Coefficient Of Infection Research Articles

Identification of Resistance to <i>Puccinia striiformisf</i>. sp. <i>tritici</i> (<i>Pst</i>) in Some Commercial and Elite Bread Wheat Lines

Stripe rust is caused by <i>Puccinia striiformisf</i>. sp. <i>tritici</i> (<i>Pst</i>) threatening wheat production in Ethiopia. The emerged virulent stripe rust races at one point of the world spread to the rest of wheat-producing countries by the wind as well as human travels and damaged popular resistant wheat cultivars thereby posing food insecurity. However, wheat cultivars succumb to new Pst race (s) soon after their release from research centers. This study aimed to determine stripe rust resistance in some Ethiopian commercial and elite bread wheat lines. In 2017, a total of 37 commercial and elite bread wheat lines were exposed to stripe rust in under the disease hot spot areas (Kulumsa and Meraro) Arsi zone Oromia regional state. In the second year (2018), 22 promising lines consisting of 16 commercial bread wheat and 6 elite’s lines were evaluated both at seedling and adult plant growth stages. The seedling test was conducted in the greenhouse at Kulumsa research center using three Pst races. In field evaluations, terminal severity (TRS), coefficient of infection (CI), area under disease progress curve (AUDPC), disease progress rate (DPR), and spike infection (SI) were considered. Of the 37 commercial and elite bread wheat lines, 19 (51.4%) exhibited lower or equal disease reaction compared to the resistant check (Enjoy) across locations and seasons. Eleven bread wheat lines showed both adult plant and seedling resistance. The 37 commercial wheat lines that showed field resistance was further exposed to three Pst races at the seedling stage and 11 exhibited seedling resistance to all races. This study has identified seedling and adult plant resistance in some commercial and elite bread wheat lines to the prevailing Pst races.

Development of infectious clones of mungbean yellow mosaic India virus (MYMIV, Begomovirus vignaradiataindiaense) infecting mungbean [Vigna radiata (L.) R. Wilczek] and evaluation of a RIL population for MYMIV resistance.

Yellow mosaic disease (YMD) is a major constraint for the low productivity of mungbean, mainly in South Asia. Addressing this issue requires a comprehensive approach, integrating field and challenge inoculation evaluations to identify effective solutions. In this study, an infectious clone of Begomovirus vignaradiataindiaense (MYMIV) was developed to obtain a pure culture of the virus and to confirm resistance in mungbean plants exhibiting resistance under natural field conditions. The infectivity and efficiency of three Agrobacterium tumefaciens strains (EHA105, LBA4404, and GV3101) were evaluated using the susceptible mungbean genotype PS16. Additionally, a recombinant inbred line (RIL) population comprising 175 lines derived from Pusa Baisakhi (MYMIV susceptible) and PMR-1 (MYMIV resistant) cross was developed and assessed for YMD response. Among the tested Agrobacterium tumefaciens strains, EHA105 exhibited the highest infectivity (84.7%), followed by LBA4404 (54.7%) and GV3101 (9.80%). Field resistance was evaluated using the coefficient of infection (CI) and area under disease progress curve (AUDPC), identifying seven RILs with consistent resistant reactions (CI≤9) and low AUDPC (≤190). Upon challenge inoculation, six RILs exhibited resistance, while RIL92 displayed a resistance response, with infection occurring in less than 10% of plants after 24 to 29 days post inoculation (dpi). Despite some plants remaining asymptomatic, MYMIV presence was confirmed through specific PCR amplification of the MYMIV coat protein (AV1) gene. Quantitative PCR revealed a very low relative viral load (0.1-5.1% relative fold change) in asymptomatic RILs and the MYMIV resistant parent (PMR1) compared to the susceptible parent (Pusa Baisakhi). These findings highlight the potential utility of the developed infectious clone and the identified MYMIV-resistant RILs in future mungbean breeding programs aimed at cultivating MYMIV-resistant varieties.

