Breakdown Of Resistance Research Articles

Material properties and performance of ErAs:In(Al)GaAs photoconductors for 1550 nm laser operation

ErAs:In(Al)GaAs photoconductors have proven to be outstanding devices for photonic terahertz (0.1–10 THz) generation and detection with previously reported sub-0.5 ps carrier lifetimes. We present the so far most detailed material characterization of these superlattices composed of ErAs, InGaAs, and InAlAs layers grown by molecular beam epitaxy. The variation of the material properties as a function of the ErAs concentration and the superlattice structure is discussed with focus on source materials. Infrared spectroscopy shows an absorption coefficient in the range of 4700–6600 cm−1 at 1550 nm, with shallow absorption edges toward longer wavelengths caused by absorption of ErAs precipitates. IV characterization and Hall measurements show that samples with only 0.8 monolayers of electrically compensated ErAs precipitates (p-delta-doped at 5×1013 cm−2) and aluminum-containing spacer layers enable high dark resistance (∼10–20 MΩ) and high breakdown field strengths beyond 100 kV/cm, corresponding to >500 V for a 50 μm gap. With higher ErAs concentration of 1.6 ML (2.4 ML), the resistance decreases by a factor of ∼40 (120) for an otherwise identical superlattice structure. We propose a theoretical model for calculation of the excess current generated due to heating and for the estimation of the photocurrent from the total illuminated current. The paper concludes with terahertz time-domain spectroscopy measurements demonstrating the strengths of the material system and validating the proposed model.

Postbreakdown Transient Characteristics of a Gas-Filled Plasma Closing Switch

Gas-filled plasma closing switches (PCSs) are essential components of high energy density pulsed power systems used to generate short, high-power (tens MW to several GW) impulses. In practical applications, PCSs are required to operate in high-current (tens kA), high-voltage (10s-100s kV) regimes, to produce fast-rising ns and sub-ns HV impulses. The transient impedance of a PCS affects the rise time of the generated impulses and the power delivered to the load. Thus, the design and optimization of PCSs require detailed information on the dynamic plasma resistance. This article is focused on an investigation of the time-dependent resistance of the plasma channel(s) formed between the electrodes of a multielectrode PCS. Experimentally measured underdamped current and voltage waveforms were used to obtain the transient plasma resistance of the PCS. The PCS was filled with different gases: dry air, CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and a 90%/10% Ar/O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture, in the pressure range from 0 up to 10 bar (gauge). It was found that the plasma resistance drops rapidly from a few hundreds of ohms to a few hundreds of milliohms due to the Joule heating of the breakdown channel. The methods proposed by Braginskii and Kushner to model the transient postbreakdown resistance were used to obtain analytical plasma resistances for all of the gases. These resistances have been compared with the transient resistance obtained using a Kirchhoff analysis of the lumped-element, postbreakdown RLC circuit. Based on this comparison, the suitability of the chosen analytical methods to determine the transient breakdown resistance in gases is discussed. The obtained results will help in the optimization of the operational performance of PCSs filled with environmentally friendly, low environmental impact gases.

Breeding Strategies and Challenges in the Improvement of Blast Disease Resistance in Finger Millet. A Current Review.

Climate change has significantly altered the biodiversity of crop pests and pathogens, posing a major challenge to sustainable crop production. At the same time, with the increasing global population, there is growing pressure on plant breeders to secure the projected food demand by improving the prevailing yield of major food crops. Finger millet is an important cereal crop in southern Asia and eastern Africa, with excellent nutraceutical properties, long storage period, and a unique ability to grow under arid and semi-arid environmental conditions. Finger millet blast disease caused by the filamentous ascomycetous fungus Magnaporthe oryzae is the most devastating disease affecting the growth and yield of this crop in all its growing regions. The frequent breakdown of blast resistance because of the susceptibility to rapidly evolving virulent genes of the pathogen causes yield instability in all finger millet-growing areas. The deployment of novel and efficient strategies that provide dynamic and durable resistance against many biotypes of the pathogen and across a wide range of agro-ecological zones guarantees future sustainable production of finger millet. Here, we analyze the breeding strategies currently being used for improving resistance to disease and discuss potential future directions toward the development of new blast-resistant finger millet varieties, providing a comprehensive understanding of promising concepts for finger millet breeding. The review also includes empirical examples of how advanced molecular tools have been used in breeding durably blast-resistant cultivars. The techniques highlighted are cost-effective high-throughput methods that strongly reduce the generation cycle and accelerate both breeding and research programs, providing an alternative to conventional breeding methods for rapid introgression of disease resistance genes into favorable, susceptible cultivars. New information and knowledge gathered here will undoubtedly offer new insights into sustainable finger millet disease control and efficient optimization of the crop’s productivity.

