Evaluation of Spray and Point Inoculation Methods for the Phenotyping of Puccinia striiformis on Wheat

Sensitivity of Puccinia triticina f. sp. tritici from China to Triadimefon and Resistance Risk Assessment

Wheat leaf rust, caused by Puccinia triticina f. sp. tritici (Pt), is distributed widely in wheat-producing areas and results in serious yield losses worldwide. In China, leaf rust has been largely controlled with a demethylation inhibitor (DMI) fungicide, triadimefon. Although high levels of fungicide resistance in pathogens have been reported, no field failure of wheat leaf rust to DMI fungicides has been reported in China. A resistance risk assessment of triadimefon to Pt was investigated in the present study. The sensitivity of 197 Pt isolates across the country to triadimefon was determined, and the density distribution of EC50 values (concentration at which mycelial growth is inhibited by 50%) showed a continuous multimodal curve because of the extensive use of this fungicide in wheat production, with a mean value of 0.46 μg/ml. The majority of the tested Pt isolates were sensitive to triadimefon, whereas 10.2% developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. No correlation was observed between triadimefon and tebuconazole and hexaconazole, which have the similar mode of action, or pyraclostrobin and flubeneteram, which have different modes of action. Overexpression of the target gene Cyp51 led to the triadimefon resistance of Pt. The risk of resistance to triadimefon in Pt may be low to moderate. This study provided important data for fungicide resistance risk management against wheat leaf rust.

Field response and molecular screening of European wheat germplasm against powdery mildew at the Himalayan region of Pakistan

Wheat powdery mildew possesses a significant threat to wheat crops not only on a global scale but also in the northern region of Pakistan. Recognizing the need for effective measures, the exploration and utilization of exotic germplasm take on critical importance. To address this, a series of trials were made to investigate the response of 30 European (EU) lines, in addition to the local checks (Siran, Atta-Habib (AH) and Ghanimat-e-IBGE) against wheat powdery mildew at the Himalayan region of Pakistan. The study involved field testing from 2018 to 2022 across multiple locations, resulting in 38 different environments (location × year). In addition to field evaluations, molecular genotyping was also performed. The disease was absent on the tested lines during 2018, 2019, and 2020 whereas it ranged from 0 to 100% at Chitral location during 2021, where 100% was observed only for one EU wheat line "Matrix." The disease prevailed only at Gilgit location (0-60% for EU wheat line "F236") and at Nagar location (0-10% for EU wheat lines Substance and Nelson) during the disease season of 2022. Most of the EU wheat lines showed very low ACI values, due to an overall low disease pressure. Matrix showed the maximum ACI (1.54) followed by Ritter (1.25) and Bli_autrichion (0.87), whereas the minimum (0.1) was for Substance, JB_Asano, and KWS_Loft followed by Canon (0.19), all exhibiting partial resistance. The molecular marker-based screening revealed that Pm38 was the most prevalent and detected in 100% of wheat lines followed by Pm39 (60%) and Pm8 (30%). Six wheat lines (20%) possessed all three Pm genes (Pm8, Pm38, and Pm39) concurrently. The variability observed in this study can be utilized in future breeding efforts aimed at developing resistant wheat varieties.

Effect of green synthesized cerium oxide nanoparticles on fungal disease of wheat plants: A field study

Recently, there has been considerable attention towards the production of environmentally friendly nanoparticles (NPs). In this investigation, the successful synthesis of cerium oxide nanoparticles (CeO2 NPs) was achieved by employing an eco-friendly technique that utilized an extract from the leaves of local plant quinoa (Chenopodium quinoa L.). The synthesized CeO2 NPs were subjected to characterization using state-of-the-art methods. The prepared CeO2 NPs contained a round shape with clusters and have a size of 7-10 nm. To assess how effective CeO2 NPs derived from C. quinoa were against Ustilago tritici, a fungal disease that negatively affects wheat crop globally, a study was performed on two varieties of wheat crop comprised of Arooj (V1) and Akber (V2), cultivated under field conditions. CeO2 NPs were applied foliarly twice to the wheat crop at four different concentrations: T0 (0 mg/L), T1 (50 mg/L), T2 (75 mg/L), and T3 (100 mg/L). The results revealed that the control group (T0) exhibited the highest disease severity index (DSI) with a value of 75% compared to the other concentrations of CeO2 NPs on both varieties. At a concentration of 100 mg/L of CeO2 NPs, the DSI dropped to a minimum of 35% and 37% on both V1 and V2 respectively. These findings indicated that an increase in the concentration of CeO2 NPs has a beneficial impact on disease severity. Similar patterns have also been observed with disease incidence (DI), with the greatest efficacy observed at a concentration of 100 mg/L of CeO2 NPs. Our investigation has shown that CeO2 NPs exhibitd significant antifungal potential against U. tritici which may be a promising strategy to mitigate fungal disease and crop losses globally.

