Puccinia Striiformis Research Articles

Identification of additional sources of resistance to Puccinia striiformis f. sp. hordei (PSH) in a collection of barley genotypes adapted to the high input condition

AbstractA total of 336 barley genotypes consisting of released cultivars, advanced lines, differentials and local landraces from the ICARDA barley breeding programme were screened for seedling and adult‐plant resistances to barley stripe rust pathogen (Puccinia striiformis f. sp. hordei [PSH]). Seedling resistance tests were undertaken at Shimla, India by inoculating 336 barley genotypes with five prevalent PSH races [Q (5S0), 24 (0S0‐1), 57 (0S0), M (1S0) and G (4S0)] in India. Barley genotypes were also evaluated at the adult‐plant stage for stripe rust resistance at Durgapura (Rajasthan, India) in 2013 and 2014, and at Karnal (Haryana, India) in 2014 under artificial PSH infection in fields, using a mixture of the five races. Twelve barley genotypes (ARAMIR/COSSACK, Astrix, C8806, C9430, CLE 202, Gold, Gull, Isaria, Lechtaler, Piroline, Stirling, and Trumpf) were resistant to all five PSH races at the seedling and adult‐plant stages. Two of these genotypes, Astrix and Trumpf, were part of international differentials and reveal that five races were avirulent to genes Rps4 (yr4), rpsAst, rpsTr1 and rpsTr2. These genes were highly effective against PSH races prevalent in India. The virulence/avirulence formula reported in this study helped to determine the effectiveness of PSH resistance genes against Indian races. Forty‐five genotypes showed adult‐stage plant resistance (APR) in the field. The identified PSH resistant genotypes may possess novel resistance genes and might serve as potential donors of PSH resistance at seedling and APR in the future. Further research is needed to determine the nature of resistance genes through allelic studies and mapping of these genes.

Isolation of Virulence Factors in Five High Virulence Races of Wheat Stripe Rust (Puccinia striiformis f. sp. tritici) and Identifies Sources of Resistance

Isolation of Virulence Factors in Five High Virulence Races of Wheat Stripe Rust (Puccinia striiformis f. sp. tritici) and Identifies Sources of Resistance

Evaluation of Wheat Germplasms for the Identification of Resistant Sources to Yellow Rust Caused by Puccinia striiformis West. Tritici

Evaluation of Wheat Germplasms for the Identification of Resistant Sources to Yellow Rust Caused by Puccinia striiformis West. Tritici

Characterisation of wheat germplasm for slow rust resistance against Puccinia striiformis

Thirty-seven wheat germplasm were screened under artificial epiphytotic conditions against stripe rust of wheat at University Research Farm, Chatha, during Rabi, 2013–2014 and 2014–2015. On the basis of final rust severity (FRS), AURPC (Area Under Rust Progress Curve) and CI (Coefficient of Infection), 8 genotypes ((DWR 16, HD2281, VL616, K65, UP2121, HD2329, HD2307 and Lal Bahadur) exhibited partial resistance against the disease. PCR profiles revealed co-dominant pattern with distinct fragment of 150 bp in 14 germplasm, showing the presence of Yr18 gene and 229 bp band in 16 germplasm exhibited absence of Yr18.

Resistance evaluation of differentials and commercial wheat cultivars to stripe rust (Puccinia striiformis) infection in hot spot regions of Canada

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat in Canada. This study presents the results from resistance evaluation of Yr genes and western Canadian wheat cultivars from different milling classes, to natural infection in southern Alberta and British Columbia which are considered hot spots of stripe rust occurrence in Canada, due to proximity to Pacific Northwest of the United States where stripe rust epidemics are frequent. Genes Yr1, Yr5, Yr15, and YrSP were effective in all environments; Yr17 and Yr28, which were earlier reported ineffective to existing stripe rust races at the seedling stage in Canada, were effective at adult plant stages in most of the environments because of warmer climates in southerly locations, a favourable condition for expression of the genes. Yr17 is common in winter wheat cultivars and only reported spring wheat cultivar carrying it is CDC Stanley, which can serve as donor parent in breeding programs. Gene Yr24/26 was not very effective in western prairies although reported as effective in eastern prairies. Residual resistance from combination of defeated genes (Yr3, Yr7, Yr9, Yr27) in some supplementary differentials was observed. Most cultivars carry slow-rusting, pleiotropic adult-plant resistance gene Yr18 and some Yr29, which were effective in some locations. These genes failed to provide complete protection under high disease pressure. Seedling and adult plant resistance genes Yr5, Yr15, Yr17 and Yr18, Yr36, respectively could be good targets for resistance breeding. Stacking adult plant resistance genes with seedling resistance genes can provide durable resistance to stripe rust.

