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Ug99 is a devastating race of Puccinia graminis f.sp. tritici possessing virulence against resistant genes Sr31 and Sr24. This race is highly adoptive and has spread quite rapidly with 13 known variants covering 13 different countries. For reducing the vulnerability of wheat in south Asia to the Ug99, breeding durable resistant varieties is important. India, second largest wheat producer, falls in the predicted pathway of Ug99. Most of the Indian germplasm possesses Sr31 and Sr24 in their background. HUW468, a well adopted variety of north eastern plains zone (NEPZ) of India, carries durable resistance gene Sr2. To strengthen it, a MABB program was initiated to introgressed two major genes (Sr50 and SrWeb) using a donor line PMBWIR4 from CIMMYT. The foreground selection was performed with Xgwm47 for SrWeb and IB267 for Sr50 followed by the background selection by using 128 polymorphic SSR markers covering all chromosomes. Backcross progenies of HUW468 were screened in the field condition by using of Pgt race 21A-2 at IARI, Regional Station, Indore located in the central India. Superior selected lines from BC2F4:5 generation was planted at three locations in India namely; Varanasi, Indore and Dharwad. HUW468-09-25-47-09 and HUW468-09-25-47-56 were selected from BC2F5 generation having Sr50 and SrWeb along with Sr2 gene, superior agronomic performance and with 93.5% and 92.7% genome recovery, respectively. These two lines also possess 6-10 % yield superiority over the recipient parent HUW468. These lines have been submitted for registration in NBPGR (National Bureau of Plant Genetic Resources), India.
The basidiomycetous fungus, Puccinia graminis f. sp. tritici (Pgt) causes stem rust disease as one of the most destructive wheat pathogens, worldwide. TTKSK and other Pgt races under Ug99 race group are considered as major threats to wheat production in east Africa and CWANA region by defeating the stem rust resistance gene Sr31, while its ineffectiveness was reported in Iran in 2007. Race TKTTF of Pgt caused a severe stem rust epidemic in southern Ethiopia in 2013, and was spread to Europe through 2016 Sicily outbreak. This research describes race identification of Iranian isolates collected during the widespread distribution of stem rust in 2014-16. Purified urediniospores of 123 Pgt isolates were separately inoculated on seedlings of 20 North American differential wheat cultivars carrying different Sr resistance gene/s. Infection types were recorded at 14 days post inoculation (dpi) using Stakman et al. 0-4 scale. Based on the letter code nomenclature, we identified the Pgt races TKTTF, TTTTF, TTKSK, TTKTK, PKTTF, TKSTF, PKSTF, PKTTC, PTRTF, PTTTF, PKSTC, TTRTF, TKSTC and PKRTF in Iran. TKTTF and TTTTF were determined as prevalent Iranian Pgt races. This is the first report of race TTKTK, a new variant of Ug99 race group with virulence on Sr31 and SrTmp resistance genes, in Iran. Since TTKTK primarily occurred in south west of Iran, the migration route for this new race seems to be similar to race TTKSK. The high race variation observed in this study could indicate a high genetic diversity among P. graminis f. sp. tritici populations in Iran, as a wheat center of origin.
Stem rust Ug99 and related race group are one of the major constraints of wheat production in Kenya. The challenge has been largely due to rapid evolution of races within lineage defeating resistance genes resulting in boom and burst cycles. Understanding of the pathogen population structure in major wheat growing regions in Kenya gives comprehensive information of the predominant races as well as capturing new races which may have potential of causing epidemics. Such information can have significant impact on effective gene stewardship in breeding resistant varieties. Using 11 Pgt Simple Sequence Repeats (SSR) markers we analyzed 104 single uredinial-pustule samples. Allele frequency distribution ranged from 2 to 6 per locus with an average of 3.27 per locus. Observed heterozygosity ranging from 0.297-1.000 (mean HO=?0.809) was significantly different (P< 0.001) than the expected heterozygosity (0.264 to 0.507; mean HE=?0.407) indicating that the population is asexual. Analysis of molecular variance (AMOVA) showed that the majority of the variation occurred within the samples (98%) rather than between regions (2%). Analysis of 104 samples identified 21 multiple locus genotypes (MLGs). MLG.19 was observed across the three region analyzed that is Central Rift, North Rift and Mount Kenya while MLG.18 was predominant in Mount Kenya. Based on SSR genotypes of reference isolates, Pgt clade IV (race TKTTF) was associated with MLG.16 in Central Rift Kenya while clade I (race TTKSK) had a unique MLG.10. These results indicated two main groups corresponding to Clade I (Ug99 race group) and Clade IV (race TKTTF race group). This minimum spanning network analysis pattern points to the Pgt population being asexual due to mutation. These preliminary results suggest that Pgt population in Kenya is asexual in nature. Further analysis is being conducted to ascertain geographical structure as well as compare the results with the 2011 data.
