CSIRO Agriculture and Food, Australia
Timothy Hewitt, Peng Zhang, Zacharias A. Pretorius, Narayana Upadhyaya, Rohit Mago, Sambasivam Periyannan, Xiuying Kong, Burkhard Steuernagel, Brande H. Wulff, Evans S. Lagudah
Multiple rust resistance gene combinations are considered as a practical solution for providing durable rust resistance and preventing resistance breakdown arising from single gene deployment. The stem rust resistance locus Sr26, originally derived from Thinopyrum ponticum and introgressed into wheat as a chromosome translocation, is one of the very few genes conferring durable resistance for almost 40 years to all known races of stem rust, including the highly virulent stem rust race Ug99 (TTKSK) and its derivatives (Dundas et al. 2015). To understand the underlying mechanisms of its unusual long-term effectiveness and to explore allelic diversity in different Th. ponticum accessions for other functional alleles that may offer new sources of resistance, we used comparative genomics and gene capture techniques (Resistance gene enrichment sequencing, RenSeq) as complementary strategies for isolating the target gene (Steuernage et al. 2016). Sr26 region was first mapped using NB-LRR (Nucleotide-binding site and leucine-rich repeat) sequences from the orthologous gene members located on the long arm of chromosome 6D from Aegilops tauschii (the D-genome donor of wheat) reference genome. Subsequently, we revealed a cluster of NB-LRR sequences located at the distal end of the Th. ponticum introgression segment that were absent in the smallest interstitial Sr26 deletion mutant. Therefore, we substantially narrowed down the genetic interval for Sr26. In addition to this approach, we subjected the mutant population to RenSeq pipeline. A candidate gene of Sr26 has been successfully identified to be a NBS-LRR type resistance gene. Validation of the gene candidate by complementation studies is currently in progress. In order to enhance durable resistance, genetic stocks of Sr26 from different backgrounds as well as a panel of Sr26-APR (Adult Plant Resistance) gene combinations have been generated to further investigate the resistance response of Sr26 in combination with different multi-pathogen APR genes.
University of Sydney Plant Breeding Institute
Naeela Qureshi, Vallence Nsaiyera, Pakeer Kandiah, Mesfin Gesesse, Mandeep Randhawa, Mumta Chhetri, Bosco Chenayek, James Kolmer, Miroslav Valarik, Zaroslav Dolezel, Beat Keller, Matthew Hayden, Justin Faris, Harbans Bariana, Vanessa Wells
Dr. Norman Borlaug stated that rust never sleeps and this enables rust pathogens to produce new strains capable of putting rust resistance genes to rest. These pathogens continue to pose threats to global wheat production. Wheat breeders have made significant progress to control rust outbreaks using conventional selection technologies; however, some critical shifts in pathogen populations have let them down. Rapid evolution in molecular marker technologies in the last 15 years and refinement of phenomic facilities have expedited the process of discovery and characterisation of rust resistance genes to underpin the development and validation of markers closely linked with genetically diverse sources of resistance. A high proportion of the formally named rust resistance genes were characterized in the 21st century and markers closely linked with these genes have been developed and validated. The marker tagged sources of resistance to three rust diseases have equipped the wheat breeding community with tools to deploy combinations of all stage and adult plant resistance genes in future wheat cultivars. The question that whether we have enough resistance genes discovered to compete against the ever-awake rust pathogens. In our opinion, we cannot be complacent and discovery needs to continue to ensure food security. This presentation will discuss the role of advances in phenomic and genomic technologies to achieve durable rust control in wheat.
