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Key Message: A physical map of Secale cereale chromosome 6R was constructed using deletion mapping, and a new stripe rust resistance gene Yr83 was mapped to the deletion bin of FL 0.73-1.00 of 6RL. Rye (Secale cereale L., RR) possesses valuable genes for wheat improvement. In the current study, we report a resistance gene conferring stripe rust resistance effective from seedling to adult plant stages located on chromosome 6R. This chromosome was derived from triticale line T-701 and also carries highly effective resistance to the cereal cyst nematode species Heterodera avenae Woll. A wheat-rye 6R(6D) disomic substitution line exhibited high levels of seedling resistance to Australian pathotypes of the stripe rust (Puccinia striiformis f. sp. tritici; Pst) pathogen and showed an even greater resistance to the Chinese Pst pathotypes in the field. Ten chromosome 6R deletion lines and five wheat-rye 6R translocation lines were developed earlier in the attempt to transfer the nematode resistance gene to wheat and used herein to map the stripe rust resistance gene. These lines were subsequently characterized by sequential multicolor fluorescence in situ hybridization (mc-FISH), genomic in situ hybridization (GISH), mc-GISH, PCR-based landmark unique gene (PLUG), and chromosome 6R-specific length amplified fragment sequencing (SLAF-Seq) marker analyses to physically map the stripe rust resistance gene. The new stripe rust resistance locus was located in a chromosomal bin with fraction length (FL) 0.73-1.00 on 6RL and was named Yr83. A wheat-rye translocation line T6RL (#5) carrying the stripe rust resistance gene will be useful as a new germplasm in breeding for resistance.

Key Message: We report transfer of a rust resistance gene named SrB, on the 6Ae#3 chromosome, to wheat by recombination with the 6Ae#1 segment carrying Sr26 and development of a linked marker. A stem rust resistance gene from a South African wheat W3757, temporarily named SrB, has been transferred onto chromosome 6A. Line W3757 is a 6Ae#3 (6D) substitution line in which the Thinopyrum ponticum chromosomes carry SrB. Crosses were made between W3757 and a T6AS·6AL-6Ae#1 recombinant line named WA-5 carrying the stem rust resistance gene Sr26 on a chromosome segment from another accession of Th. ponticum. The 6Ae#1 and 6Ae#3 chromosomes had previously been shown to pair at meiosis and were polymorphic for the distally located RFLP probes BCD001 and MWG798. A recombinant plant (Type A) was identified carrying a distal chromosome segment from the 6Ae#3 chromosome and a sub-terminal segment from the 6Ae#1 chromosome. Rust tests on the recombinant Type A showed the infection type for SrB. Segregation and linkage data combined with genomic in situ hybridization studies demonstrated that SrB had been transferred to wheat chromosome arm 6AL by recombination between the Thinopyrum chromosome segments. A recombinant positive for the 6Ae#1-6Ae#3 chromosome showed enhanced stem rust resistance compared to the 6Ae#3 addition line in repeated rust tests. A diagnostic PCR-based marker was developed for the 6Ae#3 chromosome segment on the Type A recombinant carrying SrB that distinguishes it from the Sr26-containing segment. A stem rust resistant line which combines SrB with Sr26 would be a great addition to the pool of resistant germplasm for wheat breeders to achieve more durable and effective control of stem rust because virulence has not been found for either of these two genes.

Key Message: Wheat- Aegilops speltoides recombinants carrying stem rust resistance genes Sr32 and SrAes1t effective against Ug99 and PCR markers for marker-assisted selection. Wild relatives of wheat are important resources for new rust resistance genes but underutilized because the valuable resistances are often linked to negative traits that prevent deployment of these genes in commercial wheats. Here, we report ph1b-induced recombinants with reduced alien chromatin derived from E.R. Sears' wheat-Aegilops speltoides 2D-2S#1 translocation line C82.2, which carries the widely effective stem rust resistance gene Sr32. Infection type assessments of the recombinants showed that the original translocation in fact carries two stem rust resistance genes, Sr32 on the short arm and a previously undescribed gene SrAes1t on the long arm of chromosome 2S#1. Recombinants with substantially shortened alien chromatin were produced for both genes, which confer resistance to stem rust races in the TTKSK (Ug99) lineage and representative races of all Australian stem rust lineages. Selected recombinants were back crossed into adapted Australian cultivars and PCR markers were developed to facilitate the incorporation of these genes into future wheat varieties. Our recombinants and those from several other labs now show that Sr32, Sr39, and SrAes7t on the short arm and Sr47 and SrAes1t on the long arm of 2S#1 form two linkage groups and at present no rust races are described that can distinguish these resistance specificities.