A novel MADS-box transcription factor PstMCM1-1 is responsible for full virulence of Puccinia striiformis f. sp. tritici.

In many eukaryotes, transcription factor MCM1 gene plays crucial roles in regulating mating processes and pathogenesis by interacting with other co-factors. However, little is known about the role of MCM1 in rust fungi. Here, we identified two MCM1 orthologs, PstMCM1-1 and PstMCM1-2, in the stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst). Sequence analysis indicated that both PstMCM1-1 and PstMCM1-2 contain conserved MADS domains and that PstMCM1-1 belongs to a group of SRF-like proteins that are evolutionarily specific to rust fungi. Yeast two-hybrid assays indicated that PstMCM1-1 interacts with transcription factors PstSTE12 and PstbE1. PstMCM1-1 was found to be highly induced during early infection stages in wheat and during pycniospore formation on the alternate host barberry (Berberis shensiana). PstMCM1-1 could complement the lethal phenotype and mating defects in a mcm1 mutant of Saccharomyces cerevisiae. In addition, it partially complemented the defects in appressorium formation and plant infection in a Magnaporthe oryzae Momcm1 mutant. Knock down of PstMCM1-1 resulted in a significant reduction of hyphal extension and haustorium formation and the virulence of Pst on wheat. Our results suggest that PstMCM1-1 plays important roles in the regulation of mating and pathogenesis of Pst most likely by interacting with co-factors.

Inheritance and Linkage of Virulence Genes in Chinese Predominant Race CYR32 of the Wheat Stripe Rust Pathogen Puccinia striiformis f. sp. tritici.

Puccinia striiformis f.sp. tritici (Pst) is the causal agent of stripe (yellow) rust on wheat. It seriously threatens wheat production worldwide. The obligate biotrophic fungus is highly capable of producing new virulent races that can overcome resistance. Studying the inheritance of Pst virulence using the classical genetic approach was not possible until the recent discovery of its sexual stage on barberry plants. In the present study, 127 progeny isolates were obtained by selfing a representative Chinese Yellow Rust (CYR) race, CYR32, on Berberis aggregate. The parental isolate and progeny isolates were characterized by testing them on 25 wheat lines with different Yr genes for resistance and 10 simple sequence repeat (SSR) markers. The 127 progeny isolates were classified into 27 virulence phenotypes (VPs), and 65 multi-locus genotypes (MLGs). All progeny isolates and the parental isolate were avirulent to Yr5, Yr8, Yr10, Yr15, Yr24, Yr26, Yr32, and YrTr1; but virulent to Yr1, Yr2, Yr3, Yr4, Yr25, Yr44, and Yr76. The VPs of the parental isolate to nine Yr genes (Yr6, Yr7, Yr9, Yr17, Yr27, Yr28, Yr43, YrA, and YrExp2) and the avirulence phenotype to YrSP were found to be heterozygous. Based on the segregation of the virulence/avirulence phenotypes, we found that the VPs to Yr7, Yr28, Yr43, and YrExp2 were controlled by a dominant gene; those to Yr6, Yr9, and YrA (Yr73, Yr74) by two dominant genes; those to Yr17 and Yr27 by one dominant and one recessive gene; and the avirulence phenotype to YrSP by two complementary dominant genes. Molecular mapping revealed the linkage of 10 virulence/avirulence genes. Comparison of the inheritance modes of the virulence/avirulence genes in this study with previous studies indicated complex interactions between virulence genes in the pathogen and resistance genes in wheat lines. The results are useful for understanding the plant-pathogen interactions and developing wheat cultivars with effective and durable resistance.