Omsk State Agricultural University, Omsk, Russia
Elena Salina, Yuriy Zelenskiy, Alma Kokhmetova, Mehran Patpour, Mogens Hovmøller, Pablo Olivera, Les Szabo, Yue Jin, Marcel Meyer, Chris Gilligan, Matthew Hort, Dave Hodson, Alexey Morgunov
Short season, high latitude spring wheat is grown on 7 million ha in Western Siberia and 10 million ha in Northern Kazakhstan. Despite relatively low wheat yields (1.5 t/ha), the region is extremely important for regional and global food security. Leaf rust dominates, occurring three years out of five, especially in favorable years with higher rainfall. Since 2010, stem rust has been observed at an increasing number of sites. The first large-scale stem rust outbreak occurred in 2015 and affected about 0.5-1 million ha in Omsk, Western Siberia. In 2016, 2 million ha were affected in the Omsk and Altay regions, while 1 million ha in the Kostanay and Northern Kazakhstan regions were affected in 2017. Estimated yield losses reached 25-35% each year. Factors associated with the outbreaks included: higher rainfall in late June and July; cultivation of susceptible varieties; and an increased area planted to winter wheat, which serves as a source of inoculum. Sampling and race analysis revealed a diverse pathogen population, indicative of a sexual recombination. A total of 51 races were identified from 31 samples taken in 2015 and 2016. All races were avirulent on Sr31. The majority of varieties released and cultivated in the region are susceptible to stem rust and require replacing. A recent study of 150 local resistant varieties and breeding lines indicated that the genetic basis of resistance was limited to Sr25, Sr31, Sr36, Sr6Ai, Sr6Ai#2, and additional unknown major genes. Adult-plant resistance to stem rust was observed in less than 20% of the germplasm. The potential impact of these large stem rust outbreaks on other wheat growing regions is being investigated by analyzing spore wind dispersal patterns. Further research is required to understand and mitigate the sudden appearance of stem rust as a disease of economic importance.
Study at Omsk State Agrarian University was supported by the Russian Science Foundation (project No. 16-16-10005).
University of Eldoret
Julius Ochuodho, Ruth Wanyera, Sridhar Bhavani, Les Szabo
Stem rust Ug99 and related race group are one of the major constraints of wheat production in Kenya. The challenge has been largely due to rapid evolution of races within lineage defeating resistance genes resulting in boom and burst cycles. Understanding of the pathogen population structure in major wheat growing regions in Kenya gives comprehensive information of the predominant races as well as capturing new races which may have potential of causing epidemics. Such information can have significant impact on effective gene stewardship in breeding resistant varieties. Using 11 Pgt Simple Sequence Repeats (SSR) markers we analyzed 104 single uredinial-pustule samples. Allele frequency distribution ranged from 2 to 6 per locus with an average of 3.27 per locus. Observed heterozygosity ranging from 0.297-1.000 (mean HO=?0.809) was significantly different (P< 0.001) than the expected heterozygosity (0.264 to 0.507; mean HE=?0.407) indicating that the population is asexual. Analysis of molecular variance (AMOVA) showed that the majority of the variation occurred within the samples (98%) rather than between regions (2%). Analysis of 104 samples identified 21 multiple locus genotypes (MLGs). MLG.19 was observed across the three region analyzed that is Central Rift, North Rift and Mount Kenya while MLG.18 was predominant in Mount Kenya. Based on SSR genotypes of reference isolates, Pgt clade IV (race TKTTF) was associated with MLG.16 in Central Rift Kenya while clade I (race TTKSK) had a unique MLG.10. These results indicated two main groups corresponding to Clade I (Ug99 race group) and Clade IV (race TKTTF race group). This minimum spanning network analysis pattern points to the Pgt population being asexual due to mutation. These preliminary results suggest that Pgt population in Kenya is asexual in nature. Further analysis is being conducted to ascertain geographical structure as well as compare the results with the 2011 data.