Simplifying Barley Leaf Rust Research: An Easy and Reproducible Infection Protocol for Puccinia hordei on a Small Laboratory Scale

Barley (Hordeum vulgare) is one of the most important agricultural crops in the world, but pathogen infections regularly limit its annual yield. A major threat is the infection with the biotrophic leaf rust fungus, Puccinia hordei. Rust fungi have a complex life cycle, and existing resistances can be easily overcome. To address this problem, it is crucial to develop barley varieties with improved and durable resistance mechanisms. An essential step towards this goal is a simple and reproducible infection protocol to evaluate potential resistance phenotypes in the lab. However, available protocols sometimes lack detailed procedure or equipment information, use spore application methods that are not suitable for uniform spore dispersion, or require special mineral oils or engineered fluids. In addition, they are often optimized for pathogen-dedicated greenhouses or phytochambers, which may not be available to every research institute. Here, we describe an easy and user-friendly procedure to infect barley with Puccinia hordei on a small laboratory scale. This procedure utilizes inexpensive and simple tools to evenly split and apply spores to barley leaves. The treated plants are incubated in affordable and small phytocabinets. Our protocol enables a quick and reproducible infection of barley with leaf rust, a method that can easily be transferred to other rust fungi, including stripe rust, or to other plant species. Key features Step-by-step infection protocol established for barley cv. Golden Promise, the gold standard genotype for genetic transformation Plant age-independent protocol Precise spore application by using inexpensive pipe cleaners for uniform symptom formation and increased reproducibility No specialized equipment needed Includes simple spore harvesting method Protocol is applicable to other biotrophic pathogens (stripe rust or powdery mildew) and other plants (e.g., wheat) Protocol is also applicable for a detached leaf assay Graphical overview.

The Keys to Controlling Wheat Rusts: Identification and Deployment of Genetic Resistance

Rust diseases are among the major constraints for wheat production worldwide due to the emergence and spread of highly destructive races of Puccinia. The most common approach to minimize yield losses due to rust is to use cultivars that are genetically resistant. Modern wheat cultivars, landraces, and wild relatives can contain undiscovered resistance genes, which typically encode kinase or nucleotide-binding site leucine rich repeat (NLR) domain containing receptor proteins. Recent research has shown that these genes can provide either resistance in all growth stages (all-stage resistance; ASR) or specially in later growth stages (adult-plant resistance; APR). ASR genes are pathogen and race-specific, meaning can function against selected races of the Puccinia fungus due to the necessity to recognize specific avirulence molecules in the pathogen. APR genes are either pathogen-specific or multipathogen resistant but often race-nonspecific. Prediction of resistance genes through rust infection screening alone remains complex when more than one resistance gene is present. However, breakthroughs during the past half century such as the single-nucleotide polymorphism-based genotyping techniques and resistance gene isolation strategies like mutagenesis, resistance gene enrichment, and sequencing (MutRenSeq), mutagenesis and chromosome sequencing (MutChromSeq), and association genetics combined with RenSeq (AgRenSeq) enables rapid transfer of resistance from source to modern cultivars. There is a strong need for combining multiple genes for better efficacy and longer-lasting resistance. Hence, techniques like gene cassette creation speeds up the gene combination process, but their widespread adoption and commercial use is limited due to their transgenic nature.

Distinguishing Puccinia striiformis f. sp. tritici Isolates Using Genomic Sequencing: A Case Study

We are reporting on the utilization of high-throughput sequencing and different sequencing analysis tools to delineate identification of different isolates of the stripe rust fungal pathogen Puccinia striiformis f. sp. tritici (Pst). Different approaches are shown: utilization of rDNA sequences and random sequences that may be very useful to make sure that isolates belong to Pst and to distinguished closely related isolates. Identification of unique/lost sequences could lead to the identification of effectors associated with specific isolates.

