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Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most prevalent diseases of wheat worldwide and can lead to severe yield reductions. Identifying genes involved in powdery mildew resistance will be useful for disease resistance breeding and control. Calreticulin (CRT) is a member of multigene family widely found in higher plants and is associated with a variety of plant physiological functions and defense responses. However, the role of CRT in wheat resistance to powdery mildew remains unclear. TaCRT3 was identified from the proteomic sequence of an incompatible interaction between the wheat (Triticum aestivum) cultivar Xingmin 318 and the Bgt isolate E09. Following analysis of transient expression of the GFP-TaCRT3 fusion protein in Nicotiana benthamiana leaves, TaCRT3 was localized in the nucleus, cytoplasm, and cell membrane. Transcript expression levels of TaCRT3 were significantly upregulated in the wheat-Bgt incompatible interaction. More critically, knockdown of TaCRT3 using virus-induced gene silencing resulted in attenuated resistance to Bgt in wheat. Histological analysis showed a significant increase in Bgt development in TaCRT3-silenced plants, whereas the pathogen-related gene was significantly downregulated in TaCRT3-silenced leaves. In addition, overexpression of TaCRT3 in wheat enhanced the resistance to powdery mildew, the growth of Bgt was significantly inhibited, and the area of H2O2 near the infection site and the expression of defense-related genes of the salicylic acid pathway significantly increased. These findings imply that TaCRT3 may act as a disease resistance factor that positively regulates resistance to powdery mildew, during which SA signaling is probably activated. [ABSTRACT FROM AUTHOR]

Abstract Background Wheat powdery mildew is an obligate biotrophic pathogen infecting wheat, which can pose a serious threat to wheat production. In this study, transcriptome sequencing was carried out on wheat leaves infected by Blumeria graminis f. sp. tritici from 0 h to 7 d. Results KEGG and GO enrichment analysis revealed that the upstream biosynthetic pathways and downstream signal transduction pathways of salicylic acid, jasmonic acid, and ethylene were highly enriched at all infection periods. Trend analysis showed that the expressions of hormone-related genes were significantly expressed from 1 to 4 d, suggesting that 1 d-4 d is the main period in which hormones play a defensive role. During this period of time, the salicylic acid pathway was up-regulated, while the jasmonic acid and ethylene pathways were suppressed. Meanwhile, four key modules and 11 hub genes were identified, most of which were hormone related. Conclusion This study improves the understanding of the dynamical responses of wheat to Blumeria graminis f. sp. tritici infestation at the transcriptional level and provides a reference for screening core genes regulated by hormones.

Background: Wheat powdery mildew is an obligate biotrophic pathogen infecting wheat, which can pose a serious threat to wheat production. In this study, transcriptome sequencing was carried out on wheat leaves infected by Blumeria graminis f. sp. tritici from 0 h to 7 d. Results: KEGG and GO enrichment analysis revealed that the upstream biosynthetic pathways and downstream signal transduction pathways of salicylic acid, jasmonic acid, and ethylene were highly enriched at all infection periods. Trend analysis showed that the expressions of hormone-related genes were significantly expressed from 1 to 4 d, suggesting that 1 d-4 d is the main period in which hormones play a defensive role. During this period of time, the salicylic acid pathway was up-regulated, while the jasmonic acid and ethylene pathways were suppressed. Meanwhile, four key modules and 11 hub genes were identified, most of which were hormone related. Conclusion: This study improves the understanding of the dynamical responses of wheat to Blumeria graminis f. sp. tritici infestation at the transcriptional level and provides a reference for screening core genes regulated by hormones. [ABSTRACT FROM AUTHOR]

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt), is one of the serious diseases that attack wheat plants during the growing season. The Bgt virulence was screened against 16 Egyptian wheat cultivars and 21 powdery mildew differential lines carrying different (Pm) resistance genes in two regions (Kafr-Elsheikh and El-Minya) in Egypt 2021–2022. Broad-spectrum virulence and high diversity were observed at both regions. Regional populations of Bgt in Egypt are independent of each other. Genes, Pm2a, Pm3a, Pm1b, Pm3b, Pm21, Pm34, Pm36, Pm37, Pm53, PmNCA6, PmMIAG12, and PmNCAG13 were nationally effective, while Pm4a, Pm4b, Pm6, and Pm8 appeared to be defeated throughout the country affected by broad-spectrum virulence. Field responses showed that only four cultivars, Misr-1, Misr-2, Sakha-95 and Shandweel-1 were resistant in both regions. A strong correlation was recorded between FDS and AUDPC which implies that wheat pathologists and breeders may be able to assess their lines by a single scoring at an appropriate time. Phenotypic and genotypic data proved that ineffective Pm8 was present in four susceptible cultivars, Sakha-93, Sakha-94, Gemmeiza-10, and Gemmeiza-11, while it was present in combination with effective Pm3a in two resistant cultivars, Sakha-95 and Shandweel-1. This suggests that cultivar susceptibility may be attributed to the existence of ineffective gene Pm8 potentially suppressed by effective Pm3a in hexaploid-resistant wheat. Pyramiding effective resistance genes particularly those that have a suppression effect like Pm3a may be a viable option to avoid the risk of broad-spectrum Bgt virulence at a regional scale. [ABSTRACT FROM AUTHOR]

Powdery mildew is one of the most devastating diseases on wheat and is caused by the obligate biotrophic phytopathogen Blumeria graminis f. sp. tritici (Bgt). Due to the complexity of the large genome of wheat and its close relatives, the identification of powdery mildew resistance genes had been hampered for a long time until recent progress in large-scale sequencing, genomics, and rapid gene isolation techniques. Here, we describe and summarize the current advances in wheat powdery mildew resistance, emphasizing the most recent discoveries about the identification of genes conferring powdery mildew resistance and the similarity, diversity and molecular function of those genes. Multilayered resistance to powdery mildew in wheat could be used for counteracting Bgt, including durable, broad spectrum but partial resistance, as well as race-specific and mostly complete resistance mediated by nucleotide-binding and leucine rich repeat domain (NLR) proteins. In addition to the above mentioned layers, manipulation of susceptibility (S) and negative regulator genes may represent another layer that can be used for durable and broad-spectrum resistance in wheat. We propose that it is promising to develop effective and durable strategies to combat powdery mildew in wheat by simultaneous deployment of multilayered immunity. [ABSTRACT FROM AUTHOR]

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgth is one of the most important diseases on wheat worldwide and can lead to a large reduction in wheat production. Class III peroxidases (PODs). a kind secretory enzyme and members of a multigene family in higher plants, have been linked to various plant physiological functions and defensive responses. However, the role of PODs in wheat resistance to Bgt remains unclear. TaPOD70, a class III POD gene, was identified from the proteomics sequencing of the incompatible interaction between wheat (Triticum aestivum) cultivar Xingmin 318 and Bgt isolate E09. After transient expression of the TaPOD70-GFP fusion protein in Nicotiana benthamiana leaves, TaPOD70 was located in the membrane region. Yeast secretion assay suscepshowed that TaPOD70 was a secretory protein. Furthermore, Bax-induced programmed cell death was inhibited by transient expression of TaPOD70 in N. benthamiana. The transcript expression level of TaPOD70 was significantly upregulated in the wheat-Bgt compatible interaction. More crucially. knocking down TaPOD70 using virus-induced gene silencing increased wheat resistance to Bgt compared with the control plants. response to Bgt. histological analyses indicated that hyphal development of Bgt was significantly reduced, whereas H~O~ production was enhanced in TbPOD70-silenced leaves. These findings imply that TaPOD70 may act as a susceptibility factor. adversely regulating wheat resistance to Bgt. [ABSTRACT FROM AUTHOR]

[Objective] The candidate GPCR proteins of three trophic pathogenic fungi of wheat were searched and their properties were ana- lyzed, which laid a theoretical foundation for further searching of new pesticide targets. [Method] The study selected three trophic pathogenic fungi, whose whole genome sequence had been published. Based on the typical structure characteristics of GPCR proteins, three online pro- tein transmembrane prediction programs (TOPCONS, TMHMM, Philius) were used to search for candidate GPCR proteins in the pathogenic fungi. The sequence length, theoretical isoelectric point, instability coefficient and the strongest hydrophilic (hydrophobic) residues of can- didate GPCR proteins of different trophic fungi were compared and analyzed. [Result】 There were 11, 32 and 69 candidate GPCR proteins in Blumeria graminis f. sp. tritici, Zymoseptoria tritici and Parastagonospora nodorum, respectively, and the average protein sequence length of GPCR was 396 aa. The average theoretical isoelectric point, instability coefficient, hydrophilicity and hydrophobicity of the above candidate proteins were about 8.78, 40, -2.70 and 3. 20, respectively, while the distribution of the strongest hydrophilic (hydrophobic) residues were inconsistent. The genetic relationships of the 112 candidate GPCR proteins were clustered into three categories with 71, 36 and 5 pro- teins, respectively. [Conclusion] The number of candidate GPCR proteins of viable fungi was the least among the three trophic wheat patho- genic fungi, whereas the number of dead fungi was the most, and the number of semi-viable fungi was in between. Different candidate GPCR proteins had certain homogeneity in theoretical isoelectric point, instability coefficient and other physicochemical properties and genetic rela- tionships, but the strongest hydrophilic and hydrophobic amino acid residues were relatively different. [ABSTRACT FROM AUTHOR]