Genome-wide associations for multiple pest resistances in a Northwestern United States elite spring wheat panel.

Northern areas of the western United States are one of the most productive wheat growing regions in the United States. Increasing productivity through breeding is hindered by several biotic stresses which slow and constrain targeted yield improvement. In order to understand genetic variation for stripe rust (Puccinia striiformis f. sp. tritici), Septoria tritici blotch (Mycosphaerella graminicola), and Hessian fly (Mayetiola destructor) in regional germplasm, a panel of 408 elite spring wheat lines was characterized and genotyped with an Illumina 9K wheat single nucleotide polymorphism (SNP) chip to enable genome-wide association study (GWAS) analyses. Significant marker-trait associations were identified for stripe rust (38 loci), Septoria tritici blotch (8) and Hessian fly (9) resistance. Many of the QTL corresponded with previously reported gene locations or QTL, but we also discovered new resistance loci for each trait. We validated one of the stripe rust resistance loci detected by GWAS in a bi-parental mapping population, which confirmed the detection of Yr15 in the panel. This study elucidated well-defined chromosome regions for multiple pest resistances in elite Northwest germplasm. Newly identified resistance loci, along with SNPs more tightly linked to previously reported genes or QTL will help future breeding and marker assisted selection efforts.

Characterization of Partial Resistance to Stripe Rust (Puccinia striiformis f.sp. tritici) in some Egyptian Wheat Cultivars

Characterization of Partial Resistance to Stripe Rust (Puccinia striiformis f.sp. tritici) in some Egyptian Wheat Cultivars

Quantitative identification of crop disease and nitrogen-water stress in winter wheat using continuous wavelet analysis

It is necessary to quantitatively identify different diseases and nitrogen-water stress for the guidance in spraying specific fungicides and fertilizer applications. The winter wheat diseases, in combination with nitrogen-water stress, are therefore common causes of yield loss in winter wheat in China. Powdery mildew (Blumeria graminis) and stripe rust (Puccinia striiformis f. sp. Tritici) are two of the most prevalent winter wheat diseases in China. This study investigated the potential of continuous wavelet analysis to identify the powdery mildew, stripe rust and nitrogen-water stress using canopy hyperspectral data. The spectral normalization process was applied prior to the analysis. Independent t-tests were used to determine the sensitivity of the spectral bands and vegetation index. In order to reduce the number of wavelet regions, correlation analysis and the independent t-test were used in conjunction to select the features of greatest importance. Based on the selected spectral bands, vegetation indices and wavelet features, the discriminate models were established using Fisher’s linear discrimination analysis (FLDA) and support vector machine (SVM). The results indicated that wavelet features were superior to spectral bands and vegetation indices in classifying different stresses, with overall accuracies of 0.91, 0.72, and 0.72 respectively for powdery mildew, stripe rust and nitrogen-water by using FLDA, and 0.79, 0.67 and 0.65 respectively by using SVM. FLDA was more suitable for differentiating stresses in winter wheat, with respective accuracies of 78.1%, 95.6% and 95.7% for powdery mildew, stripe rust, and nitrogen-water stress. Further analysis was performed whereby the wavelet features were then split into high-scale and low-scale feature subsets for identification. The accuracies of high-scale and low-scale features with an overall accuracy (OA) of 0.61 and 0.73 respectively were lower than those of all wavelet features with an OA of 0.88. The detection of the severity of stripe rust using this method showed an enhanced reliability (R2 =0.828). Keywords: winter wheat, crop disease, powdery mildew, stripe rust, nitrogen-water stress, continuous wavelet analysis, quantitative identification DOI: 10.25165/j.ijabe.20181102.3467 Citation: Huang W J, Lu J J, Ye H C, Kong W P, Mortimer A H, Shi Y. Quantitative identification of crop disease and nitrogen-water stress in winter wheat using continuous wavelet analysis. Int J Agric & Biol Eng, 2018; 11(2): 145–152.