Inheritance and Linkage of Virulence Genes of Puccinia striiformis f. sp. hordei

Puccinia striiformis f. sp. hordei (Psh) causing barley stripe rust has only recently been known to be heteroecious, for which reason the inheritance of its virulence has not been analyzed. Herein, we selfed a Psh isolate, XZ-19-972, on Berberis aggregata and obtained 53 progenies. The virulence phenotypes (VPs) for these progenies were identified on 11 barley differentials, and their genotypes were assessed with 22 Kompetitive allele specific PCR-single nucleotide polymorphism (KASP-SNP) markers. In total, 18 VPs were detected among progenies, 17 (VP2-VP18) of which, corresponding to 43 isolates, were different from the parental isolate showing VP1. Of the 53 progenies, 8 exhibited increased virulence and 34 decreased virulence. One progeny, belonging to VP18, showed a different virulence formula but without a virulence increase or decrease. The parental isolate and all progenies were avirulent to yrc6 but virulent to yrc7. The parental isolate was heterozygous in terms of avirulence/virulence to nine barley resistance gene loci. KASP-SNP marker analysis identified 36 multilocus genotypes, based on which a linkage map was constructed, with total genetic distance intervals of 516.07 cM, spanning 16 avirulence or virulence loci. Taken together, our results provide important insights into the inheritance and virulence diversity of Psh.

Effect of Phytosynthesized Selenium and Cerium Oxide Nanoparticles on Wheat (Triticum aestivum L.) against Stripe Rust Disease

In this study, selenium nanoparticles (SeNPs) and cerium oxide nanoparticles (CeONPs) were synthesized by using the extract of Melia azedarach leaves, and Acorus calamusas rhizomes, respectively, and investigated for the biological and sustainable control of yellow, or stripe rust, disease in wheat. The green synthesized NPs were characterized by UV-Visible spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The SeNPs and CeONPs, with different concentrations (i.e., 10, 20, 30, and 40 mg/L), were exogenously applied to wheat infected with Puccinia striformis. SeNPs and CeONPs, at a concentration of 30 mg/L, were found to be the most suitable concentrations, which reduced the disease severity and enhanced the morphological (plant height, root length, shoot length, leaf length, and ear length), physiological (chlorophyll and membrane stability index), biochemical (proline, phenolics and flavonoids) and antioxidant (SOD and POD) parameters. The antioxidant activity of SeNPs and CeONPs was also measured. For this purpose, different concentrations (50, 100, 150, 200 and 400 ppm) of both SeNPs and CeONPs were used. The concentration of 400 ppm most promoted the DPPH, ABTS and reducing power activity of both SeNPs and CeONPs. This study is considered the first biocompatible approach to evaluate the potential of green synthesized SeNPs and CeONPs to improve the health of yellow, or stripe rust, infected wheat plants and to provide an effective management strategy to inhibit the growth of Puccinia striformis.

Plant-Based Titanium Dioxide Nanoparticles Trigger Biochemical and Proteome Modifications in Triticum aestivum L. under Biotic Stress of Puccinia striiformis

In this study, we evaluated bioinspired titanium dioxide nanoparticles (TiO2 NPs) that elicited biochemical and proteome modifications in wheat plants under the biotic stress caused by Puccinia striiformis f. sp. tritici (Pst). Biosynthesis of TiO2 NPs was confirmed using UV-Vis spectrophotometry, energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. We found that the nanoparticles with crystalline nature were smaller than 100 nm. The results of FTIR analysis showed the presence of potential functional groups exhibiting O-H, N-H, C-C, and Ti-O stretching. The TiO2 NPs of different concentrations (20, 40, 60, and 80 mg L-1) were exogenously applied to wheat plants under the biotic stress caused by Pst, which is responsible for yellow stripe rust disease. The results of the assessment of disease incidence and percent disease index displayed time- and dose-dependent responses. The 40 mg L-1 TiO2 NPs were the most effective in decreasing disease severity. The bioinspired TiO2 NPs were also evaluated for enzymatic (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), and nonenzymatic metabolites (total proline, phenolic, and flavonoid contents) in wheat plants under stripe rust stress. The 40 mg L-1 TiO2 NPs were effective in eliciting biochemical modifications to reduce biotic stress. We further evaluated the effects of TiO2 NPs through gel- and label-free liquid chromatography-mass spectrometry (LC-MS) proteome analysis. We performed proteome analysis of infected wheat leaves and leaves treated with 40 mg L-1 TiO2 NPs under stripe rust stress. The functional classification of the proteins showed downregulation of proteins related to protein and carbohydrate metabolism, as well as of photosynthesis in plants under biotic stress. An upregulation of stress-related proteins was observed, including the defense mechanisms and primary metabolic pathways in plants treated with 40 mg L-1 TiO2 NPs under stress. The experimental results showed the potential of applying biogenic TiO2 NPs to combat fungal diseases of wheat plants and provided insight into the protein expression of plants in response to biotic stress.

