The barley immune receptor Mla recognizes multiple pathogens and contributes to host range dynamics

Puccinia striiformis is the causal pathogen for stripe (yellow) rust of cereals. Puccinia striiformis f. sp. tritici causing wheat stripe rust and a variant of P. striiformis causing barley grass stripe rust (BGYR) are endemic to Australia. Puccinia striiformis f. sp. hordei causing barley stripe rust is exotic and a potential threat to the Australian barley industry. Sequence identity of 100% was detected among Puccinia striiformis f. sp. hordei Puccinia striiformis f. sp. tritici and BGYR in the internal transcribed spacers regions of rRNA. In the intergenic regions of rRNA, Puccinia striiformis f. sp. tritici and BGYR were identical with Puccinia striiformis f. sp. hordei showing 64% sequence identity to the former. A robust dendrogram with isolates of P. striiformis f. sp. tritici, BGYR and P. striiformis f. sp. hordei forming distinct clusters was generated using variation detected by Random Amplified Polymorphic DNA (RAPD), Inter-Simple Sequence Repeat (ISSR) and Simple Sequence Repeat (SSR) markers. Size variation in the intergenic region of rRNA and variation in the SSR RJ24 profile are recommended as diagnostic tools to distinguish P. striiformis f. sp. hordei from P. striiformis f. sp. tritici and BGYR in a sample of stripe rust on barley. An incursion of P. striiformis f. sp. hordei should still be regarded as a significant threat to the Australian barley industry.

Stem rust [causal organism: Puccinia graminis f. sp. tritici (Pgt)], stripe rust [Puccinia striiformis f. sp. tritici (Pst)], and leaf rust [Puccinia triticina (Pt)] are important fungal diseases of wheat in Central Asia and worldwide. Therefore, identification of seedling and adult plant resistance (APR) genes is of major importance for the national wheat breeding program in many countries. The objectives of this study were to identify genes that confer seedling and APR resistances in widely grown wheat cultivars, landraces and advanced lines from Tajikistan. A total of 41 wheat accessions were inoculated with eleven races of Pgt, twelve races of Pst and nine races of Pt for postulation of Sr (stem rust), Yr (yellow or stripe rust), and Lr Lr (leaf rust) resistance genes at the seedling stage. In addition, all of the accessions were tested in field trials for the response to stem rust and stripe rust. Genes for seedling stem rust resistance (i.e. Sr5, Sr6, Sr11, Sr31, and Sr38), stripe rust resistance (Yr9, Yr17, and Y27), and leaf rust resistance (Lr16 and Lr26) were postulated in the Tajik wheat. The presence of the pleiotropic APR genes Sr2/Yr30/Lr27 (associated with pseudo-black chaff phenotype) and Lr34/Yr18/Sr57 (associated with leaf tip necrosis phenotype), and also Lr37 were assessed in the field and confirmed with linked molecular markers. In most of the wheat accessions, resistance genes could not be postulated because their infection types did not match the avirulence or virulence profile of the Pgt, Pst and Pt races tested. Six, seven, and nine accessions were identified that likely possess new genes for resistance to stem rust, stripe rust, and leaf rust, respectively, which have not been described previously. The research demonstrates the presence of effective seedling resistance and APR genes in widely grown wheat accessions that could facilitate further rust resistance breeding in the national wheat breeding program in Tajikistan.

Yellow (stripe) rust of wheat (Triticum aestivum L.), caused by Puccinia striiformis f. sp. tritici, is a serious problem of wheat production in many parts of the world including Egypt. Virulence patterns of wheat stripe rust were studied under the field conditions in four growing seasons (2013 to 2017) at Sakha Agriculture Research Station by planting international stripe rust trap nursery of differentials sets, isogenic lines and some Egyptian genotypes. The results revealed that stripe rust resistance genes Yr2+, Yr5, Yr10, Yr15 and YrND were effective, while Yr18 and Yr29 were partially effective during study periods showing moderate susceptibility. Genes Yr2, Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr32, and gene combinations Yr27+Yr18 (Opata 85) were found susceptible. Chinese 166 with resistance gene Yr1 has shown susceptible reaction in 2014/2015 growing season. Among the twenty commercial genotypes; Misr 1, Misr 3, Gemmeiza 7, and Sakha 95 were resistant. On other hand, some of the most important commercial genotypes i.e. Sids 12, Giza 168, Misr 2 and Sakha 61, known as resistant to the previously characterized races of yellow rust in Egypt became susceptible in this study. The genes found effective against yellow rust under natural conditions could be deployed singly or in combination to develop yellow stripe resistant and high yielding wheat varieties in Egypt.

BackgroundWheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a major pathogenic threat, particularly in regions with favorable moist conditions during the growing season, resulting in significant commercial losses. This study investigates the variations in wheat plant responses to pathogen stress and the potential biocontrol effects of fungal endophytes against stripe rust. Due to the challenges associated with culturing the obligate biotrophic basidiomycete fungi on artificial media, there is a dire need for eco-friendly, economical, and safe biocontrol alternatives.MethodsWe explored the biocontrol potential of two indigenous fungal endophytes, Curvularia lunata (DT-4) and Aspergillus fumigatus (DT-8), against wheat stripe rust in two susceptible wheat varieties.ResultsOur results revealed that both fungal strains significantly improved wheat grain germination and secondary metabolites induction in two wheat varieties. The Morocco variety showed enhanced seed germination (63.6 % DT-4, 72.7% DT-8), plant growth (48.9% DT-4, 55.6% DT-8), and seedling fresh weight (126% DT-4, 110% DT-8), highlighting their potential as biocontrol agents. Treated wheat plants with DT-4 and DT-8 consortia after infection with strip rust (Puccinia striiformis) suspension (SR-S) exhibited enhanced resistance to stripe rust, evidenced by increased antioxidant enzyme activities SOD, CAT, and POD (54.5, 54.6, 112.7%), reduced lipid peroxidation (42.1%), and decreased disease severity (80%). Similarly, wheat grain of TD-1 variety treated with fungus culture filtrate showed maximum germination for seeds (38.5% DT-4, 53.8% DT-8), plant growth (54.5% DT-4, 31.8% DT-8), and seedling fresh weight (125% DT-4, DT-8). A significant increase is observed in the antioxidant enzyme activities SOD, CAT, and POD (59.2, 71.9, 104.6%), reduction in lipid peroxidation (32.8%), and decreased disease severity (80%).ConclusionThese findings suggest that Aspergillus fumigatus and Curvularia lunata induce the anti-pathogenic metabolites, defense-related protein, antioxidant enzymes, resistance genes, salicylic acid (SA), and jasmonic acid (JA) biosynthesis. Together, these responses enhance the overall defensive capacity of wheat against stripe rust, providing a sustainable and ecologically friendly alternative to synthetic fungicides for controlling wheat stripe rust.

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

Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe (yellow) rust, is an obligate, biotrophic fungus. It was difficult to study the genetics of the pathogen due to the lack of sexual reproduction. The recent discovery of alternate hosts for P. striiformis f. sp. tritici makes it possible to study inheritance and map genes involved in its interaction with plant hosts. To identify avirulence (Avr) genes in P. striiformis f. sp. tritici, we developed a segregating population by selfing isolate 12-368 on barberry (Berberis vulgaris) plants under controlled conditions. The dikaryotic sexual population segregated for avirulent/virulent phenotypes on nine Yr single-gene lines. The parental and progeny isolates were whole-genome sequenced at >30× coverage using Illumina HiSeq PE150 technology. A total of 2,637 high-quality markers were discovered by mapping the whole-genome sequencing (WGS) reads to the reference genome of strain 93-210 and used to construct a genetic map, consisting of 41 linkage groups, spanning 7,715.0 centimorgans (cM) and covering 68 Mb of the reference genome. The recombination rate was estimated to be 1.81 ± 2.32 cM/10 kb. Quantitative trait locus analysis mapped six Avr gene loci to the genetic map, including an Avr cluster harboring four Avr genes, AvYr7, AvYr43, AvYr44, and AvYrExp2 Aligning the genetic map to the reference genome identified Avr candidates and narrowed them to a small genomic region (<200 kb). The discovery of the Avr gene cluster is useful for understanding pathogen evolution, and the identification of candidate genes is an important step toward cloning Avr genes for studying molecular mechanisms of pathogen-host interactions.IMPORTANCE Stripe rust is a destructive disease of wheat worldwide. Growing resistant cultivars is the most effective, easy-to-use, economical, and environmentally friendly strategy for the control of the disease. However, P. striiformis f. sp. tritici can produce new virulent races that may circumvent race-specific resistance. Therefore, understanding the genetic basis of the interactions between wheat genes for resistance and P. striiformis f. sp. tritici genes for avirulence is useful for improving cultivar resistance for more effective control of the disease. This study developed a high-quality map that facilitates genomic and genetic studies of important traits related to pathogen pathogenicity and adaptation to different environments and crop cultivars carrying different resistance genes. The information on avirulence/virulence genes identified in this study can be used for guiding breeding programs to select combinations of genes for developing new cultivars with effective resistance to mitigate this devastating disease.