TCAP FAC‐WIN6 Elite Barley GWAS Panel QTL. I. Barley Stripe Rust Resistance QTL in Facultative and Winter Six‐Rowed Malt Barley Breeding Programs Identified via GWAS

ABSTRACTThe fungal disease barley stripe rust (BSR, causal agent Puccinia striiformis f. sp. hordei) can greatly reduce yield and quality of malt barley (Hordeum vulgare L.), a valuable crop in the distilling and brewing industries. Yield losses of up to 70% have been reported. Resistant cultivars are the most sustainable defense against BSR, especially those cultivars with pyramids of quantitative disease resistance (QDR) genes. The Oregon State University (OSU) barley breeding program has selected for BSR resistance for decades and has released cultivars with BSR resistance. We wanted to determine the number and effect of the loci underlying that resistance, as well as whether it was conferred by QDR or race‐specific qualitative loci. To test these, we used BSR resistance quantitative trait loci (QTL) mapping via genomewide association studies (GWAS) in adult‐plant field trials (3 yr, one location) and race‐specific seedling greenhouse trials (five races). The FAC‐WIN6, a GWAS panel composed of 300 lines that represent the OSU and University of Minnesota facultative and winter six‐rowed malt barley breeding programs, was used in genotyping and phenotyping. The FAC‐WIN6 was developed as part of the USDA‐ARS Triticeae Coordinated Agricultural Project but was not developed specifically for BSR resistance. In total, we detected three race‐specific QTL in greenhouse trials (one of which was also significant in field trials) and 14 QTL significant in field trials only with 2.3 to 20.7% additive reduction in percentage disease severity. At least five QTL were considered novel. These results indicated that the OSU breeding program had both QDR and race‐specific loci for BSR resistance. We suspected that its BSR resistance distributions in the FAC‐WIN6 might align with the major population structure patterns in ways that would be difficult to account for with a GWAS model alone. Therefore, based on post hoc diagnostics, we report a qualitative “usability” level for each QTL.

Low pathotype diversity in a recombinant Puccinia striiformis population through convergent selection at the eastern Himalayan centre of diversity (Nepal)

Worldwide Puccinia striiformis f. sp. tritici (Pst) epidemics have been reported to be driven by few genetic lineages, while a high diversity is evident at the Pst Himalayan centre of diversity. This study investigated the relationship between pathotype diversity and genetic structure in Nepal, the eastern Himalayan region, which has been largely unexplored. Despite the high genetic diversity and recombinant structure detected through microsatellite genotyping, characterization of virulence phenotypes for 62 isolates identified only eight pathotypes, with two pathotypes predominant over all the populations. This is in contrast to the Pakistani and Chinese recombinant populations, where high pathotype diversity is associated with genetic diversity. The most prevalent Nepali pathotype was not a unique clonal lineage, but was represented by seven multilocus genotypes from four distinct genetic subgroups, suggesting strong directional selection on virulence genes, resulting in convergent pathotypes in distinct genetic groups. This convergent selection is discussed in comparison with clonal French and recombinant Pakistani populations. Additionally, the Nepali Pst population carried virulence to 17 out of 24 tested yellow rust resistance genes (Yr), with the absence of virulence to Victo and Early Premium and resistance genes Yr5, Yr10, Yr15, Yr24 and Yr26. Virulence to Yr2, Yr7, Yr27 and YrSu were fixed in all isolates, in line with the deployment of these resistance genes in Nepal. The results reflect the influence of resistance gene deployment on selection of virulence and pathotypes in a recombinant pathogen population, which must be considered in the context of durable resistance gene deployment.

Secretome Characterization and Correlation Analysis Reveal Putative Pathogenicity Mechanisms and Identify Candidate Avirulence Genes in the Wheat Stripe Rust Fungus Puccinia striiformis f. sp. tritici.

Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases of wheat worldwide. Planting resistant cultivars is an effective way to control this disease, but race-specific resistance can be overcome quickly due to the rapid evolving Pst population. Studying the pathogenicity mechanisms is critical for understanding how Pst virulence changes and how to develop wheat cultivars with durable resistance to stripe rust. We re-sequenced 7 Pst isolates and included additional 7 previously sequenced isolates to represent balanced virulence/avirulence profiles for several avirulence loci in seretome analyses. We observed an uneven distribution of heterozygosity among the isolates. Secretome comparison of Pst with other rust fungi identified a large portion of species-specific secreted proteins, suggesting that they may have specific roles when interacting with the wheat host. Thirty-two effectors of Pst were identified from its secretome. We identified candidates for Avr genes corresponding to six Yr genes by correlating polymorphisms for effector genes to the virulence/avirulence profiles of the 14 Pst isolates. The putative AvYr76 was present in the avirulent isolates, but absent in the virulent isolates, suggesting that deleting the coding region of the candidate avirulence gene has produced races virulent to resistance gene Yr76. We conclude that incorporating avirulence/virulence phenotypes into correlation analysis with variations in genomic structure and secretome, particularly presence/absence polymorphisms of effectors, is an efficient way to identify candidate Avr genes in Pst. The candidate effector genes provide a rich resource for further studies to determine the evolutionary history of Pst populations and the co-evolutionary arms race between Pst and wheat. The Avr candidates identified in this study will lead to cloning avirulence genes in Pst, which will enable us to understand molecular mechanisms underlying Pst-wheat interactions, to determine the effectiveness of resistance genes and further to develop durable resistance to stripe rust.

Pathogenomic Analysis of Wheat Yellow Rust Lineages Detects Seasonal Variation and Host Specificity.

Recent disease outbreaks caused by (re-)emerging plant pathogens have been associated with expansions in pathogen geographic distribution and increased virulence. For example, in the past two decades’ wheat yellow (stripe) rust, Puccinia striiformis f. sp. tritici, has seen the emergence of new races that are adapted to warmer temperatures, have expanded virulence profiles, and are more aggressive than previous races, leading to wide-scale epidemics. Here, we used field-based genotyping to generate high-resolution data on P. striiformis genetics and carried out global population analysis. We also undertook comparative analysis of the 2014 and 2013 UK populations and assessed the temporal dynamics and host specificity of distinct pathogen genotypes. Our analysis revealed that P. striiformis lineages recently detected in Europe are extremely diverse and in fact similar to globally dispersed populations. In addition, we identified a considerable shift in the UK P. striiformis population structure including the first identification of one infamous race known as Kranich. Next, by establishing the genotype of both the pathogen and host within a single infected field sample, we uncovered evidence for varietal specificity for genetic groups of P. striiformis. Finally, we found potential seasonal specificity for certain genotypes of the pathogen with several lineages identified only in samples collected in late spring and into the summer, whereas one lineage was identified throughout the wheat growing season. Our discovery of which wheat varieties are susceptible to which specific P. striiformis isolates, and when those isolates are prevalent throughout the year, represents a powerful tool for disease management.

Four azoles’ profile in the control of Septoria, yellow rust and brown rust in wheat across Europe

Leaf diseases cause major yield losses in winter wheat every year across Europe. Septoria leaf blotch – STB (Zymoseptoria tritici) is the most serious leaf disease in Northern Europe, but also yellow rust (Puccinia striiformis) and brown rust (Puccinia triticina) are known to cause major problems in some regions and seasons. Problems with fungicide resistance in the populations of Z. tritici have caused concerns for future control options. With the aim of investigating the differences in azole performances against STB, yellow rust and brown rust, 40 field trials were carried out during two seasons (2015 and 2016) in 10 different countries across Europe covering a diversity of climatic zones and agricultural practices. Four single triazoles (epoxiconazole, prothioconazole, tebuconazole and metconazole) and two mixtures of azoles (epoxiconazole + metconazole; prothioconazole + tebuconazole) were tested at full and half rates. Regarding control of yellow rust and brown rust similar control patterns were seen across Europe and treatments with epoxiconazole and tebuconazole provided between 80 and 100% control. In contrast lower levels of control and major variations in azole performances against STB were seen across Europe, with ranking of the azoles tested varying significantly across the continent. Similarly, the CYP51 mutation frequencies varied greatly across Europe with a clear pattern of decreasing frequencies from west to east of all investigated mutations except I381V and A379G. Azoles were most effective against STB when used as mixtures, either as epoxiconazole + metconazole or prothioconazole + tebuconazole. This was especially clear in the western parts of Europe with high frequencies of CYP51 mutations D134G, V136C and S524T in local Z. tritici populations. Effectiveness of all single azoles decreased from 2015 to 2016 except for tebuconazole and azole mixtures, the mixtures providing more robust control across all sites and sensitivities. The average EC50 values for Z. tritici from the trial sites measured for the four azoles showed different levels of cross-resistance and similarly did the efficacy ranking from the azoles. Across all trials full rates of azole mixtures were best at increasing yields, by up to 20%. Single azoles increased yields between 14 and 18%. The greatest yield responses were measured at the sites where yellow rust was the primary disease controlled.

