Stem Rust Race Ug99 Research Articles

Virulence Survey of Puccinia striiformis in Israel Revealed Considerable Changes in the Pathogen Population During the Period 2001 to 2019.

A total of 353 urediniospore isolates of Puccinia striiformis f. sp. tritici (Pst) collected in Israel during 2001 to 2019 were analyzed. Pst pathogenicity was studied with a set of 20 differentials (17 Avocet and 3 other lines). Three periods were compared: 2001 to 2007, 2009 to 2016, and 2017 to 2019. No virulence to Yr5 or Yr15 was detected. Virulence frequencies on Yr4, Yr10, Yr24, and YrSp genes rose to the moderate level (0.28 to 0.44) in 2017 to 2019. Virulence frequencies to Yr2 and Yr9 decreased. One Pst phenotype was identified in all three periods, but its frequency drastically decreased from 0.74 in 2001 to 2016 to 0.21 in 2017 to 2019. The most probable scenario of emergence of wheat yellow rust in Israel is wind dissemination of Pst urediniospores from the Horn of Africa. Variability of the Pst population increased amid considerable evolution with two major transformations in 2009 and 2017. The first modification can be attributed to changes in wheat genetic background in Israel due to deployment of new cultivars resistant to yellow rust since 2004. The second shift in 2017 can be primarily explained by intensive deployment of wheat cultivars resistant to the stem rust race Ug99 in the 2010s in the Horn of Africa. This led to changing genetic backgrounds of the cultivated wheats in the donor region and development and long-distance spread of new Pst phenotypes to Israel. Two singular multivirulent Pst phenotypes were identified in 2019, one of them being closely related to the aggressive Warrior race. Such phenotypes may potentially defeat existing resistances.

Detection of Lr19/Sr25 in segregating populations of wheat (Triticum aestivum L.) using robust molecular markers

Marker assisted breeding (MAB) technology has been proved effective to transfer the genes of interest and also increased the accuracy of selection in wheat improvement programmes. The Agropyron elongatum derived 7D.7Ag translocation carrying Lr19/Sr25 is not only effective against leaf rust pathotypes but also effective against stem rust race Ug99 and its variants. Therefore, wheat breeding lines carrying Lr19/ Sr25 translocation segment have been developed worldwide. The present study was aimed for developing wheat genotypes with Lr19/ Sr25 using Xwmc221, PSY1-E1 and Gb DNA markers in segregating populations of wheat. We could infer that Xwmc221, PSY1-E1 and Gb are effective molecular markers to tag Lr19/Sr25 in segregating generations of wheat. The data also revealed consistency between host pathogen interaction (HPI) test and Xwmc221, PSY1-E1 and Gb molecular markers for selecting lines with Lr19/Sr25 in segregating generations. This work not only confirmed the robustness of the three Lr19/Sr25 markers but also demonstrated the application of both genotyping and phenotyping in making full-proof selection of superior progenies with gene of interest in wheat.

Combating Ug99 - Current Scenario

The yield potential of wheat crop is not achieved abundantly because of disease pressure. One of the most destructive of such diseases is stem rust (SR). SR caused by Puccinia graminis f. sp. tritici (Pgt), had been controlled successfully during three decades throughout the world with deployment of semi-dwarf resistant cultivars in the last half of previous century. During 1999 appearance and dispersion of stem rust race Ug-99 in Uganda (a virulent race against Sr31) created an alarming situation worldwide. Widespread germplasm was protected by gene Sr31 found susceptible to this terrible strain as the gene was protecting 80% wheat lines cultivated throughout planet. The emergence of the Ug99 race of stem rust in Africa and the Middle East together with the appearance of new strains in Europe catalyzed a main effort to recognize sources of stem rust resistance genes against new virulent strains and incorporate these genes into wheat lines. Scientific community addressed the dilemma in time and efforts did not go waste. Worldwide concern regarding the danger to global wheat production caused by Ug99 led to breeding wheat for durable resistance against disease and achieved considerably. This success is attributed to team work of experts and serves as an example for research workers in future. However, the continued emergence of stem rust variants that overcome new resistance genes, demands an amplified emphasis on pathogen evolution and virulence mechanisms. A major role for BGRI is to keep ‘the eye on the ball’ with regard to all these aspects. This article enables us to design strategy to tackle a situation which appears without alarm but in this case intellectuals coordinated each other and solution became possible. The same principle does not apply in plant pathology but in Human pathology and Veterinary pathology.

