified by sequential non-denaturing fluorescence in situ hybridization (ND-FISH) using multiple Oligo-based probes. Different ND-FISH patterns were observed between S. cereale 6R and S. africanum 6R(afr). With reference to the physical map of the draft genome sequence of rye inbred line Lo7, a comprehensive PCR marker analysis indicated that insertions and deletions had occurred by random exchange between chromosomes 6R and 6R(afr). A survey of the wheat- S. africanum 6R(afr) lines for disease resistance indicated that a powdery mildew resistance gene(s) was present on the long arm of 6R(afr) at FL0.85–1.00, and that a stripe rust resistance gene(s) was located in the terminal region of 6R(afr)S at FL0.95–1.00. The wheat-S. africanum 6R(afr) introgression lines also displayed superior agronomic traits, indicating that the chromosome 6R(afr) may have little linkage drag in the wheat background. CONCLUSIONS: The combination of molecular and cytogenetic methods allowed to precisely identify the chromosome rearrangements in wheat- S. africanum 6R(afr) substitution, deletion and translocation lines, and compare the structural difference between chromosomes 6R and 6R(afr). The wheat- S. africanum 6R(afr) lines containing gene(s) for powdery mildew and stripe rust resistance could be used as novel germplasm for wheat breeding by chromosome engineering.