Inheritance of Virulence, Construction of a Linkage Map, and Mapping Dominant Virulence Genes in Puccinia striiformis f. sp. tritici Through Characterization of a Sexual Population with Genotyping-by-Sequencing.

Puccinia striiformis f. sp. tritici, the wheat stripe rust pathogen, is a dikaryotic, biotrophic, and macrocyclic fungus. Genetic study of P. striiformis f. sp. tritici virulence was not possible until the recent discovery of Berberis spp. and Mahonia spp. as alternate hosts. To determine inheritance of virulence and map virulence genes, a segregating population of 119 isolates was developed by self-fertilizing P. striiformis f. sp. tritici isolate 08-220 (race PSTv-11) on barberry leaves under controlled greenhouse conditions. The progeny isolates were phenotyped on a set of 29 wheat lines with single genes for race-specific resistance and genotyped with simple sequence repeat (SSR) markers, single nucleotide polymorphism (SNP) markers derived from secreted protein genes, and SNP markers from genotyping-by-sequencing (GBS). Using the GBS technique, 10,163 polymorphic GBS-SNP markers were identified. Clustering and principal component analysis grouped these markers into six genetic groups, and a genetic map, consisting of six linkage groups, was constructed with 805 markers. The six clusters or linkage groups resulting from these analyses indicated a haploid chromosome number of six in P. striiformis f. sp. tritici. Through virulence testing of the progeny isolates, the parental isolate was found to be homozygous for the avirulence loci corresponding to resistance genes Yr5, Yr10, Yr15, Yr24, Yr32, YrSP, YrTr1, Yr45, and Yr53 and homozygous for the virulence locus corresponding to resistance gene Yr41. Segregation was observed for virulence phenotypes in response to the remaining 19 single-gene lines. A single dominant gene or two dominant genes with different nonallelic gene interactions were identified for each of the segregating virulence phenotypes. Of 27 dominant virulence genes identified, 17 were mapped to two chromosomes. Markers tightly linked to some of the virulence loci may facilitate further studies to clone these genes. The virulence genes and their inheritance information are useful for understanding the host-pathogen interactions and for selecting effective resistance genes or gene combinations for developing stripe rust resistant wheat cultivars.

Mapping of QTLs associated with resistance to common bunt, tan spot, leaf rust, and stripe rust in a spring wheat population

