Septoria tritici blotch (STB) is a devastating fungal disease affecting durum and bread wheat cultivation worldwide. The search for resistance sources in untapped genetic resources may speed up breeding for STB resistance. Ethiopian durum wheat landraces represent a valuable source of allelic diversity for several traits, including disease resistance. In this study, we measure STB phenotypes under natural infection on two interconnected populations: i) a diversity panel comprising 318 Ethiopian durum wheat lines, mostly farmer varieties, and ii) a nested association mapping (NAM) population developed from a subset of the diversity panel. Phenology, yield and yield component traits were concurrently measured in the populations. We evaluated the distribution of STB resistance in Ethiopian genetic materials and the relationship existing between STB resistance and agronomic traits. STB resistance sources were found in landraces as well as in NAM lines. The genetic material was genotyped with more than 13 thousand genome-wide SNP markers to describe the linkage disequilibrium and genetic structure existing within the panels. The genotyping information was combined with phenotypes to identify marker-trait associations and loci involved in STB resistance. We identified several loci, each explaining up to 10% of the phenotypic variance for disease resistance. We developed KASP markers tagging the most interesting loci to allow the uptake of our results in a breeding perspective. Our results showed that the Ethiopian untapped allelic diversity bears a great value for studying the molecular basis of STB resistance and for breeding for resistance in local and international material.
Primary Author: Fadda, Bioversity International
Keywords: Ethiopia
Disease surveillance and monitoring has been regularly organized by Wheat Research Centre (WRC), in major wheat growing areas of Bangladesh since 2010-11 to track the current status of common diseases, first outbreak of new disease(s), the pathogen hotspot and identify new virulent races. Besides the paper based traditional survey, scientists of WRC are now using different tools like Smartphone/Tablet with supporting applications. Several trainings were arranged under DGGW project on rust tool box in Bangladesh. Among all smartphone applications, RustSurvey is the easiest and handy application which integrates with the SAARC Surveillance Toolbox.
A disease surveillance program on wheat blast was organized in Mid February 2017 followed by hands on training in collaboration with CIMMYT and CU, USA. Out of 103 sites surveyed, 33 sites were found infected with wheat blast. Overall disease incidence was comparatively lower than the previous season with low disease severity (5-10%). Surveillance program on rust diseases was also conducted in early March 2016. Among 102 rust survey sites stem rust and yellow rust was not found, but leaf rust occurred with varying levels of severity depending on field locations, sowing times and cultivars grown. About 52% of the 102 fields investigated had leaf rust, and almost 73% of the infected fields showed low (<20%), 21% moderate (20-40%) and only 6% showed high (more than 40%) disease severity. Timely (15-30 November) planted crops largely escaped or had less disease compared to those planted late in the season. The predominant cultivar Prodip as well as BARI Gom 25 and 26 showed zero to high disease levels with MSS type reactions. BARI Gom 21, 28, 29 and 30 were free from leaf rust infection. Furthermore, Spot blotch was found in most of the region with low to high level field incidence depending on crop growth stage.
Primary Author: Farhad, Wheat Research Centre, Bangladesh Agricultural Research Institute
Keywords: surveillance
Evaluation of candidate lines to develop resistant varieties at multiplications in Pakistan is a regular activity which has been successfully done for many years. This approach assists in generation of future resistant cultivars around appropriate genes combinations thereby providing durable resistance outputs for wheat productivity. This year, National Uniform Wheat Yield Trial (NUWYT) comprised of 60 candidate lines. Among these 15 lines were also present in the last years NUWYT. The two years data revealed that there was only one line V-12066 resistant to all three rusts during the two consecutive seasons 2015-16 and 2016-17. Four candidate lines NR-487, V-122557, PR-115 and NRL-1123 were found resistant to yellow and leaf rust during 2015-16 and 2016-17. A candidate line DN-111 was found resistant to leaf and stem rust. There were three lines NW-1-8183-8, NW-5-20-1 and MSH which were found resistant to leaf rust only during two consecutive seasons. Similarly, two candidate lines V-122559 and QS-3 were found resistant to stem rust only, while one line NR-443 was resistant to yellow rust only. The present study provide the screening and evaluation system of Pakistan for promoting and releasing the resistant wheat varieties.