Drought: Malnutrition and Parasitism

The relation between nutrition and parasitism is discussed in short, after which some general observations are given on the drought problem in the Zaria area. Sedentary herds were most severely affected, mainly by secondary effects of the drought, i.e. the breakdown of resistance to parasitic infections. Cattle and sheep from the drought-affected areas showed high prevalence of helminth infections at the end of dry season. Some suggestions are given on the prevention of helminthiasis during drought periods, especially in relation to sedentary herds.

Field screening of rice (Oryza sativa L.) genotypes for resistance to bacterial leaf blight (Xanthomonas oryzae pv. oryzae) disease

Rice is the most important crop in Nepal followed by maize and wheat in terms of area (1.4 million ha), production (5.15 million) and productivity (3.5 mt/ha). Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae is considered to be the most widespread and destructive disease of rice in both irrigated and rainfed environments in Nepal. Use of host plant resistance is the most feasible and economical way to combat this disease. However, breakdown of resistance of a variety often occurs after few years of release due to genetic adaptation of the pathogen. Regular screening of the genotypes is utmost for developing the resistant genotypes. Considering the point, this investigation effort has been made to screen the rice genotypes against BLB under natural field condition at Khajura, Banke during 2018 and 2019. In the study, plants were assessed by measuring disease severity (percentage of leaf diseased) and area under the disease progress curve (AUDPC). Differences in resistance among the rice genotypes were observed in both of the tested year. Among the screened 150 rice genotypes during 2018, 6 genotypes scored resistant (R), 81 moderately resistant (MR), 59 moderately susceptible (MS) and 4 susceptible (S) to BLB. Whereas, in 2019, among the tested 315 rice genotypes, none of the genotypes were resistant, 183 MR, 131 MS and 1 S to BLB disease. This showed that the tested genotypes were composed of different genetic background.&#x0D;

Effect of foliar application of fungicides, Neem extract and Butter Milk on yellow rust, plant growth and yield parameters of wheat

Ever dynamic Puccinia striiformis f.sp. tritici, evolving into new virulences has led to frequent breakdown of resistance in wheat varieties in Punjab. Therefore, timely and need based application of fungicides to manage yellow rust of wheat is very important. Azoxystrobin + difenoconazole 325 SC, azoxystrobin + cyproconazole 280 SC, azoxystrobin + tebuconazole 320 SC, pyraclostrobin + epoxiconazole 175 SE, tebuconazole 25 EC each @ 0.1%, captan + hexaconazole 75 WP@ 0.3% and trifloxistrobin + tebuconazole 75 WG @ 0.6% proved highly effective and gave almost complete control of yellow rust and inhibited sporulation in trials conducted during 2016–17 and 2017–18 crop season. An increase of up to 30.2 per cent in thousand grain weight and 40.2 per cent in grain yield was observed with these fungicidal treatments. Improved plant growth attributes like tillering and plant height was also observed along with disease control. The efficacy of neem leaf extract, fermented butter milk and neem leaf extract + fermented butter milk was low as compared to fungicides. However, being indigenous home production, it resulted in highest cost-benefit ratio i.e. 1: 11.86. Maximum thousand grain weight of 45.6g and yield of 57.03q/ha was observed in azoxystrobin+difenoconazole 325 SC, which was 30.2 and 40.3 per cent more than control, respectively.

