Northwest A&F University
Xiaoguo Zhu, Zhensheng Kang
RNA interference (RNAi) is a powerful genetic tool to accelerate research in plant biotechnology and to control biotic stresses by manipulating target gene expression. However, the potential of RNAi in wheat to efficiently and durably control the devastating stripe rust fungus Puccinia striiformis f. sp. tritici (Pst), remained largely under explored, so far. To address this issue, we generated transgenic wheat lines expressing double-stranded RNA targeting PsFUZ7 transcripts of Pst. We analyzed expression of PsFUZ7 and related genes, and resistance traits of these transgenic wheat lines. We show that PsFUZ7 is an important pathogenicity factor that regulates infection and development of Pst. A PsFUZ7 RNAi construct stably expressed in two independent transgenic lines of wheat confers strong resistance to Pst. Pst hyphal development is strongly restricted, and necrosis of cells in plant resistance responses was induced significantly. We conclude that trafficking of RNA molecules from wheat plants to Pst may lead to a complex molecular dialogue between wheat and the rust pathogen. Moreover, we confirm the RNAi-based crop protection approaches can be used as a novel control strategy against rust pathogens in wheat.
Instituto Nacional de Investigaci?n Agropecuaria (INIA) La Estanzuela
Paula Silva, Clara Pritsch, Miguel Raffo, Silvia Pereyra, Silvia German
Wheat stem rust (SR), caused by Puccinia graminis f. sp. tritici, (Pgt) is considered one of the most destructive diseases of the wheat crop. As Sr24 and Sr31 are the most widely used resistance genes in the Southern Cone of America, wheat crops in this region is under threat of SR outbreaks posed by the potential migration of virulent Pgt Ug99-lineage races (Ug99+). Efforts have to be made to develop adapted lines resistant to Ug99+. Genes Sr26, Sr32 and Sr39 are effective to both Ug99+ and local races of the pathogen. This work is aimed to pyramid two and three of the resistance genes in two locally adapted wheat cultivars (G?nesis 2375 and G?nesis 6.87). Donor lines of Sr26, Sr32 and Sr39 (developed by I. Dundas, University of Adelaide, Australia) and molecular markers Sr26#43, csSr32#1 and Sr39#22r (developed by R. Mago et al., University of Adelaide) were used. Lines with two-gene combinations were developed in two steps. First, tree-way crosses were made by crossing heterozygous F1 plants (derived from crossings donor lines) to either one of the two adapted wheat cultivars. Subsequently, tree-way F1 plants were genotyped and only those with two-gene combinations were backcrossed (BC) twice to the adapted cultivars. Among three-way F1 plants, two-genes combinations were confirmed for Sr26+Sr32 (8 out of 31), Sr26+Sr39 (2 of 115) and Sr32+Sr39 (26 out of 103). In the BC1F1 generation, Sr26+Sr32, Sr26+Sr39 and Sr32+Sr39 combinations corresponded with 9, 9 and 45 out of 99, 27 and 241 plants, respectively. In 2017, 1345 BC2F1 plants are being grown to obtain BC2F2. We plan to intercross plants with two-gene combinations to obtain lines with the three genes which will be used as sources of resistance to develop cultivars with presumably longer lasting resistance to wheat SR.
ICAR-Indian Institute of Wheat and Barley Research, Karnal
Satish Kumar, Ratan Tiwari, Gyanendra Pratap Singh
Stripe rust, is a major constraint to wheat production in the more than 12.8 m ha region of the Northern Hills and North Western Plains zones in India. The previously deployed resistance genes Yr9 and Yr27 are no longer effective. New sources of resistance (Yr5, Yr10, Yr15, Yr24) became available under the umbrella of an Indo-Australian collaborative project. A set of advanced backcross derivative lines out yielded the checks in preliminary evaluations and were promoted to station-level (16 lines) and national (5 lines) trials. A new cohort of resistance genes (Yr47, Yr51, Yr57) are now available and are being used in the breeding program. Resistance genes Yr17, Yr18, Yr31, Yr36, Yr40, Yr53, YrC591, and Yr70 are also being used. The recent progress in development of high yielding, stripe rust resistant lines will help to address future threats from stripe rust.
