Complementary resistance genes in wheat selection 'Avocet R' confer resistance to stripe rust

This study reports the inheritance and genetic mapping of the YrA (temporary name of convenience to describe the specificity) seedling resistance to wheat stripe rust (caused by Puccinia striiformis f. sp. tritici; Pst) in a resistant selection of the Australian cv. Avocet [Avocet R (AvR)-AUS 90660]. Genetic analysis was performed on F-2 populations and F-3 generation families from crosses between wheats that carried and lacked the YrA resistance. Greenhouse seedling tests with two avirulent Pst pathotypes (104 E137 A- and 108 E141 A-) confirmed that the YrA resistance was inherited as two complementary dominant genes. Ninety-two doubled haploid (DH) lines from a cross between the Australian cv. Teal (Pst susceptible) and AvR were used for DArT-Seq genotypic analysis to map the seedling resistance. Marker-trait association analysis using 9035 DArT-Seq loci mapped the genes to the long arms of chromosomes 3D (3DL) and 5B (5BL), respectively. F-2 populations from crosses between susceptible DH lines that carried either the 3DL or 5BL marker genotypes confirmed the complementary gene model. Fluorescence in situ hybridization (FISH) analysis determined that Teal carries a reciprocal T5B-7B translocation. FISH analysis also identified a 5BL chromosomal deletion in Avocet S relative to AvR that further validated the complementary gene model and possibly explained the heterogeneity of closely related wheats carrying the YrA resistance. The individual loci of the complementary YrA resistance were designated Yr73 (3DL) and Yr74 (5BL). Candidate single gene reference stocks will be permanently accessioned following cytological analysis to avoid the T5B-7B translocation.