Exploration of Rhenium Volcanogenic Deposit and Technology of Its Development

Rhenium is widely used in manufacturing industry and metallurgy. Today the consumption of rhenium is high, but there are very few deposits in the world where it is mined. Thus, the aim of the study is to identify areas of distribution of rhenium on Kudryavy volcano, located on the islands of the Kuril ridge (Russia). In this connection, during the field period, we took samples of a volcanic massif weighing 70 kg, and also studied the geothermal fields with a pyrometer. Laboratory research included the study of composition of samples by the method of inductively coupled plasma mass spectrometry and spectrometric analysis. The article defines the zones of distribution of rhenium mineralization, presents the results of measurements of the temperature of geothermal fields and the elemental composition of technological samples. The geology, development technology is described, the analysis of the destruction of rocks, determined by the acoustic method, the specific resistance of breakdown during electrothermal loosening is given. The parameters of the tubular shovel conveyor at which the productivity of 88 m3/h is achieved. The results obtained will make it possible to identify promising geothermal fields, determine the development technology, and contribute to the study of volcanic deposits.

Fast developing Russian wheat aphid biotypes remains an unsolved enigma.

Diuraphis noxia, commonly known as the Russian wheat aphid, is an economically important cereal pest species, highly invasive and reproduces mostly asexually. Remarkably, many new virulent populations continue to develop, despite the lack of genetic diversity in the aphid. Russian wheat aphid is a phloem feeder and is therefore engaged in a continuous arms battle with its cereal host, with the acquisition of virulence central to the breakdown of host resistance. In the review, most attention is given to recent topics about mechanisms and strategies whereby the aphid acquires virulence against its host, with special reference given to the role of noncoding RNA elements, bacteria, and the epigenetic pathway in possibly directing virulence.

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties.

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.

Genome Analysis of Two Newly Emerged Potato Late Blight Isolates Sheds Light on Pathogen Adaptation and Provides Tools for Disease Management.

Phytophthora infestans, the causal agent of the Irish Potato Famine in the 1840s, is one of the most destructive crop pathogens that threaten global food security. Host resistance (R) genes may help to control the disease, but recognition by through the gene products can be evaded by newly emerging isolates. Such isolates are dangerous as they may cause disease outbreaks under favorable conditions. However, our lack of knowledge about adaptation in these isolates jeopardizes an apt response to resistance breakdown. Here we performed genome and transcriptome sequencing of HB1501 and HN1602, two field isolates from distinct Chinese geographic regions. We found extensive polymorphisms in these isolates, including gene copy number variations, nucleotide polymorphisms, and gene expression changes. Effector encoding genes, which contribute to virulence, show distinct expression landscapes in P. infestans isolates HB1501 and HN1602. In particular, polymorphisms at multiple effectors required for recognition (Avr loci) enabled these isolates to overcome corresponding R gene based resistance. Although the isolates evolved multiple strategies to evade recognition, we experimentally verified that several R genes such as R8, RB, and Rpi-vnt1.1 remain effective against these isolates and are valuable to potato breeding in the future. In summary, rapid characterization of the adaptation in emerging field isolates through genomic tools inform rational agricultural management to prevent potential future epidemics.

Genomic Profiling of Virulence in the Soybean Cyst Nematode Using Single-Nematode Sequencing.

Soybean cyst nematode (SCN) is one of the most important diseases in soybean. Currently, the main management strategy relies on planting resistant cultivars. However, the overuse of a single resistance source has led to the selection of virulent SCN populations, although the mechanisms by which the nematode overcomes the resistance genes remain unknown. In this study, we used a nematode-adapted single-cell RNA-seq approach to identify SCN genes potentially involved in resistance breakdown in Peking and PI 88788 parental soybean lines. We established for the first time the full transcriptome of single SCN individuals allowing us to identify a list of putative virulence genes against both major SCN resistance sources. Our analysis identified 48 differentially expressed putative effectors (secreted proteins required for infection) alongside 40 effectors showing evidence of novel structural variants, and 11 effector genes containing phenotype-specific sequence polymorphisms. Additionally, a differential expression analysis revealed an interesting phenomenon of coexpressed gene regions with some containing putative effectors. The selection of virulent SCN individuals on Peking resulted in a profoundly altered transcriptome, especially for genes known to be involved in parasitism. Several sequence polymorphisms were also specific to these virulent nematodes and could potentially play a role in the acquisition of nematode virulence. On the other hand, the transcriptome of virulent individuals on PI 88788 was very similar to avirulent ones with the exception of a few genes, which suggest a distinct virulence strategy to Peking.

