|Rouse, Matthew - Matt|
|WILLIAMSON, SHARON - North Carolina State University|
|PRETORIUS, ZACHARIAS - University Of The Free State|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2015
Publication Date: 2/20/2016
Citation: Babiker, E.M., Bonman, J.M., Gordon, T.C., Chao, S., Rouse, M.N., Brown Guedira, G.L., Williamson, S., Pretorius, Z.A. 2016. Rapid identification of resistance loci effective against Puccinia graminis f. sp. tritici race TTKSK in 33 spring wheat landraces. Plant Disease. 100(2):331-336.
Interpretive Summary: Stem rust is potentially the most important disease of wheat worldwide. A new and highly virulent race of the stem rust pathogen, commonly referred to as ‘Ug99’, was identified in Uganda in 1998. To discover new sources of resistance to Ug99 for use by US wheat breeders, thousands of wheat landrace accessions from the USDA-ARS National Small Grains Collection were tested previously in a field stem rust screening nursery in Kenya and 78 accessions showed a high level of resistance. However, only new resistance genes are of great interest to wheat breeders. To determine if a gene is new or not, it is necessary to genetically map it to a specific location on a chromosome of wheat. Genetic mapping methods rely upon genotyping many lines from mapping population is relatively costly and time consuming. In contrast, a method known as ‘bulked segregant analysis’, or BSA for short, deals with DNA bulks collected form two groups of plants classified as either resistant or susceptible to the disease. BSA can be a fast and inexpensive approach to locate Sr genes to specific region in the chromosome. The purpose of the present study was to identify the most promising resistant accessions for further characterization and mapping. Seedling response to Ug99, molecular markers linked to specific Sr genes, population segregation ratios, and BSA results were used to select three accessions as being most likely to have new resistance genes. The significant SNP markers associated with the Sr genes in these accessions will be used in further work to map and characterize these potentially novel resistance genes.
Technical Abstract: Wheat breeders worldwide are seeking new sources of resistance to Puccinia graminis f. sp tritici race TTKSK. To prioritize field-resistant landraces for follow-up genetic studies to test for the presence of new resistance genes, seedling response to Pgt race TTKSK, molecular markers linked to specific Sr genes, segregation ratios among progeny from crosses, and bulked segregant analyses (BSA) were used. Thirty three accessions with seedling resistance to race TTKSK were crossed to a susceptible genotype, LMPG-6. The segregation ratios of stem rust reactions in F2 seedlings fit a single dominant gene model in 31 populations and progeny from two crosses gave ambiguous results. Using the 90K wheat SNP genotyping platform, BSA showed that the seedling resistance in 29 accessions is probably controlled by loci on chromosome 2BL. The BSA from the three remaining accessions revealed that the seedling resistance is most likely controlled by new genes. To confirm the BSA results from the F2 populations, two populations were advanced to F2:3 and screened against race TTKSK. Segregation of the F2:3 families fit a 1:2:1 ratio for a single dominant gene. Using the F2:3 families, BSA located the TTKSK locus on chromosome 6DS to the same location as Sr42.