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Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, [Pst] is a widespread and damaging disease of wheat (Triticum aestivum L.), causing significant losses in yield and quality. During the 2015, eight stripe rust physiological races were identified in greenhouse tests i.e. 0E0, 6E4, 70E20, 128E28, 134E244, 143E245, 250E174, and 450E214. Race 0E0 was the most common and avirulent race, and races 143E245, and 450E214 had high virulence on most of tested Yr resistance gene wheat lines. In the same season, an unusual stripe rust infection occurred in spring wheat at Sakha region in Egypt. Some of the most important commercial cultivars such as (Misr 2, Giza 168 and Sakha 61), known as resistant to the previously characterized races of Pst in Egypt have become susceptible under field conditions. Infections of stripe rust was observed on some wheat lines with Yr genes previously known to be resistant, such as Yr1, Yr17 and Yr32, in a yellow-rust trap nursery at Sakha (30.601400? N, 31.510383? E), northern Egypt. Independent race analysis of collected samples from four governorates i.e. Kafrelsheikh, Al-Sharqia, Dakahleia and Damietta at Sakha Agricultural Research Station in Kafrelsheikh confirmed the detection of a new Pst race in Egypt. Aggressive races with virulence to Yr27 were detected on differentials with Yr27 (Yr27/6*Avocet S), and (Ciano 97) during the 2012 in Egypt. In addition, the Warrior race (virulent on: Yr1, Yr2, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr25, Yr32, and YrSp) was observed in the 2015 crop season, which indicated continued changes in the Pst the population. In Europe, the Warrior race first identified in 2011 in the United Kingdom, has caused significant change in yellow rust susceptibility of several varieties of both wheat and triticale. In a conclusion, some of wheat cultivars, known to be resistant, were shifted to susceptible due to these new races.
Rust diseases in wheat are the major threat to wheat production and yield gains. The breakdown in resistance of certain major genes and new emerging aggressive races of rusts are causing serious concerns in all main wheat growing areas of the world. Therefore, it is the need of the hour to search for new sources of resistance genes or QTL's for effective utilization in future breeding programs. In total 100 wheat genotypes were evaluated for seedling and adult-plant resistance to stem rust races TKTTF and TTKSK at Tel Hadya-Syria, and Njoro-Kenya, and Kelardasht-Iran. Evaluation to Yr27 virulent stripe rust race was carried out at Tel Hadya and Terbol-Lebanon research stations. In this study we used genome wide association studies (GWAS) to identify markers or QTLs linked to stem rust and stripe rust races using Diversity Arrays Technology (DArT?) in selected 35 Iranian wheat genotypes. The association of markers and phenotypes was carried out using a unified mixed-model approach (MLM) as implemented in the genome association and prediction integrated tool (GAPIT). Out of 3,072 markers, 986 were polymorphic and used for marker trait associations. A total of 44 DArT markers were identified to be significantly (p<=0.01) associated with studied traits in 16 genomic regions 1A, 1B, 2A, 4A, 6A, 7A, 1B.1R, 2B, 3B, 4B, 5B, 5B.7B, 6B, 7D and an unknown region. Among associated markers, 34 were linked to stem and nine to stripe rust. They were found on 16 genomic regions on chromosome arms 1A, 1B, 2A, 4A, 6A, 7A, 1B.1R, 2B, 3B, 4B, 5B, 5B.7B, 6B, 7D and an unknown region. Associated markers explained phenotypic variation ranging from 21 to 65%. In addition to validation of previously identified genes, this study revealed new QTL's linked to stem and stripe rust which will assist breeders to develop new resistant varieties.