Races Identification of Wheat Rusts in Syria during the 2019 Growing Season

Kharouf, Sh., Sh. Hamzeh and M.F. Azmeh. 2021. Races Identification of Wheat Rusts in Syria during the 2019 Growing Season. Arab Journal of Plant Protection, 39(1): 1-13. Wheat rust diseases, caused by Puccinia striiformis f. sp. tritici (stripe or yellow rust), P. triticina f. sp. tritici (leaf or brown rust) and P. graminis f. sp. tritici (stem or black rust) are important factors affecting both durum and bread wheat production in Syria. Considerable losses were caused by these diseases, especially stripe rust, estimated at more than one million metric tons, in the 2010 season, out of 5 million anticipated production. Therefore, it is essential to monitor and follow the movement of these three rust physiological races. In the 2019 growing season, 165 wheat fields were surveyed, and 312 samples were collected and characterized. Ten races of stripe rust were identified in ten locations, of which, four represent new record in Syria, namely the races 16E154, 69E150, 264E46 and 258E64. In addition, four races of leaf rust were identified in four locations, one of which (BKLP) is a new record in Syria. In addition, three previously recorded stem rust races were identified from three different locations. It should be mentioned that the newly recorded races of stripe rust are able to overcome resistance genes Yr1 and Yr5, on which the resistance of durum wheat cultivars such as "Cham3" depended, with a disease severity of 40S recorded in the same locations. It is also worth noting that the stripe rust race 462E128 (warrior) was not detected in the isolates studied. Likewise, the stem rust race Ug99 was also not identified, and because of the aggressiveness of this race, continuous inspection through field surveys accompanied with pathogenicity tests is essential during the coming seasons. Keywords: Stripe (yellow) rust, Leaf (brown) rust, stem (black) rust, race identification, wheat, Syria

Identification of new sources of resistance to stem rust race Ug99 (TTKSK) in wheat genotypes

Stem rust disease which caused by Puccinia graminis f. sp. tritici is one of the major wheat production constraints in the high lands of central, south eastern and north western part of Ethiopia. The disease had caused up to 100% yield loss on the unprotected wheat farms. This study was conducted to identify new sources of resistance to stem rust disease. After the removal of genotypes that showed a major gene (race specific) resistance expression at seedling test, 60 selected genotypes were evaluated for their adult plant resistance to stem rust and agronomic traits across three locations (Debrezeit, Adet and Kulmsa) using a 5 × 12 alpha lattice design with three replications. Genotypes showed a highly significant difference (p = 0.001) on the traits of final rust severity (FRS), area under disease progress curve (AUDPC), coefficient of infection (CI) and apparent infection rate (r) at different locations. Moreover, combined analysis of variance also showed the presence of highly significant effects of genotypes, environments and GE interaction on the magnitude of FRS, AUDPC, CI, r, days to maturity (DM), plant height (PH), hectoliter weight (HLW), thousands kernel weigh (TKW) and grain yield (GY) across testing locations. The correlation analysis revealed the presence of positive highly significant (p<0.001) relationship of FRS with both CI (r=0.894) and AUDPC (r=0.877). A positive and highly significant (p<0.001) correlation was also observed between CI and AUDPC (r=0.996) of the tested genotypes. Principal component analysis indicated that only the first four principal components (PCs) explained 86.58% of the total variation among the tested genotypes. Cluster analysis also confirmed the presence of variation among the tested genotypes by dividing them into five major groups. In this study, four bread wheat genotypes (G12, G60, G31 and G52) were found to be resistant to stem rust disease across the three locations and could be used as source of stem rust resistance in future wheat improvement program.

