Wheat is one of the three most important food crops of Nepal for which rusts (Puccinia triticina, P.striiformis and P.graminis) are major biotic stresses. Leaf rust is widespread and causes 14-20% yield losses and speculated that P.triticina over summer on self-sown wheat in hills of Nepal. Twenty two different pathotypes of P.triticina have been recorded while thirteen leaf rust resistant genes (Lr1, Lr3, Lr10, Lr13, Lr14a, Lr16, Lr17, Lr19, Lr23, Lr26, Lr27, Lr31 and Lr34) either singly or in combinations, impart resistance to wheat genotypes in Nepal. Yellow rust is also a major disease in mid and lower hills, river basin and valleys, causing 30-80 % grain yield losses. Twenty-nine pathotypes of P.striiformis have been recorded till now in Nepal while nine Yr genes (Yr2, Yr2 KSA, YrA, Yr6, Yr7, Yr9, Yr27, GA, and SU) have been postulated. Stem rust is a minor and sporadic disease in central, western, mid-western region late in the season. Nine Sr genes (Sr2, Sr5, Sr7b, Sr8, Sr8a, Sr9b, Sr11, Sr25 and Sr31) have been characterized. Vijay was the first Ug99 resistant wheat variety released for cultivation. Previous experiences show that Nepal served as a focal point of wheat rusts for further spread in the Gangetic plains of India due to presence of more than 25 species of Berberis in hills of Nepal. Efforts are underway to survey rusts infection on Berberis spp. Use of Tilt (Propiconazole), Triadimefon (Bayleton) and Indar (RH-124) was found effective to reduce leaf rust as well as foliar blight. Cultivation of resistant varieties in Nepal not only reduces rust severity in this country but also minimizes crop losses in other neighboring countries especially India. This demands the need for regional collaboration in South Asia to combat wheat rusts.
Primary Author: Mahto, Plant Pathology Division, Nepal Agricultural Research Council (NARC), Nepal
Crops vary greatly in their tolerance to heat stress. Among the major staples wheat is considered the most sensitive. Wheat production is severely threatened in many countries by heat stress especially during reproductive and grain-filling stages. For recent decades due to change in global climate, the qualitative and quantitative yield of wheat is affected. To meet the demand of food requirements of ever increasing population there is a need to develop varieties which can tolerate heat stress for which screening of germplasm is pre requisite. In the present study, 30 genotypes were used to check their response to heat stress using randomized complete block design following two different sowing dates. Analysis of variance and multivariate analysis were used for finding important traits and best genotypes in relation to heat stress. High broad sense heritability coupled with high genetic advance was measured for gluten and zeleny indicating the presence of additive gene effect for these traits. Principal component analysis showed that under heat stress conditions genotype 11, 14, 15, 20 and 30 performed well. These genotypes were also found resistant to yellow and brown rust and can be used in further breeding programs for development of heat tolerant, rust resistant genotypes.
Primary Author: Makhdoom, Wheat Research Institute, Ayub Agricultural Research Institute,Faisalabad,Pakistan
In recent years, wheat stem rust, caused by Puccinia graminis f.sp. tritici, has been reconsidered in Iran due to its prevalence and the emergence of the dangerous Ug99 race. This study was conducted to understand pathogenic variation in the population of P. graminis f.sp. tritici, detection of effective genes, and identification of resistance in Iranian commercial wheat cultivars or advanced lines, by planting stem rust trap nurseries under natural disease infection in several regions of Iran during the 2016-2017 cropping season. The trap nursery in each location included 48 wheat lines each carrying a single gene of stem rust (Sr) resistance, seven lines each carrying Sr multigenes, eight additional lines to confirm four Sr genes, 149 commercial wheat cultivars or advanced lines from Iran, plus several susceptible checks. The percentage leaf area affected (disease severity) and infection type were recorded at adult plant stage when disease was well developed on flag leaves of susceptible checks. Results showed presence of virulence for several Sr genes in one or more locations. However, the single genes of Sr13, Sr23, Sr24, and two complex genes of Sr7a+Sr6+Sr12 and Sr6+Sr24+Sr36+Sr1RS-Am were still effective against stem rust in all locations. The results of evaluations of commercial wheat cultivars or advanced lines showed that approximately 16% the genotypes tested including wheat cultivars Gonbad, Shiroudi, Chamran-2, Baharan, Dena, Karkheh, and Arya were resistant in all locations.