Genetic Inheritance of Stripe Rust (Puccinia Striiformis) Resistance in Bread Wheat Breeding Lines at Seedling and Maturity Stages

One hundred and five (105) bread wheat (Triticum aestivum L.) genotypes, including five commercial checks, were screened for stripe rust resistance at seedling and adult plant stages. Seedlings grown under controlled conditions were screened for disease resistance after 12 days concerning disease incidence percentage after inoculation. K-means cluster analysis divided the genotypes into five different classes according to the presence of virulence/avirulence profile, i.e., class 1, 2, 3, 4 and 5. The same set of genotypes was grown under field conditions for adult plant resistance. Data for disease scoring and different yield and yield-related parameters was recorded. A comparison of breeding lines indicated that all studied traits were negatively affected by disease incidence. Further cluster analysis ranked the genotypes into three distinct groups with Group I and III being the most diverse. Thirteen stripe rust resistance lines were identified using seedling and adult plant resistance strategies. Correlation analysis indicated a negative association between stripe rust incidence and yield and yield-related traits, particularly grains per spike, grain weight per spike, thousand-grain weight, and grain yield per plant. These findings suggested that stripe rust resistance negatively affects yield and yield related traits. The breeding programs aiming at the development of high yielding varieties must also focus on stripe rust resistance.

Sensitivity and Resistance Risk Assessment of Puccinia striiformis f. sp. tritici to Triadimefon in China

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat that seriously threatens production safety in wheat-producing areas worldwide. In China, the disease has been largely controlled with the fungicide triadimefon. Although high levels of fungicide resistance in other fungal pathogens have been reported, failure to control Pst with any fungicides has seldomly been reported, and fungicide sensitivity of Pst has not been evaluated in China. The distribution of triadimefon-resistant Pst isolates was investigated in the present study. The baseline sensitivity of 446 Pst isolates across the country to triadimefon was determined, and the concentration for 50% of maximal effect showed a unimodal distribution curve, with a mean value of 0.19 μg ml^-1. The results indicated a wide range of sensitivity to triadimefon, with more insensitive isolates collected from Pst winter-increasing areas and northwest oversummering areas, whereas more sensitive isolates were collected from southwest oversummering areas and epidemic areas of Xinjiang and Tibet. The majority of the tested Pst isolates were sensitive to triadimefon; only 6.79% had developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in the urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. Positive cross-resistance was observed between triadimefon and tebuconazole or hexaconazole, but not between pyraclostrobin or flubeneteram. The point mutation Y134F in the 14α-demethylase enzyme (CYP51) was detected in triadimefon-resistant isolates. A molecular method (kompetitive allele-specific PCR) was established for the rapid detection of Y134F mutants in the Pst population. Two genotypes with one point mutation Y134F conferred resistance to triadimefon in Pst. The risk of resistance to triadimefon in Pst may be low to moderate. This study provided important data for establishment of high throughput molecular detection methods, fungicide resistance risk management, and the development of new target fungicides.

Wheat stem rust recorded for the first time in decades in Ireland

Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici (Pgt), occurs in most wheat-growing areas worldwide, and, in western Europe since 2013, has started to re-emerge after many decades of absence. Following this trend across western Europe, in 2020, we also detected and recorded wheat stem rust for the first time in five decades in experimental plots across five locations in Ireland. To examine the potential origin of the Irish Pgt infection in 2020, we carried out transcriptome sequencing on 12 Pgt-infected wheat samples collected across Ireland and compared these to 76 global P. graminis isolates. This analysis identified a close genetic relationship between the Irish Pgt isolates and those from Ethiopia collected in 2015 after a severe stem rust epidemic caused by the TKTTF Pgt race, and with the UK-01 Pgt isolate that was previously assigned to the TKTTF race. Subsequent pathology-based race profiling designated two Irish isolates and recent UK and French Pgt isolates to the TKTTF Pgt race group. This suggests that the Irish Pgt occurrence most probably originated from recent long-distance windborne dispersal of Pgt urediniospores from neighbouring countries in Europe where we confirmed the Pgt TKTTF race continues to be prevalent. The identification of wheat stem rust in Ireland at multiple locations in 2020 illustrates that the disease can occur in Ireland and emphasizes the need to re-initiate local monitoring for this re-emergent threat to wheat production across western Europe.