Field Screening of tomato breeding lines for improved resistance against Tomato Yellow Leaf Curl Virus (TYLCV)

The tomato represents an extensively cultivated crop within tropical and subtropical regions of the world for their fresh market and processing attribute. However, its production frequently encounters substantial setbacks due to notable losses associated with diseases such as Tomato Yellow Leaf Curl Virus (TyLCV). To address this challenge, the current study aimed to assess the resistance or susceptibility of selected 25 tomato breeding lines for TyLCV under natural field screenings to mimic real-world scenarios in accordance with the disease reaction score of Banerjee and Kalloo (1987). The field screening results showed that, the check Arka Vishes line demonstrated high resistance (HR) to TLCV, with reduced PDS, PDI values and a low coefficient of infection (CI). Several lines, including CBE SL 101, CBE SL 105, CBE SL 108, CBE SL 110, and CBE SL 114, exhibited a resistant (R) reaction, while others, such as CBE SL 102, CBE SL 107, CBE SL 112, CBE SL 120, and Arka Rakshak, displayed moderate resistance (MR). Conversely, lines CBE SL 103, CBE SL 104, CBE SL 106, CBE SL 109, CBE SL 111, CBE SL 115, CBE SL 117, and CBE SL 123 showed moderate susceptibility (MS), and the remaining lines, namely CBE SL 113, CBE SL 116, CBE SL 118, CBE SL 119, CBE SL 121, and CBE SL 122, were deemed susceptible to TLCV. The varying disease responses observed across these lines provide valuable insights into the complex dynamics of host-pathogen interactions in tomato plants, informing strategies for disease management and breeding efforts aimed at enhancing resistance to TLCV.

Biopotential of Cyanobacteria, Fulvic Acid and Nano-chitosan in Controlling Leaf Rust of Wheat

Biocontrol agents, including Cyanobacteria, Spirulina platensis and Nostoc calcicole, as well as Fulvic Acid and nano-chitosan were tested to control leaf rust of wheat under field conditions during 2021/2022 and 2022/2023 growing seasons. All biocontrol agents significantly reduced all parameters for disease severity i.e. coefficient of infection (CI), the average coefficient of infection (ACI) and the area under disease progress curve (AUDPC) compared to untreated control. The best treatments were nano-chitosan which recorded efficacy of 91.17% followed by S. platensis (90.2%) in the application of two sprays for disease control. All biocontrol agents significantly increased grain yield components of wheat. Applications of two sprays were more effective than one spray. From our research work it can be concluded that S. platensis, N. calcicole, Fulvic Acid and nano-chitosan can be used for controlling leaf rust disease as a safe alternative to chemical fungicides.

Genome wide association study for stripe rust resistance in elite spring bread wheat genotypes (Triticum aestivum L.) in Morocco

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases affecting wheat (Triticum aestivum L.) worldwide. Developing and deploying resistant cultivars is the most cost-effective and environmentally friendly method of combating this disease. However, because the pathogen continues to mutate, resistance genes are quickly overpowered by newly virulent Pst races, requiring the continuous identification and introduction of resistance genes to create resistant wheat varieties. To identify closely linked markers for possible use in marker-assisted selection a genome-wide association study was conducted using rust data at adult plant stages for 200 elite spring bread wheat genotypes and 13151 SNP markers. Stripe rust resistance was evaluated under rainfed conditions at the ICARDA Merchouch station in Morocco during the 2019–2020 and 2020–2021 crop seasons. The genotypes were classified into five distinct categories based on the coefficient of infection (CI), 18 genotypes were highly resistant, while 42 were moderately resistant (21%), additionally, 73 were intermediate (37%), while 26 were moderately susceptible (13%), and the remaining 41 genotypes highly susceptible. Thirteen markers were associated with stripe rust resistance through GWAS analysis using a general linear model. Four of these markers for adult plant resistance (Kukri c8390 1515, CAP7 c5481 96, Excalibur c35203 334, and BS00017187 51) on chromosomes 1B, 5B, 3B, and 7B, correspondingly, are of particular importance and could be used for marker-assisted selection to pyramid rust resistance genes in wheat breeding programs.