Use of large-scale computational resources has permitted the first quantitative study of airborne migration routes of fungal spores between numerous key epidemiological hot-spots of wheat stem rust in Africa, the Middle East and the Indian subcontinent. By coupling a state-of-the-art Lagrangian particle dispersion model (NAME) with mechanistic epidemiological models, we simulate turbulent atmospheric transport of large ensembles of fungal spores from source sites. The models use highly resolved global meteorological datasets from the UK Meteorological Office. We consider release of P. graminis uredinospores from numerous source locations over an 11 year period (2003-2014) and simulate atmospheric trajectories over a 10 km2 spatial sampling grid to elucidate spore deposition rates at national, regional, and continental spatial scales. Our systematic exploration permits the first quantitative perspective and ranking of likely airborne transmission routes of wheat stem rust. We identify migration trends within and between the “Rift valley epidemiological zone”, the Middle East, the Indian Subcontinent, as well as South Africa. Our results indicate (I) consistent seasonal dispersal patterns, (II) likely airborne transmission of stem rust from the Middle East to North-East Africa, and (III) suggest that there is considerable risk of spread of Ug99 or other virulent races from Eastern Yemen to the Indian subcontinent. Model results indicate that over the 11 year study period, viable spore deposition occurred between Eastern Yemen and Pakistan on average 22 days per year during overlapping wheat growing seasons. The validity of the modelling framework has been successfully tested by comparison with survey data from the 2013 epidemic outbreak in Ethiopia, and was recently used as a risk assessment tool to provide rapid response advice in different East-African countries. Known stem rust race distributions are also supportive of the model outputs. The research we have been doing allows a quantitative perspective on likely airborne transmission routes of Ug99 or other virulent races of wheat rust. By that we hope to provide new insights and recommendations for future risk assessment, survey and control strategies and also to contribute to fundamental understanding of epidemiological spread on regional and continental scales. The work we would like to present is the result of a joint effort of Dr Laura Burgin and Dr Matt Hort from the UK Meteorological office, Dr Dave Hodson from CIMMYT, and Dr James Cox, Matthew Hitchings and me from the Epidemiology and Modelling group of Prof Gilligan in Cambridge.
Primary Author: Marcel Meyer, University of Cambridge
Wheat is an economically important food crop in South Africa and production is influenced by a number of diseases caused by fungal pathogens, especially leaf rust, stem rust, stripe rust and Fusarium head blight. The aim of the study is to combine durable rust and FHB resistances into a single wheat line with a high percentage of cv. Krokodil genetic background. Two sets of wheat lines respectively resistant to the three rusts or FHB were developed from different breeding programs at the University of the Free State. These lines were used as parents to combine durable rust and FHB resistance genes/QTL into a single line. Three of the best rust resistant lines were selected as female parents containing rust resistance genes/QTL Lr19, Lr34/Yr18/Sr57, Sr2, Sr26, Sr39 and QYr.sgi-2B.1. FHB resistant BC2F2 and BC2F6 lines were selected as male parents; these lines contained different combinations of Fhb1, Qfhs.ifa-5A-1 and Qfhs.ifa-5A-2. All parental lines were evaluated using molecular markers to confirm the presence of the expected genes/QTL. More than 100 crosses were made between the rust and FHB resistant parents. Since the parents were not homozygous for all markers, leaf material from six-week-old F1 seedlings was collected for marker-assisted selection and to identify the best plants with combined rust and FHB resistances. The best selected lines will be use to develop a backcross population using cv. Krokodil as the recurrent parent. Lines with different combinations of resistance genes/QTL are currently being evaluated in the field to confirm the presence of these genes/QTL.
Primary Author: Mare, Department of Plant Sciences, University of the Free State, South Africa
Wheat contributes directly to food security and the national economy in Nepal. Of the rusts of wheat, stripe rust causes the most frequent and severe yield losses. Race changes can lead to damaging epidemics. To better understand factors that influence regional diversity of the stripe rust and stem rust pathogens, we surveyed rusts on barberry in 2012 and 2013. Nepal has a high diversity of barberry (30 species) and elevational habitats that extend the seasonal distributions of wheat and barberry. The greatest diversity occurs from 2,700 m and above, and distributions range from 1,200 to 4,500 m. We surveyed locations in all regions (central, eastern, western, and far-western) of the hill zone. Barberry was common between 1,300 and 1,800 m where wheat is grown. In the far-western region, barberry was found near all the wheat fields we surveyed. Between 1,300 and 1,800 m, Berberis asiatica is the most common species. B. aristata is present at the upper end of this range. Aecial infections on barberry occurred in patchy distributions in both 2012 and 2013. Collections of aecia on barberry were made at 5 locations and are being identified by inoculation studies using a range of grass hosts. Additionally, the rust samples are being evaluated by real-time PCR assays using species-specific ITS primer/probes for detection of Puccinia graminis or P. striiformis. Preliminary results for 32 single-aecia samples from 2012 were negative for P. graminis; 7 were positive for the P. striiformis complex.