Resistance genes Sr2, Sr22, Sr24, Sr25 and Sr26 confer adult plant resistance to Pgt race TTKSK (=Ug99). Ten Egyptian wheat varieties and four bread wheat entries from CIMMYT were screened with five DNA markers to determine the presence of these genes, and were evaluated for stem rust response at Sakha and Sids during the successive growing seasons of 2015/16 and 2016/17. Varieties Giza 171, Sakha 94, Gemmeiza 11, and CIMMYT lines 6043, 6091, 6107 and 6197 were resistant with severities ranging from TrR to 5MR/MS. Sr2 was present in all entries; Sr24 was present in one local Egyptian cultivar (Misr2); Sr25 was present in Misr 1, Misr 2, Gemmeiza 9, Gemmeiza 11, and lines 6091 and 6197; and Sr26 was present in line 6197.
Wheat stripe (Puccinia striiformis f. sp. tritici,=Pst) and stem (Puccinia graminis f. sp. tritici =Pgt) rusts are the most important wheat disease in Egypt as well as present in all wheat growing areas. This study to evaluate a set of tester lines of wheat carrying stripe Yr's, stem Sr's rust genes and selected Egyptian varieties have been studied for their response to Pst and Pgt at adult plant stage under field conditions in Sakha Agriculture Research Station, during the 2011 to 2014 growing seasons. The results revealed that stripe rust, it has been observed that the new race Yr27-virulence to Pst. In addition pathotypes were virulent for Yr2, Yr6, Yr7, Yr8, Yr9, Yr27, while Yr18 showed moderate susceptibility. On the other hand, Yr1, Yr5, Yr10, Yr15, Yr17, Yr32 and YrSP exhibited high levels of resistance. Regarding, evaluation of resistance genes sources of stem rust on ICARDA, CIMMYT wheat germplasm, and Egyptian wheat varieties released i.e. Misr1 and Misr2 which having Ug99_resistance genes Sr2 and Sr25 were found susceptible to Pgt, also Sr31 recorded infection moderately susceptible to susceptible at adult stage. Genes Sr2 complex, Sr24, Sr26, Sr27, and Sr32 were resistant at adult plant stages. The combination of Sr26 with Sr2 and Sr25 provided stem rust resistance in some CIMMYT wheat germplasm. The objectives of this work are: race analysis of wheat stem and stripe rust disease, evaluation the level and distribution of wheat stripe and stem rust in Egypt, and identification the resistance genes in commercial varieties or new promising lines using standard and molecular genetic markers. Egyptian germplasm such as Misr1, and Misr2 and others tester lines of wheat carrying stem rust Sr's were evaluative under field condition at adult stage in Egypt during 2014 growing season, Egyptian cultivars Misr1 and Misr2 were susceptible rated 10S-20S and Sr31 rated MSS. that results clearly presence a new Sr31-virulence. On other hand, genes Sr2 complex, Sr24, Sr26, Sr27 and Sr32 were resistant and combination of Sr26 with (Sr2 and Sr25) produced stem rust resistance in some CIMMYT wheat germplasm. Shahin et al., 2015, in APS Annual Meeting, Aug. 1-5, Pasadena, CA, US, (In Press).