Primary Author: Fayyaz, Crop Diseases Research Institute, National Agricultural Research Center, Park Road Islamabad, Pakistan
Keywords: stripe rust, leaf rust, stem rust
P. triticina has a biotrophic relationship with wheat and needs certain elements from the wheat host for a successful life cycle. In recent years, several long lasting, minor resistance genes have been cloned, and their function suggests that the resistance is not due to a classic NB-LRR gene, but a gene that functions in a biotrophic pathway. The hypothesis was proposed that modification of a susceptibility gene can provide broad, long lasting resistance. To test this hypothesis, Thatcher was treated with EMS and screened for changes in susceptibility. M5 lines were evaluated in the greenhouse with BBBD Race 1 and 5 lines were identified. Also, M5 lines were planted in the field to verify the resistance and test the resistance effectiveness to natural infections of P. triticina. The same five lines were resistant in the field. Resistance ranged from few pustules, a race specific-like reaction, lesion mimics with few or no pustules, and near immunity. These lines were backcrossed to Thatcher, and resistant F2 plants were bulked and sequenced. Gene candidates will be identified and discussed.
Primary Author: Fellers, USDA-ARS HWWGRU
Keywords:
Wheat cultivar McNair 701 carries resistance gene SrMcN and is used as a differential line to identify Pgt races using the international letter code nomenclature. The inheritance and location of the resistance gene has not been characterized. We developed a doubled haploid (DH) population from cross LMPG/McNair 701 to study the genetics and chromosomal location of SrMcN. A DH population inoculated with race QCCJB segregated 100 resistant : 94 susceptible, a 1:1 ratio (?2=0.186, P=0.666, NS) indicative of segregation at a single locus. This gene was mapped to chromosome 2DL using the Infinium 90k platform. The map position of SrMcN was similar to that of Sr54, one of two genes previously found in Norin 40. Comparison of stem rust seedling reactions using 12 diverse Pgt races indicated that McNair 701 and an Sr54 line derived from Norin 40 had an identical pattern of responses and similar low infection types (IT=12-) to races LCBNB and QCCJB. Based on the chromosomal location on 2DL and identical seedling responses to Sr54, it is likely that the resistance gene in McNair 701 formerly known as SrMcN is Sr54. This finding will be confirmed by a test of allelism.
Primary Author: Fetch, Agriculture & Agri-Food Canada
Keywords: stem rust
During the past 15 years, significant efforts have been directed to develop the grass species Brachypodium distachyon as a genetically tractable model for monocot plants, especially economically valuable cereals such as wheat, barley and oat. Such efforts have led to an increasing availability of genomic, genetic and bioinformatics tools designed to bypass the experimental challenges faced when addressing important biological questions in complex systems. Moreover, such advances may translate in the use of other valuable species of Brachypodium (e.g., B. hybridum), which are not nearly as well characterized as B. distachyon. Given the 2050 global food demands and needs to increase grain production we seek to develop innovative and sustainable approaches to decrease crop yield losses due to rust fungi. One possible strategy is the use of transgenic plants harboring non-host resistance-related genes from closely related species. B. distachyon and B. hybridum can serve as potential sources to engineer plant resistance against highly destructive rust fungi, such as Puccinia graminis and P. coronata. Advancing our understanding of non-host resistance in monocot species has been a slow process. However, the amenability of Brachypodium as a model system offers a means to accelerate scientific discovery of factors controlling non-host pathogen interactions involving stem and crown rust fungi. In a multi-pronged approach, we are leveraging genetic and genomic tools, as well as generating new resources to provide foundational knowledge in order to support plant genetic engineering programs.
Primary Author: Figueroa, Department of Plant Pathology, University of Minnesota, USA
Keywords: genetics, bioinformatics
Rye stem rust (caused by Puccinia graminis f. sp. secalis, Pgs) causes considerable yield losses in rye crops grown in continental climates. In Germany, stem rust resistance in rye has attracted little attention until now. In order to implement resistance breeding, it is of utmost importance to (1) analyze Pgs populations in terms of diversity and pathotype distribution, and (2) identify resistance sources in winter rye populations. Within a three-year research project, we analyzed 389 single-pustule-isolates, collected mainly from German rye-growing areas, on 15 rye inbred differentials with different avirulence/virulence patterns; among them, 226 pathotypes were identified and only 56 occurred more than once. The majority of isolates infected 5-6 differentials. This high diversity was confirmed by a Simpson index of 0.99, a high Shannon index (5.27) and an evenness index of 0.97. In parallel, we investigated stem-rust resistance among and within 122 genetically heterogeneous rye populations originating from 19 countries across 3 to 15 environments (location-year combinations) in two replicates. While 7 German commercial rye populations were highly susceptible, 11 non-adapted populations, mainly from Russia, Austria and the USA, were highly resistant, harboring 32-70% resistant stems on plots averaged across 8 to 10 environments. Selections for low disease severity at the adult-plant stage in the field also displayed resistance in leaf-segment tests (r=0.86, P<0.01). In conclusion, rye stem rust pathogen populations are highly diverse and the majority of resistances in rye populations are race-specific. The new Pgs isolate set firstly developed within the project covers the current spectrum of virulences and can be used to assess the effectiveness of stem rust resistance genes or sources. New pathotypes can be detected using this differential set and farmers and industry can be alerted to circumvent economic damage. In the long term, resistances from non-adapted populations should be introgressed into commercial rye cultivars.