Seed and Plant Improvement Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Kamal Shahbazi, Jabbar Alt Jafarby, Mohammad Sadegh Khavarinejad, Farzad Afshari, Farshad Bakhtiar, Habibollah Soghi
In this project to obtain resistant wheat breeding lines/cultivars to stem rust disease, new cultivars and lines of the north breeding program were evaluated in greenhouse with races collected in 2014 from northern regions of Iran, Moghan and Gorgan. Artificial inoculation in greenhouse indicated none of the races had virulence on Sr11, Sr13, Sr24, Sr25, Sr26, Sr27, Sr29, Sr31, Sr32, Sr33, Sr37, Sr39, Sr40, and SrTmp. In order to evaluate seedling resistance, 143 wheat cultivars and new lines under greenhouse conditions were inoculated with four isolates of stem rust in four separate experiments in a randomized complete block design with three replications. Evaluation of the northern germplasm under greenhouse conditions showed that some of the genotypes were resistant against all four isolates. The resistance of some of these new lines was also confirmed in Kenya. Regarding other desirable agronomic characteristics, some of these lines will be introduced as new cultivars in the northern region of Iran.
University of Queensland, St. Lucia
Adnan Riaz, Jonathan Powell, Timothy Fitzgerald, Kemal Kazan, Neena Mitter, Evans Lagudah, Lee T. Hickey
The Lr34/Yr18/Sr57/Pm38/Ltn1 multi-resistance locus has been deployed and remained effective in wheat cultivars for more than 100 years. The durability and pleiotropic nature makes Lr34 a unique and highly valuable resource for rust resistance breeding. Despite its functional annotation as an ABC transporter, the mode of action is unknown. Considering this, we aimed to decipher molecular factors and signaling components essential for Lr34 function using RNA-seq of Chara resistant (Lr34) and Chara mutant (heavy ion irradiation, HII) susceptible wheat lines. Screening of Chara and Chara HII lines with Lr34-specific markers confirmed the integrity of Lr34 in both lines; however, phenotyping confirmed rust and powdery mildew susceptibility in the Chara HII lines. Plants were grown under controlled conditions and infected with Puccinia triticina pathotype 76-1,3,5,7,9,10,12,13+Lr37 at the flag leaf stage. Flag leaves were sampled at 0, 24, 48, 72, 96 and 168 hours post inoculation (hpi) from mock and infected plants. Based on real-time PCR analysis of basal defense genes and the Lr34 gene, we selected 72 hpi for RNA-seq with four biological replicates per condition. The samples were sequenced on an Illumina Hiseq 4000 at the Beijing Genomics Institute, China. A total of 9.0 Gb of sequence (2.25 Gb/library) from 16 libraries for four conditions was obtained. Differential expression analysis was performed using the Tuxedo analysis pipeline with standard parameters. Analysis revealed deletion of DNA fragments with collinear gene order on chromosomes 1A, 2D, 5A, 5B, 5D and 7D of Chara HII mutants. To determine the significance of the deletions we performed bulk segregant analyses on segregating F2 populations of Chara ? Chara HII crosses. Analyses revealed key genomic regions associated with Lr34-functional resistance and we are in the process of validating candidate genes using qPCR.
Crop Diseases Research Institute, National Agricultural Research Center, Park Road Islamabad, Pakistan
Anjum Munir, Khalil Ahmed Khanzad, Javed Iqbal Mirza, Shahzad Asad, Atiq ur Rehman Rattu, Muahmmad Imtiaz
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.
National Research Council of Canada (NRC)-Saskatoon
Kerry Boyle, Tammy Francis, Peng Gao, Brittany Polley, Christine Sidebottom, Brent McCallum, Harpinder Randhawa, Tom Fetch, Randy Kutcher, Sylvie Cloutier, Pierre R. Fobert
Most rust resistant genes in wheat are race-specific (R), with relatively few genes conferring resistance only at the adult stage that have been described as slow rusting genes (APR). Pyramiding multiple R, APR or APR+R genes has been used successfully over many years to achieve durable rust resistance. To further enhance this strategy, a genetic genomics approach was exploited to identify genes with different resistant mechanisms and the most effective gene pyramids.