The Federal Research Center Institute of Cytology and Genetics, The Siberian Branch of the Russian Academy of Sciences
Vyacheslav Piskarev, Irina Leonova, Ekaterina Bukatich, Elena Salina
Stem and leaf rusts affect the winter and spring wheat in the Novosibirsk region. During 2008-2017 leaf rust incidence was generally moderate, from 20 to 40%. A leaf rust outbreak occurred in 2015 when incidence increased up to 80%. Leaf rust severity on the 'Thatcher' NILs ranged from immune or resistant to highly susceptible host response with maximum severity of 90S. Lines carrying genes Lr17, Lr18, Lr24, Lr29, Lr35, Lr37, Lr44, and LrW remained almost free of infection for the whole time of inspection. Genes Lr12, Lr13, Lr28, Lr34, and Lr38 exhibited moderate resistance but they did not provide sufficient level of resistance in favorable conditions. Since race-specific genes Lr24 and Lr29 are still effective in the neighboring Novosibirsk and Omsk regions, they might be recommended for breeding purposes in Western Siberia.
In 2016 stem rust was more prevalent and widespread in the region than ever before. Disease incidence ranged between 4.5 - 60% with high severity up to 80S in six fields from seven observed locations. The 4th ISRTN and varieties carrying Sr31 of West Siberian germplasm were assessed in field trials to monitor the virulence of the local population. There was no virulence to Sr9b, Sr9e, Sr20, Sr28, Sr29, Sr33, Sr39, Sr40, SrWld, Sr2 complex. Possible virulence to Sr6, Sr11, Sr12, Sr13, Sr17, Sr24, Sr25, Sr30, Sr31, Sr35, Sr38, Sr44, Sr57 was observed with low frequency. Entries genotyped for gene Sr31 were scored as MS and S. However, follow up race analysis work is needed to determine the actual stem rust races present and confirm the suspected possible observed virulence on Sr31.
Agriculture and Agri-Food Canada, Lethbridge, Alberta
Gurcharn Brar, Randy Kutcher, Raman Dhariwal
Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat in western Canada. Although stripe rust was an issue in southern Alberta for many years, it became important in other parts of the country after a dramatic population shift in 2000, resulting from an invasive race. Sporadic epidemics of the disease are common and cause considerable loss, due to which, an intermediate level of resistance to stripe rust was required for new varietal registrations beginning 2017. Virulence surveys are of key importance in germplasm and cultivar development as they provide breeders and pathologists the information needed to better understand host-pathogen interactions and the effectiveness of Yr genes. Virulence characterization revealed a wide range of virulence phenotypes exhibited by 33 Pst races in western Canada, although only 2-3 races were predominant. The expression of Yr genes may differ between controlled conditions and natural field conditions as previously reported. Thus, stripe rust differentials and wheat cultivars grown in western Canada are also screened at multiple locations in every year. At present, all stage resistance genes Yr1, Yr4, Yr5, Yr15, Yr76, and YrSP are effective against the predominant Pst races, whereas at the adult stage under field conditions, Yr2, Yr17, Yr28, or those carried by Yamhill are also effective. Seedling resistance genes Yr7, Yr10, Yr17, or Yr27 were the most common in Canadian wheat cultivars. Of these, only Yr17 is effective under field conditions. Adult plant resistance genes Yr18 and Yr29 are carried by many cultivars, but are not effective under high disease pressure. The effectiveness of each resistance gene may vary between the eastern and western prairies of western Canada due to differences in virulence. Regular virulence surveys using contemporary and regional cultivars facilitate the development of rust resistant cultivars.