Wheat is the world's most widely grown food crop. New races of pathogens frequently overcome current resistant varieties. To address this issue Algeria has strategies for immediate action, medium term protection and long-term research efforts to develop new resistant wheat varieties. Yellow rust is a very important disease of wheat in Algeria where 60% of the wheat crop is grown under cooler high elevation climate conditions (2?C ? 15?C). Crop losses reached 80% during the 2004/2005 epidemics. Strategies adopted to reduce the risk of wheat rust are ongoing yearly surveillance, awareness, and early warning systems to farmers; and breeding and developing new varieties with high yield potential and durable resistance. Several highly resistant varieties (Tiddis, Boumerzoug, Massine, Akhamokh and Yacine) were selected and promoted following seed multiplication and commercial release. They are also widely used in crosses to improve local varieties. The newly released varieties are being distributed to farmers that grow susceptible varieties. This gene deployment will provide a natural barrier between eastern to western Algeria to intercept the major direction of air flow. Fungicide control is now routinely applied soon after rust detection or even preemptively. The level of awareness for wheat rusts across Algeria is now very high. Training among farmers for visual detection is widely promoted by plant protection and extension services. These strategies have been very effective in mitigating the threat of wheat stripe rust such that losses have not exceeded 10% over the last five years.
Stripe rust caused by Puccinia striiformis f.sp.tritici, is one of the major diseases of wheat in the world. Experiments were carried out at two sites in Ethiopia (Kulumsa and Meraro) during the 2015 cropping season to evaluate the response of 198 elite bread wheat genotypes and two checks to the prevailing races of stripe rust at adult plant and seedling stage. The genetic profile of these genotypes was assessed using 13006 SNP markers and an association mapping was explored to determine marker?trait association. About 72.5% and 42.5% of the lines exhibited resistance at Kulumsa and Meraro, respectively. Out of 198 genotypes tested in the greenhouse, 31% exhibited common resistance for Kubsa and mixed stripe rust isolate. Only 8966 of the SNPs were polymorphic, only these were used for association mapping analysis. These markers spanned an average density of 3.47 cM per marker, with the poorest density on the D genome. Almost half of these markers were on known chromosomes, but had no position on the consensus map of bread wheat. Analysis of population structure revealed the existence of three clusters and the estimated genomic wide Linkage Disequilibrium (LD) decay in this study ranged from 0 to 50 cM. 53 SNPs in ten genomic regions located on wheat chromosome 1AL, 2AL, 2BL, 2DL, 3BL, 4BL, 4DL, 5AS, 7AL and 7BL were identified. Thirty nine SNP markers in five genomic regions at Kulumsa and 14 SNP markers in six genomic regions at Meraro explained more than 25.5% and 35.1% of phenotypic variability respectively. For seedling stage, 21 markers in ten genomic regions located on wheat chromosomes 1B, 2A, 2B, 3A, 3B, 4B, 4D, 5A, 6B and 7B were associated with resistant. These loci may be useful for choosing parents and incorporating new resistance genes into locally adapted cultivars.
Wheat stripe rust, caused by basidiomycete fungus Puccinia striiformis f. sp. tritici (Pst), is a damaging disease worldwide. The recent discovery demonstrated the fungus depends on living wheat and aecial hosts, mainly barberry (Berberis) species, to complete its life cycle. In China, we determined that, under natural conditions, the sexual cycle of Pst occurs based on collections of Pst isolates from the diseased barberry in the past three years. However, no direct evidence to support whether barberry plays a role in spreading inoculums to wheat field to cause stripe rust was detected. In the present study, we recovered 103 Pst samples from natural-infected B. shensiana in the western Shaanxi in spring 2016, and also collected 107 Pst isolates from neighboring wheat fields. Phenotype and genotype of the two Pst populations were tested using a set of Chinese differential hosts for Pst and SSR markers, respectively. The phenotype tests showed that 57 race types produced from the barberry-derived Pst populations, consisting of 58 known races, such as CYR 34, CYR32, G22-14, and Su11-14-3, and 45 new races. Many of the two Pst populations shared the same race types. The genotype tests indicated the barberry-derived Pst population produced a rich genotype, obviously higher than the wheat-derived Pst populations. The seven same genotypes were found on 40 isolates of the former and 26 of the latter. Our results provide evidence to support that sexual cycle of Pst occurs regularly in nature in China and that barberry provides inoculums to neighboring wheat fields, triggering stripe rust infections in the spring. This could be a reason why the Chinese Pst populations represent extreme genetic diversity.