Primary Author: Maria Newcomb, USDA-ARS Arid Land Agricultural Research Center
Since 1998, when Pgt race TTKSK (Ug99) was first identified in Uganda, seven variants in the Ug99 race group have been reported in nine countries in eastern and southern Africa. Five of these variants (TTKSK, TTKST, TTTSK, PTKSK, and PTKST) have been observed in Kenya. Increased surveillance efforts in recent years have enabled detection of new virulence combinations that threaten wheat production. Three new variants in the Ug99 race group were identified from samples collected in 2013 and 2014 in Kenya. A new race, TTHST that is identical to TTKST but avirulent on Sr30 (IT 2-), was identified from a sample collected in the Central Rift Valley Region in 2013. In 2014, two new races, TTKTK and TTKTT, were identified from a total of nine samples (six collected from cv. Robin, and one from each of Eagle10, NJRBW II, and barley) in multiple regions. These two races are of special concern as both are virulent on SrTmp, a gene that is effective against all previously known races in the Ug99 group. Resistance gene SrTmp is postulated to be the source of TTKSK resistance in cv. Robin (released in 2011 in Kenya, also postulated to have Sr2) and cv. Digalu (released in 2005 in Ethiopia). The presence of new races with virulence on SrTmp may explain the high levels of stem rust severity observed in wheat cultivar Robin in Kenya in the past two years. Genotypic relationships between these new races and known races in the Ug99 race group are being characterized using SNP markers. Cultivars and elite breeding lines from Kenya, CIMMYT, and the US are being evaluated for seedling reactions to race TTKTT. With the detection of these new races, there are a total of eight variants in the Ug99 race group in Kenya.
Primary Author: Maria Newcomb, USDA-ARS Arid Land Agricultural Research Center
Leaf rust is an important worldwide disease on wheat caused by the fungus Puccinia triticina. Great infections on durum wheat occurred in Southern Spain in the 2000s but diminished in recent years due to deployment of resistant varieties and application of fungicides by farmers. A leaf rust survey was carried out from the 2009-15 period to monitor the virulence spectrum of the prevailing pathotypes. A total of 84 leaf rust isolates were collected on durum wheat fields. From those, single culture were obtained and used to inoculate a set of 27 differential isolines of the susceptible variety Thatcher. In addition 8 durum varieties with known Lr genes were also included.
The main highlight is that the resistance conferred by the popular Lr14a gene was broke up in 2013, but since then virulence to this gene is not widespread. In total, 23% of the isolates were virulent to the lines containing Lr14a. Lr1, Lr3, Lr3bg, Lr16, Lr24, Lr26, and Lr28 are very effective. Lines carrying Lr2c, Lr10, Lr14b, Lr20, Lr23, and LrB displayed susceptibility to most isolates. The durum varieties Jupare (Lr27+Lr31), Guayacan (Lr61), Storlom (Lr3+) and Camayo (LrCam) are also resistant against all isolates tested. Diversification of Lr genes is needed in the coming varieties to delay the appearance of new virulent races.
Primary Author: Martinez-Moreno, University of Seville
The recent emergence of new widely virulent and aggressive strains of rusts (particularly stripe and stem rust) is threatening Italian durum wheat (Triticum turgidum L. var. durum) production, especially under the trend of higher temperature and humidity. A big effort has been undertaken to explore the genetic variability for resistance to these fungal pathogens and discovering novel resistance genes. In particular, a wide set of tetraploid wheat lines was genotyped with several thousands of SNP markers and used for association mapping. This large collection consisted of a group of durum wheat cultivars, produced from the beginning of the last century up to now, a collection of wild emmer wheats (T. dicoccoides), and lines belonging to other wild and domesticated tetraploid subspecies, as a large untapped source of genetic diversity. In a tight cooperation with the University of Minnesota, this collection was evaluated for reaction to several races of stem and stripe rust pathogens in both controlled greenhouse and field conditions. Among the genotypes belonging to the collection are parents of segregating populations which were used for the validation of mapping results. Novel resistance loci were identified, that can be incorporated into new durum varieties through breeding programs. The QTLs found in this study, together with those available in literature, were projected to the recently sequenced durum wheat genome in order to define more precisely the chromosome regions and candidate genes involved in resistance to rusts. Lines which were resistant to multiple races of rust pathogens were also found among both T. dicoccoides and durum wheat cultivars as a source of resistance genes, whose cloning will be undertaken based on the results here obtained.
This study was supported by the Italian Ministry of Foreign Affairs and International Cooperation, with the special grant RES-WHEAT.
Primary Author: Mastrangelo, CREA-Research Centre for Cereal and Industrial Crops
Leaf rust disease, caused by the fungal pathogen Puccinia triticina, is a major biotic constraint of wheat production worldwide. Genetic resistance is the most effective, economic, and environmentally safe method to control and reduce losses caused by this disease. More than 70 leaf rust resistance genes have been identified and mapped to specific chromosomes; however, continuous evolution of new leaf rust races requires constant search for new sources of resistance with novel QTL/genes. The objectives of this study were to identify sources of resistance, and to map genomic loci associated with leaf rust resistance using genome wide association study (GWAS) approach. Phenotypic evaluation of 297 spring wheat genotypes against a prevalent race of leaf rust in Georgia revealed that most of the genotypes were susceptible, and only 24 genotypes were found resistant. Furthermore, GWAS detected 10 markers on chromosomes 2A, 2B, 6A, 7A, and 7B significantly associated with leaf rust resistance. A marker on chromosome 7AS was identified revealing a novel genomic region associated with leaf rust resistance. The new identified sources of resistance and QTL could be used in wheat breeding programs to improve leaf rust resistance.
Primary Author: Mergoum, The University of Georgia (UGA)