Development of the novel wheat-tetraploid Thinopyrum elongatum 4EL small fragment translocation lines with the stripe rust resistance gene Yr4EL

Stripe rust, caused by Puccinia striiformis f. sp. tritici , is a devastating wheat disease worldwide. Deployment of disease resistance ( R ) genes in cultivars is the most effective way to control the disease. The all-stage stripe rust R gene Yr4EL from tetraploid Thinopyrum elongatum was previously introduced into common wheat through the 4D (4E) substitution and T4DS·4EL translocation lines. To further map and utilize Yr4EL , Chinese Spring (CS) mutant pairing homoeologous gene ph1b was used to introduce recombination between chromosomes of 4EL and common wheat by crossing program. Two homozygous small fragment translocation lines T4DS·4DL-4EL and T5AS·5AL-4EL with Yr4EL resistance were selected using molecular markers and confirmed by genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), and 660K SNP array analyses. The Yr4EL is located about 35 Mb (577.76~612.97 Mb) from the terminal of the chromosome arm 4EL based on the diploid Th. elongatum reference genome. In addition, two competitive allele-specific PCR (KASP) markers were developed and showed co-segregation with Yr4EL , which can facilitate molecular marker-assisted selection in wheat breeding programs. T4DS·4DL-4EL lines were crossed and backcrossed with wheat cultivars SM482 and CM42 to obtain pre-breeding lines with stripe rust resistance and good agronomic traits, showing great potential for wheat breeding. These results will provide new germplasm for wheat stripe rust resistance breeding, as well as provide solid foundation for Yr4EL fine mapping and cloning.