Several new combinations of rust genes were created and tested in the Thatcher background, revealing synergistic ("booster") effects involving Lr21 with Lr16. With QTL mapping approach, we found that genes combined from 7D, 1B and 7B conferred an almost immune response to leaf rust, while genes from 7D, 1B and 3B provided an almost immune response to stripe rust. With a genomics approach, a large scale transcriptome analysis was conducted on key rust resistant genes including six R genes, three APR genes and one gene pyramid with Lr34+Lr16 over a time series during the infection process of both seedlings and adult plants. Detailed transcriptome analysis of gene expression associated with different major and minor leaf rust genes, alone or in combination, identified common and unique aspects of defense responses. For example, Lr9 is different from the other three leaf rust genes tested, with resistance triggered at a very early stage, consistent with pre-haustorial resistance. R genes Lr21 and Lr16 were also significantly different compared to other R and APR genes. With gene co-expression network analysis, a shared unique gene module mediated by Lr34 and Lr67 was also identified. This large transcriptome dataset also allowed the development of a rust-wheat interactome atlas for rust functional genomics research in wheat.
Khaoula El Hassouni, Priyanka Gupta, Hafssa Kabbaj, Meryam Zaim, Amadou Tidiane Sall, Bouchra Belkadi, Ayed Al-Abdallat, Ahmed Amri, Rodomiro Ortiz, Michael Baum
Durum wheat is the tenth most important crop in the world, but its cultivation is mostly limited to harsh, arid, and heat prone marginal lands. Breeding for tolerance to these conditions is often considered the most strategic approach to ensure adaptation, especially when paired with best agronomical practices. The word 'adaptation' summarizes all the research efforts conducted to identify the many traits controlling the mechanisms for withstanding or escaping the traceries of the environment. It can be summarized as "GGE vs E". The durum wheat breeding program of ICARDA deploys targeted phenotyping methods in combination with genomic scans to dissect these 'adaptive' traits into simple loci. These loci can then be pyramided via a combination of international field testing, markers assisted selection, genetically-driven crossing schemes, and genomic selection to derive climate-ready cultivars. Here, several examples of this approach are presented and their implications for 'adaptation' are discussed.
Cereal Laboratory, Wheat Research Institute, Faisalabad, Punjab, Pakistan
Hira Shair, Anjum Javed, Muhammad Abdullah, Makhdoom Hussain, Javed Ahmed
Globally, more than two billion people are undernourished in the world and deficient in key vitamins and minerals, making it the world's greatest health risk factor. Among these, iron and zinc are of greater significance from human nutrition perspective, ranking them 5th and 6th in developing countries. The population most vulnerable to these micronutrient deficiencies is women and children. Iron deficiency results about 1.62 billion people as anemic, largely preschool children (47%). It is responsible for approximately 20854 deaths and two million disability adjusted life years (DALYs) among children under five years old, whereas, zinc deficiency is responsible for approximately 4% of deaths and 16 million DALYs, among children under age five. This leads to malnutrition ultimately leading to a disabled society.
Widespread accessibility of these nutrients is the solution to cater malnutrition. Wheat, the "staff of life," consumed by masses can help eradicate "hidden hunger." For this, fortification and bio-fortification are highly talked about, but one having limitations in reaching the masses and other a long term intervention, respectively, suitability of planting times to screen out varieties high in zinc and iron, is an on-field solution. In a study, wheat varieties; Punjab-11, Millat-11 and Galaxy-13 were selected from three planting times, with an interval of one month. Results reveal varieties exhibited their natural genotypic response but planting time impact on Zn and Fe were visibly significant. 30th December gave higher contents of Fe and Zn as compared to previous planting dates of the same year. Iron on an overall basis ranged from (135.0-147.0) ppm, while Zinc gave a confined range of (30.2-33.2) ppm. Thus, concluded that comparatively delayed sowing favours the mineral content concentration in wheat grains. And these creamed out varieties can readily be used in crosses with high yielding varieties, in order to make our wheat mineral sufficient.