The features of wheat rust development and the resistance of local cultivars in Kazakhstan
Kazakh Research Institute of Plant Protection and Quarantine, Kazakhstan
The climatic conditions of Kazakhstan are suitable to grow the high-quality grain of spring wheat on an area of 12-14 mil.ha. The country’s sharply continental climate limits the wheat yield as well as biotic stresses. Among latter factors, diseases significantly reduce yield up to 25% and more during epyphytoties. In the Northern Kazakhstan the considerable threat for common wheat comes from leaf rust (Puccinia triticina), stem rust (Puccinia graminis), septoria (Stagonospora nodorum, Septoria tritici), and tan spot (Pyrenophora tritici-repentis); yellow rust (Puccinia striiformis) infects wheat plants in the South and South-east regions, where the winter wheat is more common. Epiphytoties of leaf rust were observed in 2000, 2002, 2005, and 2007. Many years research has led to conclusion that local wheat varieties do not possess resistance to mentioned diseases. Last year screening of 46 cultivars at Kostanay province designated virulence to local pathotypes, except of couple of them (Kazakhstanaskaya 19 and Karabalykskaya 20). Russian varieties (Omskaya 37, Omskaya 39, Omskaya 41, Uralo-sibirskaya, Pamyati Mayestrenka, Lyubava, and Altayskaya zhnitza) demonstrated “slow rusting”. In the period of 2001-2014 the effectiveness to leaf rust was identified using Thatcher isogenic lines under northern Kazakhstan conditions and showed avirulence to local Pt pathotypes in lines carrying Lr9, Lr24, Lr29, Lr35, and Lr37 as well as the pyramid of Lr genes and/or “slow rusting” genes. The essential spread of stem rust was recorded in 2007, 2008, 2013, and 2014. Taking into account the absence of local sources of infection. In addition, the monitoring of pathogen with use of a set of lines with Sr genes detected the absence of aggressive race within north of Kazakhstan. In order to create resistant cultivars the sources of resistance are recommended to apply from current study.
Identification of slow stripe rusting wheat genotypes
Indian Institute of Wheat and Barley Research (IIWBR), India
Stripe or yellow rust is a constraint to wheat production on about 12.8 m ha in the Northern Hills and North Western regions of India. Varieties resistant at the time of release become susceptible usually within a few years due to new pathogen races. The present study conducted in 2013-14 was undertaken to identify slow stripe rusting genotypes among a panel of 192 advanced breeding lines and popular cultivars. All genotypes were planted in two replications and a susceptible control was planted after every 20 plots. The nursery, grown at Karnal, was inoculated with a mixture of prevalent Pst races 78S84 and 46S119. Genotypes were categorized into distinct groups based on area under disease progress curve (AUDPC) values, viz. 22 lines with AUDPC values 1-100, 18 lines with values 101-200, 43 lines with values 201-500, and remaining lines with higher values. Apart from rust-free lines assumed to carry all-stage resistance genes, lines with AUDPC values of less than 500 and having AUDPC values <20% of those of the susceptible check (maximum AUDPC value, 2500) were considered to be slow rusting. Some of the popular cultivars (HS 507, HS 542, WH 1105, HD 3086, DPW 621-50, HD 3059) currently grown in northern India showed slow rusting. The information generated can be utilized in improving the levels of stripe rust resistance in current cultivars.
Gene-assisted selection using a pedigree dissection approach to identify Yr genes in wheat breeding materials
Safiabad Agricultural Research Center, Iran
Yellow rust is the most dangerous of the wheat rusts worldwide. Disease management involves breeding and fungicide application, with the former being more cost effective and environmentally acceptable. Despite the release of numerous yellow rust resistant cultivars in many countries, new aggressive strains inevitably overcome the resistances in a zigzag or ‘boom and bust’manner. For example, Chamran (Attila-50-Y), released in 1997 in Iran, immediately became the most popular cultivar nationally. In 2012-2013, a new aggressive Pst strain overcame the resistance in Chamran as well as Vee/Nac (an early maturity line suitable for the wheat-maize cropping system) in Khuzestan, a major wheat-producing region in the southwest of the country. Evaluations of wheat germplasm at the Safiabad Agricultural Research Center (North Khuzestan) identified 17 completely or partially resistant lines. Pedigree analyses of resistant lines identified Batavia, Genaro 81, Opata, Pastor, Trap and Yaco as possible sources of resistance. Genotype information of these cultivars obtained from the http://wheatpedigree.net/ database indicated the presence of Yr33, Yr30+Yr18 and Yr31 in Batavia, Opata and Pastor, respectively. Genaro 81, Trap and Yaco carry Yr18. Currently, F2 populations of 34 crosses of 17 resistant lines to locally adapted cultivars Chamran and Vee/Nac are undergoing field selection in a nursery inoculated with the 2012-2013 aggressive race. The progenies of selected plants will undergo further testing and selected homozygous F3 lines will be genotyped for markers associated with Yr18 (Xgwm295-7D), Yr30 (flanking markers Xgwm533.1 - Xgwm493-3B), Yr31 (Xgwm630/Xgwm374-2B (Lr13/Lr23)) and Yr33 (flanking markers Xgwm111 - Xgwm437-7D).
