Towards understanding the molecular mechanisms of heat stress tolerance, we have analyzed heat stressed substractive cDNA libraries and undertaken genome-wide transcriptome exploration for genes associated with spike photosynthetic efficiency during thermal stress. The photosynthetic efficiencies of Aegilops tauschii and Ae. speltoides were also compared. While the former displayed nearly complete recovery of PSII, the adverse effect was more pronounced in the latter. Functional characterization of heat stress-associated transcription factors and thermal stress-associated proteins was also undertaken e.g. TaHSF, TabZIP, TaZnF and TaMIPS, and TaLTPs in the Indian wheat germplasm. Functional characterization of the three heat stress transcription factors was upregulated under high temperatures and other abiotic stresses. They also showed early flowering and better performance with respect to their growth and yield after heat stress. Additionally, we have identified various interacting components associated with thermal stress-mediated plant signaling partners during thermal stress.
Primary Author: Khurana, University of Delhi South Campus, New Delhi
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Wild emmer wheat (Triticum dicoccoides, (DIC)) is an important source of resistance to stripe rust due to presence of Puccinia striiformis in its natural habitats with high humidity and relatively low temperatures that are favorable for stripe rust development. Previously, we showed that DIC accessions from northern Israel were highly resistant to stripe rust. According to the rust responses of three DIC accessions (G25, H52, G303) and mapping of the resistance to relatively close, but different, genetic positions on chromosome 1BS, three different resistance genes were assumed to be present. However, the development of additional critical recombinants and new higher resolution genetic maps for these three genes in subsequent work led us to place YrH52 and YrG303 in the same genetic interval as Yr15, suggesting that the three putative genes are allelic or identical. The recent cloning of Yr15 allowed us to test this hypothesis using an EMS mutagenesis approach. We sequenced the Yr15 locus in five yrH52 and three yrG303 susceptible mutants and identified missense point mutations associated with the susceptible phenotype in each one. Thus, YrH52 and YrG303 may not be new genes. Further work is under way to determine if these genes are allelic or identical.
Primary Author: Klymiuk, Institute of Evolution and the Department of Evolutionary and Environmental Biology, University of Haifa, Israel
Keywords: stripe rust, resistance genes
Wheat rust diseases are a major cause of yield losses of this crop. Yellow (Puccinia striiformis f. sp. tritici) rust is of the most widespread and dangerous disease of wheat and is the major factor that adversely affects wheat yield and quality. The use of genetic host resistance is the most effective, economical and environmentally safe method of controlling stripe rust that allows elimination of fungicides and minimize crop losses from this disease. Due to the threat of the development of epiphytoties of rust disease it is necessary to identify new donors of resistance to yellow rust and to develop resistant wheat breeding material. In the present study, attention was drawn to the effective yellow rust resistance genes Yr5, Yr10 and Yr15, which were identified in the process of molecular screening of wheat germplasm. Genetic analysis using S23M41 molecular marker linked to Yr5 revealed the presence of this gene in 17 out of 136 promising lines. Thirteen genotypes screened with Xbarc8 generated the DNA fragment associated with Yr15. Three advanced lines with Yr10 were identified using the SCAR marker. Three lines carrying two Yr genes (Yr5 and Yr15) were detected. Combination of Yr5 and Yr10 were found in 15 wheat lines. We identified a number of wheat genotypes highly resistant to stripe rust, which could be further evaluated to release new resistant varieties or to be used in the breeding program.
Primary Author: Kokhmetova, Institute of Plant Biology and Biotechnology
Keywords: molecular markers, resistance genes, stripe rust
The leaf rust pathogen, Puccinia triticina is widespread across all major wheat growing regions worldwide. Collections of P. triticina were obtained from common and durum wheat in North America, South America, Europe, South Africa, the Middle East, East Africa, Russia, Central Asia, China, Pakistan and New Zealand in order to determine the genetic diversity within each region and genetic relationship between regions. A total of 831 single uredinial isolates were characterized for virulence to isogenic lines of Thatcher wheat and for molecular genotype at 23 SSR loci. The isolates in East Africa and Europe were the most diverse for the average number of effective alleles per locus, while the populations in Russia and North America were the least diverse. The isolates in Europe and South America had the highest number of multilocus genotypes of 81 and 75, respectively, and were the most diverse for Shannon's genotypic diversity. All populations had significantly higher levels of Ho compared to He at individual SSR loci, and had highly significant values of Ia and rd which indicated clonal reproduction. Europe had the highest number of distinct SSR genotype groups with eight, and Russia had only two SSR groups. The populations in North America and South America; Russia and Central Asia; the Middle East and East Africa; were closely related for SSR genotype based on Nei's genetic distance. Based on k means clustering and DAPC of SSR genotypes, isolates virulent to durum wheat were placed into a single separate group, and isolates virulent to common wheat were placed into five other groups. Twenty-seven SSR genotypes were found in different continental regions. Isolates with identical or highly related SSR genotypes also had identical or similar virulence, which indicated historical and current migration of P. triticina worldwide.