Rye (Secale cereale genome RR), a close relative of common wheat, possesses valuable resistance genes for wheat improvement. Due to the co-evolution of pathogen virulence and host resistance, some resistance genes derived from rye have lost effectiveness. Development and identification of new, effective resistance genes from rye is thus required. In the current study, wheat-rye line WR56 was produced through distant hybridization, embryo rescue culture, chromosome doubling and backcrossing. WR56 was then proved to be a wheat-rye 2RL ditelosomic addition line using GISH (genomic in situ hybridization), mc-FISH (multicolor fluorescence in situ hybridization), ND-FISH (non-denaturing FISH), mc-GISH (multicolor GISH) and rye chromosome arm-specific marker analysis. WR56 exhibited a high level of adult plant resistance to powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt). This resistance was carried by the added 2RL telosomes and presumed to be different from Pm7 which is also located on chromosome arm 2RL but confers resistance at the seedling and adult stages. WR56 will be a promising bridging parent for transfer of the resistance to a more stable wheat breeding line. A newly developed 2RL-specific KASP (kompetitive allele specific PCR) marker should expedite that work.

Wheat powdery mildew caused by a biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a widespread airborne disease which continues to threaten global wheat production. One of the most chemical-free and cost-effective approaches for the management of wheat powdery mildew is the exploitation of resistant cultivars. Accumulating evidence has reported that more than 100 powdery mildew resistance genes or alleles mapping to 63 different loci (Pm1-Pm68) have been identified from common wheat and its wild relatives, and only a few of them have been cloned so far. However, continuous emergence of new pathogen races with novel degrees of virulence renders wheat resistance genes ineffective. An essential breeding strategy for achieving more durable resistance is the pyramiding of resistance genes into a single genotype. The genetics of host-pathogen interactions integrated with temperature conditions and the interaction between resistance genes and their corresponding pathogen a virulence genes or other resistance genes within the wheat genome determine the expression of resistance genes. Considerable progress has been made in revealing Bgt pathogenesis mechanisms, identification of resistance genes and breeding of wheat powdery mildew resistant cultivars. A detailed understanding of the molecular interactions between wheat and Bgt will facilitate the development of novel and effective approaches for controlling powdery mildew. This review gives a succinct overview of the molecular basis of interactions between wheat and Bgt, and wheat defense mechanisms against Bgt infection. It will also unleash the unsung roles of epigenetic processes, autophagy and silicon in wheat resistance to Bgt. [ABSTRACT FROM AUTHOR]

With the increase of temperature in the winter wheat-growing regions in China, the high-temperature-resistant Blumeria graminis f. sp. tritici (Bgt) isolates developed in the fields. To clarify the key infection stages and the roles of heat shock protein (HSP) genes of high-temperature-resistant Bgt isolates defending high temperature, 3 high-temperature-resistant and 3 sensitive Bgt isolates were selected from 55 isolates after determination of temperature sensitivity. And then they were used to investigate the infection stages and the expression levels of HSP genes, including Bgthsp60, Bgthsp70, Bgthsp90, and Bgthsp104, at 18°C and 25°C. The formation frequency of abnormal appressoria and inhibition rate of haustoria formation of high-temperatureresistant isolates at 25°C were lower than those of high-temperature-sensitive isolates, while major axis of microcolonies of high-temperature-resistant isolates was higher than those of high-temperature-sensitive isolates at 25°C. The results indicated that haustoria formation and hyphal expansion were the key infection stages of defense against heat stress in high-temperatureresistant isolates. Further analyses of HSP genes found the expression levels of Bgthsp60 and Bgthsp70c were upregulated at 24 and 72 h post-inoculation in high-temperature-resistant isolates, while no significant difference was observed for Bgthsp90 and Bgthsp104 genes. Taken together, the basis of high-temperature-resistant Bgt isolates is associated with induced expression of Bgthsp60 and Bgthsp70c response to heat stress in haustoria formation and hyphal expansion stages. [ABSTRACT FROM AUTHOR]

The most commonly used method to control wheat powdery mildew is by fungicides. The aim of the present study is to determine the duration of the fungicide activity of three fungicides: azoxystrobin; triadimenol; tebuconazole+spiroxamine+triadimenol. They were applied in three concentrations in phenophase 3-4 leaf of susceptible wheat variety. After treatment, each day one pot of the tested fungicide concentrations was inoculated with Blumeria graminis f. sp. tritici. When using azoxystrobin at concentrations of 0.2%, 0.4%, 0.8%, symptoms of powdery mildew appeared on plants inoculated with Blumeria graminis f.sp. tritici in the next day after treatment. When using triadimenol, first symptoms appeared in plants inoculated with the pathogen on the next day after applying a concentration 0.12%, on the second day after applying a concentration 0.25% and on the third day after treatment with a concentration 0.5%. With tebuconazole+spiroxamine+triadimenol, first postules appeared on plants inoculated with Blumeria graminis f. sp. tritici on the third day after treatment with a concentration 0.15%, on the 13th day after treatment with a concentration 0.3% and on the 14th day after treatment with a concentration 0.6%. This fungicide at a concentration of 0.6% (13 days) and 0.3% (12 days) has the longest duration of fungicide activity. [ABSTRACT FROM AUTHOR]

Wheat powdery mildew caused by a biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a widespread airborne disease which continues to threaten global wheat production. One of the most chemical-free and cost-effective approaches for the management of wheat powdery mildew is the exploitation of resistant cultivars. Accumulating evidence has reported that more than 100 powdery mildew resistance genes or alleles mapping to 63 different loci (Pm1-Pm68) have been identified from common wheat and its wild relatives, and only a few of them have been cloned so far. However, continuous emergence of new pathogen races with novel degrees of virulence renders wheat resistance genes ineffective. An essential breeding strategy for achieving more durable resistance is the pyramiding of resistance genes into a single genotype. The genetics of host-pathogen interactions integrated with temperature conditions and the interaction between resistance genes and their corresponding pathogen a virulence genes or other resistance genes within the wheat genome determine the expression of resistance genes. Considerable progress has been made in revealing Bgt pathogenesis mechanisms, identification of resistance genes and breeding of wheat powdery mildew resistant cultivars. A detailed understanding of the molecular interactions between wheat and Bgt will facilitate the development of novel and effective approaches for controlling powdery mildew. This review gives a succinct overview of the molecular basis of interactions between wheat and Bgt, and wheat defense mechanisms against Bgt infection. It will also unleash the unsung roles of epigenetic processes, autophagy and silicon in wheat resistance to Bgt.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive fungal disease of wheat throughout the world. Utilization of effective powdery mildew resistance genes and cultivars is considered as the most economic, efficient, and environmental-friendly method to control this disease. Synthetic hexaploid wheat (SHW), which was developed through hybridization of diploid Aegilops and tetraploid wheat, is a valuable genetic resource for resistance to powdery mildew. SHW line YAV249 showed high levels of resistance to powdery mildew at both the seedling and adult stages. Genetic analysis indicated that the resistance was controlled by a single dominant gene, temporarily designated PmYAV. Bulked segregant analysis with wheat 660K single nucleotide polymorphism (SNP) array scanning and marker analysis showed that PmYAV was located on chromosome 2AL and flanked by markers Xgdm93 and Xwgrc763, respectively, with genetic distances of 0.8 cM and 1.2 cM corresponding to a physic interval of 1.89 Mb on the Chinese Spring reference genome sequence v1.0. Sequence alignment analysis demonstrated that the sequence of PmYAV was consistent with that of Pm4a but generated an extra splicing event. When inoculated with different Bgt isolates, PmYAV showed a significantly different spectrum from Pm4a, hence it might be a new resistant resource for improvement of powdery mildew resistance. The flanked markers GDM93 and WGRC763, and the co-segregated markers BCD1231 and JS717/JS718 were confirmed to be easily performed in marker-assisted selection (MAS) of PmYAV. Using MAS strategy, PmYAV was transferred into the commercial cultivar Kenong 199 (KN199) and a wheat line YK13 was derived at generation BC3F3 from the population of YAV249/4*KN199 due to its excellent agronomic traits and resistance to powdery mildew. In conclusion, an alternative splicing variant of Pm4 was identified in this study, which informed the regulation of Pm4 gene function. [ABSTRACT FROM AUTHOR]