Convergent Rewiring of the Virulence Regulatory Network Promotes Adaptation of Ralstonia solanacearum on Resistant Tomato.

The evolutionary and adaptive potential of a pathogen is a key determinant for successful host colonization and proliferation but remains poorly known for most of the pathogens. Here, we used experimental evolution combined with phenotyping, genomics, and transcriptomics to estimate the adaptive potential of the bacterial plant pathogen Ralstonia solanacearum to overcome the quantitative resistance of the tomato cultivar Hawaii 7996. After serial passaging over 300 generations, we observed pathogen adaptation to within-plant environment of the resistant cultivar but no plant resistance breakdown. Genomic sequence analysis of the adapted clones revealed few genetic alterations, but we provide evidence that all but one were gain of function mutations. Transcriptomic analyses revealed that even if different adaptive events occurred in independently evolved clones, there is convergence toward a global rewiring of the virulence regulatory network as evidenced by largely overlapping gene expression profiles. A subset of four transcription regulators, including HrpB, the activator of the type 3 secretion system regulon and EfpR, a global regulator of virulence and metabolic functions, emerged as key nodes of this regulatory network that are frequently targeted to redirect the pathogen’s physiology and improve its fitness in adverse conditions. Significant transcriptomic variations were also detected in evolved clones showing no genomic polymorphism, suggesting that epigenetic modifications regulate expression of some of the virulence network components and play a major role in adaptation as well.

Genome-wide association study of resistance to PstS2 and Warrior races of Puccinia striiformis f. sp. tritici (stripe rust) in bread wheat landraces.

Stripe or yellow rust, caused by Puccinia striiformis Westend. f. sp. tritici is a major threat to bread wheat production worldwide. The breakdown in resistance of certain major genes and newly emerging aggressive races of stripe rusts pose serious concerns in all main wheat growing areas of the world. To identify new sources of resistance and associated QTL for effective utilization in future breeding programs an association mapping (AM) panel comprising of 600 bread wheat landraces collected from eight different countries conserved at ICARDA gene bank were evaluated for seedling and adult plant resistance against the PstS2 and Warrior races of stripe rust at the Regional Cereal Rust Research Center (RCRRC), Izmir, Turkey during 2016, 2018 and 2019. A set of 25,169 informative SNP markers covering the whole genome were used to examine the population structure, linkage disequilibrium and marker-trait associations in the AM panel. The genome-wide association study (GWAS) was carried out using a Mixed Linear Model (MLM). We identified 47 SNP markers across 19 chromosomes with significant SNP-trait associations for both seedling stage and adult plant resistance. The threshold of significance for all SNP-trait associations was determined by the false discovery rate (q) ≤ 0.05. Three genomic regions (QYr.1D_APR, QYr.3A_seedling and QYr.7D_seedling) identified in this study do not correspond to previously reported Yr genes or QTL, suggesting new genomic regions for stripe rust resistance.

Tomato Yellow Leaf Curl Virus-Resistant and -Susceptible Tomato Genotypes Similarly Impact the Virus Population Genetics.