Stem rust caused by Puccinia graminis f. sp. tritici (Pgt) is a destructive disease on bread and durum wheat. Following the identification and distribution of Ug99, major national and international efforts have been made to detect additional spread and emergence of new Pgt races. Since 2011, GRRC has accepted to receive live samples of stem rust year round, and up to 2014, a total of 428 dried samples of Pgt infected wheat tissue were received from 15 African and Asian countries, i.e., Azerbaijan, Egypt, Ethiopia, Iran, Iraq, Kenya, Lebanon, Nepal, Rwanda, Sudan, Tanzania, Turkey, Uganda, Yemen and Zimbabwe. Additional samples were received from Germany, Sweden and Denmark, where wheat stem rust re-emerged in 2013-2014. Recovery procedures using susceptible seedlings of cv. Morocco was done upon arrival and a total of 269 samples were successfully recovered, multiplied and stored in liquid nitrogen until further use. To date, 140 Pgt isolates have been pathotyped based on the method of Jin et al. (2008). Subsets of isolates were selected for molecular characterization including SNP genotyping and shipped to USDA-ARS, Cereal Disease Lab (CDL). The Pgt race TKTTF was widely distributed and found in ten countries including Egypt, Ethiopia, Iran, Iraq, Lebanon, Sudan, Turkey and the three European countries. Races of the Ug99 lineage were frequently observed in Africa. Clear indication of a new race in the Ug99 race group with additional virulence for SrTmp, TTKTK, was observed in samples from four African countries in 2014. PCR diagnostics developed by CDL confirmed the new race being member of the Ug99-lineage. The experimental work was supported by the DRRW project and new research facilities were funded by Aarhus University.
Use of large-scale computational resources has permitted the first quantitative study of airborne migration routes of fungal spores between numerous key epidemiological hot-spots of wheat stem rust in Africa, the Middle East and the Indian subcontinent. By coupling a state-of-the-art Lagrangian particle dispersion model (NAME) with mechanistic epidemiological models, we simulate turbulent atmospheric transport of large ensembles of fungal spores from source sites. The models use highly resolved global meteorological datasets from the UK Meteorological Office. We consider release of P. graminis uredinospores from numerous source locations over an 11 year period (2003-2014) and simulate atmospheric trajectories over a 10 km2 spatial sampling grid to elucidate spore deposition rates at national, regional, and continental spatial scales. Our systematic exploration permits the first quantitative perspective and ranking of likely airborne transmission routes of wheat stem rust. We identify migration trends within and between the “Rift valley epidemiological zone”, the Middle East, the Indian Subcontinent, as well as South Africa. Our results indicate (I) consistent seasonal dispersal patterns, (II) likely airborne transmission of stem rust from the Middle East to North-East Africa, and (III) suggest that there is considerable risk of spread of Ug99 or other virulent races from Eastern Yemen to the Indian subcontinent. Model results indicate that over the 11 year study period, viable spore deposition occurred between Eastern Yemen and Pakistan on average 22 days per year during overlapping wheat growing seasons. The validity of the modelling framework has been successfully tested by comparison with survey data from the 2013 epidemic outbreak in Ethiopia, and was recently used as a risk assessment tool to provide rapid response advice in different East-African countries. Known stem rust race distributions are also supportive of the model outputs. The research we have been doing allows a quantitative perspective on likely airborne transmission routes of Ug99 or other virulent races of wheat rust. By that we hope to provide new insights and recommendations for future risk assessment, survey and control strategies and also to contribute to fundamental understanding of epidemiological spread on regional and continental scales. The work we would like to present is the result of a joint effort of Dr Laura Burgin and Dr Matt Hort from the UK Meteorological office, Dr Dave Hodson from CIMMYT, and Dr James Cox, Matthew Hitchings and me from the Epidemiology and Modelling group of Prof Gilligan in Cambridge.
Wheat stem rust is one of the major wheat yield limiting factors in Ethiopia. A stem rust epidemic occurred in the wheat belts of Arsi and Bale zones in the 2013-2014 crop season caused by Pgt race TKTTF that is virulent to the widely grown Ug99-resistant variety Digelu. This epidemic highlighted the need for wheat varieties with resistance to multiple Pgt races. This study was therefore, carried out to evaluate the reaction of the major Ethiopian varieties and advanced breeding lines against the dominant Pgt races in Ethiopia. Races TKTTF, TTKSK, TRTTF and JRCQC were isolated from field samples and multiplied on the susceptible cultivar McNair starting in May 2014. Four wheat stem rust nurseries, each inoculated with a single Pgt race, were established at Kulumsa and monitored from July through October, 2014. Each nursery included 34 entries in two replicates and 137 entries in a single replicate, augmented with six sets of five repeating checks. An additional nursery established at Debre Zeit, containing 551 entries in an augmented design, was evaluated with the epidemic Pgt race TKTTF. These entries included the most relevant Ethiopian bread and durum wheat breeding lines and cultivars, and 34 seedling-susceptible lines to evaluate the race-specificity of adult plant resistance. Stem rust severities for the four races ranged from trace to 80 %. Out of all entries evaluated, 10 were resistant to all four Pgt races, while 11 entries were effective to three of the four races. At Debre Zeit, 31.4% of the entries were resistant to Pgt race TKTTF. This study showed that rapid isolation and increase of Pgt races in Ethiopia is possible to facilitate field screening of breeding lines to select for candidate cultivars with resistance to multiple virulent races of Pgt.