Identification of novel resources for panicle blast resistance from wild rice accessions and mutants of cv. Nagina 22 by syringe inoculation under field conditions

Panicle blast is the most severe type of rice blast disease. Screening of rice genotypes for panicle blast resistance at the field level requires an efficient and robust method of inoculation. Here, we standardized a method that can be utilized for both small- and large-scale screening and assessment of panicle blast infection and disease reaction. The method involves inoculation of Magnaporthe oryzae spore culture in the neck of the rice panicle using a syringe and covering the inoculation site with wet cotton wrapped with aluminum foil to provide the required humidity for spore germination. The method was standardized using panicle blast-resistant cv. Tetep and susceptible cv. HP2216 inoculated with Mo-ni-025 isolate of M. oryzae. The method was evaluated at phenotypic as well as molecular level by expression analysis of disease responsive pathogenesis-related (PR) genes. We found this method simple, robust, reliable, and highly efficient for screening of large germplasm sets of rice for panicle blast. This was validated by screening the wild rice germplasm for panicle blast response in the field using three M. oryzae strains and subsequently with the most virulent strain in 45 EMS-induced mutants of Nagina 22 shortlisted based on field screening in a blast hotspot region. We identified five novel blast disease-resistant wild rice genotypes and 15 Nagina 22 mutants that can be used in breeding programmes.

Distinct Life Histories Impact Dikaryotic Genome Evolution in the Rust Fungus Puccinia striiformis Causing Stripe Rust in Wheat

Stripe rust of wheat, caused by the obligate biotrophic fungus Puccinia striiformis f.sp. tritici, is a major threat to wheat production worldwide with an estimated yearly loss of US $1 billion. The recent advances in long-read sequencing technologies and tailored-assembly algorithms enabled us to disentangle the two haploid genomes of Pst. This provides us with haplotype-specific information at a whole-genome level. Exploiting this novel information, we perform whole-genome comparative genomics of two P. striiformis f.sp. tritici isolates with contrasting life histories. We compare one isolate of the old European lineage (PstS0), which has been asexual for over 50 years, and a Warrior isolate (PstS7 lineage) from a novel incursion into Europe in 2011 from a sexual population in the Himalayan region. This comparison provides evidence that long-term asexual evolution leads to genome expansion, accumulation of transposable elements, and increased heterozygosity at the single nucleotide, structural, and allele levels. At the whole-genome level, candidate effectors are not compartmentalized and do not exhibit reduced levels of synteny. Yet we were able to identify two subsets of candidate effector populations. About 70% of candidate effectors are invariant between the two isolates, whereas 30% are hypervariable. The latter might be involved in host adaptation on wheat and explain the different phenotypes of the two isolates. Overall, this detailed comparative analysis of two haplotype-aware assemblies of P. striiformis f.sp. tritici is the first step in understanding the evolution of dikaryotic rust fungi at a whole-genome level.

Distinct Life Histories Impact Dikaryotic Genome Evolution in the Rust Fungus Puccinia striiformis Causing Stripe Rust in Wheat

Stripe rust of wheat, caused by the obligate biotrophic fungus Puccinia striiformis f.sp. tritici, is a major threat to wheat production worldwide with an estimated yearly loss of US $1 billion. The recent advances in long-read sequencing technologies and tailored-assembly algorithms enabled us to disentangle the two haploid genomes of Pst. This provides us with haplotype-specific information at a whole-genome level. Exploiting this novel information, we perform whole-genome comparative genomics of two P. striiformis f.sp. tritici isolates with contrasting life histories. We compare one isolate of the old European lineage (PstS0), which has been asexual for over 50 years, and a Warrior isolate (PstS7 lineage) from a novel incursion into Europe in 2011 from a sexual population in the Himalayan region. This comparison provides evidence that long-term asexual evolution leads to genome expansion, accumulation of transposable elements, and increased heterozygosity at the single nucleotide, structural, and allele levels. At the whole-genome level, candidate effectors are not compartmentalized and do not exhibit reduced levels of synteny. Yet we were able to identify two subsets of candidate effector populations. About 70% of candidate effectors are invariant between the two isolates, whereas 30% are hypervariable. The latter might be involved in host adaptation on wheat and explain the different phenotypes of the two isolates. Overall, this detailed comparative analysis of two haplotype-aware assemblies of P. striiformis f.sp. tritici is the first step in understanding the evolution of dikaryotic rust fungi at a whole-genome level.