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (an obligate biotrophic pathogen) is a worldwide threat to wheat production that occurs over a wide geographic area in China. For monitoring genetic variation and virulence structure of Blumeria graminis f. sp. tritici in Liaoning, Heilongjiang, and Sichuan in 2015, 31 wheat lines with known Powdery mildew resistance genes and 2 EST-SSR markers were used to characterize the virulence and genetic diversity. Results indicated that 90% of all isolates were virulent on Pm3c, Pm3e, Pm3f, Pm4a, Pm5, Pm6 (Timgalen), Pm7, Pm16, Pm19, and Pm1 + 2 + 9 and 62.6% to 89.9% of isolates were virulent on Pm3a, Pm3b, Pm3d, Pm4b, Pm6 (Coker747), Pm8, Pm17, Pm20, Pm23, Pm30, Pm4 + 8, Pm5 + 6, Pm4b + mli, Pm2 + mld, Pm4 + 2X, Pm2 + 6. The Pm13 and PmXBD genes were effective against most collected isolates from Liaoning and Heilongjiang Provinces. Only Pm21 exhibited an immune infection response to all isolates. Furthermore, closely related isolates within each region were distinguished by cluster analyses using EST-SSR representing some gene exchanges and genetic relationships between the flora in Northeast China (Liaoning, Heilongjiang) and Sichuan. Only 45% of the isolates tested show a clear correlation between EST-SSR genetic polymorphisms and the frequency of virulence gene data. However, the EST-SSR polymorphism of isolated genes did not correspond to the virulence diversity of isolates in the single-gene lineage identification of hosts. [ABSTRACT FROM AUTHOR]

A recessive gene PmQ conferring powdery mildew resistance was previously localized on the long arm of chromosome 2B in winter wheat landrace Qingxinmai. Breeder-friendly molecular markers are necessary for introgressing this gene into adapted wheat backgrounds for developing disease-resistant wheat cultivars. Three Kompetitive allele-specific PCR (KASP) markers were developed and validated based on SNP variants detected by Bulked segregant analysis-RNA-Seq (BSR-Seq) analysis using a recombinant inbred population derived from cross Qingxinmai × 041133. Two polymorphic SSR markers were also developed from the motifs in the Chinese Spring reference genome sequences of the target genomic region. Those markers were incorporated into a more saturated genetic linkage map for PmQ. The two flanking markers, Xicsq405 and Xicsk18, are 1.1 and 0.9 cM from PmQ, respectively. The KASP marker Xicsk19 produced unique amplification pattern in 158 out of 160 wheat cultivars or breeding lines. This marker with the gene-linked SSR markers Xicsqc, Xicsqd and Xicsq405 provides an efficient means in molecular marker-assisted selection for PmQ in wheat breeding. The corresponding genomic region of PmQ in the Chinese Spring reference genome has a conserved synteny with the genomes of sequenced wheat cultivars and Triticum durum, T. diccocoides, T. uratu, and barley. The annotation of the two genes, TraesCS2B01G517400.1 and TraesCS2B01G517700.1, associated with plant defense against pathogens placed a start for cloning PmQ. [ABSTRACT FROM AUTHOR]

The globally distributed causal agent of powdery mildew on wheat, Blumeria graminis f. sp. tritici (Bgt), is one of the most rapidly adapting plant pathogens and requires monitoring for shifts in virulence to wheat resistance (Pm) genes. Virulence frequencies were assessed in a total of 346 Bgt isolates from several countries that had either lately recorded increasing powdery mildew epidemics (Brazil, South Africa, and Australia) or not recently been surveyed (Turkey and Russia). The results were compared to previously published surveys of United States and Egyptian Bgt (390 isolates). Many of the Pm genes that have potentially been employed longer (Pm1a-Pm17) were shown to have lost effectiveness, and the complexity of virulence to those genes was higher among Brazilian isolates than those from any other country. Some cases of high virulence frequency could be linked to specific Pm gene deployments, such as the widespread planting of cultivar Wyalkatchem (Pm1a) in Australia. Virulence was also assessed to a set of Pm genes recently introgressed from diploid and tetraploid wheat relatives into a hexaploid winter wheat background and not yet commercially deployed. The isolate collections from Fertile Crescent countries (Egypt and Turkey) stood out for their generally moderate frequencies of virulence to both the older and newer Pm genes, consistent with that region's status as the center of origin for both host and pathogen. It appeared that the recently introgressed Pm genes could be the useful sources of resistance in wheat breeding for other surveyed regions. [ABSTRACT FROM AUTHOR]

We examined the molecular basis of triazole resistance in Blumeria graminis f. sp. tritici (wheat mildew, Bgt), a model organism among powdery mildews. Four genetic models for responses to triazole fungicides were identified among US and UK isolates, involving multiple genetic mechanisms. Firstly, only two amino acid substitutions in CYP51B lanosterol demethylase, the target of triazoles, were associated with resistance, Y136F and S509T (homologous to Y137F and S524T in the reference fungus Zymoseptoria tritici). As sequence variation did not explain the wide range of resistance, we also investigated Cyp51B copy number and expression, the latter using both reverse transcription-quantitative PCR and RNA-seq. The second model for resistance involved higher copy number and expression in isolates with a resistance allele; thirdly, however, moderate resistance was associated with higher copy number of wild-type Cyp51B in some US isolates. A fourth mechanism was heteroallelism with multiple alleles of Cyp51B. UK isolates, with significantly higher mean resistance than their US counterparts, had higher mean copy number, a high frequency of the S509T substitution, which was absent from the United States, and in the most resistant isolates, heteroallelism involving both sensitivity residues Y136+S509 and resistance residues F136+T509. Some US isolates were heteroallelic for Y136+S509 and F136+S509, but this was not associated with higher resistance. The obligate biotrophy of Bgt may constrain the tertiary structure and thus the sequence of CYP51B, so other variation that increases resistance may have a selective advantage. We describe a process by which heteroallelism may be adaptive when Bgt is intermittently exposed to triazoles., (© 2024 The Author(s). Molecular Plant Pathology published by British Society for Plant Pathology and John Wiley & Sons Ltd. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

SUMMARY: Cultivated wheat is continually exposed to various pathogens. Blumeria graminis f. sp. tritici (Bgt) causes powdery mildew disease and significant yield loss. Pm60 was cloned from Triticum urartu and confers race‐specific powdery mildew resistance in wheat. Pm60a and Pm60b are allelic variants of Pm60 and have two leucine‐rich repeat motifs deletions and insertions, respectively, which were detected in other T. urartu accessions. Through map‐based cloning, virus‐induced gene silencing, and stable transformation assays, we demonstrated that Pm60a and Pm60b conferred Bgt E09 resistance resembling that provided by Pm60. However, the homozygous Pm60a (but not Pm60 or Pm60b) transformants driven by the native promoters lacked race‐specific resistance when they were inoculated with Bgt E18. As all three T. urartu accessions contained the three foregoing alleles, they had high resistance to Bgt E18. Pyramiding Pm60a with either of the allelic genes in F1 plants did not cause mutual allele suppression or interference with Bgt E18 resistance. Deletion (but not insertion) of the two leucine‐rich repeat motifs in Pm60a substantially narrowed the resistance spectrum. In T. urartu accession PI428210, we identified another locus adjacent to Pm60a and resistant to Bgt E18. Characterization of the alleles at the Pm60 locus revealed their diversity and similarity and may facilitate wheat breeding for resistance to powdery mildew disease caused by B. graminis f. sp. tritici. Significance Statement: In the present study, we identified Pm60a and Pm60b, which are allelic variants at the Pm60 locus. The three foregoing alleles confer resistance to Bgt E09, which causes powdery mildew disease in wheat. Bgt E18 resistance was only absent in Pm60a transgenic plants as this allele has two leucine‐rich repeat (LRR) motif deletions. Pyramiding Pm60a with Pm60 or Pm60b did not hinder Bgt E18 resistance in wheat. Assays involving 54 Bgt isolates confirmed that deletion of the two LRR motifs in Pm60a markedly narrows the Bgt resistance spectrum. In contrast, the insertion of additional LRR motifs in Pm60b did not enhance Bgt resistance. The foregoing findings demonstrated diversity and similarity among alleles at the Pm60 locus and may support wheat breeding for powdery mildew disease resistance. [ABSTRACT FROM AUTHOR]

