Seed & Plant Improvement Institute (SPII), AREEO, Karaj, Iran
Ramin Roohparvar, Safarali Safavi, Gholamhossein Ahmadi
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.
Jianping Zhang, Peng Zhang, Robert Park, Narayana Upadhyaya, Robert McIntosh, Sambasivam Periyannan, Brande Wulff, Burkhard Steuernagel, Evans Lagudah
Evolution of rust pathogens continues to pose challenges to global wheat production. Major resistance (R) genes, which encode proteins of the NBS-LRR (Nucleotide-binding site, leucine-rich repeat) family, have been a valuable resource for breeders to minimise yield losses from infection. Many wheat varieties harbor numerous R genes that could be identified and cloned in order to engineer more sustainable disease control. The advent of targeted gene enrichment and next-generation sequencing (NGS) has allowed rapid cloning of specific R genes, thus enhancing efforts to pyramid these genes and investigate their underlying resistance mechanisms. Several R genes present different phenotypes in certain genetic backgrounds, and cloning them would be an important step towards uncovering their interactions. Hybrid necrosis is one such phenotype observed in crosses of wheat genotypes involving the R gene Lr13 and complementary genes, Ne1 and Ne2, occurring in different allelic forms. It was recently concluded that Lr13 and an allele of Ne2 are actually the same gene based on genetic and mutational studies. The capability of Lr13 to confer both leaf rust resistance and hybrid necrosis cannot be answered without first cloning it. The lack of tightly linked markers coupled with the proximal 2BS chromosomal location of Lr13 does not make it easily amenable to map-based cloning. The NGS-based pipeline MutRenSeq (mutagenesis and R-gene enrichment sequencing) was used on EMS (Ethyl methanesulfonate) induced, susceptible Lr13 mutants along with support from comparative genomics to ascertain candidate gene sequences for Lr13, which are at advanced stages of screening and confirmation. Definite proof that a single gene is involved will only come with transformation studies when the cloned Lr13 candidate transformed into a susceptible line confers both a resistance phenotype in the transgenic line and a necrotic phenotype in the offspring of crosses between the transgenic line and a line possessing Ne1.
Chris K. Sørensen, Rodrigo Labouriau, Annemarie Justesen, Mogens Hovmøller
Host vernalisation and temperature strongly affect the susceptibility of winter crops to pathogenic fungi. However, how the interaction of these environmental factors influence host susceptibility to Puccinia striiformis, the yellow (stripe) rust fungus, is poorly understood. An experimental system was developed to examine the effect of vernalisation, temperature regime (standard; 18 day/12 night °C and low; 12 day/6 night °C) and plant growth (seedling and adult plant stages) on changes in susceptibility of agronomically important winter wheat and triticale genotypes to P. striiformis races ('Warrior' and 'Kranich') highly predominant in several European countries. Host genotypes exposed to prolonged periods of low temperature, termed vernalisation, reduced disease susceptibility on specific winter host genotypes, although its effect differed considerably by the temperature regime and the P. striiformis race deployed. The influence of vernalisation on host susceptibility was more apparent at low temperature for the 'Warrior' race and at standard temperature for the 'Kranich' race. Triticale genotypes inoculated with the 'Kranich' race were particularly affected by the influence of vernalisation and temperature regime by displaying a shift towards reduced susceptibility at standard temperature. The effect of plant growth stage, i.e., vernalised seedlings versus adult plants, was most evident for the 'Warrior' race at standard temperature and at low temperature for the 'Kranich' race by revealing a lower infection type at the adult plant stage. The research findings presented here contributed to a better understanding of the role of environmental factors in host susceptibility. This, in fact, will aid in the development of more efficient early-warning systems and disease management strategies to the yellow rust fungus and in the decision making for the deployment of winter wheat and triticale genotypes.
National Agronomic Institute of Tunisia
Sana Kamel, Elhem, Elfahem, Wissal Feriani, Hanen Sbei
In order to identify sources of resistance to tan spot caused by Pyrenophora tritici-repentis, 359 local wheat accessions were evaluated for reaction to the Oued-Mliz isolate in controlled conditions and in the field. Two and three assessments were carried out at the seedling and adult stages, respectively. There was a highly significant accession effect and 4.2% of accessions were highly resistant in both controlled conditions and the field. Assessments at the seedling stage were positively correlated with each other, and assessments in the adult stage were also positively correlated. However, assessments at the seedling stage were negatively correlated with those at the adult stage. One hundred and fifty five accessions with known origins (from 15 localities belonging to four districts) were projected on a graph defined by the two axes: reactions at the seedling stage and reactions at the adult stage. After placing the average reactions at the seedling and adult stages on the graph, four groups of accessions were obtained: accessions that were resistant to both stages, accessions that were resistant at the adult stage only, accessions that were resistant at the seedling stage only, and accessions that were susceptible at both stages. All four groups were found in each district. However, considering localities, reactions of accessions were highly variable. For example, accessions originating from Menzel Hbib were genetically variable and were represented in each of the four groups, whereas accessions from Sidi El Hani were all resistant at both stages. Further work is needed to study the genetic variability within and between localities and to better understand the resistant accessions.