Genetic analysis and physical mapping of oat adult plant resistance loci against Puccinia coronata f. sp. avenae.

Six quantitative trait loci (QTL) for adult plant resistance (APR) against oat crown rust (Puccinia coronata f. sp. avenae) were identified from mapping three recombinant inbred populations (RILs). Using genotyping-by-sequencing with markers called against the OT3098 v1 reference genome, the QTL were mapped on six different chromosomes, namely: Chr1D, Chr4D, Chr5A, Chr5D, Chr7A, and Chr7C. Composite interval mapping with marker cofactor selection showed that the phenotypic variance explained by all identified QTL for coefficient of infection range from 12.2 to 46.9%, while heritability estimates ranged from 0.11 to 0.38. The significant regions were narrowed down to intervals of 3.9 to 25 cM, equivalent to physical distances of 11 to 133 Mb. At least two flanking SNP markers were identified within 10 cM of each QTL that could be used in marker-assisted introgression, pyramiding, and selection. The additive effects of the QTL in each population were determined using SNP haplotype data, which showed significantly lower coefficient of infection (CI) in lines homozygous for the resistant alleles. Analysis of pairwise linkage disequilibrium also revealed high correlation of markers and presence of linkage blocks in the significant regions. To further facilitate marker-assisted breeding, Polymerase Chain Reaction Allelic Competitive Extension (PACE) markers for the APR loci were developed. Putative candidate genes were also identified in each of the significant regions, which include resistance gene analogs that encode for kinases, ligases, and predicted receptors of avirulence proteins from pathogens.

Exploring Iranian wheat landraces for stripe rust resistance genes and validation of selected genes using molecular markers

Puccinia striiformis Westend. f. sp. tritici Eriksson (Pst), the causal agent of stripe rust, is known as an important and destructive pathogen that causes critical wheat losses in many parts of the world. Employing effective resistant genotypes is a safe and operative strategy to combat the disease. Iran is located in the Fertile Crescent, the co-epicentre of wheat and its biotic stresses. Iranian wheat landraces may carry important sources of resistance against rust diseases. Adult plant reactions of 467 Iranian wheat landraces to stripe rust were studied in two cropping seasons in Fars province. One hundred and six landraces showed acceptable levels of resistance and were selected for further seedling and molecular studies based on their lower infection type, coefficient of infection (CI) and average coefficient of infection (ACI). The presence of Yr4, Yr10, Yr24 and Yr32 resistance genes were postulated using 10 different Pst isolates including PstS10, PstS7, PstS3, PstS2+V27, PstS11, PstS8, PstS13, PstS6, PstS0 and Me2018 under greenhouse conditions. Field and greenhouse reactions of near-isogenic lines reconfirmed the presence of the studied Yr resistance genes in 20 genotypes. Moreover, Xcfb3530 150 , Xpsp3000, Xgwm11, and Xwmc198 SSR markers were employed to identify and validate the presence of the above corresponding genes. The presence of Yr4, Yr10, Yr24 and Yr32 resistance genes in five (1.07%), 10 (2.14%), five (1.07%) and seven (1.5%) experimental landraces were confirmed, respectively. Six genotypes are harbouring more than one resistance gene. These effective resistance sources can be employed in national and international breeding programs.