Wheat genotypes resistant to powdery mildew (Blumeria graminis f. sp. tritici , Bgt) provide a sustainable means for disease control. We developed a pair of near-isogenic lines H962R and H962S with contrasting reactions to powdery mildew from a residue heterozygous line. H962R was resistant to 127 out of the 136 Bgt isolates collected from the major wheat-producing regions of China and showed a similar virulence/avirulence pattern as Fuzhuang 30, Xiaobaidong, and Hongquanmang carrying resistance allele of Pm5e , but H962S was resistant to none of them. A dominant gene was responsible for the powdery mildew resistance of H962R as revealed by the genetic analysis using segregating populations derived from a cross between H962R and H962S. Molecular marker analysis detected a resistance locus, designated PmH962 , on a genetic interval of the chromosome arm 7BL where Pm5e resides. This locus was co-segregated with the functional marker of Pm5e. The PCR-based sequence alignment of Pm5e demonstrated that H962R had an identical sequence as Fuzhuang 30 (haplotype HapGA), and H962S possessed the same sequence as the powdery mildew susceptible cultivar Kenong 199. The genomic compositions of lines H962R and H962S were highly comparable as evidenced by only a small percentage of SNP variations detected by the 16K Genotyping by Target Sequencing (GBTS) SNP array and the 90K Illumina iSelect Wheat SNP array. The two lines performed similarly in the yield-related and plant growth traits investigated, except for greater kernel weight in H962R than in H962S. This indicates that Pm5e has no deleterious effect and can be served as an excellent disease resistance gene in wheat breeding. [ABSTRACT FROM AUTHOR]

Effective strategies to reduce the occurrence of wheat powdery mildew include the use of resistant varieties and application of fungicides. However, most studies rarely focus on the quantitative value of fungicide reduction using resistant varieties. To explore how the fungicides performed on different resistant wheat varieties to powdery mildew, field experiments were conducted during wheat growing seasons in 2018/19 and 2019/20 to investigate the control efficacies of enostroburin⋅epoxiconazole 18% SC and triadimefon 20% EC to wheat powdery mildew on a highly resistant wheat variety ("Baofeng104") and a highly susceptible wheat variety ("Jingshuang16"). The analyses of variance on control efficacies showed that the control efficacies of enostroburin⋅epoxiconazole 18% SC to wheat powdery mildew were mostly significantly higher than triadimefon 20% EC under the same conditions (i.e., varieties, dosages). However, both fungicide and variety resistance made variabilities in the mildew disease index and played a significant role in mildew management. Particularly, the variety resistance made the greatest contribution in mildew-reducing, and the disease index could significantly be reduced on the highly resistant variety even in the absence of fungicide treatment. The control efficacies to mildew on the highly susceptible variety mainly depended on the high efficiency of fungicides whereas the highly resistant variety were mainly by virtue of variety resistance through the comparative analyses of linear regression models. Furthermore, the random-coefficient regression models and quantile models quantificationally expounded that the relationships between active ingredient dosage and disease index or control efficacy varied from the effects of variety, fungicide, and year, particular from variety. Thus, a dosage reference table of enostroburin⋅epoxiconazole 18% SC or triadimefon 20% EC for different resistant wheat varieties were provided; it would be helpful for users to formulate an appropriate dosage of fungicide on mildew management in the field and avoid overusing or superfluous application. Further study needs to consider the effects of fungicide reduction on wheat yields, only then the maximum-economic benefits on mildew management can be determined. [ABSTRACT FROM AUTHOR]

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a severe leaf disease in wheat (Triticum aestivum). To elucidate the effect of powdery mildew on cell redox homeostasis in grains, three wheat cultivars with different resistance, Xi'nong 979 (susceptible), Zhengmai 379 (moderately susceptible), and Zhengmai 103 (resistant), were inoculated with Bgt in the field, and the changes in gene transcription and activity of the antioxidant enzymes in developing grains were analysed. The results showed that the gene expression patterns and enzyme activity changes of guaiacol peroxidase (POD), catalase (CAT), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and 1‐Cys peroxiredoxin (1‐Cys Prx) were similar under powdery mildew conditions. They increased significantly at 10–20 days after anthesis (DAA) in susceptible cultivars and at 20–30 DAA in the resistant cultivar. However, they showed a significant decrease in susceptible cultivars at 20–30 DAA. The gene expression and enzyme activity of ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) increased continuously during grain development, especially in susceptible cultivars. The results demonstrated that the antioxidant systems were induced under mild powdery mildew conditions, which was conducive to the synchronous regulation of reactive oxygen species (ROS). However, under severe powdery mildew conditions, the antioxidant systems were inhibited and the regulation of ROS was restricted, resulting in the breakdown of cell redox homeostasis. It is speculated that powdery mildew infection can inhibit the activity of some metabolic proteins (transcription factors or enzymes), change the carbon and nitrogen metabolism of grain cells, and further change the quality of wheat grains. [ABSTRACT FROM AUTHOR]

Wheat genotypes resistant to powdery mildew (Blumeria graminis f. sp. tritici, Bgt) provide a sustainable means for disease control. We developed a pair of near-isogenic lines H962R and H962S with contrasting reactions to powdery mildew from a residue heterozygous line. H962R was resistant to 127 out of the 136 Bgt isolates collected from the major wheat-producing regions of China and showed a similar virulence/avirulence pattern as Fuzhuang 30, Xiaobaidong, and Hongquanmang carrying resistance allele of Pm5e, but H962S was resistant to none of them. A dominant gene was responsible for the powdery mildew resistance of H962R as revealed by the genetic analysis using segregating populations derived from a cross between H962R and H962S. Molecular marker analysis detected a resistance locus, designated PmH962, on a genetic interval of the chromosome arm 7BL where Pm5e resides. This locus was co-segregated with the functional marker of Pm5e. The PCR-based sequence alignment of Pm5e demonstrated that H962R had an identical sequence as Fuzhuang 30 (haplotype HapGA), and H962S possessed the same sequence as the powdery mildew susceptible cultivar Kenong 199. The genomic compositions of lines H962R and H962S were highly comparable as evidenced by only a small percentage of SNP variations detected by the 16K Genotyping by Target Sequencing (GBTS) SNP array and the 90K Illumina iSelect Wheat SNP array. The two lines performed similarly in the yield-related and plant growth traits investigated, except for greater kernel weight in H962R than in H962S. This indicates that Pm5e has no deleterious effect and can be served as an excellent disease resistance gene in wheat breeding.

Effective strategies to reduce the occurrence of wheat powdery mildew include the use of resistant varieties and application of fungicides. However, most studies rarely focus on the quantitative value of fungicide reduction using resistant varieties. To explore how the fungicides performed on different resistant wheat varieties to powdery mildew, field experiments were conducted during wheat growing seasons in 2018/19 and 2019/20 to investigate the control efficacies of enostroburin⋅epoxiconazole 18% SC and triadimefon 20% EC to wheat powdery mildew on a highly resistant wheat variety (“Baofeng104”) and a highly susceptible wheat variety (“Jingshuang16”). The analyses of variance on control efficacies showed that the control efficacies of enostroburin⋅epoxiconazole 18% SC to wheat powdery mildew were mostly significantly higher than triadimefon 20% EC under the same conditions (i.e., varieties, dosages). However, both fungicide and variety resistance made variabilities in the mildew disease index and played a significant role in mildew management. Particularly, the variety resistance made the greatest contribution in mildew-reducing, and the disease index could significantly be reduced on the highly resistant variety even in the absence of fungicide treatment. The control efficacies to mildew on the highly susceptible variety mainly depended on the high efficiency of fungicides whereas the highly resistant variety were mainly by virtue of variety resistance through the comparative analyses of linear regression models. Furthermore, the random-coefficient regression models and quantile models quantificationally expounded that the relationships between active ingredient dosage and disease index or control efficacy varied from the effects of variety, fungicide, and year, particular from variety. Thus, a dosage reference table of enostroburin⋅epoxiconazole 18% SC or triadimefon 20% EC for different resistant wheat varieties were provided; it would be helpful for users to formulate an appropriate dosage of fungicide on mildew management in the field and avoid overusing or superfluous application. Further study needs to consider the effects of fungicide reduction on wheat yields, only then the maximum-economic benefits on mildew management can be determined.

Summary: The biotrophic fungal pathogen Blumeria graminis f. sp. tritici (Bgt) is a crucial factor causing reduction in global wheat production. Wild wheat relatives, for example Thinopyrum intermedium, is one of the wild‐used parents in wheat disease‐resistant breeding. From T. intermedium line, we identified the aspartic protease gene, TiAP1, which is involved in resistance against Bgt. TiAP1 is a secreted protein that accumulates in large amounts at the infection sites of Bgt and extends to the intercellular space. Yeast two‐hybrid, luciferase complementation imaging and bimolecular florescent complimentary analysis showed that TiAP1 interacted with the chitin deacetylase (BgtCDA1) of Bgt. The yeast expression, purification and in vitro test confirmed the chitin deacetylase activity of BgtCDA1. The bombardment and VIGS‐mediated host‐induced gene silencing showed that BgtCDA1 promotes the invasion of Bgt. Transcriptome analysis showed the cell wall xylan metabolism, lignin biosynthesis‐related and defence genes involved in the signal transduction were up‐regulated in the transgenic TiAP1 wheat induced by Bgt. The TiAP1 in wheat may inactivate the deacetylation function of BgtCDA1, cause chitin oligomers expose to wheat chitin receptor, then trigger the wheat immune response to inhibit the growth and penetration of Bgt, and thereby enhance the resistance of wheat to pathogens. [ABSTRACT FROM AUTHOR]

