Wheat stem rust, caused by Puccinia graminis f. sp. tritici, can cause severe yield losses on susceptible wheat varieties and cultivars. Although stem rust can be controlled by the use of genetic resistance, population dynamics of P. graminis f. sp. tritici can frequently lead to defeat of wheat stem rust resistance genes. P. graminis f. sp. tritici race TKTTF caused a severe epidemic in Ethiopia on Ug99-resistant ‘Digalu’ in 2013 and 2014. The gene Sr11 confers resistance to race TKTTF and is present in ‘Gabo 56’. We identified seven single-nucleotide polymorphism (SNP) markers linked to Sr11 from a cross between Gabo 56 and ‘Chinese Spring’ exploiting a 90K Infinium iSelect Custom beadchip. Five SNP markers were validated on a ‘Berkut’/‘Scalavatis’ population that segregated for Sr11, using KBioscience competitive allele-specific polymerase chain reaction (KASP) assays. Two of the SNP markers, KASP_6BL_IWB10724 and KASP_6BL_IWB72471, were predictive of Sr11 among wheat genetic stocks, cultivars, and breeding lines from North America, Ethiopia, and Pakistan. These markers can be utilized to select for Sr11 in wheat breeding and to detect the presence of Sr11 in uncharacterized germplasm.
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Rust of cereals are considered to be an important disease in many countries, including Azerbaijan. One of these is stem rust caused by Puccinia graminis f. sp. tritici (Pgt). Extensive research on the identification of wheat stem rust resistance genes and effectiveness of these genes in various geographical regions have been conducted. Genetic resistance is one of the most effective ways for controlling stem rust. Sixty-nine stem rust resistance genes (including 45 identified Sr genes and 24 genes with temporary designations) are registered in the Komugi Wheat Genetics Resource Database. It is important to use proper combinations of resistance genes in developing lasting resistance wheat. The main purpose of the study was to identify lines caring Sr11, Sr26 and Sr31 genes, which are effective to the predominant Pgt races in Azerbaijan. Durum and bread wheat genotypes differing in their disease resistance, productivity and other physiological traits were chosen from the wheat gene bank of the Research Institute of Crop Husbandry (Baku, Azerbaijan) for analysis. DNA extraction was carried out according to standard CTAB protocol. RT-PCR performed using KASP markers (KASP_6BL_BS0074288_51 and KASp_6BL_Tdurum contig55744_822) identified nine durum genotypes (out of 34 genotypes) and seven wheat genotypes (out of ten genotypes), caring Sr11. Using the dominant STS marker (Sr26#43) a diagnostic 207 bp amplicon for Sr26 gene, was observed in 11 of the 42 wheat genotypes tested. In eight of the 42 wheat genotypes tested, the diagnostic 1,110 bp amplicon was observed using the Lr26-Sr31-Yr9 locus specific marker iag95, characteristic of Sr31 gene located at 1BL.1RS translocation. For the first time, wheat germplasm in Azerbaijan was analyzed using KASP genotyping technology and genetic resources, and resulted in the identification of wheat lines with effective resistant to Puccinia graminis f. sp. tritici race TKTTF.
The recently identified Puccinia graminis f. sp. tritici (Pgt) race TTKSK (Ug99) poses a severe threat to global wheat production because of its broad virulence on several widely deployed resistance genes. Additional virulences have been detected in the Ug99 group of races, and the spread of this race group has been documented across wheat growing regions in Africa, the Middle East (Yemen), and West Asia (Iran). Other broadly virulent Pgt races, such as TRTTF and TKTTF, present further difficulties in maintaining abundant genetic resistance for their effective use in wheat breeding against this destructive fungal disease of wheat. In an effort to identify loci conferring resistance to these races, a genome-wide association study was carried out on a panel of 250 spring wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT), six wheat breeding programs in the United States and three wheat breeding programs in Canada.
The lines included in this study were grouped into two major clusters, based on the results of principal component analysis using 23,976 SNP markers. Upon screening for adult plant resistance (APR) to Ug99 during 2013 and 2014 in artificial stem rust screening nurseries at Njoro, Kenya and at Debre Zeit, Ethiopia, several wheat lines were found to exhibit APR. The lines were also screened for resistance at the seedling stage against races TTKSK, TRTTF, and TKTTF at USDA-ARS Cereal Disease Laboratory in St. Paul, Minnesota; and only 9 of the 250 lines displayed seedling resistance to all the races. Using a mixed linear model, 27 SNP markers associated with APR against Ug99 were detected, including markers linked with the known APR gene Sr2. Using the same model, 23, 86, and 111 SNP markers associated with seedling resistance against races TTKSK, TRTTF, and TKTTF were identified, respectively. These included markers linked to the genes Sr8a and Sr11 providing seedling resistance to races TRTTF and TKTTF, respectively. We also identified putatively novel Sr resistance genes on chromosomes 3B, 4D, 5A, 5B, 6A, 7A, and 7B.
Our results demonstrate that the North American wheat breeding lines have several resistance loci that provide APR and seedling resistance to highly virulent Pgt races. Using the resistant lines and the SNP markers identified in this study, marker-assisted resistance breeding can assist in development of varieties with elevated levels of resistance to virulent stem rust races including TTKSK.