Identification of genetic immunity to the warrior race and local population of stripe rust using conventional techniques in winter wheat genotypes

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

Evaluation of resistance of Turkish bread wheat (Triticum aestivum) varieties to recently emerged Puccinia striiformis f. sp. tritici races

Using genetic diversity has made significant contribution to stripe rust resistance to improve wheat production. However, rapid evolution of the Puccinia striiformis f. sp. tritici (Pst), and emergence of virulent races can negatively affect the wheat genotypes with race-specific resistance gene(s). In this study, reactions of 130 bread wheat varieties, released from 1931 to 2014, were evaluated to recently emerged Pst races in Turkey, PSTr-6 and PSTr-23, at seedling and adult-plant stages. 65.4% and 67.7% of wheat varieties showed susceptible reaction to PSTr-6 and PSTr-23 at seedling stage, respectively. Moreover, coefficient of infection (CI) values generated by infection type (IT) and disease severity (DS) data demonstrated that PSTr-23 (59.78) was more virulent than PSTr-6 (57.93) at adult-plant stage. In addition to these, the presence of important yellow rust (Yr) genes in these varieties was investigated at molecular level. It was determined that the frequencies of three Yr genes, Yr5, Yr10 and Yr15, among these varieties were 1.5, 6.2 and 3.8%, respectively. However, none of them had Yr36 and only one variety had Yr5+Yr10 combination with frequency of 0.7%. In conclusion, most varieties have not these Yr genes and possess a moderately resistance/susceptible reaction to both races in general.

RECALCITRANCE POTENTIAL OF WHEAT HYBRIDS AND LOCAL CULTIVAR AGAINST YELLOW RUST DISEASE AND WEEDS DENSITY UNDER CLIMATIC CONDITION OF PESHAWAR, KHYBER PAKHTUNKHWA

Wheat cultivars can be severely affected by new race of leaf and stripe rust which possessing Yr27 resistance gene in Pakistan and worldwide during previous four years. Thus, great importance could be given to develop new wheat cultivar that could resist leaf and stripe rust diseases. Yellow rust disease is caused by certain pathogens like basidiomycete fungus Puccina striiformis Westend f. species tritici Eriks, it is one of the most devastating foliar diseases of wheat in Pakistan and worldwide. Two years experiments were conducted in Agronomy Research Farm, The University of Agriculture Peshawar, Pakistan to evaluate the potential response of wheat hybrid lines (18A-1 and 18A-2) in comparison with local check (Ghaneemat-2016) against yellow rust disease.Results exhibited that wheat hybrid 18A-1 depicted resistant (R) with coefficient of infection (CI) of 0.1. Hybrid wheat 18A-2 showed host reaction (10MR) with coefficient of infection (4.0). Contrary to this, local wheat variety (Ghaneemat-2016) showed moderate susceptibility (30MS) type of host reaction with 24 CI value during season 2018-19. A moderate resistant (MR) type of host reaction with CI (16.0) was observed for local variety (Ghaneemat-2016) during season 2019-20. Among wheat hybrids 18A-2 depicted no visible infection while 18A-1 exposed resistant 1R type of host reaction with CI (0.2) during 2019-20.Chinese wheat hybrids have the high potential to resist against yellow rust as compared with local check variety. Higher weeds density, fresh and dry weeds density increased by increasing irrigation frequencyfor local check Ghaneemat-2016 when sown early (15th November). Conclusively, from the study it is statedin wheat breeding program, identification of molecular markers facilitates the marker assisted selection of the resistance genes against yellow rust diseases, furthermore molecular markers should be used for marker assisted permitted that efficiently screening the large population.

English

Production of wheat in Ethiopia is under danger from wheat stem rust, which is brought on by the disease Puccinia graminis f.sp. tritici and has resulted in a yield loss of 100%. An investigation was conducted in a hotspot area (Debere Zeit, Ethiopia) to evaluate the status of Ethiopian durum wheat cultivars for their level of stem rust resistance in the field. During the main seasons of 2017, 2020, and 2021, 34 durum wheat varieties with three susceptibility checks were examined. Terminal Rust Severity (TRS), Coefficient of Infection (CI) and Area under Disease Progress Curve (AUDPC) were used to measure stem rust field resistance. Analysis of all disease parameters was carried out using R studio. Due to their low levels of AUDPC, ACI, and TRS values combined with MR infection type, two commercial varieties (Oda and Tob-66) may have a significant resistance gene(s) and seven varieties (Boohie, Kilinto, Ginchi, Robe, Toltu, Lelisso, and Bekelcha) showed a moderate level of field resistance with MR to MRMS responses and may have adult plant resistance mediated by minor resistance genes. Stem rust was found to affect 73.5% of the Ethiopian durum cultivars. Therefore, this study suggests that the national breeding effort should focus on local durum cultivars rather than the ones that were imported. Key words: Field resistance, durum wheat, stem rust, Puccinia graminis f.sp tritici.