To incorporate resistance genes of powdery mildew (Pm) and leaf rust (Lr) effectively in breeding programs allelic interaction should be explored. The response and molecular patterns of three Pm genes, Pm3, Pm8, Pm17, and three Lr genes, Lr10, Lr24, and Lr26 were investigated in 15 Egyptian wheat cultivars. Postulation of different Pm and Lr resistance genes in Egyptian wheat cultivars was carried out according to seedling phenotyping data that resulted from inoculation with a set of five pathotypes of Blumeria graminis f. sp. tritici and twelve pathotypes of Puccinia triticina. Responses and molecular patterns revealed the presence of resistance genes Pm3 and Lr10 in the cultivar Misr-1, Pm17, and Lr24 in the cultivar Giza-171, and Pm8 and Lr26 in a further ten cultivars. Molecular markers confirmed the presence of Pm8 and Lr26 in six wheat cultivars, Sakha-94, Sakha-95, Gemmeiza-10, Gemmeiza-11, Sids-13, and Shandweel-1. The presence of Pm17 in Giza-171 was confirmed by the STS marker iag95. A comparison of phenotypic and genotypic data between cultivars Giza-171 and Amigo demonstrated that Pm17 in cv Giza-171 is allelic to Pm8. The existence of Lr24 in Giza-171 was confirmed by using STS marker J09. Based on these results, Pm17 and Lr24 in Giza-171 may be located on translocated chromosomes. In cv Misr-1, the presence of Pm3 and Lr10 on the same region of 1AS chromosome could represent a rare recombination event. Field responses revealed specific resistance of Misr-1 and Giza-171, which may be attributed to the presence of Pm3 and Lr10 in Misr-1 and Pm17 and Lr24+ additional genes in Giza-171. [ABSTRACT FROM AUTHOR]

Wheat powdery mildew (Blumeria graminis f. sp. tritici, Bgt) has become a principal disease occurring annually in Egypt followed by rusts which have been effectively controlled using resistance genes. Survey for fresh infected samples of powdery mildew was collected from fields of farmers and International Wheat Programs of five provinces, i.e., El-Gharbia, Kafr Sheikh, Dakahlia, Menoufia and Behera in Delta Egypt during 2019 and 2020 growing seasons. A total of 37 powdery mildew genes (Pm) including 16 known differentials were evaluated at the seedling stage for resistance and to identify the Bgt pathotypes prevailing in Delta Egypt. 84 isolates of powdery mildew, seven pathotypes were identified in the 2019 season, i.e., BIOE, FOOE, MOIE, MOOE, POEE, OOOE, POCE, while six pathotypes: MOOE, MMOE, COOE, CKKE, MOKE and HOOE were identified in the 2020 season. The pathotype MOOE showed the highest frequency of occurrence during the two seasons (62.16% and 62.18%), respectively. No virulence frequencies were detected in 27.02% of the tested Pm-genes, i.e., Pm11, Pm13, Pm16, Pm24, Pm25, Pm29, Pm32, Pm35, Pm36 and Pm37 during the two seasons of the study. Twenty-four of the 37 Pm-genes showed 5.56 up to 100% virulence frequencies during the two seasons of study, whereas three of the Pm-genes, i.e., Pm1b, Pm12 and Pm34 showed some fluctuations in virulence frequency with values of 16.67% in 2019 season, and 5.55%, 13.89% and 27.78% virulence frequencies in 2020, respectively. [ABSTRACT FROM AUTHOR]

Germin and germin-like proteins (GLPs) play multifaceted roles in plants and participate in signaling processes associated with host–pathogen interactions and response to abiotic stress signaling. Despite the important roles in plant survival and response to the environment, few reports exist about the activity and function of the GLP family in common wheat (Triticum aestivum L.). In this study, we performed a genome-wide identification of the GLP family in wheat and identified 258 GLP genes. Through phylogenetic analysis, the GLPs of Arabidopsis, rice, and wheat were divided into six groups, and each group had a similar genetic structure and a conserved motif. Chromosome 4B has the largest cluster region of TaGLPs among all chromosomes. The cis-regulatory elements in the promoter of TaGLPs, which are critical for the function of wheat GLPs and related to stress and development, are detected. The expression profiles of wheat GLPs under Blumeria graminis f. sp. tritici (Bgt) invasion were investigated using the RNA sequencing analysis and validated using quantitative real-time polymerase chain reaction (qRT-PCR) method. Most of the Bgt resistance-related TaGLP genes are located on the fourth homologous group chromosomes, indicating that pathogens resistance-related TaGLP genes repeat in large tandem in specific chromosomal regions during evolution. These results will help us understand the function of the GLP family in wheat and explore the mechanism of wheat GLPs genes in biotic resistance. [ABSTRACT FROM AUTHOR]

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a major disease of wheat (Triticum aestivum) in Ontario, which can cause 20% yield loss. The development of resistant commercial wheat cultivars is the most economical means of controlling this disease, but only if the resistance genes used are incompatible with the virulence phenotypes present in the pathogen population. The virulence structure of Bgt in Ontario was examined in 2018 and 2019. Of the 42 single colony isolates collected in Ontario greenhouses and commercial fields, 40 virulence phenotypes, assigned VP1 to VP40, were identified on a set of 24 single-gene differential genotypes. Of the 24 resistance genes possessed by the differential genotypes, eight genes including Pm1a, Pm1b, Pm1c, Pm12, Pm16, Pm21, Pm37, and MlAG12 were effective against all of the Bgt isolates. Four genes including Pm3d, Pm29, Pm34, and NCAG13 were mostly effective with resistance reactions to more than 80% of the isolates. There were no significant differences in numbers of virulence genes per isolate between the two years, or between the greenhouse and field origins. The virulence frequencies of Bgt isolates for these effective and mostly effective genes were also not significantly affected by the year of collection and their origins, suggesting that the Bgt population is relatively stable. The effective genes identified in this study may be deployed singly or used for gene pyramiding in wheat breeding programs for developing powdery mildew-resistant cultivars in Ontario. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) plays an important role in the regulation of protective processes under stresses of various nature. In contrast to abiotic stresses, when a plant and a pathogen interact, this phytohormone is in most cases a negative regulator of resistance. However, even with a similar nature of pathogenesis, ABA can produce different effects. For example, ABA treatment in different experiments induced either a decrease or an increase in the susceptibility of cereals to powdery mildew. The aim of this work was to study the immunomodulatory properties of exogenous ABA depending on its concentration in the pathosystem composed of wheat Triticum aestivum L. plants and powdery mildew pathogen Blumeria graminis (DC.) Speer f. sp. tritici (syn. Erysiphe graminis). We studied the change in the number of pathogen colonies on susceptible wheat leaves (Zarya and Tavrichanka varieties) when two-week-old seedlings were treated with various ABA concentrations (0–9 μM) before and immediately after they were infected. When whole plants were used in the experiment, ABA was added to Knop’s solution; in experiments with detached leaves floating in Petri dishes, aqueous solutions of the phytohormone were used. Our results show that the magnitude and direction of the effect of exogenous ABA on the number of colonies of the pathogen depends on its concentration and the time of application relative to the moment of infection. ABA concentration dependence was variable in form: similar concentrations could be inhibitory, resulting in the minimum number of colonies, or stimulating, with the maximum number of colonies. At the same time, the pre-infection use of ABA was more likely to be inhibitory. The non-monotonicity and variation of the form of concentration dependence could probably account for the contradictory literature data on the immunomodulatory properties of ABA. The complex nature of the concentration dependence and the corresponding variation in the immunological state within a fairly wide range seem to ensure the Abscisic acid (ABA) plays an important role in the regulation of protective processes under stresses of various nature. In contrast to abiotic stresses, when a plant and a pathogen interact, this phytohormone is in most cases a negative regulator of resistance. However, even with a similar nature of pathogenesis, ABA can produce different effects. For example, ABA treatment in different experiments induced either a decrease or an increase in the susceptibility of cereals to powdery mildew. The aim of this work was to study the immunomodulatory properties of exogenous ABA depending on its concentration in the pathosystem composed of wheat Triticum aestivum L. plants and powdery mildew pathogen Blumeria graminis (DC.) Speer f. sp. tritici (syn. Erysiphe graminis). We studied the change in the number of pathogen colonies on susceptible wheat leaves (Zarya and Tavrichanka varieties) when two-week-old seedlings were treated with various ABA concentrations (0–9 μM) before and immediately after they were infected. When whole plants were used in the experiment, ABA was added to Knop’s solution; in experiments with detached leaves floating in Petri dishes, aqueous solutions of the phytohormone were used. Our results show that the magnitude and direction of the effect of exogenous ABA on the number of colonies of the pathogen depends on its concentration and the time of application relative to the moment of infection. ABA concentration dependence was variable in form: similar concentrations could be inhibitory, resulting in the minimum number of colonies, or stimulating, with the maximum number of colonies. At the same time, the pre-infection use of ABA was more likely to be inhibitory. The non-monotonicity and variation of the form of concentration dependence could probably account for the contradictory literature data on the immunomodulatory properties of ABA. The complex nature of the concentration dependence and the corresponding variation in the immunological state within a fairly wide range seem to ensure the