Dissection of Cell Death Induction by Wheat Stem Rust Resistance Protein Sr35 and Its Matching Effector AvrSr35.

Nucleotide-binding leucine-rich repeat receptors (NLRs) are the most abundant type of immune receptors in plants and can trigger a rapid cell-death (hypersensitive) response upon sensing pathogens. We previously cloned the wheat NLR Sr35, which encodes a coiled-coil (CC) NLR that confers resistance to the virulent wheat stem rust race Ug99. Here, we investigated Sr35 signaling after Agrobacterium-mediated transient expression in Nicotiana benthamiana. Expression of Sr35 in N. benthamiana leaves triggered a mild cell-death response, which is enhanced in the autoactive mutant Sr35 D503V. The N-terminal tagging of Sr35 with green fluorescent protein (GFP) blocked the induction of cell death, whereas a C-terminal GFP tag did not. No domain truncations of Sr35 generated cell-death responses as strong as the wild type, but a truncation including the NB-ARC (nucleotide binding adaptor) shared by APAF-1, R proteins, and CED-4 domains in combination with the D503V autoactive mutation triggered cell death. In addition, coexpression of Sr35 with the matching pathogen effector protein AvrSr35 resulted in robust cell death and electrolyte leakage levels that were similar to autoactive Sr35 and significantly higher than Sr35 alone. Coexpression of Sr35-CC-NB-ARC and AvrSr35 did not induce cell death, confirming the importance of the leucine-rich repeat (LRR) domain for AvrSr35 recognition. These findings were confirmed through Agrobacterium-mediated transient expression in barley. Taken together, these results implicate the CC-NB-ARC domains of Sr35 in inducing cell death and the LRR domain in AvrSr35 recognition.

First Report of Puccinia graminis f. sp. tritici Race PTKSK, a Variant of Wheat Stem Rust Race Ug99, in South Africa

First Report of <i>Puccinia graminis</i> f. sp. <i>tritici</i> Race PTKSK, a Variant of Wheat Stem Rust Race Ug99, in South Africa

Molecular Cytogenetic Characterization of two Triticum-Secale-Thinopyrum Trigeneric Hybrids Exhibiting Superior Resistance to Fusarium Head Blight, Leaf Rust, and Stem Rust Race Ug99.

Fusarium head blight (FHB), leaf rust, and stem rust are the most destructive fungal diseases in current world wheat production. The diploid wheatgrass, Thinopyrum elongatum (Host) Dewey (2n = 2x = 14, EE) is an excellent source of disease resistance genes. Two new Triticum–Secale–Thinopyrum trigeneric hybrids were derived from a cross between a hexaploid triticale (X Triticosecale Wittmack, 2n = 6x = 42, AABBRR) and a hexaploid Triticum trititrigia (2n = 6x = 42, AABBEE), were produced and analyzed using genomic in situ hybridization and molecular markers. The results indicated that line RE21 contained 14 A-chromosomes, 14 B-chromosomes, three pairs of R-chromosomes (4R, 6R, and 7R), and four pairs of E-chromosomes (1E, 2E, 3E, and 5E) for a total chromosome number of 2n = 42. Line RE62 contained 14 A-chromosomes, 14 B-chromosomes, six pairs of R-chromosomes, and one pair of translocation chromosomes between chromosome 5R and 5E, for a total chromosome number of 2n = 42. At the seedling and adult growth stages under greenhouse conditions, line RE21 showed high levels of resistance to FHB, leaf rust, and stem rust race Ug99, and line RE62 was highly resistant to leaf rust and stem rust race Ug99. These two lines (RE21 and RE62) display superior disease resistance characteristics and have the potential to be utilized as valuable germplasm sources for future wheat improvement.

