Determination, characterisation and combination of novel resistance genes to stripe and stem rust in wheat

Triticum aestivum L., commonly known as bread wheat, characterized by a chromosomal composition of 2n = 6x = 42 (AABBDD), is a significant source of dietary protein and daily calorie intake for much of the global population. Stripe rust (Puccinia striiformis Westend. f. sp. tritici Eriks) and stem rust (Puccinia graminis f. sp. tritici Erikss & E. Henning) now pose substantial threats to overall wheat production worldwide, since most rust resistance genes in wheat have been overcome by virulent rust fungus races. It is essential to enhance genetic resistance against these devastating diseases.Wheat acquires crucial reservoirs of new resistance genes through introgressions from derivatives of Secale cereale, Leymus mollis, Leymus racemosus, and Thinopyrum junceiforme. This study systematically examined seedling resistance to various stripe rust races to identify new sources of resistance. Six wheat-rye introgression lines (SLU124, SLU125, SLU126, SLU127, SLU128 and SLU129) containing rye chromosomes 4R, 5R, and 6R were identified as carriers of previously undiscovered resistance genes against stripe rust races. Seedling assays confirmed that the stripe rust resistance in line SLU126 was retained over multiple generations. Using genotyping-by-sequencing (GBS) platforms and aligning putative GBS-SNPs with fully annotated rye NLR genes, three Kompetitive Allele-Specific PCR (KASP) markers were designed specifically for a chromosomal region at chromosome 6R, associated with two distinct stripe rust resistance genes. The development and validation of the wheat-rye cryptic translocation 6DS.6DL.6RL.6DL, featuring newfound stripe rust resistance genes, were conducted through seedling resistance assays and molecular analysis. The stripe rust resistance gene in family 29-N3-5 onthe rye chromosome 6RL arm was provisionally designated YrSLU. Extensive molecular marker analysis and multiple-generation seedling assays revealed that stripe rust resistance in SLU124 is located on the 4RL chromosome arm of rye. Two KASP markers located on the 4RL chromosome were identified as being closely associated with two stripe rust resistance genes in resistant plants of a SLU124 population. Using marker-assisted gene pyramiding, stem rust resistance gene Sr59 and stripe rust resistance gene YrSLU were combined in a single wheat genotype.Overall, this thesis demonstrated the advantages of marker-assisted gene pyramiding in transferring multiple disease resistance genes within a single genotype. Incorporation of these resistance genes into wheat has expanded the gene pool for combating destructive diseases.