Kenya Agricultural and Livestock Research Organization
Ruth Wanyera, Bernard Otukho, Bernice Waweru, Hellen Wairimu, Sridhar Bhavani
Emergence of Pgt race Ug99 and rapid proliferation of lineal highly virulent races imminently threaten Kenyan wheat. Devastating epidemics have led to huge losses among smallholder farmers who invariably are unable to spray appropriately and in situations where susceptible varieties are grown. To combat stem rust, the Kenya wheat improvement program seeks to release high yielding stable genotypes with suitable levels of disease resistance. Moreover, detection of genotypes that are adapted to rain-fed environments is an overarching objective. Six hundred and seventeen genotypes from various CIMMYT nurseries (PCBW, EPCBW, PCHPLUS, and 9th SRRSN) were selected based on plant type and reaction to stem rust at Njoro. The reconstituted nursery-KSRON, was sown in the main season of 2016 at Njoro and Timau for further evaluation. Forty red grained lines depicting R-MR infection types, severity of 30% or less, and average Thousand Kernel Weight of >40g were then selected to constitute a yield trial. At each of eight diverse environments, trials also comprising four commercial varieties as checks, were designed in RCBD, three replicates laid out in contiguous array of 8 rows x 10 m plots. Genotype (G), Environment (E) and GE interactions effects were estimated by fitting the AMMI model to yield data, supported by a biplot visualization of the results. Analysis revealed significant (P ?0.01) genotype (G), environment (E), and GE interactions. The first three principal components (PC) explained ~78% of the observed variation. Environment was the predominant source contributing over 85% to total sum of squares. The biplot pointed to at least four environments that were highly correlated. By classifying genotypes based on Shukla's stability variance and Kang's stability rating, six genotypes (R1402, R1411, R1424, R1481, R1484, and R1486) were deemed high yielding and stable, and thus suitable candidates for further testing through the release pipeline.
University of Bologna, Italy/ International Center for Agricultural Research in the Dry Areas, Morocco
Hafssa Kabbaj, khaoula El hassouni, Elisabetta Frascaroli, Angelo Petrozza, Stephan Summerer, Marco Maccaferri, Miguel Sanchez-Garcia, Roberto Tuberosa, Filippo M. Bassi
Global food security is faced with many threats including population growth and changing climate. To cope with these threats a new paradigm shift is required to ensure sufficient and sustainable crop production. Hybrid technology could represent a partly strategic solution for durum wheat, but the understanding of its heterotic behavior is very limited. In this study, 53 F1 plants were produced via half diallel scheme and North Carolina design II, using as parental elite lines selected on the basis of their genetic distance. These hybrids along with their parents were evaluated for different physiological and root traits on a precision phenotyping platform (Lemnatec) at different levels of water stress. Additionally, a second root test was conducted in near field condition via a basket method to determine shallow or deep rooting behavior. Hybrids with the most heterotic combinations in terms of above and below ground biomass were identified. However, in order to ensure adequate pollination between heterotic parents, their flowering time must overlap. To identify good matching partners, a GWAS study was conducted to identify genomic regions associated with the control of flowering time in durum wheat. A total of 384 landraces and modern germplasm were assessed at 13 environments with different temperatures and day length throughout the season. Genotyping was conducted by 35K Axiom array to generate 8,173 polymorphic SNPs. In total, 12 significant QTLS for landraces and 17 QTLs for modern germplasm were identified consistently across environments. These two results when combined will allow to predict the best parental partners for hybrid production via markers screening on the basis of their genetic similarity to the most heterotic groups, and with matching flowering times.