Primary Author: Flath, Julius Kuehn-Institut, Institute of Plant Protection in Field Crops and Grassland, Germany
Keywords: genetic diversity, stem rust, winter rye
In addition to causing Fusarium head blight of wheat and other cereals, Fusarium graminearum is associated with dozens of wild or weedy grass species. Their role in the disease cycle and evolution of the pathogen has not been established despite their widespread distribution. A three-year survey of wild grasses in New York (USA) found that inflorescences and overwintered stems were frequently colonized by F. graminearum. Through a series of controlled laboratory experiments, wheat and five common grass species were compared for their potential to support inoculum production. Artificially infested stem tissue from several grasses both retained F. graminearum at higher rates through a single winter and supported greater ascospore production per dry gram than wheat. Susceptibility of these species to root and crown rot was measured with a modified seed germination assay and a diverse panel of F. graminearum isolates. Differences were seen between host species, and some grasses were resistant to infection. Our results indicate that wild grass species may support significant F. graminearum inoculum production while differing in their suitability for root and crown colonization. Studying interactions between F. graminearum and alternative host plants can improve our understanding of evolution in a broad host range pathogen and our ability to predict the risk of crop epidemics. We are currently evaluating isolates collected from wild grasses for mycotoxin production and aggressiveness on wheat.
Primary Author: Fulcher, Cornell University
Keywords:
Hexaploid synthetics have become widely used in bread wheat improvement in recent years, enabling the introduction of specific traits as well as enhancing genetic diversity and development of valuable germplasm. This study demonstrated the difference between two groups of primary synthetics in terms of development rate, plant height, rust reactions, and productivity components. During 2015 and 2016, three groups of synthetics were studied in Azerbaijan (3 sites): Baku (0 masl) under irrigated conditions, Gobustan (850 masl) under dry rainfed conditions and Ujar (20 masl) under irrigated conditions with high salinity. Germplasm was also evaluated for diseases and agronomic traits in Omsk (Russia) in 2016.
All primary synthetics were resistant to leaf rust, several to stem rust, and few to stripe rust. Stripe rust occurred in all years at all sites, proving its importance as major wheat pathogen. Its severity reached intermediate levels in Baku in 2016 (33.7%) and in Gobustan in 2015 (26.8%), and epidemic level in Gobustan in 2016 (72.7%). Gobustan also experienced high levels of stem rust in 2016. These two diseases substantially reduced grain productivity in Gobustan in 2016, especially 1000 kernel weight (30.2 g) and grain weight per spike (1.17 g). . Superior genotypes from all three groups were identified that combine high expression of spike productivity traits and stress tolerance index. Five superior synthetics were selected from each of the three groups, based on grain weight per spike. Only four of these demonstrated resistance to stripe rust (entries 13, 15, 31, and 32). Japanese synthetics (group 3) were susceptible to stripe rust but all demonstrated resistance to stem rust. Synthetics from groups 1 and 3 were all resistant to leaf rust when tested under severe disease pressure in Omsk in 2016.
Primary Author: Gadimaliyeva, Genetic Resources Institute, Azerbaijan
Keywords: resistance
Stripe rust of wheat was estimated to cause losses of A$127 m annually in Australia. Although stripe rust can be controlled through the use of chemicals, breeding for resistance is considered to be the best means of control. Identification and characterization of diverse sources of resistance is essential to achieve durable stripe rust control. A common wheat landrace AWCC618 showed resistance (IT 1CN) to Australian Puccinia striiformis f. sp. tritici (Pst) pathotypes. AWCC618 was crossed with the susceptible genotype Avocet S (AvS) to determine the genetic basis of resistance. Seedling tests on 123 AWCC618/AvS F3 families using Australian Pst pathotype 134 E16 A+ 17+ 27+ indicated monogenic inheritance of resistance (22HR:68SEG:33HS; χ21:2:1=3.34, non-significant at P=0.05 and 2 d.f.). The resistance locus was temporarily named YrAW3. Selective genotyping of eight homozygous resistant (HR) and eight homozygous susceptible (HS) F3 families using the 90K SNP Infinium assay tentatively located YrAW3 on chromosome 6A. The AWCC618/AvS population was advanced to F6 for detailed mapping of the target region. YrAW3 appears to be a new locus. AWCC618 was crossed with three current Australian cultivars to transfer YrAW3 to modern wheat backgrounds. Backcross-derivatives will also be useful for validation of linked markers.
Primary Author: Gessese, The University of Sydney Plant Breeding Institute, Australia
Keywords: Australia, stripe rust, genetics