Cytogenetic analysis and molecular mapping of inheritance of resistance in barley to Puccinia striiformis
The University of Sydney, Plant Breeding Institute, Australia
Plants are generally non-hosts to most diseases. Barley is a host to Puccinia striiformis f. sp. hordei, but is a near non-host to P. striiformis f. sp. tritici (Pst) and to P. striiformis f. sp. pseudohordei (Psp), which cause stripe rust on wheat and barley grass (Hordeum murinum, H. leporinum), respectively. This study was carried out to determine the inheritance of resistance in barley line 81882/BS1 using the mapping population: 81882/BS1/Biosaline-19. 81882/BS1 is a H. vulgare derivative of cv. Vada
, carrying an introgression from H. bulbosum on chromosome 2HS, and Biosaline-19 is susceptible to both Pst and Psp. Phenotyping of F3 lines with Psp culture 981549 and Pst pathotype 134 E16 A+ showed that 81882/BS1 carried two genes for resistance to Psp, and three genes for resistance to Pst. Cytogenetic analysis and molecular mapping were performed to further characterize the resistance of 81882/BS1 to Psp. Joint phenotypic and cytogenetic analysis indicated that at least one of the genes for resistance to Psp was associated with the H. bulbosum introgression previously located on chromosome 2H (Zhang unpublished). Preliminary molecular mapping of 15 non-segregating resistant and 15 non-segregating susceptible lines using >10K DArTseq molecular markers located the second gene on chromosome 1H. This gene was probably contributed by Vada. Further studies are underway to confirm the locations of these two loci by fine mapping.
Determining the breeding value of CIMMYT’s International Bread Wheat Nursery (IBWSN) entries for leaf, stem and stripe rust resistance
Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, USA
The quest for durable rust resistance in wheat is burgeoning with the emergence of new virulent races. Breeders challenged with this unceasing plant-pathogen arms race have to devise strategies for effective evaluation and exploitation of the rust resistance genes. Considering the likely presence of useful variation for rust resistance in CIMMYT’s international bread wheat screening nurseries (IBWSN), we implemented genomic prediction in the 45th and 46th IBWSN entries to determine their genomic estimated breeding values (GEBV’s) for leaf, stem and stripe rust resistance. The 350 lines (45th IBWSN) and 329 lines (46th IBWSN) were phenotyped in replicated trials over two to three years in El Batan, Mexico (leaf rust); Njoro, Kenya (stem rust) and Toluca, Mexico (stripe rust). The filtered genotyping data for these two nurseries comprised of 6,786 and 11,218 genotyping by sequencing (GBS) markers. Our objective was to compare the GEBV’s estimated by four different models: multiple linear regression (MLR) with QTL-linked markers as fixed effects; Genomic-best linear unbiased prediction (G-BLUP); G-BLUP mixed model which includes QTL linked markers as fixed effects and Bayesian least absolute shrinkage and selection operator (LASSO). We observed that the prediction accuracies (calculated using 10-fold cross validation) were the highest for stripe rust (0.52 to 0.61), followed by stem rust (0.42 to 0.65) and leaf rust (0.15 to 0.45). Among the models, the MLR gave the lowest prediction accuracies (0.15,0.42 and 0.52), while G-BLUP (0.45,0.59 and 0.59), mixed G-BLUP (0.38,0.65 and 0.62) and the Bayesian LASSO (0.45,0.58 and 0.61) yielded relatively higher and almost similar accuracies. Overall, our results are promising and indicate that using genome-wide markers is advantageous than including only significant QTL-linked markers. We hope that implementing genomic prediction in breeding programs, would help to achieve rapid gains from selection and revolutionize our efforts in combating the rust pathogen.
Expression of adult plant resistance to stripe rust in selected Australian wheat genotypes
The University of Sydney, Faculty of Agriculture and Environment, Plant Breeding Institute, Australia
Wheat stripe rust can be managed using adult plant resistance (APR). Knowledge of the growth stage at onset of APR is crucial for integrated management of this disease. Wheat varieties Annuello, Baxter, EGA Kidman, GBA Sapphire, Janz, Kennedy, Livingston, Spitfire, Sunstate, Sunvale, Wyalkatchem, Yitpi, and Avocet NILs carrying Yr18 and Yr18+29, all carrying adult plant stripe rust resistance, were compared for expression of APR under greenhouse conditions. Weekly plantings of all genotypes and susceptible controls Mace and Morocco permitted simultaneous comparisons of infection at the seedling, tillering, jointing, flag leaf, and head emergence stages. Ten replicates of each genotype at the five different growth stages were inoculated with Pst pathotype 134 E16,A+,17+,27+. Percentages of leaf area affected by stripe rust and host response were recorded at 14, 17, 20, 24, 28 and 31 days post inoculation to establish the latent period. With one exception all genotypes including the controls showed latent periods of less than 14 days when inoculated at the seedling, tillering and stem elongation, or jointing growth stages; Spitfire had a latent period of more than 17 days when inoculated at jointing. At the flag leaf and head emergence stages, all genotypes except the controls Mace and Morocco had latent periods of greater than 20 days. The results indicate that the onset of APR in Spitfire was earlier (at jointing) than the other genotypes, and that the resistance remained effective until head emergence and beyond. The information generated shows the importance of information regarding stripe rust development within specific wheat genotypes, and in supporting decisions on chemical intervention to control this disease.
Genetic diversity among Puccinia graminis f. sp. secalis and winter rye populations
Julius Kuehn-Institut, Institute of Plant Protection in Field Crops and Grassland, Germany
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.