Resistance to powdery mildew is an important trait of interest in many wheat breeding programs. The information on genes conferring resistance to powdery mildew in wheat cultivars is useful in parental selection. Winter wheat breeding line DH51302 derived from Liangxing 99 and cultivar Shimai 26 derived from Jimai 22 showed identical infection patterns against 13 isolates of Blumeria graminis f. sp. tritici (Bgt) that causes wheat powdery mildew. DH51302 and Shimai 26 were crossed to a powdery mildew susceptible cultivar Zhongzuo 9504 and the F2:3 families were used in molecular localization of the resistance genes. Fourteen polymorphic markers, which were linked to Pm52 from Liangxing 99, were used to establish the genetic linkage maps for the resistance genes PmDH51302 and PmSM26 in DH51302 and Shimai 26, respectively. These genes were placed in the same genetic interval where Pm52 resides. Analysis of gene-linked molecular markers indicated that PmDH51302 and PmSM26 differed from other powdery mildew resistance genes on chromosome arm 2BL, such as Pm6, Pm33, Pm51, MlZec1, MlAB10, and Pm64. Based on the results of reaction patterns to different Bgt isolates and molecular marker localization, together with the pedigree information, DH51302 and Shimai 26 carried the same gene, Pm52, which confers their resistance to powdery mildew.

A recessive gene PmQ conferring powdery mildew resistance was previously localized on the long arm of chromosome 2B in winter wheat landrace Qingxinmai. Breeder-friendly molecular markers are necessary for introgressing this gene into adapted wheat backgrounds for developing disease-resistant wheat cultivars. Three Kompetitive allele-specific PCR (KASP) markers were developed and validated based on SNP variants detected by Bulked segregant analysis-RNA-Seq (BSR-Seq) analysis using a recombinant inbred population derived from cross Qingxinmai × 041133. Two polymorphic SSR markers were also developed from the motifs in the Chinese Spring reference genome sequences of the target genomic region. Those markers were incorporated into a more saturated genetic linkage map for PmQ. The two flanking markers, Xicsq405 and Xicsk18, are 1.1 and 0.9 cM from PmQ, respectively. The KASP marker Xicsk19 produced unique amplification pattern in 158 out of 160 wheat cultivars or breeding lines. This marker with the gene-linked SSR markers Xicsqc, Xicsqd and Xicsq405 provides an efficient means in molecular marker-assisted selection for PmQ in wheat breeding. The corresponding genomic region of PmQ in the Chinese Spring reference genome has a conserved synteny with the genomes of sequenced wheat cultivars and Triticum durum, T. diccocoides, T. uratu, and barley. The annotation of the two genes, TraesCS2B01G517400.1 and TraesCS2B01G517700.1, associated with plant defense against pathogens placed a start for cloning PmQ.

Summary: Plant nucleotide‐binding leucine‐rich repeat receptors (NLRs) act as intracellular sensors for pathogen‐derived effector proteins and trigger an immune response, frequently resulting in the hypersensitive cell death response (HR) of the infected host cell. The wheat (Triticum aestivum) NLR Pm2 confers resistance against the fungal pathogen Blumeria graminis f. sp. tritici (Bgt) if the isolate contains the specific RNase‐like effector AvrPm2. We identified and isolated seven new Pm2 alleles (Pm2e–i) in the wheat D‐genome ancestor Aegilops tauschii and two new natural AvrPm2 haplotypes from Bgt. Upon transient co‐expression in Nicotiana benthamiana, we observed a variant‐specific HR of the Pm2 variants Pm2a and Pm2i towards AvrPm2 or its homolog from the AvrPm2 effector family, BgtE‐5843, respectively. Through the introduction of naturally occurring non‐synonymous single nucleotide polymorphisms and structure‐guided mutations, we identified single amino acids in both the wheat NLR Pm2 and the fungal effector proteins AvrPm2 and BgtE‐5843 responsible for the variant‐specific HR of the Pm2 variants. Exchanging these amino acids led to a modified HR of the Pm2–AvrPm2 interaction and allowed the identification of the effector head epitope, a 20‐amino‐acid long unit of AvrPm2 involved in the HR. Swapping of the AvrPm2 head epitope to the non‐HR‐triggering AvrPm2 family member BgtE‐5846 led to gain of a HR by Pm2a. Our study presents a molecular approach to identify crucial effector surface structures involved in the HR and demonstrates that natural and induced diversity in an immune receptor and its corresponding effectors can provide the basis for understanding and modifying NLR–effector specificity. Significance Statement: We have identified seven new alleles of the wheat nucleotide‐binding leucine‐rich repeat immune receptor (NLR) Pm2 and analyzed the molecular determinants defining the specificity towards the corresponding fungal effector proteins from wheat powdery mildew. Our study presents a molecular approach to identify crucial effector surface structures involved in immune responses and demonstrates that natural and induced diversity in an immune receptor and its corresponding effectors can provide the basis for understanding and modifying NLR–effector specificity. [ABSTRACT FROM AUTHOR]

Abstract Background Blumeria graminis f. sp. tritici (Bgt), the causal agent of wheat powdery mildew severely affects yield security wheat production in China. Understanding the virulence structure and genetic variations of this pathogen is important for breeding wheat lines resistant to wheat powdery mildew. However, information related to genes controlling resistance remains elusive. This study analyzes the virulence structure and the genetic diversity of pathogenic Bgt populations isolated from northeastern (Liaoning, Heilongjiang) and northwestern (Gansu) China, two representative wheat producing areas, on 37 wheat cultivars each carrying a known powdery mildew resistance (Pm) gene. Results Bgt isolates from northeastern China show higher frequencies of virulence genes than populations from Gansu Province. Many of the known Pm genes failed to provide resistance in this study. However, Pm21 provided 100% resistance to all isolates from all three provinces, obtained during two consecutive years, while Pm13 provided 100% resistance in Gansu. Pm13, Pm16, Pm18, and Pm22 also showed partial resistance in northeastern China, while Pm16, Pm18, Pm22, Pm5 + 6 and Pm2 + 6 +? maintained some resistance in Gansu. Genetic diversity among populations in different regions was detected by cluster analyses using expressed sequence tag-simple sequence repeat (EST-SSR). When the genetic similarity coefficient is relatively high, populations from the same regional origin are mostly clustered into one group while populations from different regions exhibit large genetic differences. Conclusion Pm21 remains the best choice for breeding programs to maintain resistance to Bgt. Only 58% of the isolates tested show a clear correlation between EST-SSR genetic polymorphisms and frequency of virulence gene data.

Summary: Pm1a, the first powdery mildew resistance gene described in wheat, is part of a complex resistance (R) gene cluster located in a distal region of chromosome 7AL that has suppressed genetic recombination.A nucleotide‐binding, leucine‐rich repeat (NLR) immune receptor gene was isolated using mutagenesis and R gene enrichment sequencing (MutRenSeq). Stable transformation confirmed Pm1a identity which induced a strong resistance phenotype in transgenic plants upon challenge with avirulent Blumeria graminis (wheat powdery mildew) pathogens.A high‐density genetic map of a B. graminis family segregating for Pm1a avirulence combined with pathogen genome resequencing and RNA sequencing (RNAseq) identified AvrPm1a effector gene candidates. In planta expression identified an effector, with an N terminal Y/FxC motif, that induced a strong hypersensitive response when co‐expressed with Pm1a in Nicotiana benthamiana.Single chromosome enrichment sequencing (ChromSeq) and assembly of chromosome 7A suggested that suppressed recombination around the Pm1a region was due to a rearrangement involving chromosomes 7A, 7B and 7D. The cloning of Pm1a and its identification in a highly rearranged region of chromosome 7A provides insight into the role of chromosomal rearrangements in the evolution of this complex resistance cluster. [ABSTRACT FROM AUTHOR]

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici ( Bgt ), is one of the most prevalent diseases of wheat worldwide and can lead to severe yield reductions. Identifying genes involved in powdery mildew resistance will be useful for disease resistance breeding and control. Calreticulin (CRT) is a member of multigene family widely found in higher plants and is associated with a variety of plant physiological functions and defense responses. However, the role of CRT in wheat resistance to powdery mildew remains unclear. TaCRT3 was identified from the proteomic sequence of an incompatible interaction between the wheat ( Triticum aestivum ) cultivar Xingmin 318 and the Bgt isolate E09. Following analysis of transient expression of the GFP-TaCRT3 fusion protein in Nicotiana benthamiana leaves, TaCRT3 was localized in the nucleus, cytoplasm, and cell membrane. Transcript expression levels of TaCRT3 were significantly upregulated in the wheat- Bgt incompatible interaction. More critically, knockdown of TaCRT3 using virus-induced gene silencing resulted in attenuated resistance to Bgt in wheat. Histological analysis showed a significant increase in Bgt development in TaCRT3 -silenced plants, whereas the pathogen-related gene was significantly downregulated in TaCRT3 -silenced leaves. In addition, overexpression of TaCRT3 in wheat enhanced the resistance to powdery mildew, the growth of Bgt was significantly inhibited, and the area of H 2 O 2 near the infection site and the expression of defense-related genes of the salicylic acid pathway significantly increased. These findings imply that TaCRT3 may act as a disease resistance factor that positively regulates resistance to powdery mildew, during which SA signaling is probably activated., Competing Interests: The author(s) declare no conflict of interest.