Susceptibility of Winter Wheat and Triticale to Yellow Rust Influenced by Complex Interactions between Vernalisation, Temperature, Plant Growth Stage and Pathogen Race

Environmental factors influence the disease susceptibility of crop plants. In this study, we established an experimental system to investigate the effects of vernalisation, temperature and plant growth stage on the susceptibility of winter wheat and winter triticale to Puccinia striiformis, the causal agent of yellow (stripe) rust. Two temperature regimes: standard (18 °C day/12 °C night) and low (12 °C day/6 °C night), vernalised and non-vernalised seedlings, vernalised adult plants and two pathogen races were investigated. At low temperatures, vernalisation reduced the susceptibility of seedlings exposed to the ‘Warrior’ race, while this was only the case for five out of eight varieties exposed to the ‘Kranich’ race. Changing from standard to low temperature resulted in increased susceptibility of non-vernalised seedlings of seven varieties inoculated with the ‘Warrior’ race and five varieties inoculated with the ‘Kranich’ race. Increased susceptibility at low temperature was also detected for several varieties at the adult plant growth stage. Comparisons between vernalised seedlings and adult plants revealed an effect of plant growth stage on disease susceptibility (e.g., Adult Plant Resistance) in five varieties at standard temperature for the ‘Warrior’ race and in five and four varieties at standard and low temperature respectively, for the ‘Kranich’ race. The complex and unpredictable interactions between environment and pathogen influencing yellow rust susceptibility of individual varieties stress the importance of phenotyping for disease resistance under different environmental conditions and pathogen populations. The environmental impact on rust susceptibility should also be taken into account in early-warning systems targeting wheat and triticale breeding programmes and growers.

Trade-Off Between Triadimefon Sensitivity and Pathogenicity in a Selfed Sexual Population of Puccinia striiformis f. sp. Tritici

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases of wheat and has been largely managed using demethylation inhibitor (DMI) fungicide triadimefon in China. To determine the sensitivity of Pst, a Chinese Pst isolate and its sexually produced progeny isolates were tested with triadimefon using the detached leaf method. The half maximal effective concentration (EC₅₀) values varied greatly among the progeny isolates, ranging from 0.06 mg L^–1 to 7.89 mg L^–1. Twenty-six of the 56 tested progeny isolates were less sensitive to triadimefon than the parental isolate. A single-nucleotide mutation at the 401 position resulting in an amino acid change from tyrosine (Y) to phenylalanine (F) in the 134th codon (Y134F) of the cytochrome P450 sterol 14a-demethylase enzyme (CYP51), the target gene of DMI fungicide, was identified in the parental isolate. The 87 tested progeny isolates segregated into 19 homozygous wild type (AA), 40 heterozygous (AT), and 28 homozygous mutant (TT) genotypes, fitting a 1:2:1 ratio (χ² = 2.43; P = 0.30). The mutant isolates had higher EC₅₀ values than the wild type isolates. Significant differences in logEC₅₀ were found between the mutant isolates and the wild type isolates (P = 2.2e^–16). However, homozygous and heterozygous mutant isolates were not significantly different (P = 0.21), indicating dominant mutation. Twenty-two progeny isolates were used to inoculate a susceptible wheat variety, and latency period and lesion growth were recorded to compare wild type and mutant isolates for the pathogenicity fitness components. A moderate but significant negative correlation was detected between lesion growth and sensitivity to triadimefon (r = −0.53; P = 0.01). No significant variation in lesion growth was found between homozygous and heterozygous mutant isolates (P = 0.83). In the case of latency period and triadimefon sensitivity, no significant correlation was found (P = 0.17). These results are useful for understanding reduced sensitivity in the pathogen population and improving stripe rust management.