Puccinia striiformis f. sp. tritici causes stripe rust (yellow rust) of wheat and is highly variable in virulence toward wheat with race-specific resistance. During 2010, wheat stripe rust was the most widespread in the recorded history of the United States, resulting in large-scale application of fungicides and substantial yield loss. A new differential set with 18 yellow rust (Yr) single-gene lines was established and used to differentiate races of P. striiformis f. sp. tritici, which were named as race PSTv in distinction from the PST races identified in the past. An octal system was used to describe the virulence and avirulence patterns of the PSTv races. From 348 viable P. striiformis f. sp. tritici isolates recovered from a total of 381 wheat and grass stripe rust samples collected in 24 states, 41 races, named PSTv-1 to PSTv-41, were identified using the new set of 18 Yr single-gene differentials, and their equivalent PST race names were determined on the previous set of 20 wheat cultivar differentials. The frequencies and distributions of the races and their virulences were determined. The five most predominant races were PSTv-37 (34.5%), PSTv-11 (17.5%), PSTv-14 (7.2%), PSTv-36 (5.2%), and PSTv-34 (4.9%). PSTv-37 was distributed throughout the country while PSTv-11 and PSTv-14 were almost restricted to states west of the Rocky Mountains. The races had virulence to 0 to 13 of the 18 Yr genes. Frequencies of virulences toward resistance genes Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44, YrTr1, and YrExp2 were high (67.0 to 93.7%); those to Yr1 (32.8%) and YrTye (31.3%) were moderate; and those to Yr10, Yr24, Yr32, and YrSP were low (3.4 to 5.7%). All of the isolates were avirulent to Yr5 and Yr15.

Stripe (Yellow) rust caused by<i> Puccinia striiformis </i>f.sp. <i>tritici (Pst) </i>is important wheat diseases causing serious damage on cultivated susceptible wheat variety. The wheat yellow rust assessment was conducted during main rainy season of 2018/19 at Ada’a, Lume and Gimbichu using zigzag method of diseases assessment. Disease data’s, agro-eological data and other important parameters were recorded. The disease was prevalent at all districts by diverse incidence and severity ranges. This implies that yellow rust is distributed wheat disease at all surveyed potential districts. The highest yellow rust prevalence 62.5% was recorded at Gimbichu district: conversely; the lowest prevalence percentage 31.25% was recorded at Ada’a district. The highest severity and incidence of yellow rust 60% and 100%, respectively was recorded at Ada’a district with susceptible reaction; while the lowest severity and incidence (30% and 5%) respectively was recorded at Lume districts with moderately susceptible reaction. Yellow rust is governed by many for the distributions and occurrence. Highest yellow rust incidence 100 S was recorded from field cultivated with bread wheat kakaba and Kubsa varieties at growth stage of Milk to matured stage. Local cultivar has shown lowest incidence and severity percentage with moderately susceptible responses than improved varieties.

Wheat stripe rust, caused by Puccinia striiformis West. f. sp. tritici Eriks. ＆Henn. (Pst), is a serious fungal disease. Identification of new genes associate with stripe rust resistance is important for developing disease resistant wheat cultivars and studying the mechanism of disease resistance. Trihelix is a plant specific transcription factor family, which is involved in regulation of growth and development, morphogenesis, and response to stresses. So far, no study reports on the relationship between the Trihelix family and wheat stripe rust. In this study, a gene in the GTγ subfamily of Trihelix family, designated TuGTγ-3, was cloned from Triticum urartu Tum. (2n=2x=14, AA). The results of sequencing demonstrated that TuGTγ-3 gene consisted of a complete open reading frame (ORF), and its coding sequence was 1329 bp in length, which encoded a protein with 442 amino acids. The predicted molecular weight of this protein was 50.31 kDa and the theoretical isoelectric point was 6.12. Bioinformatic analysis revealed that TuGTγ-3 protein had a monopartite nuclear localization signal (GLPMQKKMRYT), and had neither transmembrane domain nor signal peptide. The conserved trihelix domain, the fourth α-helix and the CC domain were located in the regions of Q115?R187, F234?Y241 and K362?K436, respectively. Dissection of secondary structure showed that TuGTγ-3 protein comprised of 43.89% α-helix, 9.51% extended strand, 9.95% β-turn and 36.65% random coil structures. Based on the BLAST search against the genome database of common wheat from IWGSC, TuGTγ-3 was located on the long arm of chromosome 5A. Transient expression experiment using onion inner epidermal cell showed that the fusion protein TuGTγ-3-GFP distributed mainly in nuclear and slightly in cytoplasm. Expression profiles in different organs indicated that expression level of TuGTγ-3 was much higher in leaves than that in roots or leaf sheaths, and the expression in leaves was extremely up-regulated by infection of the Pst race CYR32. Furthermore, the BSMV-VIGS experiment demonstrated that the transcription factor TuGTγ-3 positively regulated resistance to stripe rust in T. urartu.