Summary: Powdery mildew poses severe threats to wheat production. The most sustainable way to control this disease is through planting resistant cultivars.We report the map‐based cloning of the powdery mildew resistance allele Pm5e from a Chinese wheat landrace. We applied a two‐step bulked segregant RNA sequencing (BSR‐Seq) approach in developing tightly linked or co‐segregating markers to Pm5e. The first BSR‐Seq used phenotypically contrasting bulks of recombinant inbred lines (RILs) to identify Pm5e‐linked markers. The second BSR‐Seq utilized bulks of genetic recombinants screened from a fine‐mapping population to precisely quantify the associated genomic variation in the mapping interval, and identified the Pm5e candidate genes.The function of Pm5e was validated by transgenic assay, loss‐of‐function mutants and haplotype association analysis. Pm5e encodes a nucleotide‐binding domain leucine‐rich‐repeat‐containing (NLR) protein. A rare nonsynonymous single nucleotide variant (SNV) within the C‐terminal leucine rich repeat (LRR) domain is responsible for the gain of powdery mildew resistance function of Pm5e, an allele endemic to wheat landraces of Shaanxi province of China.Results from this study demonstrate the value of landraces in discovering useful genes for modern wheat breeding. The key SNV associated with powdery mildew resistance will be useful for marker‐assisted selection of Pm5e in wheat breeding programs. [ABSTRACT FROM AUTHOR]

Summary: Powdery mildew, a fungal disease caused by Blumeria graminis f. sp. tritici (Bgt), has a serious impact on wheat production. Loss of resistance in cultivars prompts a continuing search for new sources of resistance.Wild emmer wheat (Triticum turgidum ssp. dicoccoides, WEW), the progenitor of both modern tetraploid and hexaploid wheats, harbors many powdery mildew resistance genes. We report here the positional cloning and functional characterization of Pm41, a powdery mildew resistance gene derived from WEW, which encodes a coiled‐coil, nucleotide‐binding site and leucine‐rich repeat protein (CNL). Mutagenesis and stable genetic transformation confirmed the function of Pm41 against Bgt infection in wheat.We demonstrated that Pm41 was present at a very low frequency (1.81%) only in southern WEW populations. It was absent in other WEW populations, domesticated emmer, durum, and common wheat, suggesting that the ancestral Pm41 was restricted to its place of origin and was not incorporated into domesticated wheat.Our findings emphasize the importance of conservation and exploitation of the primary WEW gene pool, as a valuable resource for discovery of resistance genes for improvement of modern wheat cultivars. [ABSTRACT FROM AUTHOR]

The effect of simulated climate changes by applying different temperatures and CO₂ levels was investigated in the Blumeria graminis f. sp. tritici/wheat pathosystem. Healthy and inoculated plants were exposed in single phytotrons to six CO₂+temperature combinations: (1) 450 ppm CO₂/18–22°C (ambient CO₂ and low temperature), (2) 850 ppm CO₂/18–22°C (elevated CO₂ and low temperature), (3) 450 ppm CO₂/22–26°C (ambient CO₂ and medium temperature), (4) 850 ppm CO₂/22–26°C (elevated CO₂ and medium temperature), (5) 450 ppm CO₂/26–30°C (ambient CO₂ and high temperature), and (6) 850 ppm CO₂/26–30°C (elevated CO₂ and high temperature). Powdery mildew disease index, fungal DNA quantity, plant death incidence, plant expression of pathogenesis-related (PR) genes, plant growth parameters, carbohydrate and chlorophyll content were evaluated. Both CO₂ and temperature, and their interaction significantly influenced powdery mildew development. The most advantageous conditions for the progress of powdery mildew on wheat were low temperature and ambient CO₂. High temperatures inhibited pathogen growth independent of CO₂ conditions, and no typical powdery mildew symptoms were observed. Elevated CO₂ did not stimulate powdery mildew development, but was detrimental for plant vitality. Similar abundance of three PR transcripts was found, and the level of their expression was different between six phytotron conditions. Real time PCR quantification of Bgt was in line with the disease index results, but this technique succeeded to detect the pathogen also in asymptomatic plants. Overall, future global warming scenarios may limit the development of powdery mildew on wheat in Mediterranean area, unless the pathogen will adapt to higher temperatures.

Powdery mildew is a common, economically important disease in the wheat growing area of Serbia. A large-scale virulence survey of its causal agent Blumeria graminis f. sp. tritici population was performed in the period 1995–2013. A total of 1013 isolates were recovered from the collected chasmothecial samples. Among them, 862 unique pathotypes were identified using a differential set of 20 wheat lines with known powdery mildew (Pm) resistant genes. The pathogen was highly diverse. Number of virulence genes (virulence complexity) per isolate was large, supporting a constant need to extend the differential set of wheat with newly identified Pm genes. Virulence frequencies to Pm6, Pm7, and Pm5+8 were high throughout the 19-year period, in contrast with that to Pm5+6, which was consistently at a low level. The most significant change in the population was observed for virulence to the Pm2+4b+6 gene combination, with an increasing frequency of virulence to this gene combination over the years. High virulence complexity and genetic diversity of the population are the most influential factors for the damaging epidemics that this pathogen can cause.

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Saccharin and its parental compound probenazole (PBZ) are plant activators of effective defense responses to (hemi) biotrophic pathogens. Here, we demonstrate that pretreatment of wheat seedlings with saccharin or PBZ results in a significant reduction of powdery mildew caused by Blumeria graminis f. sp. tritici. Transcriptional analysis revealed the expression of 15 defense-related genes including PR genes, WCI genes, LOX, AOS, NPR1, PAL and WRKY genes in wheat seedlings exposed to either saccharin or PBZ. Moreover, the saccharin- and PBZ-enhanced expression of those genes during fungal infection further proved a close correlation with increased resistance in wheat. [ABSTRACT FROM AUTHOR]

The increasing severity and prevalence of powdery mildew aided by extensive use of semi-dwarf cultivars and high levels of nitrogenous fertilizers are causing significant yield losses in wheat. Resistant cultivars are the most cost-effective and environmentally friendly approach to manage the disease. The objective of this study was to identify quantitative trait loci (QTL) for powdery mildew resistance in a doubled haploid (DH) population from a cross between leading Chinese cultivars, Yangmai 16 and Zhongmai 895. A high-density genetic map comprising of 14,480 non-redundant markers (equal to 148,179 SNPs) in 21 wheat chromosomes was constructed by genotyping the population with the Wheat 660 K SNP array. The DH population was phenotyped for powdery mildew resistance at the adult plant stage in multiple field trials, including four environments in the 2016–2017 cropping season and two environments in 2017–2018. Composite interval mapping detected six stable QTL explaining 3.8–23.6% of the phenotypic variance across environments. QPmyz.caas-5DS, QPmyz.caas-6BL and QPmyz.caas-7BS, are probably new QTL for powdery mildew resistance. One SNP marker closely linked to QPmyz.caas-6BL, the most stable QTL, was converted into a Kompetitive Allele-Specific PCR marker (K_AX-94973433) and validated on 103 commercial wheat cultivars. Significantly lower maximum disease severities of cultivars with the resistance-associated allele than those with the susceptibility-associated allele at QPmyz.caas-6BL in some environments indicated partial effectiveness of the marker. The novel QTL and their closely linked markers identified in the present study should facilitate development of cultivars with improved powdery mildew resistance. [ABSTRACT FROM AUTHOR]