Primary Author: Kolmer, USDA-ARS Cereal Disease Laboratory
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Stem rust caused by Puccinia graminis f.sp. tritici (Pgt) is one of the major constraints to wheat (Triticum aestivum) production worldwide. Pgt races have rapidly evolved in several geographical regions due to the deployment of single resistance genes resulting in boom and bust cycles, hence combinations of resistance genes through pyramiding ensures durability of resistance in wheat varieties. Spring wheat line CI14275 displayed high levels of field resistance to stem rust in Kenya and USA compared to the parents in its pedigree (Thatcher, Kenya Farmer & Lee). To understand the genetics of resistance in CI14275, 114 Recombinant Inbred lines (RILs) were developed from the cross CI14275/LMPG-6 and screened for seedling response to Pgt races TTTTF, TPMKC, TRTTF, TTKSK & RTQQC. Chi-square goodness of fit tests suggested one-gene, three-genes, and four-genes segregated for response to races TTTTF, TPMKC and RTQQC, respectively. The RILs were all susceptible to races TTKSK and TRTTF. CI14275 showed intermediate low infection types only against races TPMKC (23-) and TTTTF (1+3C). Field screening of the population was completed in Kenya, Ethiopia and St. Paul where CI14275 showed high levels of resistance TMR (Kenya), 5MS (Ethiopia) and 5RMR (St. Paul) against the prevalent races in the stem rust screening platforms. LMPG-6 displayed susceptible responses ranging from 70S-90S in the three locations. 90K wheat Single Nucleotide Polymorphism (SNP) marker platform will be used to genotype parents and the population.
Primary Author: Kosgey, University of Minnesota, St. Paul, MN 55108, U.S.A
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Two broad categories of resistance genes in wheat have been described. One group represents the so called seedling resistance or the ‘gene for gene’ class that often provides strong resistance to some but not all strains of a rust species. The other category referred to as adult plant resistance provide partial resistance that is expressed in adult plants during the critical grain filling stage of wheat development. A few seedling rust resistance genes have been cloned in wheat and other cereals and are predominantly from the nucleotide binding site/leucine rich repeat class which is associated with localized cell death at the pathogen entry site. Until recently, the molecular basis of race non-specific, partial and slow rusting adult plant resistance genes were unknown. Gene products that differ from known plant resistance genes were revealed from the recent cloning of the Yr18, Yr36 and Lr34 adult plant genes in wheat. The available range of diverse resistance gene sequences provide entry points for developing genebased markers and will facilitate selection of germplasm containing unique resistance gene combinations.
Primary Author: Kota, CSIRO Plant Industry, Australia
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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.
Primary Author: Koyshibayev, Kazakh Research Institute of Plant Protection and Quarantine, Kazakhstan
Keywords: Kazakhstan, varieties
Emmer wheat (Triticum dicoccum L.), tetraploid species (AABB) and spelt wheat (Triticum spelta L.), hexaploid species (AABBDD) are old world hulled wheat species cultivated centuries ago in different parts of the world. These species were later replaced by higher yielding bread and durum wheat in the last centuries. Grain yield is influenced by grain number per unit area and grain size which correlates positively with grain weight. Increasing the grain number was extensively and intensively explored in the past 100 years of wheat breeding which has nearly reached to saturation and leaves little room for further yield increase due to grain number?grain size trade off. Grain size/grain weight is believed to be major driving force for further improvement of wheat yield. Both the species have been characterised with larger grain size and higher grain weight; therefore an ideal source to improve the grain size/grain weight while maintaining the grain number per spike in the cultivated bread wheat. A total of 25 accessions each of emmer and spelt wheat with good grain size and weight were crossed with 5 elite bread wheat lines. In the F2 generation, recombinant lines with good grain size, higher grain weight and grains number were further backcrossed with bread wheat. Stable lines with free threshing were obtained at BC4F4 generations and were analysed for quality. Thousand grain weight (TGW) and harvest index (HI) ranged from 46-55g and 0.47-0.58 in stable lines respectively. Stable lines yielded 16-21% than the high yielding check while number of grains per spike was maintained as that of check. Stable lines involving spelt crosses have higher grain size, TGW and HI than emmer wheat crosses. Stable lines could be released directly as cultivar or else used as one of the parents in the wheat improvement programme.