Wheat powdery mildew and stripe rust, caused by Blumeria graminis f.sp.tritici (syn. Erysiphe graminis f.sp.tritici) and Puccinia striiformis Westend., respectively, are two important fungal diseases of wheat in many regions in the world that cause significant annual yield losses. In the present study, a dominant powdery mildew and a dominant stripe rust resistance gene in wheat line 101-3 which derived from the progenies of the wide cross between common wheat and Dasypyrum villosum Candary L., was located on chromosome 6B and 1B, respectively, by monosomic analyses. The two genes are different from known resistance genes on chromosome 6B for powdery mildew and 1B for stripe rusts, suggesting that the two genes might be novel resistance genes for powdery mildew and stripe rust, respectively. It is uncertain whether the two genes are allelic or lined with other resistance genes located on chromosome 6B for powdery mildew and 1B for stripe rust. Further allelism tests are necessary to determine the relationships between the resistance gene and other genes located on chromosome 6B for powdery mildew and 1B for stripe rust through molecular markers.

New Technologies, Tools and Approaches for Improving Crop Breeding

Wheat stripe rust caused by the Puccinia striiformis f. sp. tritici (Pst) is a major and devastating biotic stress inducing notable product losses in wheat (Triticum spp.). Possibility of the breakdown of important genes conferring resistance against to stripe rust and the threat of emergence of new aggressive races remain a concern in all wheat growing areas around the world. Therefore, breeding programs must continue screening of wide genetic diversity to improve new varieties with different gene combinations against race changes. Within this scope, 140 wheat genotypes obtained from various countries and programs were evaluated in terms of their reactions to stripe rust at both seedling and adult-plant stages in 2020 and 2021 growing seasons. The adult-plant stage evaluations of these genotypes were conducted under artificial inoculation of PstS7 (Warrior) race at Haymana location of Field Crops Central Research Institute in Ankara and under naturally occurring local stripe rust population at Menemen location of Aegean Agricultural Research Institute in Izmir. Whereas the seedling stage tests were carried out using the PstS7 race under controlled conditions at Pest and Disease Resistance Unit of the Field Crops Central Research Institute. More than 80% of the genotypes tested at both locations exhibited immune, resistant, and moderately resistant reactions at the adult-plant stage, while only 36.4% of the genotypes exhibited resistance reactions at the seedling stage. The coefficients of infection (CI) of the genotypes were calculated by using the stripe rust reaction and disease severity of each genotype. Following scales were used for classification of the genotypes based on the CI: 0 = Immune; 0.1-5.0 = Resistant; 5.01-20.0 = Moderately Resistant; 20.1-40.0 = Moderately Susceptible; 40.1-100 = Susceptible. In conclusion, 101 genotypes (72.1%) evaluated at both locations were found to be immune, resistant, and moderately resistant to both the PstS7 race and local stripe rust population. These genotypes have been proposed as resistance gene sources for cultivars to be developed.

Leaf (brown) rust (LR) and stripe (yellow) rust (YR), caused by Puccinia triticina and P. striiformis f. sp. tritici, respectively, significantly reduce wheat production worldwide. Disease-resistant wheat varieties offer farmers one of the most effective ways to manage these diseases. The common wheat (Triticum aestivum L.) Arableu#1, developed by the International Maize and Wheat Improvement Center and released as Deka in Ethiopia, shows susceptibility to both LR and YR at the seedling stage but a high level of adult plant resistance (APR) to the diseases in the field. We used 142 F5 recombinant inbred lines (RILs) derived from Apav#1 × Arableu#1 to identify quantitative trait loci (QTLs) for APR to LR and YR. A total of 4,298 genotyping-by-sequencing markers were used to construct a genetic linkage map. The study identified four LR resistance QTLs and six YR resistance QTLs in the population. Among these, QLr.cim-1BL.1/QYr.cim-1BL.1 was located in the same location as Lr46/Yr29, a known pleiotropic resistance gene. QLr.cim-1BL.2 and QYr.cim-1BL.2 were also located on wheat chromosome 1BL at 37 cM from Lr46/Yr29 and may represent a new segment for pleiotropic resistance to both rusts. QLr.cim-7BL is likely Lr68 given its association with the tightly linked molecular marker cs7BLNLRR. In addition, QLr.cim-3DS, QYr.cim-2AL, QYr.cim-4BL, QYr.cim-5AL, and QYr.cim-7DS are probably new resistance loci based on comparisons with published QTLs for resistance to LR and YR. Our results showed the diversity of minor resistance QTLs in Arableu#1 and their role in conferring near-immune levels of APR to both LR and YR, when combined with the pleiotropic APR gene Lr46/Yr29.