Stem rust is a potentially destructive fungal disease of wheat worldwide. In 1998 Pgt pathotype TTKSK virulent to Sr31 was detected in Uganda. The same pathotype was confirmed in Lorestan and Hamedan provinces of Iran in 2007. We used a derivative of race TTKSK to phenotype 62 Iranian wheat landraces (resistant to stripe rust in a previous study) at the seedling stage to this new pathotype (TTSSK). Twenty eight accessions were evaluated for the presence of resistance genes Sr2, Sr22, Sr24, Sr25, Sr26, Sr35, Sr36 and Srweb using SSR markers. None carried Sr2, Sr24 or Sr26, but the presence of Sr22, Sr25, Sr35 and Sr36 was indicated. Some susceptible landraces predicted to carry Sr2 by marker analysis require further investigation. To evaluate defense gene expression in compatible and incompatible stem rust interactions we sampled resistant and susceptible cultivars at 0, 12, 18, 24, 72 hours post-inoculation (hpi). ?-1,3 glucanase expression was studied using qGLU-S and qGLUU-AS primers and a real-time PCR step-one ABI machine, with ?-tubulin and EF1-? genes used as internal controls. In incompatible interactions defense gene expression was increased at 24 hpi, but in compatible interactions the highest level of expression occurred at 12 hpi and was significantly decreased at 18 hpi. The results revealed that expression of defense genes such as ?-1,3 glucanase was earlier in compatible than in incompatible interactions but the expression level was less in incompatible interactions. On the other hand, in susceptible genotypes the expression of defense genes increased immediately after inoculation and declined sharply after infection. In contrast defense gene expression in resistant genotypes began to increase after establishment of the pathogen.
In the Triticum genus, tetraploid T. turgidum is a useful resource for germplasm improvement of hexaploid common wheat (T. aestivum). Several recent studies demonstrated that Pgt race TTKSK resistant genotypes were abundantly present among seven tetraploid subspecies (T. turgidum subsp. carthlicum , dicoccum , dicoccoides , durum, polonicum , turgidum , and turanicum ). In an effort to improve common wheat for TTKSK resistance, we have been transferring stem rust resistance from tetraploid to hexaploid wheat through production of synthetic hexaploid wheat (SHW) or direct hexaploid × tetraploid hybridization followed by backcrossing. For production of SHW lines, we selected 181 unique tetraploid genotypes from the seven tetraploid subspecies for crosses with 14 accessions of Aegilops tauschii (2 n = 2 x = 14, DD) and developed 200 new SHW lines from these crosses. We are currently characterizing these lines for reaction to stem rust. So far, 80 SHW lines and their parents have been evaluated for reaction to races TTKSK, TRTTF, TTTTF and six other U.S. races and genotyped using molecular markers linked to known resistance genes previously identified in T. turgidum subsp. dicoccum and Ae. tauschii. The evaluation data showed that 42, 40, and 52 SHW were resistant to races TTKSK, TRTTF, and TTTTF respectively, with 21 lines being resistant to all three races. Based on marker analysis and race specificity, we postulated that a number of SHW lines have novel genes conferring resistance to TTKSK and other races. For gene introgression through direct hybridization, we have transferred Sr47, which was recently transferred from Ae. speltoides into durum through marker-assisted chromosome engineering, from durum into adapted hard red spring wheat germplasm. The new SHW lines and adapted germplasm carrying unique stem rust resistance genes from the tetraploids represent new sources of stem rust resistance for hexaploid wheat improvement.