Genetic Relationship of Stripe Rust Resistance Genes Yr34 and Yr48 in Wheat and Identification of Linked KASP Markers.

The Australian continent was free from wheat stripe rust caused by Puccinia striiformis f. sp. tritici until exotic incursions occurred in 1979 and 2002. The 2002 incursion enabled the identification of a new stripe rust resistance gene (Yr34) in the advanced breeding line WAWHT2046. In this study, we developed and validated markers closely linked with Yr34, which is located in the distal region in the long arm of chromosome 5A. Four kompetitive allele-specific polymerase chain reaction (KASP) and three sequence-tagged site (STS) markers derived from the International Wheat Genome Sequencing Consortium RefSeq v1.0 scaffold-77836 cosegregated with Yr34. Markers sun711, sun712, sun725, sunKASP_109, and sunKASP_112 were shown to be suitable for marker-assisted selection in a validation panel of 71 Australian spring wheat genotypes, with the exception of cultivar Orion that carried the Yr34-linked alleles for sunKASP_109 and sunKASP_112. Markers previously reported to be linked with adult plant stripe rust resistance gene Yr48 also cosegregated with Yr34. Wheat genotypes carrying Yr34 and Yr48 produced identical haplotypes for the Yr34-linked markers identified in this study and those previously reported to be linked with Yr48. Phenotypic testing of genotypes carrying Yr34 and Yr48 showed that both genes conferred similar seedling responses to pre-2002 and post-2002 P. striiformis f. sp. tritici pathotypes. Further testing of 600 F2 plants from a cross between WAWHT2046 and RIL143 (Yr48) with P. striiformis f. sp. tritici pathotype 134 E16A+Yr17+Yr27+ failed to reveal any susceptible segregants. Our results strongly suggest that Yr34 and Yr48 are the same gene, and that Yr48 should be considered a synonym of Yr34