The development of the initial material of spring common wheat for breeding for resistance to stem rust (Puccinia graminis Pers. f. sp. tritici), including the Ug99 race, in Russia

The donors of resistance of common wheat to the stem rust race Ug99 (breeding lines GT96/90, 113/00i-4, and 119/4-06rw) are involved in cross breeding with the use of the step-crossing and backcrossing methods. While developing hybrids with the spring mode of life, the donor of resistance 113/00i-4 (Sr2, Sr36, Sr39, Sr40, Sr44, Sr47) and accession 145/05i, which is resistant to leaf rust under the conditions prevalent in Russia’s Central Region but susceptible to Ug99, were used. From the obtained hybrid F4–F5 families and backcross progeny BC1F3-BC2F2-BC3F2, 137 individual plants with the homozygotic state of the alleles of 2–5 resistance genes to stem rust were selected by molecular markers. The progeny of these individual plants was tested in the North Caucasian and West Siberian regions of Russia for natural populations of stem and leaf rust and for powdery mildew in the Central Region. The lines resistant to these diseases were estimated for other economically valuable features: plant height, number of days before heading, ear productivity, weight of 1000 grains, and the protein and gluten content in the grain. The 71 spring wheat lines with multiple resistance to two or three diseases and the development of the best agronomic characteristics were selected for the Central Region and 20 lines were selected for West Siberia for further testing their competitiveness with the best varieties and lines in the breeding nurseries. As a result of the work, original source material was developed with several spring wheat resistance genes to Ug99.

Assessment of Wheat Diseases in South Omo Zone of Ethiopia

Wheat is one of the most important cereal cultivated in Ethiopia. It ranks fourth after Teff ( Eragrostis tef ), Maize ( Zea mays ) and Sorghum ( Sorghum bicolor ) in area coverage and third in total production. But, its production and productivity is prone to divers biotic and abiotic factors. Among biotic factor diseases are the one. But, the relative importance of each disease across locations has not been known and well profiled to develop sound management strategy in the studied areas. So, the assessment was done to watch and monitor the status of wheat diseases and observe wheat varieties response to wheat diseases and to determine the prevalence of new virulence races and monitor new stem rust race (ug99) spread in the region. The assessment was carried out in two kebeles of South Ari districts of South Omo zone i.e. Senegal and Senmamer kebeles of South Ari woreda in 2014 Meher cropping season. Results indicated that the highest mean infection of leaf rust (70%) was recorded on local variety at Senmamer kebele followed by Digalo variety in Senegal kebele which is 65% and fusarium head blight (47%) on Huluka variety followed by ETBW5890 variety which is 40% were recorded at Senegal kebele. Whereas at Senegal kebele 30% fusarium head blight was recorded as the highest mean infection. Whereas the mean infection of powdery mildew is 20% at Senmamer kebele which is less as compared to mean infection of leaf rust and fusarium head blight. Different studies reported that wheat is affected by different diseases. The current assessment indicated that complex diseases exists in different wheat varieties and their occurrence across kebeles was highly variable. In addition to introduction and promotion of different management practices, holistic and cumulative integrated approach is required to manage the complex wheat diseases in the studied areas.

Assessment of Wheat Diseases in South Omo Zone of Ethiopia

Wheat is one of the most important cereal cultivated in Ethiopia. It ranks fourth after Teff (Eragrostis tef), Maize (Zea mays) and Sorghum (Sorghum bicolor) in area coverage and third in total production. But, its production and productivity is prone to divers biotic and abiotic factors. Among biotic factor diseases are the one. But, the relative importance of each disease across locations has not been known and well profiled to develop sound management strategy in the studied areas. So, the assessment was done to watch and monitor the status of wheat diseases and observe wheat varieties response to wheat diseases and to determine the prevalence of new virulence races and monitor new stem rust race (ug99) spread in the region. The assessment was carried out in two kebeles of South Ari districts of South Omo zone i.e. Senegal and Senmamer kebeles of South Ari woreda in 2014 Meher cropping season. Results indicated that the highest mean infection of leaf rust (70%) was recorded on local variety at Senmamer kebele followed by Digalo variety in Senegal kebele which is 65% and fusarium head blight (47%) on Huluka variety followed by ETBW5890 variety which is 40% were recorded at Senegal kebele. Whereas at Senegal kebele 30% fusarium head blight was recorded as the highest mean infection. Whereas the mean infection of powdery mildew is 20% at Senmamer kebele which is less as compared to mean infection of leaf rust and fusarium head blight. Different studies reported that wheat is affected by different diseases. The current assessment indicated that complex diseases exists in different wheat varieties and their occurrence across kebeles was highly variable. In addition to introduction and promotion of different management practices, holistic and cumulative integrated approach is required to manage the complex wheat diseases in the studied areas.