Bangladesh Agricultural Research Institute
Paritosh Malaker, Mostofa Reza, Abdul Hakim, Krishna Roy, Rabiul Islam, Thakur Prashad Tiwari, Pawan Kumar Singh, Arun Kumar Joshi
The major diseases of wheat in Bangladesh are leaf blight and leaf rust. Yellow rust occurs occasionally with sporadic infection in the northern parts whereas stem rust was observed only in 2014. So far the country is free of Pgt race Ug99. Wheat blast, a devastating head disease, was first reported in 2016. Currently, about 65% of the wheat area in Bangladesh is covered by leaf rust resistant varieties and about 30% of the area is covered by Ug99 resistant varieties. Surveillance and monitoring of diseases is conducted regularly. In 2017, 102 sites were surveyed of which 52% had leaf rust infection. The data were uploaded to the Wheat Rust Tool Box. A separate surveillance and monitoring of wheat blast was conducted on 421 farmers? fields in 24 districts. Different levels of blast incidence were recorded in 77 fields. The Wheat Research Centre in Bangladesh works with CIMMYT and BGRI to develop high yielding rust resistant varieties. This includes screening for response to Ug99 at KALRO, Kenya. However, the current major concern of wheat is wheat blast. The popular variety BARI Gom 26 is highly susceptible to this disease and no current cultivar in Bangladesh carries an acceptable level of resistance to blast. During 2016-17, 20 varieties and advanced lines from Bangladesh and 80 from CIMMYT Mexico, were evaluated. One elite breeding line, BAW 1260, showed resistance (<10% severity) in multiple environment tests and is also resistant to leaf blight and stem rust. This line carries the 2NS translocation from Aegilops ventricosa and will be released soon for commercial cultivation. Pre-release seed multiplication is already underway for rapid dissemination. Among recently released wheat varieties BARI Gom 30 and BARI Gom 32 are moderately tolerant to blast and are being promoted for wider adoption by farmers.
Department of Plant Molecular Biology, University of Delhi South Campus
The flag leaf and spike are the prime organs in wheat (Triticum aestivum L.) which contribute majorly for spike photosynthesis and eventually aid in grain filling. In this study we have tried to elucidate the effect of abiotic stress on the grain filling and spike photosynthesis. In order to unravel the role of flag leaf, awn, and spike in wheat grain filling and spike photosynthesis, 1000-kernel weight were calculated after removing flag leaves, awns, and by shading the spike in four wheat genotypes (PBW343, C306, K7903, HD2329) for two seasons (2014-2015, 2015-2016). A significant decrease in the grain filling was observed for all the genotypes. These results indicate the role of these organs in spike photosynthesis. The role of the awn tissue was investigated in PBW343 for its role in spike photosynthesis during heat stress. Deep transcriptome sequencing of the awn tissue (PBW343) was performed and it revealed 147573 unigenes. Out of these, 394 genes were differentially expressed genes (DEGs). These DEGs constitutes 201 upregulated and 193 downregulated genes. Genes involved in photosynthesis (Ribulose bisphosphate carboxylase/oxygenase activase B, NADH dehydrogenase, Fe-S protein2), membrane integrity (ATP-dependent zinc metalloprotease FTSH6), and ion channel transporters (two-pore potassium channel3) were prominently expressed. Gene Ontology (GO) enrichment analysis represents PSII associated light-harvesting complex II catabolism, chloroplast organization, photosynthesis light harvesting in photosystemI, ethylene biosynthesis, regulation of oxidoreductase activity, stomatal closure, chlorophyll biosynthesis categories, which are highly overrepresented under heat stress conditions. Therefore, utilizing the awn transcriptome information, Rubisco activase (RCA) gene was chosen for overexpression studies in wheat and rice with the aim to enhance the photosynthetic efficiency of the spike tissue leading to higher grain filling.
The Ohio State University
Nelly Arguello-Blanco, Mao Huang
Genomic selection facilitates rapid cycling through a breeding cycle by eliminating the need to phenotype prior to selecting superior parents and crossing among them. In winter wheat we can now complete a cycle of GS in about 12 months and two greenhouse seasons. Season consists of planting F1s from the previous cycle and selfing to obtain F2 seed. The second season involves planting and genotyping the F2s, predicting their value with GS, selecting and crossing the best, and harvesting the F1 seed. Our breeding program has completed five cycles of GS in one population primarily for grain yield, over the past five years. We have completed three cycles of GS for resistance to Fusarium Head Blight in a second population. Genotyping was done using genotyping-by-sequencing. This provides an opportunity to assess the changes in the population that have occurred as a result of this rapid cycling. These include 1) changes in genomic estimated breeding values for grain yield and FHB resistance, 2) effect of selection and drift on allele frequencies including fixation, 3) effect of selection on diversity and genetic relationships, and 4) changes in linkage disequilibrium. We are conducting these analyses and will present the results.