Genetic Studies of Rust Resistance in the Triticum spp., and Puccinia graminis f. sp. tritici Pathosystem

Abstract

The challenge posed by rapidly changing wheat rust pathogens in both pathogenicity and environmental adaptation calls for the application of advanced techniques, so that efforts to breed for durable disease resistance can be sped up. This study was carried out to examine genetic variability among Australian pathotypes of Puccinia graminis f. sp. tritici (Pgt), and to identify leaf rust, stem rust and stripe rust resistance genes in Africa wheat germplasm and spring wheat landraces. Phenotypic and genotypic analysis of Pgt isolates representing two putative clonal lineages determined that pathotypes 326-1,2,3,5,6 (founding pathotype of Lineage 3) and 194-1,2,3,5,6, (Lineage 4) had a common genetic background. Simple sequence repeat (SSR) analysis showed clearly high similarity among isolates from Lineages 2, 3 and 4. Thirty-four SSR genotypes characterised by low genetic variation (FST = 0.042) were identified among 142 isolates. Genetic variation among genotypes in such clonal pathogen populations are believed to arise principally from single-step mutation. Both known and unknown seedling and APR genes functioning either singly or in combinations were detected in African germplasm and landraces. Presence of resistance genes effective against multiple rust pathogens is an asset for gene pyramiding. Known adult plant resistance (APR) genes including the pleiotropic linked genes [Lr34/Yr18/Sr57; Lr46/Yr29/Sr58; Lr67/Yr46/Sr55 and Sr2/Lr27/Yr30], Lr68 and Lr74 were identified. A genome-wide association study detected 77 SNP markers significantly associated with rust resistance genes/quantitative trait loci (QTLs) in landraces. Finally, SNPs associated with resistance to multiple pathogens, SNPs mapped in chromosome positions not previously known for rust resistance and landraces/lines carrying USR and UAPR are promising new sources of resistance.