Agriculture will benefit from a rigorous characterization of genes for adult plant resistance (APR) since this gene class was recognized to provide more durable protection from plant diseases. The present study reports the identification of APR loci to powdery mildew in German winter wheat cultivars Cortez and Atlantis. Cortez was previously shown to carry all-stage resistance gene Pm3e. To avoid interference of Pm3e in APR studies, line 6037 that lacked Pm3e but showed field resistance from doubled-haploid (DH) population Atlantis/Cortez was used in two backcrosses to Atlantis for the establishment of DH population 6037/Atlantis//Atlantis. APR was assessed in the greenhouse 10, 15, and 20 days after inoculation (dai) from the 4-leaf stage onwards and combined with single-nucleotide polymorphism data in a genome-wide association study (GWAS) and a linkage map-based quantitative trait loci (QTL) analysis. In GWAS, two QTL were detected: one on chromosome 1BL 10 dai, the other on chromosome 2BL 20 dai. In conventional QTL analysis, both QTL were detected with all three disease ratings: the QTL on chromosome 1BL explained a maximum of 35.2% of the phenotypic variation 10 dai, whereas the QTL on chromosome 2BL explained a maximum of 43.5% of the phenotypic variation 20 dai. Compared with GWAS, linkage map-based QTL analysis allowed following the dynamics of QTL action. The two large-effect QTL for APR to powdery mildew with dynamic gene action can be useful for the enhancement of wheat germplasm. [ABSTRACT FROM AUTHOR]

Powdery mildew (Blumeria graminis f. sp. tritici) is a common pathogen of bread wheat (Triticum aestivum L.), and genetic resistance is an effective and environmentally friendly method to reduce its adverse impact. The introgression of novel genes from wheat progenitors and related species can increase the diversity of disease resistance and accumulation of minor genes to improve the crop’s resistance durability. To accomplish these two actions, host genotypes without major resistances should be preferably used. Therefore, the main aim of this study was to carry out seedling tests to detect such resistances in a set of wheat accessions from the Czech gene bank and to group the cultivars according to their phenotype. Ear progenies of 448 selected cultivars originating from 33 countries were inoculated with three isolates of the pathogen. Twenty-eight cultivars were heterogeneous, and 110 cultivars showed resistance to at least one isolate. Fifty-nine cultivars, mostly from Northwest Europe, were resistant to all three isolates were more than three times more frequently recorded in spring than in winter cultivars. Results will facilitate a rational and practical approach preferably using the set of cultivars without major resistances for both mentioned methods of breeding wheat cultivars resistant to powdery mildew.

Powdery mildew, caused by Blumeria graminis f. sp. tritici ( Bgt ), is a destructive disease worldwide. Host resistance is the preferred method for limiting the disease epidemic, protecting the environment, and minimizing economic losses. In the present study, the reactions to powdery mildew for a collection of 600 wheat cultivars and breeding lines from different wheat-growing regions were tested using the Bgt isolate E09. Next, 116 resistant genotypes were identified and then crossed with susceptible wheat cultivars/lines to produce segregating populations for genetic analysis. Among them, 87, 19, and 10 genotypes displayed single, dual, and multiple genic inheritance, respectively. To identify the Pm gene(s) in those resistant genotypes, 16 molecular markers for 13 documented Pm genes were used to test the resistant and susceptible parents and their segregating populations. Of the 87 wheat genotypes that fitted the monogenic inheritance, 75 carried the Pm2a allele. Three, two, one, and two genotypes carried Pm21 , Pm6 , Pm4 , and the recessive genes pm6 and pm42 , respectively. Four genotypes did not carry any of the tested genes, suggesting that they might have other uncharacterized or new genes. The other 29 wheat cultivars/lines carried two or more of the tested Pm genes and/or other untested genes, including Pm2 , Pm5 , Pm6 , and/or pm42 . It was obvious that Pm2 was widely used in wheat production, whereas Pm1 , Pm24 , Pm33 , Pm34 , Pm35 , Pm45 , and Pm47 were not detected in any of these resistant wheat genotypes. This study clarified the genetic basis of the powdery mildew resistance of these wheat cultivars/lines to provide information for their rational utilization in different wheat-growing regions. Moreover, some wheat genotypes which may have novel Pm gene(s) were mined to enrich the diversity of resistance source., Competing Interests: The author(s) declare no conflict of interest.

Powdery mildew caused by Blumeria graminis f. sp. tritici is a threat to wheat production in China. Mapping quantitative trait loci (QTL) for resistance to powdery mildew and developing breeder-friendly markers are important initial steps in breeding resistant cultivars. An all-stage resistance gene and several QTL were identified using a population of 254 recombinant inbred lines developed from a Jingdong 8/Aikang 58 cross. The population was evaluated for powdery mildew resistance across six field environments over three consecutive growing seasons utilizing two different mixtures of B. graminis f. sp. tritici isolates, named #Bgt-HB and #Bgt-BJ . Using genotypic data obtained from the Wheat TraitBreed 50K single-nucleotide polymorphism array, seven stable QTL were identified on chromosome arms 1DL, 2AL, 2DS, 4DL, 5AL, 6BL.1, and 6BL.2. The QTL on 2AL conferred all-stage resistance to B. graminis f. sp. tritici race E20 in greenhouse tests and explained up to 52% of the phenotypic variance in field trials but was resistant only against #Bgt-HB . The gene involved in this QTL was predicted to be Pm4a based on genome location and gene sequence. QPmja.caas-1DL , QPmja.caas-4DL , and QPmja.caas-6BL.1 were identified as potentially new QTL for powdery mildew resistance. QPmja.caas-2DS and QPmja.caas-6BL.1 were effective against both B. graminis f. sp. tritici mixtures, indicating their probable broad-spectrum resistance. A Kompetitive allele-specific PCR marker closely linked to QPmja.caas-2DS was developed and validated in a panel of 286 wheat cultivars. Because both Jingdong 8 and Aikang 58 have been leading cultivars and breeding parents, the QTL and marker reported represent valuable resources for wheat researchers and breeders., Competing Interests: The author(s) declare no conflict of interest.

Powdery mildew is one of the most devastating diseases on wheat and is caused by the obligate biotrophic phytopathogen Blumeria graminis f. sp. tritici ( Bgt ). Due to the complexity of the large genome of wheat and its close relatives, the identification of powdery mildew resistance genes had been hampered for a long time until recent progress in large-scale sequencing, genomics, and rapid gene isolation techniques. Here, we describe and summarize the current advances in wheat powdery mildew resistance, emphasizing the most recent discoveries about the identification of genes conferring powdery mildew resistance and the similarity, diversity and molecular function of those genes. Multilayered resistance to powdery mildew in wheat could be used for counteracting Bgt , including durable, broad spectrum but partial resistance, as well as race-specific and mostly complete resistance mediated by nucleotide-binding and leucine rich repeat domain (NLR) proteins. In addition to the above mentioned layers, manipulation of susceptibility (S) and negative regulator genes may represent another layer that can be used for durable and broad-spectrum resistance in wheat. We propose that it is promising to develop effective and durable strategies to combat powdery mildew in wheat by simultaneous deployment of multilayered immunity., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2023 Zou, Xu, Li, Wei, Zhang and Tang.)

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is an important disease in China. To characterize the virulence and diversity of the pathogen, 1082 isolates were obtained from 8 major wheat-growing regions during the spring growing season in 2011. The virulence test was performed by inoculation on detached leaves of 22 differential lines with known Pm genes. Frequencies of virulence on these genotypes ranged from 0 to 97.4%. None of the 1082 isolates was compatible to Pm21 and less than 20.0% were virulent to the genotype carrying Pm13. In contrast, the virulence frequencies of each population was more than 50.0% to differentials carrying Pm1a, Pm3b, Pm3c, Pm3f, Pm5a, Pm6 and Pm8. In total, 1028 pathotypes were detected, of which 984 were unique. Phenotypic diversity indices revealed a high level of diversity within populations. Genetic distance between different populations correlated significantly with geographical distance (Rb=0.494, P≤0.001). In addition, isolates from Xinjiang appear to form a separate group. Significant positive or negative associations between alleles at pairs of virulence loci were detected in 57 allele pairs to Pm genes. Virulence and diversity of the 8 populations suggested that varieties with effective resistance gene combinations should be developed at a regional level.

Inter-seasonal and altitudinal dynamics of airborne spores of wheat stripe rust and powdery mildew pathogens were studied in northwestern China (Gangu, Gansu) in this study. Burkard spore traps were placed in three locations of Gansu county of the Gansu province at various altitudes, named South mountain, Valley and North mountain. Airborne spore samples were collected from March 2013 to December 2015, totaling 1365 collections for each pathogen. The airborne spore concentration of both pathogen, quantified using duplex real-time PCR assay, were consistently higher in the spring and summer than in fall and winter seasons. The within-crop season airborne inoculum levels were associated with disease severity levels. No difference was found in the Area Under the Spore Concentration Progress Curve (AUSCPC) between spring and summer for both pathogens as well as among the three locations, and there was significant correlation of ten-day spore concentrations between any two of the three locations. Our findings suggest that Gangu is an important source of oversummering inoculum for both diseases with frequent exchange of airborne spores within this region. The time-series analysis demonstrated that the airborne spore concentrations of Pst for all the 10-day-spore-sum during 3 years at three locations were all significantly described by the Autoregressive Integrated Moving-Average (ARIMA) (1, 0, 0) models, while, those of Bgt fitted different models, which contributed to predicting the tendency of airborne spore concentrations for both pathogens in Gangu. [ABSTRACT FROM AUTHOR]