Point Inoculation Method for Measuring Adult Plant Response of Wheat to Stripe Rust Infection

Depending on the pathogenicity of the stripe rust fungus Puccinia striiformis f. sp. tritici, the nature of resistance in the wheat host plant, and the environment, a broad range of disease phenotypes can be expressed. Therefore, the phenotyping of partial adult plant stripe rust resistance requires reliable and repeatable procedures, especially under controlled conditions. In this study, the development of a flag leaf point inoculation method, which resulted in a 100% initial infection rate, is reported. Flag leaf inoculations were achieved by placing 6-mm antibiotic test paper discs, dipped into a urediniospore and water suspension and covered with water-proof plastic tape, on the adaxial side of leaves. Results from independent trials allowed for the statistical comparison of stripe rust lesion expansion rate in wheat entries that differ in resistance. The technique is inexpensive, reliable, and applicable to routine screening for adult plant response type, quantitative comparison of stripe rust progress, environmental influences, and pathogenicity of different isolates.

Screening of Endophytic Antagonistic Bacterium from Phellodendron amurense and Their Biocontrol Effects against Canker Rot

Thirty-four strains of bacteria were isolated from Phellodendron amurense. Using Nectria haematococca as an indicator strain, the best strain, B18, was obtained by the growth rate method. The morphological, physiological and biochemical characteristics of strain B18 and its 16S DNA gene sequence were identified, and the biocontrol effect of strain B18 was assessed in pot and field tests, as well as in a field-control test. Drilling methods were used to determine the antibacterial activity of metabolites from strain B18 and their effects on the growth of pathogen mycelia and spores. The best bacteriostatic rate was 85.4%. B18 can hydrolyse starch and oxidize glucose but does not produce gas; a positive result was obtained in a gelatine liquefaction test. According to 16S DNA gene sequencing, strain B18 is Bacillus methylotrophicus (GenBank accession number: MG457759). The results of pot and field-control trials showed 98% disease control when inoculating 10⁸ cfu/ml of the strain. The disease control effect of the B18 culture liquid (concentrations of 10⁸, 2 × 10⁶, 10⁶, 5 × 10⁵ and 2.5 × 10⁵ cfu/ml) in the field-control test was higher than 80%, and the cure rate of the original delivery solution was 96%. Therefore, in the practical forestry production, a 2.5 × 10⁵ cfu/ml culture liquidshould be applied in advance to achieve good control effects.

Additive Manufacturing of Devices Used for Collection and Application of Cereal Rust Urediniospores

Optimized inoculation procedures are an important consideration in achieving repeatable plant infection when working with biotrophic rust fungi. Several plant pathology laboratories specializing in rust research employ a system where the collection and application of fungal spores are accomplished using an exchangeable gelatin capsule. Urediniospores are collected from erumpent pustules on plant surfaces into a capsule fitted to a cyclone collector controlled by a vacuum pump. By adding light mineral oil to the same capsule, the spore suspension is then sprayed onto plants by means of a dedicated atomizer (inoculator) connected to an air pressure source. Although devices are not commercially available, modern day technologies provide an opportunity to efficiently design and manufacture collectors and inoculators. Using a process called Additive Manufacturing (AM), also known as "3D printing," the bodies of a collector and inoculator were digitally designed and then laser-sintered in nylon. Depending on availability, copper or aluminum tubes were fitted to the bodies of both devices afterward to either facilitate directed collection of spores from rust pustules on plant surfaces or act as a siphon tube to deliver the spore suspension contained in the capsule. No statistical differences were found between AM and metal inoculators for spray delivery time or spore deposition per unit area. In replicated collection and inoculation tests of wheat seedlings with urediniospore bulks or single pustule collections of Puccinia triticina and P. graminis f. sp. tritici, the causal organisms of leaf rust and stem rust, consistent and satisfactory infection levels were achieved. Immersing used devices in acetone for 60 s followed by a 2 h heat treatment at 75°C produced no contaminant infection in follow-up tests.

Cloning and Expression of the Chitinase Encoded by ChiKJ406136 from Streptomyces Sampsonii (Millard & Burr) Waksman KJ40 and Its Antifungal Effect