Genetic Variability and Aggressiveness of Tilletia indica Isolates Causing Karnal Bunt in Wheat

Karnal bunt caused by Tilletia indica is a quarantine disease of wheat causing huge economic losses due to the ban on the import of bunted grains. This study was designed to characterize pathogenicity, aggressiveness and genetic diversity of 68 Tilletia indica isolates collected from different geographic regions of Pakistan. Forty-six isolates were tested for their pathogenicity on eight wheat varieties, out of which three were non-aggressive. The coefficient of infection (CI) ranged from 15.73% (PB-25) to 10% (PB-68, PB-60, and PB-43). The isolates collected from central Punjab showed higher infestation compared to other isolates. Among the wheat varieties used for the aggressiveness study, WL-711 showed susceptible reaction with 10.88% CI, while NIFA-Barsat, HD-29, Janbaz, Bakhtawar-92, Tatara, and AARI 2011 showed resistance to the highly resistant response. These isolates were amplified using 31 random amplified polymorphic DNA (RAPD) markers and 32 inter-simple sequence repeat (ISSR) markers for diversity analysis. The principal component analysis (PCA) and analysis of molecular variance (AMOVA) showed greater divergence among isolates collected from Punjab and Khyber Pakhtunkhwa (KPK), with a moderate level of admixture. The isolates from Faisalabad (Punjab) were more aggressive compared to isolates from KPK and were clearly separated based on PCA, indicating the significant genetic distance in the populations. Our findings will assist breeders and pathologists in better understanding the pathogenic variability in Tilletia indica and in subsequent disease management.

Genetic characterization and genome-wide association mapping for stem rust resistance in spring bread wheat

BackgroundEmerging wheat stem rust races have become a major threat to global wheat production. Finding additional loci responsible for resistance to these races and incorporating them into currently cultivated varieties is the most economic and environmentally sound strategy to combat this problem. Thus, this study was aimed at characterizing the genetic diversity and identifying the genetic loci conferring resistance to the stem rust of wheat. To accomplish this, 245 elite lines introduced from the International Center for Agricultural Research in the Dry Areas (ICARDA) were evaluated under natural stem rust pressure in the field at the Debre Zeit Agricultural Research Center, Ethiopia. The single nucleotide polymorphisms (SNP) marker data was retrieved from a 15 K SNP wheat array. A mixed linear model was used to investigate the association between SNP markers and the best linear unbiased prediction (BLUP) values of the stem rust coefficient of infection (CI).ResultsPhenotypic analysis revealed that 46% of the lines had a coefficient of infection (CI) in a range of 0 to 19. Genome-wide average values of 0.38, 0.20, and 0.71 were recorded for Nei’s gene diversity, polymorphism information content, and major allele frequency, respectively. A total of 46 marker-trait associations (MTAs) encompassed within eleven quantitative trait loci (QTL) were detected on chromosomes 1B, 3A, 3B, 4A, 4B, and 5A for CI. Two major QTLs with –log10 (p) ≥ 4 (EWYP1B.1 and EWYP1B.2) were discovered on chromosome 1B.ConclusionsThis study identified several novel markers associated with stem rust resistance in wheat with the potential to facilitate durable rust resistance development through marker-assisted selection. It is recommended that the resistant wheat genotypes identified in this study be used in the national wheat breeding programs to improve stem rust resistance.