Prebreeding research of near-isogenic lines of spring bread wheat with a combination of translocations from Agropyron elongatum (Host.) P.B. and Aegilops ventricosa Tausch.

To protect bread wheat from pathogens and, in particular, rust diseases, introgressive resistance genes located in alien translocations are commonly used. However, their application in practical breeding requires prebreeding studies. They reveal the effects of translocations on the adaptive properties of plants, elements of productivity, yield, and the quality of the final product. For this purpose, we studied the L653 and L654 near-isogenic lines of spring bread wheat cultivar Dobrynya, resistant to leaf rust and carrying the combination of translocations T7DS • 7DL-7Ae#1L + T2AL • 2AS-2MV#1, which carrying genes Lr19/Sr25 from Agropyron elongatum (Host.) P.B. and Lr37/Sr38/Yr17 from Aegilops ventricosa Tausch. The recipient cv. Dobrynya and standard cv. Favorit were used as references. Phytopathological tests showed that L653 and L654 were highly resistant to Puccinia triticina at all stages of plant development and to the Puccinia graminis race Ug99 + Lr24 (TTKST), but they were moderately susceptible to the Saratov population of this pathogen. The prebreeding research of lines L653 and L654 showed that the combination of T7DS • 7DL-7Ae#1L + T2AL • 2AS-2MV#1 translocations (1) prolonged the seedling emergence–heading time by 7 days and increased the mean plant height by 10 cm; (2) they did not affect lodging resistance or 1000 kernel weight; (3) they did not affect the grain yield in either the drought years or the years of leaf rust epiphytoties; (4) they reduced plant adaptation to abrupt vegetation condition changes; and (5) they reduced the amount of gluten without affecting its strength, dough tenacity, the tenacity: extensibility ratio, flour strength, bread volume, and bread porosity. Thus, the combination of T7DS • 7DL-7Ae#1L + T2AL • 2AS-2MV#1 translocations in the genotype of spring bread wheat cv. Dobrynya determines high resistance to leaf rust and the stem rust race Ug99 + Lr24 (TTKST), being neutral with regard to agronomic performance indices.

Identification of Sr genes in new common wheat sources of resistance to stem rust race Ug99 using molecular markers

The need for new donors of resistance to the aggressive Ug99 race of Puccinia graminis Pers. f. sp. tritici Eriks. et Henn has arisen because the pathogen is approaching the territory of the Russian Federation. Seventeen known Sr genes were identified with the use of molecular markers in 6 sources of resistance to stem rust race Ug99. They included five common wheat lines and the Donskaya Polukarlikovaya cv. The investigated accessions carried genetic material of alien species (Aegilops speltoides, Ae. triuncialis, and Secale cereale). We used molecular markers associated with the effective genes to the Ug99 race: Sr2, Sr22, Sr24, Sr25, Sr26, Sr32, Sr35, Sr36, Sr39, Sr40, Sr44, and Sr47, and with genes that were ineffective but protected the wheat cultivars against the local pathogen populations: Sr9a, Sr15, Sr17, Sr19, and Sr31. On the grounds of the analysis of molecular markers the presence of two to seven known Sr genes was postulated in the analyzed wheat lines: Sr2, Sr36, Sr39, Sr40, Sr44, Sr47, and Sr15 in line 113/00i-4; Sr22, Sr32, Sr44, Sr9a, Sr17, and Sr19 in line 119/4-06rw; Sr24, Sr36, Sr40, Sr47, Sr15, Sr17, and Sr31 in line GT 96/90; and Sr22, Sr44, Sr32, and Sr15 in line 9/00w; Sr22 and Sr44 in line 141/97w. Genes Sr32 and Sr44 were identified to be effective against Ug99 and ineffective genes Sr9a, Sr17, and Sr19 in Donskaya Polukarlikovaya cv. The accessions studied may be recommended as donors of resistance to race Ug99 in wheat breeding programs.

