|Rouse, Matthew - Matt|
|PRETORIUS, ZACHARIAS - University Of The Free State|
|WANYERA, RUTH - Kenya Agricultural And Livestock Research Organization|
|NEWCOMB, MARIA - University Of Arizona|
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2016
Publication Date: 8/20/2016
Citation: Babiker, E.M., Gordon, T.C., Chao, S., Rouse, M.N., Brown Guedira, G.L., Pretorius, Z.A., Wanyera, R., Newcomb, M., Bonman, J.M. 2016. Genetic mapping of resistance to the Ug99 race group of Puccinia graminis f. sp tritici in a spring wheat landrace CItr 4311. Theoretical and Applied Genetics. 129(11):2161-2170.
Interpretive Summary: Stem rust is the most important disease of wheat worldwide. A key problem in rust disease management is that new resistant cultivars often become susceptible over time due to the evolution of new pathogen races. A new race of the stem rust pathogen with virulence to the widely deployed stem rust resistance gene Sr31, originally designated as race TTKS and commonly referred to as ‘Ug99’, was reported in Uganda in 1999. One means to overcome this problem is to deploy new effective genes in wheat cultivars. Few stem rust resistance genes derived from the bread wheat confer resistance to Ug99. The objective of this study was to elucidate the inheritance of Ug99 resistance in a wheat landrace accession CItr 4311. The seedling screening indicating a single gene controlled seedling resistance to Ug99. The recently developed wheat molecular markers, called single nucleotide polymorphisms (SNPs), were used to ‘genotype’ the population of plants developed by crossing the resistant accessions CItr 4311 with a susceptible line. With this method we found that there is a major locus for Ug99 seedling and field resistance on chromosome 2BL. Based on race specificity and the mapping results, the Sr gene in CItr 4311 was hypothesized to be one of the known genes (Sr9h). Five SNP markers identified in this study could be used in marker assisted selection to combine the Sr gene in CItr 4311 with other effective Sr genes. These results will help US wheat breeders develop new cultivars with better stem rust resistance.
Technical Abstract: Wheat landrace CItr 4311 has seedling resistance to stem rust caused by Puccinia graminis f. sp tritici Eriks. & E. Henn (Pgt) race TTKSK and field resistance to the Ug99 race group. Parents, F1 seedlings, 121 doubled haploid (DH) lines, and 124 recombinant inbred lines (RILs) developed from a cross between CItr 4311 and the susceptible line LMPG-6 were evaluated for seedling resistance to Pgt race TTKSK. Goodness-of-fit tests indicated that a single dominant gene in CItr 4311 conditioned the TTKSK resistance. The 90K wheat iSelect SNP platform was used to genotype parents and the DH population. The seedling resistance locus was mapped to the long arm of chromosome 2B. Using KASP assays, five linked SNP markers were used to verify the result in the 124 RIL, 34 wheat accessions, 46 DH lines from the LMPG-6/PI 165194 cross and F1 seedlings, and susceptible bulks derived from crosses between six resistant landrace parents with LMPG-6. The haplotype of the five SNP markers demonstrated the likely usefulness of these markers in marker assisted selection. Parents and the DH population were evaluated for field resistance in Kenya. One major QTL for the field resistance was consistently detected in the same region on chromosome arm 2BL as the seedling resistance. The Sr gene in CItr 4311 was hypothesized to be Sr9h based on race specificity, the mapping results, and haplotype similarity with lines with Sr9h..