Vulnerability studies of okra genotypes to bhendi yellow vein mosaic virus (BYVMV)

India is the leading okra producer globally, but its production suffers due to losses caused by Bhendi yellow vein mosaic virus (BYVMV) disease which is transmitted by whitefly. Due to its unstable resistance nature and limited availability of sources for resistance in cultivated types, the crop improvement programme of okra has not taken a fast pace. In this study, sixty-four distinct genotypes of okra were screened for their resistance to BYVMV under natural epiphytotic conditions of Delhi. It was found that the disease incidence (DI), coefficient of infection (CI), vulnerability index (VI), and adult whitefly count (AWC) varied significantly amongst the different okra genotypes. The highest mean DI was recorded in Pusa Sawani (86.5%) and DI was 0% in the genotypes Pusa Bhindi-5 (DOV-66), DOV-89 and DOV-92. The coefficient of infection (CI) was highest in Pusa Sawani (70.39%). Maximum VI was recorded in Pusa Sawani (83%) and 0% VI in the wild genotypes IC-141040, IC-90560 and cultivated Pusa Bhindi-5, DOV-81 and DOV-92. Similarly, AWC was maximum in Pusa Sawani (30.4) and the lowest number in DOV-26 (1.2). The number of whiteflies peaked at 80 days after sowing and subsequently decreased. Pusa Sawani was the most susceptible genotype and Pusa Bhindi-5 and DOV-92 were the most resistant genotypes based on this study. The resistant genotypes Pusa Bhindi-5 and DOV-92 can be used for the transfer of BYVMV resistance in other susceptible lines or varieties and also for hybrid development in future okra improvement programmes.

English

Stripe (yellow) rust caused by Puccinia striiformis f.sp. tritici, is one of the major diseases of wheat in the world. Development and use of resistant wheat cultivars is the most economical and environmentally friendly solution in combating wheat stripe rust. Field experiments were carried out at two sites in Ethiopia (Kulumsa and Meraro) and seedling tests were conducted at KARC greenhouse during the 2015 cropping season to evaluate the response 192 elite spring bread wheat genotypes and eight checks to the prevailing races of stripe rust at adult plant stage and seedling stage. About 72.5 and 42.5% of the lines exhibited resistance to stripe rust during the field screening at Kulumsa and Meraro, respectively. Disease was more severe at the cooler site Meraro than Kulumsa. Eighteen genotypes at Kulumsa and 16 genotypes at Merao were almost immune to the disease (severity and AUDPC of zero). Seventy-two genotypes (36%) showed resistant reaction at both locations in field condition for adult plant stage (CI < 20). For seedling, 47% for mixed isolates and 31% for kubsa isolates showed resistance reaction responses to stripe rust disease based on coefficient of infection (CI). Key words: Puccinia striiformis, resistance, susceptible, Triticum aestivum, genotypes.

Seedling and Adult Plant Resistance in the Ethiopian Bread Wheat Landraces to Stripe Rust Disease

High yielding farmers’ bread wheat cultivars are threatened by emerging race(s) of stripe (yellow) rust caused by Puccinia striiformis f.sp. tritici (Pst) in the highlands of Ethiopia. In depletion of rust resistance in commercial cultivars, researchers often look for new sources from close relatives and landraces. The objective of this study was to determine stripe rust resistance in selected Ethiopian bread wheat landraces obtained from the Ethiopian Institute of Biodiversity (IBCE). In 2017, a total of 152 accessions were exposed to the prevailing stripe rust races in hot spot areas (Kulumsa and Meraro) in Arsi zone of Oromia region. In the second year (2018), only promising landraces (57) were evaluated both at seedling and adult plant growth stages. The seedling test was conducted in the greenhouse at Kulumsa research center using three (PstS2 (v32), (PstS11) and (PstS11 v25) Pst races. In field evaluations, terminal severity (TRS), coefficient of infection (CI), area under disease progress curve (AUDPC), disease progress rate (DPR) and head infection (HI) were considred. High disease pressure was noted with 100% severity on susceptible entries at both locations and seasons. Highly significant (P<0.001) differences were noted among the landraces for all disease parameters indicated above. Of the 152 landraces, 57(38%) exhibited lower or equal disease reaction compared to the resistant check(Enkoy) across locations. Overall, 18 accessions showed resistance to the prevailing Pst races both at seedling stage and field conditions whereas14 exhibited susceptible /intermediate reaction at seedling stage, but had lower disease reaction under field conditions. This study has identified potential sources of overall and adult plant resistance in the Ethiopian bread wheat landraces to the prevailing Pst races. The authors recommend further studies to determine the diversity and/or novelity of resistance genes in selected accessions. Future wheat improvement should focus on utilization of these genetic resources to minimize the re-current outbreak of rust diseases.