The present study demonstrated that the chitinase gene ChiKJ406136 of Streptomyces sampsonii (Millard & Burr) Waksman KJ40 could be cloned using a PCR protocol and expressed in Escherichia coli (Migula) Castellani & Chalmers BL21 (DE3), and the recombinant protein had antifungal effect on four forest pathogens (Cylindrocladium scoparium Morgan, Cryphonectria parasitica (Murrill) Barr, Neofusicoccum parvum Crous, and Fusarium oxysporum Schl.) and also had the biological control effects on Eucalyptus robusta Smith leaf blight, Castanea mollissima BL. blight, Juglans regia L. blight and J. regia root rot. The results showed that ChiKJ406136 was efficiently expressed and a 48 kilodalton (kDa) recombinant protein was obtained. No significant change in protein production was observed in the presence of different concentrations of IPTG (isopropyl-b-D-thio-galactoside). The purified protein yield was greatest in the 150 mmol/L imidazole elution fraction, and the chitinase activities of the crude protein and purified protein solutions were 0.045 and 0.033 U/mL, respectively. The antifungal effects indicated that mycelial cells of the four fungi were disrupted, and the control effects of the chitinase on four forest diseases showed significant differences among the undiluted 10- and 20-fold dilutions and the control. The undiluted solution exhibited best effect. The results of this study provide a foundation for the use of S. sampsonii as a biocontrol agent and provides a new source for the chitinase gene, providing a theoretical basis for its application.

Cloning of the wheat Yr15 resistance gene sheds light on the plant tandem kinase-pseudokinase family

Yellow rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating fungal disease threatening much of global wheat production. Race-specific resistance (R)-genes are used to control rust diseases, but the rapid emergence of virulent Pst races has prompted the search for a more durable resistance. Here, we report the cloning of Yr15, a broad-spectrum R-gene derived from wild emmer wheat, which encodes a putative kinase-pseudokinase protein, designated as wheat tandem kinase 1, comprising a unique R-gene structure in wheat. The existence of a similar gene architecture in 92 putative proteins across the plant kingdom, including the barley RPG1 and a candidate for Ug8, suggests that they are members of a distinct family of plant proteins, termed here tandem kinase-pseudokinases (TKPs). The presence of kinase-pseudokinase structure in both plant TKPs and the animal Janus kinases sheds light on the molecular evolution of immune responses across these two kingdoms.

High Relative Parasitic Fitness of G22 Derivatives is Associated with the Epidemic Potential of Wheat Stripe Rust in China

In total, 13 commercial wheat cultivars around China and four races of Puccinia striiformis f. sp. tritici (namely, CYR32, CYR33, G22-9, and G22-14) were employed for a test of relative parasitic fitness (RPF) using the drop method. The RPF values were measured, including the urediniospore germination rate, the latent period, the uredinial length, the uredinial density, the infection area, the sporulation intensity, the lesion expansion speed, and the sporulation period. The results indicated that the parameters of relative parasitic fitness of the four P. striiformis f. sp. tritici races on the 13 wheat cultivars were significantly different (P = 0.00) in sporulation intensity, lesion expansion speed, uredinial length, sporulation period, uredinial density, and latent period. The urediniospore germination rates of the four P. striiformis f. sp. tritici races for the test were significantly different (P = 0.00), whereas no correlation with the different cultivars was observed (P = 1.00). The infection areas of the tested races on the different cultivars were significantly different (P = 0.00) but there were no obvious manifestations among the various races (P = 0.20). Principal component analysis (PCA) showed that the sporulation intensity represented sporulation capacity and scalability, the latent period indicated infection ability, and the urediniospore germination rate represented urediniospore vigor, all of which fully contributed to the RPF in the interaction of the four races and 13 wheat cultivars, which was calculated by the following formula: RPF = (sporulation intensity × urediniospore germination rate)/latent period. The sporulation and infection of G22-9 on the 13 large-scale cultivated cultivars were the highest, and the RPF of G22-9 was higher than that of the predominant races, CYR32 and CYR33. This result suggested that G22-9 could become a new predominant race and potentially cause epidemics of wheat stripe rust in China. To prevent potential epidemics, susceptible wheat cultivars should be withdrawn from production and breeding programs should reduce the use of Yr10 and Yr26 and use other more effective resistance genes in combination with nonrace-specific resistance for developing wheat cultivars with durable resistance to stripe rust.

Assessment of Aggressiveness of Puccinia striiformis on Wheat

A simple point-inoculation method using Novec™ 7100, a volatile engineered fluid, is presented for the assessment of aggressiveness of Puccinia striiformis isolates on seedlings of wheat. The method allows for quantification of the applied inoculum with a minimal risk of cross-contamination of rust from leaves grown side by side. The method is also applicable for the assessment of qualitative differences inferred by compatible and incompatible host-pathogen interactions, and it can be adjusted to other cereal rust and powdery mildew fungi on other host species, and other plant growth stages as appropriate.