Northwest A&F University
Dejun Han, Jia Guo, Manuel Spannagl, Jianhui Wu, Aizhong Cao, Peidu Chen, IWGSC, Lili Huang, Jun Guo, Klaus Mayer, Zhensheng, Kang
Wheat cultivation in many regions faces threats by devastating fungal infections. However, wheat cultivar 92R137 shows resistance to Puccinia striiformis infection. To isolate the stripe rust resistance gene Yr26, an integrated transcriptomic and comparative genomics approach was undertaken. Near-isogenic lines of wheat (carrying Yr26 or not) infected with two Puccinia striiformis f. sp. tritici (Pst) (Virulence or avirulence to Yr26) were analysed in a dual detailed time series RNA-seq study. The emerging IWGSC refseq v1.0 genome assembly sequence serves as a valuable template and was also used for comparative genomics studies of the gene candidate region with the genome sequences of close relatives and wheat progenitors. Using bulked segregant analysis (BSA) to identify polymorphic SNPs between parent and resistant DNA (R-bulk) and susceptible DNA (S-bulk), flanking markers for Yr26 were identified. These two markers were mapped to the Chinese spring reference genome sequence, spanning a region of about 250 kb. The synteny analysis of this candidate region in CS chr1B with chr1A, chr1D, Wild Emmer Wheat (Td_chr1A and Td_chr1B) and Barley (chr1H) identified three candidate Yr26 genes. To detect gene candidates a dual time series RNA-seq analysis was performed. Genes differently expressed between rust susceptible (NIL-S) host lines and rust resistant (NIL-R) lines, carrying the Yr26 candidate gene were analysed. Both lines were inoculated with Pst carrying different avirulence factors (Pst-CYR32 and Pst-V26), compatible or incompatible with the corresponding wheat lines. Differential gene expression analysis (DEG) between compatible and incompatible interaction revealed DEGs in the wheat genome and in the Pst genome. From a network analysis of both wheat and Pst genes, we inferred connected co-expressed modules. Resulting modules showed particular enrichments for disease resistance, defense response to fungus and cell wall components.
Ayele Badebo, Abebe Atilaw, Habtemariam Zegeye, Zerihun Tadesse, Wasihun Legesse, Terefe Fitta, Dawit Asnake
In Ethiopia, quality seed of improved varieties is the least expensive and most critical input for the sustainable production of wheat, a strategic food security crop grown by some 4.7 million households on 1.7 million hectares. Because wheat is self-pollinated, farmers can save and replant seed from their harvests for several years, without the variety losing its genetic identity. At the same time, recommended seed rates for wheat (150 to 200 kilograms per hectare) are significantly higher than those for tef (15 kg/ha) or maize (25 kg/ha), so some 255,000 tons of seed is required to sow Ethiopia's entire wheat area each year. Most of this still comes from informal seed systems; only four seed enterprises (ESE, ASE, OSE and SNNPSE) currently produce certified seed of various crops and they lack the capacity to supply enough high quality seed for the nation's approximately 20 million households. In collaboration with the Ethiopian Institute of Agricultural Research (EIAR) and through the USAID-funded project "Seed multiplication and delivery of high-yielding rust resistant bread and durum wheat varieties to Ethiopian farmers," the International Maize and Wheat Improvement Center (CIMMYT) is working to increase wheat farmers access to affordable, certified seed of improved varieties that are high-yielding and also feature durable resistance to the rust diseases. Approaches pursued include the fast-track evaluation and release of improved varieties, the pre-release or accelerated seed multiplication of released wheat varieties through formal and informal seed systems, and demonstrations and scaling up of improved wheat varieties. This paper describes best practices to address seed shortages faced by wheat farmers in 53 woredas.