Evaluation of Ethiopian Bread Wheat Cultivars for Slow Rusting Resistance to Yellow Rust (<i>Puccinia striiformis</i> f.s Tritici)

Wheat stripe rust (<i>Puccinia striiformis</i> f.s. <i>tritici</i>) is the greatest vicious rust disease in wheat-growing areas of Ethiopia. The cultivating of cultivars with polygenic gene resistance is the most efficient way of monitoring the disease. Field experiments were carried out at Kulumsa Agricultural Research Center main station and, Meraro and Bekoji substations of Ethiopia during 2019 to 2020 main cropping seasons to disclose variability for field based adult plant resistance to yellow rust among 25 newly developed bread wheat cultivars advanced in Ethiopia. Features used as criteria to identify adult plant resistance comprised response of wheat cultivars to yellow rust, Coefficient of infection (CI), relative final rust severity (FRS) and area under disease progress curve (rAUDPC) were found to be reliable to evaluate slow rusting in the cultivars. The outcomes shown that wheat cultivar only Balcha had low disease severity (< 30%) with MRMS reaction, lower rAUDPC values (>30%) and CI (< 20) and were recognized to have good level of adult plant resistance while eighty eight percent of the tested cultivars exhibited susceptible and grouped under low slow rusting resistance with high disease pressure over all three locations. Cultivars Dashen, Daka, Wane and Sanate had moderate values for slow rusting parameters and were recognized as having moderate level of slow rusting. The slow rusting cultivars identified from the present work can be used for extra management in wheat development programs.

Evaluation of Stripe Rust (&lt;i&gt;Puccinia Striformis&lt;/i&gt; f. sp. &lt;i&gt;Tritici&lt;/i&gt;) Resistance in Bread Wheat (&lt;i&gt;Triticum&lt;/i&gt; &lt;i&gt;aestivum&lt;/i&gt; L.) Genotypes in Ethiopia

Adult Plant Resistance (APR) based on partial resistance is an important and effective way to combat yellow rust (Puccinia striiformis) in wheat production. The objective of current research was planned to evaluate the response of 436 wheat (Triticum aestivum) genotypes against yellow rust resistance under field conditions during 2020 main cropping season. Over locations, Partial resistance screening was evaluated through Final Rust Severity (FRS), Area under Disease Progress Curve (AUDPC), Coefficient of Infection (CI), Relative Area under Disease Progress Curve (rAUDPC) and field reaction have used for differentiating Adult plant resistances. Responses of four hundred thirty six genotypes, one hundred fourteen wheat lines were high adult plant resistance, fifty eight lines were found to be intermediate adult plant resistant and two hundred sixty four were low adult plant resistance over location. With rAUDPC values over location twenty seven were 1-10 shown resistant, eighty seven lines were 11-30 categorized as moderately susceptible and three hundred twenty two genotypes exhibited susceptible response against yellow rust with more than 31-100 rAUDPC value. High values above 31 prcent of rAUDPC showed greater severity of yellow rust on wheat genotypes while lower rAUDPC values indicated resistance to yellow rust. Fifty bread wheat genotypes that were selected based on overall agronomic performance (biomass, spike length, number of spikes/m2, tillering capacity, stalk strength or lodging resistance, shattering resistance and diseases resistance especially yellow rust and Septoria blotch. Three genotypes were EBW192345, EBW192346 and EBW192347 extraordinarily out performed evaluated materials phenotypically in terms of agronomic performance and diseases resistance over locations. The present study revealed that the lines were having enough diversity regarding slow rusting behavior and yellow rust resistance, ranging from immunity to partial resistant lines. Present research provided the resistant wheat lines to the breeders to incorporate in their breeding program against yellow rust.