Spring wheat (Triticum aestivum L.) breeding goals in western Canada include good agronomic characteristics and good end-use quality, and also moderate to elevated resistance to diseases of economic importance. In this study, we aimed to identify quantitative trait loci (QTL) associated with resistance to common bunt (Tilletia tritici and Tilletia laevis), tan spot (Pyrenophora tritici-repentis), leaf rust (Puccinia triticina), and stripe rust (Puccinia striiformis f. sp. tritici). A total of 167 recombinant inbred lines (RILs) derived from a cross between two spring wheat cultivars, ‘Attila’ and ‘CDC Go’, were evaluated for reactions to the four diseases in nurseries from three to eight environments, and genotyped with the Wheat 90K SNP array and three gene-specific markers (Ppd-D1, Vrn-A1, and Rht-B1). The RILs exhibited transgressive segregation for all four diseases, and we observed several lines either superior or inferior to the parents. Broad-sense heritability varied from 0.25 for leaf rust to 0.48 for common bunt. Using a subset of 1203 informative markers (1200 SNPs and 3 gene-specific markers) and average disease scores across all environments, we identified two QTLs (QCbt.dms-1B.2 and QCbt.dms-3A) for common bunt, and three QTLs each for tan spot (QTs.dms-2B, QTs.dms-2D, and QTs.dms-6B), leaf rust (QLr.dms-2D.1, QLr.dms-2D.2, and QLr.dms-3A), and stripe rust (QYr.dms-3A, QYr.dms-4A, and QYr.dms-5B). Each QTL individually explained between 5.9 and 18.7% of the phenotypic variation, and altogether explained from 21.5 to 26.5% of phenotypic and from 52.2 to 86.0% of the genetic variation. The resistance alleles for all QTLs except one for stripe rust (QYr.dms-5B) were from CDC Go. Some of the QTLs are novel, while others mapped close to QTLs and/or genes reported in other studies.

Identification of stripe rust (Puccinia striiformis) resistant genes among Pakistani spring wheat by using molecular markers

Identification of stripe rust (Puccinia striiformis) resistant genes among Pakistani spring wheat by using molecular markers

Host-Induced Gene Silencing of the MAPKK Gene PsFUZ7 Confers Stable Resistance to Wheat Stripe Rust.

RNA interference (RNAi) is a powerful genetic tool to accelerate research in plant biotechnology and control biotic stresses by manipulating target gene expression. However, the potential of RNAi in wheat to efficiently and durably control the devastating stripe rust fungus Puccinia striiformis f. sp. tritici (Pst) remained largely under explored so far. To address this issue, we generated transgenic wheat (Triticum aestivum) lines expressing dsRNA targeting PsFUZ7 transcripts of Pst We analyzed expression of PsFUZ7 and related genes, and resistance traits of the transgenic wheat lines. We show that PsFUZ7 is an important pathogenicity factor that regulates infection and development of Pst A PsFUZ7 RNAi construct stably expressed in two independent transgenic wheat lines confers strong resistance to PstPst hyphal development is strongly restricted, and necrosis of plant cells in resistance responses was significantly induced. We conclude that trafficking of RNA molecules from wheat plants to Pst may lead to a complex molecular dialogue between wheat and the rust pathogen. Moreover, we confirm the RNAi-based crop protection approaches can be used, to our knowledge, as a novel control strategy against rust pathogens in wheat.

Host-induced gene silencing of an important pathogenicity factor PsCPK1 in Puccinia striiformis f. sp. tritici enhances resistance of wheat to stripe rust.

SummaryRust fungi are devastating plant pathogens and cause a large economic impact on wheat production worldwide. To overcome this rapid loss of resistance in varieties, we generated stable transgenic wheat plants expressing short interfering RNAs (siRNAs) targeting potentially vital genes of Puccinia striiformis f. sp. tritici (Pst). Protein kinase A (PKA) has been proved to play important roles in regulating the virulence of phytopathogenic fungi. PsCPK1, a PKA catalytic subunit gene from Pst, is highly induced at the early infection stage of Pst. The instantaneous silencing of PsCPK1 by barley stripe mosaic virus (BSMV)‐mediated host‐induced gene silencing (HIGS) results in a significant reduction in the length of infection hyphae and disease phenotype. These results indicate that PsCPK1 is an important pathogenicity factor by regulating Pst growth and development. Two transgenic lines expressing the RNA interference (RNAi) construct in a normally susceptible wheat cultivar displayed high levels of stable and consistent resistance to Pst throughout the T3 to T4 generations. The presence of the interfering RNAs in transgenic wheat plants was confirmed by northern blotting, and these RNAs were found to efficiently down‐regulate PsCPK1 expression in wheat. This study addresses important aspects for the development of fungal‐derived resistance through the expression of silencing constructs in host plants as a powerful strategy to control cereal rust diseases.