Inheritance of resistance to Ug99 stem rust pathogen in selected barley lines

Stem rust (Puccinia graminis tritici) race Ug99 is a devastating disease of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Barley is the world's fourth most important cereal crop after wheat, maize (Zea mays L.) and rice (Oryza sativa L.). The seedlings of F2 populations were inoculated 7–10 d after planting and when the first leaf was fully emerged (Feekes stage 1). The observed resistant (R):susceptible (S) ratio of the F2 populations HKBL-1385-13×08-UT-86 (χ20.05 = 0.480, P ≥ 0.488), HKBL-1385-13×09-N2-19 (χ20.05 = 0.641, P ≥ 0.424), ND2649 × 09-AB-78 (χ20.05 = 1.05, P ≥ 0.309) and ND25882×09-AB-78 (χ20.05 = 3.599, P ≥ 0.058) exhibited Mendelian segregation of 3R:1S suggesting that the resistance is conferred by major genes. In addition, F2 populations derived from the crosses Karne×09-N2-19 (χ20.05 = 1.343, P ≥ 0.246), Nguzo×09-AB-78 (χ20.05 = 0.429, P ≥ 0.512), ND26249×09-N2-52 (χ20.05 = 2.576, P ≥ 0.111) and ND25882×09-AB-78 (χ20.05 = 0.980, P ≥ 0.322) conformed to a phenotypic ratio of 9:7 indicating that there are genes modifying the resistance to Ug99. The results of this study suggest that there are valuable major genes for stem rust resistance that could be used to improve susceptible barley and wheat germplasm.

The development of initial material of spring common wheat for breeding for resistance to stem rust (Puccinia graminis Pers. f. sp. tritici), uncluding race Ug99, in Russia

Donors of resistance of common wheat to stem rust race Ug99 (breeding lines GT 96/90, 113/00i-4 and 119/4-06rw) are involved in cross breeding with the use of the step crossing and backcrossing method. While developing hybrids with the spring mode of life, donor of resistance 113/00i-4 (Sr2, Sr36, Sr39, Sr40, Sr44, Sr47) and accession 145/05i, which is resistant to leaf rust under the conditions of the RF Central Region but susceptible to Ug99, were used for backcrossing, 137 individual plants with the homozygotic state of alleles of 2–5 genes of resistance to stem rust were selected from the obtained hybrid families F4–F5 and backcross progeny BC1F3-BC2F2-BC3F2 by means of molecular markers. The progeny of these individual plants was tested in the North Caucasian and West Siberian regions of the RF for natural populations of stem and leaf rust and for powder mildew in the Central Region. The lines resistant to these diseases were estimated as to the other economically valuable features: plant height, number of days before heading, ear productivity, weight of 1,000 grains, protein and gluten content in grain, 71 spring wheat line with multiple resistance to two or three diseases and the development of best agronomic characters were selected for the Central region and 20 lines were selected for West Siberia for further testing of their competitiveness with the best varieties and lines in the breeding nurseries. As a result of the work, original source material was developed with several spring wheat resistance genes to Ug99.

Prebreeding research of near-isogenic lines of spring bread wheat with a combination of translocations from Agropyron elongatum (Host.) Р.В. and Aegilops ventricosa Tausch.

