Molecular Cytogenetic Characterization of a Triticum durum-Secale africanum Substitution Line for Resistance to Sripe Rust (Puccinia striiformis Eriks. f. sp. tritici)
Abstract：Species in genus Secale have provided novel rust resistance genes to protect wheat from this fungal disease. In order to transfer new stripe rust resistance gene(s) from wild Secale species, Secale africanum, we obtained a line HH41 from the advanced generation of Triticum durum-Secale africanum amphiploid (AABBRaRa) crossed with wheat(T. aestivum). Line HH41 was immune to stripe rust isolates from China, and had 42 chromosomes. Fluorescence in situ hybridization (FISH) using D-chromosome specific probe pAs1 and sequential genomic in situ hybridization (GISH) analysis using S. cereale cv. Qinglingheimai (QH) genomic DNA as probe demonstrated that a pair of wheat chromosomes 6D were absent, but a pair of S. africanum chromosomes presented in HH41. Expressed sequence tags based molecular markers also confirmed that HH41 lost 6D specific bands and amplified 6Ra specific bands, indicating that HH41 was a 6Ra(6D) substitution line. GISH analysis using genomic DNA of S. cereale cv. Qinglingheimai(QH) as a probe showed that hybridization signal covered along the chromosomes 6Ra except the telomere region of the short arm. However, the whole 6Ra chromosomes possessed hybridization signal if using genomic DNA of S. africanum for GISH analysis. FISH using Secale telomere or subtelomere tandem repetitive sequences pSc200 as a probe, no hybridization signal was detected on HH41. However, apparent signal was observed on chromosomes 6R from CS-S. cereale cv. Imperial disomic addition lines with strong signal on the telomere of the short arms were also scattered signal on the subtelomere of the long arms. It was revealed that chromosomes 6Ra of S. africanum were different from the S. cereale chromosomes 6R, especially on the telomere regions, with lost or reduced telomere or subtelomere repetitive sequences. Nine of sixteen 6R/6Ra specific markers developed by our study represented polymorphic amplification on chromosomes 6Ra of S. africanum distinct from chromosomes 6R of S. cereale, further demonstrated polymorphism exited between the two chromosome types. Based on stripe rust races evaluation, it was deduced that the stripe rust resistance in HH41 was derived from chromosomes 6Ra of S. africanum. In conclusion, the 6Ra(6D) substitution line with excellent stripe rust resistance and apparent polymorphism originated from ancient species S. africanum will serve as an important resource for translocation lines creation, valuable gene introgression and common wheat improvement