Tomato yellow leaf curl virus is a species in the genus Begomovirus and family Geminiviridae. Tomato yellow leaf curl virus (TYLCV) infection induces severe symptoms on tomato plants and causes serious yield losses worldwide. TYLCV is persistently transmitted by the sweetpotato whitefly, Bemisia tabaci (Gennadius). Cultivars and hybrids with a single or few genes conferring resistance against TYLCV are often planted to mitigate TYLCV-induced losses. These resistant genotypes (cultivars or hybrids) are not immune to TYLCV. They typically develop systemic infection, display mild symptoms, and produce more marketable tomatoes than susceptible genotypes under TYLCV pressure. In several pathosystems, extensive use of resistant cultivars with single dominant resistance-conferring gene has led to intense selection pressure on the virus, development of highly virulent strains, and resistance breakdown. This study assessed differences in TYLCV genomes isolated from susceptible and resistant genotypes in Florida and Georgia. Phylogenetic analyses indicated that Florida and Georgia isolates were distinct from each other. Population genetics analyses with genomes field-collected from resistant and susceptible genotypes from Florida and/or Georgia provided no evidence of a genetic structure between the resistant and susceptible genotypes. No codons in TYLCV genomes from TYLCV-resistant or susceptible genotypes were under positive selection, suggesting that highly virulent or resistance-breaking TYLCV strains might not be common in tomato farmscapes in Florida and Georgia. With TYLCV-resistant genotypes usage increasing recently and multiple tomato crops being planted during a calendar year, host resistance-induced selection pressure on the virus remains a critical issue. To address the same, a greenhouse selection experiment with one TYLCV-resistant and susceptible genotype was conducted. Each genotype was challenged with TYLCV through whitefly-mediated transmission serially 10 times (T1-T10). Population genetics parameters at the genome level were assessed at T1, T5, and T10. Results indicated that genomes from resistant and susceptible genotypes did not differentiate with increasing transmission number, no specific mutations were repeatedly observed, and no positive selection was detected. These results reiterate that resistance in tomato might not be exerting selection pressure against TYLCV to facilitate development of resistance-breaking strains. TYLCV populations rather seem to be shaped by purifying selection and/or population expansion.

Study and Design of a 2.45-GHz Rectifier Achieving 91% Efficiency at 5-W Input Power

To achieve a high-efficiency microwave wireless power transfer system, a high conversion efficiency rectifier is necessary. Brown (1974) designed rectifiers with approximately 3-W input power achieved 90% conversion efficiency for 2.45 GHz, and it maintains the record for maximum conversion efficiency. In this study, to design a high-efficiency and high-power rectifier, we designed a larger semiconductor metal junction area GaAs Schottky diodes possessing very low series resistance and high breakdown voltage. In addition, we built the SPICE model and package model for the diodes. The designed high conversion efficiency rectifier achieved 91% efficiency at 5-W input power for 2.45 GHz.

Localized Probing of Dielectric Breakdown in Multilayer Hexagonal Boron Nitride.

Hexagonal boron nitride (h-BN) has emerged as a promising 2D/layered dielectric owing to its successful integration with graphene and other 2D materials, although a coherent picture of the overall dielectric breakdown mechanism in h-BN is yet to emerge. Here, we have carried out a systematic study using conduction atomic force microscopy to provide insights into the process of defect generation and dielectric degradation in the progressive breakdown (PBD) and hard breakdown (HBD) stages in 2-5 nm thick chemical vapor deposition (CVD)-grown multilayer h-BN films. The PBD and HBD regimes show different behaviors. Under electrical stress in the PBD stage, defects are generated progressively in the h-BN, leading to a gradual reduction of the effective barrier resistance and continuous soft breakdowns (SBDs) of the dielectric material. Random telegraph noise nano-spectroscopy shows that low frequency noise becomes dominant after an SBD event due to the creation of additional defects around the percolation path. We also observe a wide variation in the current-voltage (I-V) breakdown plots in the PBD stage, giving rise to non-Weibull statistical distribution of the breakdown voltage. We attribute this observation to the significant thickness inhomogeneity in the CVD films. At HBD, h-BN materials are always physically removed from the film, leading to the formation of pits at the breakdown location. Interestingly, pit formation is also occasionally observed in the PBD stage under very low current compliances, suggesting that breakdown may proceed by a mixture of defect generation and material removal in h-BN CVD films.

Thermal Degradation Phenomena of Polymer Film on Magnet Wire for Electromagnetic Coils

Polymer film insulation degradation is a major problem for electric machines which leads to short circuits, overheating, and eventually the occurrence of catastrophic failure. Electrical insulation materials provide the vital function of turn-to-turn, phase-to-phase, and phase-to-ground electrical isolation for the electromagnetic coils and windings. This article investigates the characterization of early-onset degradation of thin-film magnet wire insulation at elevated temperatures from 200 to 275 $^{\circ }$ C. Sample specimens were analyzed after ageing for 100 h in terms of their physical properties (surface roughness, mass), chemical properties [Fourier transform infrared (FTIR) spectroscopy], dielectric properties (capacitance and dissipation factor), and electrical properties (voltage breakdown strength and resistance). The results show that the specimen roughness and mass increase and decrease uniformly, respectively, with increased ageing temperature. Similar degradation results trends with respect to ageing temperature for the dielectric properties and electrical insulation strength is documented. The article also reports an extended ageing study which investigates early breakdown voltage on sample specimens over a much longer time duration, that of up to 1600 h.