To protect bread wheat from pathogens and, in particular, rust diseases, introgressive resistance genes located in alien translocations are commonly used. However, their application in practical breeding demands prebreeding studies. They reveal effects of translocations on the adaptive properties of plants, performance indices, yield, and the quality of the final product. For this purpose, we studied the L653 and L654 near-isogenic lines of spring bread wheat cultivar Dobrynya, resistant to leaf rust and carrying the combination of translocations 7DS • 7 DL-7Ae#1L + 2AL • 2AS-2MV#1, which host genes Lr19/Sr25 from Agropyron elongatum (Host.) P. B. and Lr37/Sr38/ Yr17 from Aegilops ventricosa Tausch. The recipient cv. Dobrynya and standard cv. Favorite were used as references. Phytopathological tests showed that L653 and L654 were highly resistant to Puccinia triticina at all stages of plant development and to Puccinia graminis race Ug99 + Lr24 (TTKST), but they were moderately susceptible to the Saratov population of this pathogen. The prebreeding research of lines L653 and L654 showed that the combination of 7 DS • 7 DL-7Ae#1L + 2AL • 2AS-2MV#1 translocations: (1) prolonged the seedling emergence –heading time by 7 days and increased the mean plant height by 10 cm; (2) did not affect lodging resistance or 1000 kernel weight; (3) affected grain yield in neither drought years nor years of leaf rust outbreaks; (4) reduced plant adaptation to abrupt vegetation condition changes; (5) reduced gluten amount without affecting its strength, dough tenacity, tenacity : extensibility ratio, flour strength, bread volume, or bread porosity. Thus, the combination of 7DS • 7 DL-7Ae#1L + 2AL • 2AS-2MV#1 translocations in the genotype of spring bread wheat cv. Dobrynya determines high resistance to leaf rust and stem rust race Ug99 + Lr24 (TTKST), being neutral with regard to agronomic performance indices.

Identification of Sr genes in new common wheat sources of resistance to stem rust race Ug99 using molecular markers

The need for new donors of resistance to aggressive race Ug99 of Puccinia graminis Pers. f. sp. tritici Eriks. et Henn has arisen because the pest approaches the territory of Russian Federation. Identification of seventeen known Sr genes was performed with use of molecular markers in six sources of resistance to stem rust race Ug99. They included five common wheat lines and Donskaya Polukarlikovaya cv. The investigated accessions carried genetic material of alien species (Aegilops speltoides, Aе. triuncialis, Secale cereale). We used molecular markers associated with effective genes to race Ug99: Sr2, Sr22, Sr24, Sr25, Sr26, Sr32, Sr35, Sr36, Sr39, Sr40, Sr44, Sr47, and with genes that were ineffective but protected wheat cultivars against local pathogen populations: Sr9a, Sr15, Sr17, Sr19 and Sr31. On the grounds of the analysis of molecular markers the presence of two to seven known Sr genes was postulated in analyzed wheat lines :Sr2, Sr36, Sr39, Sr40, Sr44, Sr47 and Sr15 in line 113/00i-4; Sr22, Sr32, Sr44, Sr9a, Sr17 and Sr19 in line 119/4-06rw; Sr24, Sr36, Sr40, Sr47, Sr15, Sr17 and Sr31 in line GT 96/90; Sr22, Sr44, Sr32 and Sr15 in line 9/00w; Sr22 and Sr44 in line 141/97w. Genes Sr32 and Sr44 effective against Ug99 and ineffective genes Sr9a, Sr17 and Sr19 were identified in Donskaya Polukarlikovaya cv. The accessions studied may be recommended as donors of resistance to race Ug99 in wheat breeding programs.

Marker Assisted Transfer of Two Powdery Mildew Resistance Genes PmTb7A.1 and PmTb7A.2 from Triticum boeoticum (Boiss.) to Triticum aestivum (L.).