Mohammad Kassem, Ghinwa Lababedi, Naim Al-Husien
Leaf rust is the most common rust in wheat production areas of Syria and causes significant annual yield losses. Using genotypes with durable resistance is the most economical way of controlling the disease. One of the best-known leaf rust resistance genes is Lr46 that confers a slow rusting type of adult plant resistance. The main objective of this study was to identify Lr46 in durum wheat genotypes using morphological and molecular markers. Thirty-two durum wheat genotypes were evaluated for response to leaf rust at the seedling and adult plant stages. Twelve genotypes (37.5%) were resistant (R), 10 (31.25%) were moderately resistant (MR), seven (21.87%) were moderately susceptible (MS), and three (9.37%) were susceptible (S). Molecular marker analyses using SSR marker wmc44 showed that 16 genotypes (50%) carried Lr46/Yr29. The genotypes possessing the marker linked to Lr46/Yr29 could be used for selection of Lr46/Yr29 in breeding for slow rusting resistance in durum.
The University of Agriculture, Peshawar, Pakistan
Muhammad Khan, Muhammad Imtiaz, Zahoor Swati, Annemarie Justesen, Sajid Ali
Yellow rust caused by Puccinia striiformis is an important disease in Pakistan. The population structure of P. striiformis in the North Eastern Himalayan region of Pakistan have been shown to be genotypically diverse with potential role of sexual recombination (Ali et al., 2014b), while lesser diversity in the Southern districts of Khyber Pakhtunkhwa (KP)(Khan et al., 2015). This study was designed for the first time to assess disease status and analyze population structure of P. striiformis across three distant parts of Northwestern Pakistan i.e., Bajaur in North Western Agency and Swat and Buner in Malakand Agency, and was compared with other Pakistani populations. Depending on the intensity of infections caused by the pathogen in the tested varieties and breeding lines, the severity of the disease ranged from 5% to 100% during 2015. Yellow rust severity was the maximum on Morocco (100%), Gomal (100%) and KPWYT-18 (80%) and moderate on Ghanimat-e-IBGE (10%) and PS-2008, PS-2013, Tatara and Millat with 20% severity. A total of 81 single lesion samples collected on infected varieties were genotyped with 18 microsatellite markers. From these, 63 distinct multilocus genotypes (MLGs) were detected; 15 single lesion samples collected from Buner produced 15 distinct MLGs signifying very high diversity. A high genotypic diversity with clear signature of recombination was detected across all the three locations. Buner (100%) had the maximum diversity followed by Swat (97%) and Bajaur (91%). The observed diversity was almost equal to other Northeastern Himalayan populations of Pakistan, while it was high when compared to some southern populations of KP (genotypic diversity of 0.895) and other worldwide clonal populations (Ali et al., 2014a). The high diversity and recombinant population structure suggested potential role of sexual reproduction in these areas, which needs to be further explored to establish the origin of diverse virulence pattern in Pakistan.
Ayub Agricultural Research Institute, Faisalabad
Different biotic and abiotic stresses are hampering wheat yield across different geographic regions. Among biotic stresses, wheat rusts are principal cause of yield reduction. Whereas among abiotic stresses, drought is the principle cause of reduction in growth and lowering yield potential. So developing rust resistance and drought tolerance in wheat germplasm is needed, which requires assessment of genetic potential of current cultivars against these stresses to identify variation among existing germplasm. Screening of genotypes under naturally prevailing races of rust species is the better and inexpensive approach. In the present study 65 genotypes including five checks (AARI-11, Chakwal- 50, Aas- 11, Morocco and Galaxy-13) were evaluated for adult plant response to wheat rusts and water deficit conditions. Experimental material was planted in four blocks each having new entries along with repetition of five checks in augmented design. Data was recorded on morphological traits including plant height, peduncle length, spike length, productive tillers per meter, flag leaf area, number of spikelet per spike, grains per spike, single head weight, 1000 grain weight, days to maturity and grain yield per acre. Significant variation was observed among genotypes for all the studied traits. On the basis of performance G39 and G36 were better than commercial drought check Chakwal-50 in almost all the traits. However rust screening under natural rust infestation revealed that although Morocco showed susceptible (S) response yet only six genotypes were susceptible to yellow rust whereas all others were resistant. In case of leaf rust 29 were completely resistance, 25 were moderately resistant, seven were moderately susceptible and only four were completely susceptible to currently active races of leaf rust. However, in the case of stem rust, 61 genotypes showed complete resistance to stem rust, two showed moderately resistance and two were moderately susceptible. Information obtained from this study would be favorable for breeding rust resistant and drought tolerant cultivars.
University of Seville
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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.