From Prediction to Discovery of New Stripe Rust Resistance Genes in Landraces from Watkins Collection-Triticum aestivum L

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), was first detected in eastern Australia in 1979. Western Australia remained free of stripe rust until 2002, when another exotic introduction of Pst pathotype 134 E16A+ took place. This pathotype evolved to acquire virulence for stripe rust resistance genes Yr10, Yr17, Yr24, Yr27, YrJ and YrT. Annual losses due to stripe rust in Australia were estimated to be A$127 million. Deployment of combinations of resistance genes in new wheat cultivars is the most eco-friendly means of stripe rust control and it is underpinned by the identification and characterisation of genetically diverse sources of resistance. Landraces of wheat are believed to be untapped reservoir for new sources of genes for different traits including rust resistance. We evaluated 800 genotypes collected from 32 countries by Arthur Watkins for rust response variation under greenhouse and field conditions in Australia. A set of 206 lines producing low rust responses was identified. The prediction accuracies achieved with 9K bead chip SNP data paved the way for genomic selection for stripe rust resistance in wheat. Genomic regions controlling stripe rust resistance in chromosome 1A, 1B, 2A, 2B, 2D, 3A, 3B, 4A, 4B, 5A, 5B, 5D, 6A, 6B, 7A, and 7B were predicted. To validate the involvement of  these genomic regions in controlling stripe rust resistance, bi-parental mapping populations were developed and assessed for  stripe rust response variation both at the at seedling and adult plant stages. Four genes namely; Yr47 in chromosome 5B, Yr51 in 4AL, Yr57 in 3BS, and Yr63 in 7B were formally named and closely linked markers were identified. In addition, YrAW4 in chromosome 2BL, YrAW5 in 6A, YrAW6 in 5A and YrAW7 in 7A are currently being characterised for formal naming. Eight of the16 chromosomal regions identified in the genomic prediction were validated using bi-parental populations and development of segregating populations is in progress to validate the involvement of remaining genomic regions. These populations will serve as the foundation for developing diagnostic markers, high-density mapping and eventual cloning of these genes.