Primary Author: Kumaran, ICAR-Indian Agricultural Research Institute, Regional Station, Wellington, The Nilgiris, Tamilnadu, India
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Asia and North Africa (CWANA). The total acreage in CWANA is approximately 53 million hectares. Wheat stripe (yellow) rust caused by Puccinia striiformis f. sp. tritici (Pst) continuously poses a serious threat to wheat production in CWANA. Several factors have contributed to the current severe epidemics of stripe rust, including; the rapid shift of virulence in the pathogen population, genetic uniformitity of mega-cultivars, favorability of environmental conditions, and an overlapping/ continuous crop calendar. During 1985-1997 the widespread appearance of Yr9 virulent pathotypes in CWANA, and eventually in the Indian sub-continent, resulted in several epidemics that caused a series of severe crop losses in popular cultivars known to be protected by the Yr9 resistance gene. Following the Yr9 virulence epidemics, susceptible cultivars were extensively replaced with CIMMYT-derived germplasm such as Kauz, Atilla, Opata, Nacozari, Bucbuc and Crow. The resistance of many of the replacement cultivars, including the mega-cultivars in India (PBW343), Pakistan (Inquilab-91, Bakhtwar), Iran (Chamran, Shiroudi), Ethiopia (Kubsa), and Syria (Cham 8) was based on Yr27. Breakdown of Yr27 resistance in PBW343, Inquilab 91 and Chamran, in India, Pakistan, and Iran, respectively, was reported between 2002-2004. Although occasional stripe rust outbreaks appeared in some areas, unfavorable environmental conditions presumably restricted the increase of the Yr27 Pst population until 2009, when conducive environmental conditions resulted in severe epidemics in several CWANA countries e.g., Morocco, Algeria, Uzbekistan, Turkey, Iran, Azerbaijan, Georgia, and Afghanistan. Environmental conditions favouring rust development continued into 2010, with mild winters and adequate rainfall in several CWANA countries resulting in early outbreaks of stripe rust. The 2010 stripe rust outbreaks occurred throughout the major wheat growing areas in the CWANA and Caucasus countries, causing severe yield losses particularly in Syria where Cham 8 (with Yr27) occupied more than 70% of the wheat areas. Inspite of favorable environmental conditions in many areas in CWANA in 2011, similar severe stripe rust epidemics have not been reported to date. Climate change now appears to be playing a major role in Pst population dynamics in CWANA. Direct, multiple affects of climatic changes on epidemiology of rust pathogens are expected, including the survival of primary inoculum, the rate of disease development, duration of rust epidemics, and development and distribution of rust populations. Emergence of stripe rust in non-traditional areas, changes in the frequency of new race evolution, early infection of stripe rust, shifts in predicted pathways of rust migrations, and finally wide spread epidemics of stripe rust in warmer areas as a potential indicator of adaptation to high temperatures are considered as possible consequences of climatic changes. Regional pathogen surveys indicated the widespread distribution of aggressive Pst pathoype (s) with adaptation to higher temperature. In the absence of resistant varieties, fungicide application remains the only practical measure to control stripe rust. Effective disease surveillance and monitoring systems, coupled to timely application of fungicides has effectively controlled stripe rust epidemics in Iran, Turkey, and Syria during 2010-11. Regional monitoring of pathogen variability and disease development must be undertaken as a matter of high priority, and timely chemical control measures will continue to play a major role for control of stripe rust in CWANA in the short-term. In the medium to long-term, existing resistant varieties and advanced breeding lines need to be promoted and susceptible varieties have to be urgently replaced.
Primary Author: Kumarse Nazari, ICARDA
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The research was conducted at ICARDA, Rabat. Twenty-four accessions were obtained from LCRI for marker analysis. Wizard Genomic DNA Purification Kit was used for DNA extraction. DNA was extracted by CTAB method and quantified using 1.0 % (w/v) agarose gels. Total of 12 loci, 5 functional and 7 linked random DNA markers to the traits of interest were used. PowerMarker and DARwin software were used to calculate the No. of alleles and values of genetic diversity, PIC, genetic distance, and NJ dendrogram. The total No. of detected alleles was 39; and mean No. of alleles was 3.25. No. of alleles range from 1 (Dreb-B1) to 9 (Xgwm577). Genetic diversity index ranged from 0.0000 in Dreb-B1 to 0.8471 in Xgwm577. The PIC value was also varied from 0.0000 (Dreb-B1) to 0.8296 (Xgwm577). The frequency of biotic resistance linked random DNA marker allele at Xgwm144 and Xwmc44, associated with yellow and leaf rust gene was 25% each. Marker alleles Xgwm577 and Xgwm533 linked to Stb2 and Stb8 at 150 and 120bp have frequencies of 21 and 4%. The frequency of abiotic resistance showed 50% of accessions had 1R segment (1BL.1RS translocation) and 58% of accessions showed presence of 120bp allele of Xwmc89, associated with QTL for drought tolerant. Functional marker alleles of Dreb-B1 associated with drought tolerant genes showed alleles frequency in all accessions. Linked marker allele Xgwm111 linked to heat tolerant gene showed 17% allele frequency at 220bp. Rht1 and Rht2, the allele frequencies were 92 and 4%. 92% of the cultivars had photoperiod insensitive allele at Ppd-D1 locus. VrnA1a and VrnA1c primer pair amplified at 965, 876, and 484bp, allele frequency of 13 and 87%. Cluster analysis had grouped the accessions into 5 at a genetic distance level 0.15.
Primary Author: Kyari Mala, Lake Chad Research Institute, Maiduguri, Borno State-Nigeria
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