Wheat cultivation in many regions faces threats by devastating fungal infections. However, wheat cultivar 92R137 shows resistance to Puccinia striiformis infection. To isolate the stripe rust resistance gene Yr26, an integrated transcriptomic and comparative genomics approach was undertaken. Near-isogenic lines of wheat (carrying Yr26 or not) infected with two Puccinia striiformis f. sp. tritici (Pst) (Virulence or avirulence to Yr26) were analysed in a dual detailed time series RNA-seq study. The emerging IWGSC refseq v1.0 genome assembly sequence serves as a valuable template and was also used for comparative genomics studies of the gene candidate region with the genome sequences of close relatives and wheat progenitors. Using bulked segregant analysis (BSA) to identify polymorphic SNPs between parent and resistant DNA (R-bulk) and susceptible DNA (S-bulk), flanking markers for Yr26 were identified. These two markers were mapped to the Chinese spring reference genome sequence, spanning a region of about 250 kb. The synteny analysis of this candidate region in CS chr1B with chr1A, chr1D, Wild Emmer Wheat (Td_chr1A and Td_chr1B) and Barley (chr1H) identified three candidate Yr26 genes. To detect gene candidates a dual time series RNA-seq analysis was performed. Genes differently expressed between rust susceptible (NIL-S) host lines and rust resistant (NIL-R) lines, carrying the Yr26 candidate gene were analysed. Both lines were inoculated with Pst carrying different avirulence factors (Pst-CYR32 and Pst-V26), compatible or incompatible with the corresponding wheat lines. Differential gene expression analysis (DEG) between compatible and incompatible interaction revealed DEGs in the wheat genome and in the Pst genome. From a network analysis of both wheat and Pst genes, we inferred connected co-expressed modules. Resulting modules showed particular enrichments for disease resistance, defense response to fungus and cell wall components.
Emergence of new virulent races of Puccinia striiformis f. sp. tritici (Pst) to stripe (yellow) rust resistance genes in wheat (Triticum aestivum L.) has historically resulted in severe yield losses worldwide. We conducted a study to characterize the virulence profiles of Pst races prevalent in Kenya from historic (1970-1992) and recent collections (2009-2014). Pst isolates collected during surveys in Kenya were characterized at the Global Rust Research Centre (GRRC), Denmark. Yellow rust differential sets (wheat lines with known Yr resistance genes), and strain-specific sequence-characterized-amplified-region (SCAR) markers were used to group the Pst isolates as Pst1 or Pst2. Virulence to Yr1, Yr2, Yr3,Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, Yr27, and the seedling resistance in AvocetS were detected. A total of 12 virulence profiles /races were detected in isolates obtained during 1970 to 1992, while six races were detected from samples collected between 2009 to 2014. In both periods, races with virulence profiles Yr2, Yr6, Yr7, Yr8, Yr25, Yr27, Avs and Yr2, Yr6, Yr7, Yr8, Yr17, Yr25, AvS were common. The SCAR results revealed that both Pst1 and Pst2 strains were present in the Pst isolates tested, Pst1 even in isolates from the 1970s. Additional isolates were also identified with neither Pst1 nor Pst2 profiles. From our findings, race analysis is key to understand the race diversity and pre-breeding efforts for effective resistance gene deployment.