Genetic and chemical control of coffee rust (Hemileia vastatrix Berk et Br.): impacts on coffee (Coffea arabica L.) quality.

The occurrence of diseases can alter coffee (Coffea arabica L.) metabolism, causing changes in the composition of coffee beans and beverage quality. However, little is known about which aspects of coffee quality are actually altered by rust (Hemileia vastatrix Berk et Br.) and by its main control methods. The effect of chemical and genetic methods for the control of coffee rust on the quality of coffee beans and beverage was investigated. Both genetic and chemical control reduce the damage caused by the disease in the composition of coffee beans. Genotypes with resistant ancestry, even with resistance breakdown, respond better to chemical control. The combination of genetic and chemical control favors an increase in the sugar content in the beans. Despite the fact that both genetic and chemical control are effective in reducing disease damage regarding the chemical composition of beans, the quality potential of Timor Hybrid genotypes associated with the cancellation of rust expression through the joint action of genetic and chemical control favors the composition of beans and, consequently, the quantitative assessment of sensory attributes, adding value to the final product. © 2020 Society of Chemical Industry.

Rotating and stacking genes can improve crop resistance durability while potentially selecting highly virulent pathogen strains

Rotating crop cultivars with different resistance genes could slow the evolution of virulent strains of fungal pathogens, but could also produce highly virulent pathogen strains. We present a new model that links polycyclic pathogen epidemiology and population genetics in order to predict how different strategies of rotating cultivars with different resistances will affect the evolution of pathogen virulence and the breakdown of crop resistance. We modelled a situation where there were four different resistance genes that can be deployed within each crop cultivar, and four virulence genes that may be present within the pathogen. We simulated four different rotational management strategies: (i) no rotation; (ii) a different gene every year; (iii) a different gene every 5 years; and (iv) a different combination of two stacked genes each year. Results indicate that rotating cultivars can lead to longer periods of disease suppression but also to the selection of highly virulent strains. The efficacy and relative advantage of different resistant cultivar rotation strategies depended on the fitness penalties, initial virulence allele frequencies, and ability of non-virulent pathogen genotypes to grow and reproduce on resistant cultivars. By capturing the essential processes involved, our model provides a useful new tool for investigating the evolutionary dynamics of pathogen virulence and crop resistance breakdown.

Management of stem rust caused by Puccinia graminis f. sp. tritici through redeployment of wheat varieties in Northwest Ethiopia

Wheat stem rust is an important disease affecting wheat production in the world. In Ethiopia, it is one of the most destructive diseases constraining wheat production. Field experiments were carried in the districts of Adet and Aneded of Ethiopia in 2017 and 2018 main cropping seasons to manage wheat stem rust infection through reuse of old varieties. Forty-nine wheat varieties were tested in a simple lattice design with two replications. The results indicated that wheat varieties varied significantly (p < 0.05) in severity, the area under the disease progress curve, disease progress rate and grain yield. Four reaction groups of wheat varieties were identified, susceptible, moderately susceptible, moderately resistant and resistant. Varieties Hoggana, Shorima, and Sanete at Adet and varieties Hoggana, Shorima and Abola at Aneded were resistant to stem rust in both seasons. Varieties Enkoy, Sofumer, ET13A2, Tuse, Senkegna, Dinknesh, Alidoro, Tay, Honqollo, Tsehay, Mandoyu, Mitike, Medawalabu were moderately resistant to stem rust in both seasons at both locations. Similar reactions were recorded from variety KBG-01 and Dashen at Adet, and G’ambo, Galema, Danda’a, Katar, Pavon76, Guna, Densa, K6290, Sulla, Dereselign, and Dure at Aneded in both seasons. Among these varieties, Enkoy and Tsehay were abandoned due to resistance breakdown to stem rust in the 1990s. These two varieties may be reintroduced to production or may be used as sources of resistance to the prevailing races in northwest Ethiopia.