Identification of Stripe Rust (Puccinia striiformis F. sp. Tritici) Resistance in the Ethiopian Wheat Landraces

Stripe rust is caused by Puccinia striiformis f. sp. tritici (Pst) is threatening wheat production in Ethiopia. Wheat varieties succumb to new Pst race (s) soon after their release from research centers. The objective of this study was to determine stripe rust resistance in selected Ethiopian wheat landraces obtained from the Ethiopian Institute of Biodiversity (IBCE). In 2017, a total of 197 accessions (152 bread and 45 durum wheat land-races) were exposed to the prevailing stripe rust races in hot spot areas (Kulumsa and Meraro) in Arsi zone of Oromia region. In the second year 2018, only promising landraces 103 (69 bread and 34 durum)) were evaluated both at seedling and adult plant growth stages. The seedling test was conducted in the greenhouse at Kulumsa research center using three Pstraces. In field evaluations, terminal severity (TRS), coefficient of infection (CI), area under disease progress curve (AUDPC), disease progress rate (DPR) and spike infection (SI) were considered. High disease pressure was noted with 100% severity on susceptible entries at both locations and seasons. Highly significant (P<0.001) differences were noted among the landraces for all disease parameters indicated above. Of the 103 landraces, 57 (55%) exhibited lower or equal disease reaction compared to the resistant check (Enkoy) across locations and seasons. Thirty two landraces showed both adult plant and seedling resistance. The 103 Ethiopian wheat landraces that showed field resistance further exposed to three Pst races at seedling stage and 61 exhibited seedling resistance to all races. This study has identified potential sources of seedling and adult plant resistance in the Ethiopian wheat landraces to the prevailing Pst races. Future wheat improvement should focus on utilization of these genetic resources to minimize the re-current outbreak of rust diseases.

Assessing winter wheat foliage disease severity using aerial imagery acquired from small Unmanned Aerial Vehicle (UAV)

One of the major goals in all wheat (Triticum aestivum L.) breeding programs is to develop disease-resistant varieties. Unmanned Aerial Vehicles (UAVs) equipped with remote sensors can provide spectral measurements that can be used to assess foliage disease severity. Measurement of disease severity trait during the genotype selection process has always been challenging as it takes a substantial amount of time, cost, and labor to phenotype many breeding lines. This study investigates the potential use of low-cost UAV, equipped with digital cameras as a field phenotyping tool for foliage disease severity in awheat breeding program. A field experiment was conducted in 2017 and 2018 at Castroville, Texas. The experiment site has favorable weather conditions for developing wheat leaf rust (Puccinia triticina f. sp.tritici). Red, Green, and Blue band (RGB) images were acquired by flying rotary-wing UAV. Images were then processed to develop orthomosaics and three vegetation indices were calculated. The obtained image dataset was further processed to generate plot-level data. Visual notes on field response and leaf rust severity were taken to calculate the coefficient of infection (CI). A significant variation in vegetation indices was found among the wheat genotypes in both years. Normalized Difference Index (NDI), Green Index (GI), and Green Leaf Index (GLI) were linearly related to CI with R2 values ranging from 0.72 to 0.79 (p < 0.05) in 2017 and 0.63 to 0.68 (p < 0.05) in 2018. Ground-based Normalized Difference Vegetation Indices (NDVI) also showed a significant relationship with CI in both years (R2 = 0.86, p < 0.05 in 2017 and R2 = 0.83, p < 0.05 in 2018). The results showed that UAVs imaging and automated data extraction can facilitate the acquisition of high throughput phenotyping data for disease severity ratings.