In India stripe rust of wheat (Triticum aestivum L.) is important as it occurs in the severe form in North Hill Zone (NHZ) covering states of Jammu and Kashmir, Himachal Pradesh and Uttarakhand. Stripe rust thrives well under cool and moist field conditions and sometimes its epidemic is so severe that it destroys the whole crop. Although the fungicides have been applied to control this disease but their use is unfriendly to the environment and they add to the input cost of farmers. The breeding for disease resistance is an effective strategy and involves identification of stable sources of resistance and their utilization. Deployment of yellow resistance genes has helped in suppressing the intensity, effectiveness and frequency of rust epiphytotics. Many sources of yellow rust resistance exist, but these are either incompletely characterized or these have not been studied in sufficient detail needed for their designation. The present study was conducted to screen for yellow rust resistance a set of 300 wheat germplasm lines received from various national and international germplasm centers viz., CIMMYT, Mexico; CIMMYT, Ankara, Turkey; IARI sub-station, Wellington, Tamil Nadu; IIWBR, Karnal; IIWBR, Flowerdale, Shimla and SKUAST-Kashmir, Srinagar for yellow rust resistance (46S119 and 78S84 as most prevalent races) over years 2012 to 2016 under field and ployhouse conditions. The study could identify eleven wheat lines showing varying levels of resistance to yellow rust races 46S119 and 78S84 when scored at adult plant stage under both conditions. The area under disease progress curve (AUDPC) scores of the lines identified as resistant was lowest as compared to yellow rust susceptible check (Agra Local). The resistant lines identified in the study could efficiently be utilized in yellow rust breeding programmes of the country and thereby deployment of such genes over space and time for an effective and long lasting control.
Wild emmer wheat (Triticum dicoccoides, (DIC)) is an important source of resistance to stripe rust due to presence of Puccinia striiformis in its natural habitats with high humidity and relatively low temperatures that are favorable for stripe rust development. Previously, we showed that DIC accessions from northern Israel were highly resistant to stripe rust. According to the rust responses of three DIC accessions (G25, H52, G303) and mapping of the resistance to relatively close, but different, genetic positions on chromosome 1BS, three different resistance genes were assumed to be present. However, the development of additional critical recombinants and new higher resolution genetic maps for these three genes in subsequent work led us to place YrH52 and YrG303 in the same genetic interval as Yr15, suggesting that the three putative genes are allelic or identical. The recent cloning of Yr15 allowed us to test this hypothesis using an EMS mutagenesis approach. We sequenced the Yr15 locus in five yrH52 and three yrG303 susceptible mutants and identified missense point mutations associated with the susceptible phenotype in each one. Thus, YrH52 and YrG303 may not be new genes. Further work is under way to determine if these genes are allelic or identical.
The recent emergence of new widely virulent and aggressive strains of rusts (particularly stripe and stem rust) is threatening Italian durum wheat (Triticum turgidum L. var. durum) production, especially under the trend of higher temperature and humidity. A big effort has been undertaken to explore the genetic variability for resistance to these fungal pathogens and discovering novel resistance genes. In particular, a wide set of tetraploid wheat lines was genotyped with several thousands of SNP markers and used for association mapping. This large collection consisted of a group of durum wheat cultivars, produced from the beginning of the last century up to now, a collection of wild emmer wheats (T. dicoccoides), and lines belonging to other wild and domesticated tetraploid subspecies, as a large untapped source of genetic diversity. In a tight cooperation with the University of Minnesota, this collection was evaluated for reaction to several races of stem and stripe rust pathogens in both controlled greenhouse and field conditions. Among the genotypes belonging to the collection are parents of segregating populations which were used for the validation of mapping results. Novel resistance loci were identified, that can be incorporated into new durum varieties through breeding programs. The QTLs found in this study, together with those available in literature, were projected to the recently sequenced durum wheat genome in order to define more precisely the chromosome regions and candidate genes involved in resistance to rusts. Lines which were resistant to multiple races of rust pathogens were also found among both T. dicoccoides and durum wheat cultivars as a source of resistance genes, whose cloning will be undertaken based on the results here obtained.
This study was supported by the Italian Ministry of Foreign Affairs and International Cooperation, with the special grant RES-WHEAT.