Wheat is the staple food of Pakistan and country facing wheat shortage during recent years leading to food security issue. Rust diseases of wheat are significantly important causing major dent in wheat production during last season’s due to drastic climate change. Therefore, wheat germplasm was screened against wheat stripe rust during two consecutive years. Out of one hundred and five genotypes not even one showed immune response during 2018-19, 22 genotypes showed highly resistant response, 19 showed resistance response, 42 showed moderately resistance response and remaining genotypes showed susceptible response except five lines (CB-10, CB-65, CB-95, CB-84 and CB-31) that showed heterogeneous characters. Likewise, during 2019-20, 18 genotypes showed highly resistant response, 23 showed resistant response, 39 were moderately resistance and remaining genotypes showed susceptible response except four lines (CB-10, CB-65, CB-95 and CB-84) that showed heterogeneous response. For each year value of area under disease progress curve (AUDPC) of all genotypes was also calculated which falls between 100-850. Efficacy of four plant extracts (neem, garlic, ginger and bell pepper) using seed soaking method in controlling the stripe rust disease of wheat was investigated in pots experiment. During both years, minimum disease was observed in case of garlic bulb extract followed by neem leaves extract. Ginger bulb and Bell pepper fruit extract also had significant effect against wheat stripe rust. From the current study it could be suggested that using highly resistant germplasm advance lines may be developed that exhibit the resistant genes against stripe rust pathogen and it is observed that instead if using fungicides, use of botanicals not only reduced the human health hazard but also control the disease effectively.

Yr17 resistance gene (Yr17+ cultivars) induces yellow rust resistance in wheat at the seedling stage and operates throughout the plant life. A new Yr17 pathotype that overcomes resistance to wheat stripe rust in Yr17+ cultivars was first detected in 1997 in countries neighboring Luxembourg (Bayles et al., 2000). In 1999, stripe rust was suspected to occur also in this country (GDL) and, in 2003, Puccinia striiformis f. sp. tritici was identified. Disease severity was recorded in the 1999-2009 period in fungicide untreated experiments with various cultivars grown in Everlange, Christnach, Burmerange and Reuler (El Jarroudi et al., 2009). Over this 11-year period, the difference between Yr17+ (Achat, Akteur, Astron, Flair) and Yr17- (Aron, Batis, Bussard, Drifter, Ritmo,Vivant) cultivars was highly significant, the highest severity being observed in Yr17+ cultivars (mean severity of 13%) compared to Yr17- cultivars (0.2%). In 1999, Yr17+ cultivars showed the highest disease severity (19%) whereas in 2000 and 2001, the highest severity was observed in cv. Flair (Yr 17+) with 30% and 22%, respectively at Everlange, and 50% and 11%, respectively at Christnach. In both years symptoms on Yr17- cultivars were rare (severity <1%) or absent. During 2002-2009 yellow rust occurred with relatively low severity (average 6%) on Yr17+ cultivars (cv. Achat at Everlange in 2002, 2008 and 2009, cv. Akteur at Everlange and Reuler in 2007). These observations support the hypothesis of the presence in GDL of the Yr17 pathotype that overcomes the Yr17 gene. This new virulent pathotype appears more aggressive on Yr17+ than Yr17- cultivars. Since most resistant European cultivars are Yr17+, this renders control strategies based on this monogenic resistance to wheat stripe rust vain. Bayles R.A., Flath K., Hovmoller M.S., De Valavieille-Pope C.,. 2000. Breakdown of the Yr17 resistance to yellow rust of wheat in Northern Europe. Agronomie 20: 805-811. El Jarroudi M., Giraud F., Vrancken C., Junk J., Tychon B., Hoffmann L., Delfosse P,. 2009. First report of wheat leaf rust in the Grand Duchy of Luxembourg and the progress of its appearance over the 2003-2008 period. Plant Disease 93: 971-971.