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as PmTb7A.1 and PmTb7A.2, were identified in T. boeoticum acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers Ta7AL-4556232 and 7AL-4426363 were identified to be linked to the PmTb7A.1 and PmTb7A.2, at a distance of 0.6cM and 6.0cM, respectively. In the present study, following marker assisted selection (MAS), the two genes were transferred to T. aestivum using T. durum as bridging species. As many as 12,317 florets of F1 of the cross T. durum /T. boeoticum were pollinated with T. aestivum lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F1. The resulting F1s of the cross T. durum/T. boeoticum//T. aestivum were screened with marker flanking both the PM resistance genes PmTb7A.1 and PmTb7A.2 (foreground selection) and the selected plants were backcrossed to generate BC1F1. Marker assisted selection was carried both in BC1F1 and the BC2F1 generations. Introgression of alien chromatin in BC2F1 plants varied from 15.4 - 62.9 percent. Out of more than 110 BC2F1 plants showing introgression for markers linked to the two PM resistance genes, 40 agronomically desirable plants were selected for background selection for the carrier chromosome to identify the plants with minimum of the alien introgression. Cytological analysis showed that most plants have chromosome number ranging from 40-42. The BC2F2 plants homozygous for the two genes have been identified. These will be crossed to generate lines combining both the PM resistance genes but with minimal of the alien introgression. The PM resistance gene PmTb7A.1 maps in a region very close to Sr22, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to Sr22 showed introgression of Sr22 from T. boeoticum in several BC2F1 plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99.

English

Plant diseases are among the major causes of crop yield loss and food insecurity. In South Africa, stem rust caused by Puccinia graminis Pers. f. sp. tritici. Eriks. & E. Henn. (Pgt) is an important disease of wheat. Records of stem rust occurrence in South Africa date back to the late 1720’s, when it was first discovered in the south-western wheat growing areas of the Western Cape. Although growing stem rust resistant cultivars is one of the most economic and environmentally feasible strategies, one of the challenges in host-plant resistance is that Pgt frequently acquires new virulence to overcome resistance genes in existing cultivars. There is strong evidence that the pathogen continues to evolve through mutation and genetic recombination. The appearance of stem rust race Ug99 (TTKSK, North American race notation) in East Africa in 1999 and subsequent epidemics in Kenya and Ethiopia was accompanied by the occurrence of four Ug99 variants (TTKSF, TTKSP, PTKST and TTKSF+) in South Africa. These have resulted in a renewed interest in understanding the status of Pgt races and stem rust resistance in the world as well as the need for a new host-plant resistance strategy. The current review summarises up-to-date literature on the prevalence of stem rust races in South Africa, and also draws attention to the resistance genes and strategies currently deployed to combat this disease. The aim of the review was to provide perspectives on research milestones and guide future research programs for reducing losses incurred by stem rust of wheat in South Africa. Key words: Durable resistance; Pathogen variability; Puccinia graminis f. sp. tritici.

Identification and mapping in spring wheat of genetic factors controlling stem rust resistance and the study of their epistatic interactions across multiple environments

Stem rust (Puccinia graminis f. sp. tritici) is responsible for major production losses in hexaploid wheat (Triticum aestivum L.) around the world. The spread of stem rust race Ug99 and variants is a threat to worldwide wheat production and efforts are ongoing to identify and incorporate resistance. The objectives of this research were to identify quantitative trait loci (QTL) and to study their epistatic interactions for stem rust resistance in a population derived from the Canadian wheat cultivars AC Cadillac and Carberry. A doubled haploid (DH) population was developed and genotyped with DArT® and SSR markers. The parents and DH lines were phenotyped for stem rust severity and infection response to Ug99 and variant races in 2009, 2010 and 2011 in field rust nurseries near Njoro, Kenya, and to North American races in 2011 and 2012 near Swift Current, SK, Canada. Seedling infection type to race TTKSK was assessed in a bio-containment facility in 2009 and 2012 near Morden, MB. Eight QTL for stem rust resistance and three QTL for pseudo-black chaff on nine wheat chromosomes were identified. The phenotypic variance (PV) explained by the stem rust resistance QTL ranged from 2.4 to 48.8 %. AC Cadillac contributed stem rust resistance QTL on chromosomes 2B, 3B, 5B, 6D, 7B and 7D. Carberry contributed resistance QTL on 4B and 5A. Epistatic interactions were observed between loci on 4B and 5B, 4B and 7B, 6D and 3B, 6D and 5B, and 6D and 7B. The stem rust resistance locus on 6D interacted synergistically with 5B to improve the disease resistance through both crossover and non-crossover interactions depending on the environment. Results from this study will assist in planning breeding for stem rust resistance by maximizing QTL main effects and epistatic interactions.