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Phenotypic and genotypic analysis of stripe rust, leaf rust and stem rust resistance genes in Tajik wheat varieties

Rahmatov Tajik Agrarian University, 146, Tajikistan

The objective of this study was to characterize seedling and adult plant resistance to all three rusts in a set of 40 bread wheat varieties currently cultivated in Tajikistan. Gene postulation based on multi-pathotype seedling test data and adult plant responses identified Yr2, Yr9, Yr17 and Yr27; Lr10 and Lr26; and Sr5, Sr6, Sr10, Sr11, Sr31 and Sr38. The effects of slow rusting, adult plant, pleiotropic resistance genes Lr34/Yr18/Sr57 and Yr30/Lr27/Sr2 were observed in the field and confirmed with molecular markers. Furthermore, molecular markers diagnostic for Yr9/Lr26/Sr31 and Yr17/Lr37/Sr38 were assessed on all varieties. Genes Lr34/Yr18/Sr57, Yr9/Lr26/Sr31 and Yr27 were identified in varieties Sarvar, Vahdat, Oriyon, Isfara, Ormon, Alex, Sadokat, Ziroat-70, Iqbol, Shokiri, and Safedaki Ishkoshimi based on phenotypic and genotypic results. Some lines were highly resistant to stripe rust (4 varieties), leaf rust (5) and stem rust (9), but the genes responsible could not be identified. They may possess new resistance genes. We thus identified combinations of major and minor rust resistance genes in Tajik wheat varieties. These varieties can now be used by breeders in Tajikistan as crossing parents to develop new varieties with durable resistance to the rusts.

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Genetic diversity for rust resistance among Nordic spring wheat cultivars

Randhawa The University of Sydney Plant Breeding Institute, Australia

Wild relatives, landraces and cultivars from different geographical regions are demonstrated sources of resistance to wheat rusts. Identification, characterisation and provision of diverse sources of rust resistance to Australian wheat breeding companies form a key component of the Australian Cereal Rust Control Program. This study was planned to assess diversity of resistance to the three rusts among a set of Nordic spring wheat cultivars. These cultivars were tested at the seedling stage with several pathotypes of each rust pathogen. Stem rust resistance genes Sr7b, Sr8a, Sr12, Sr15, Sr17, Sr23 and Sr30 and leaf rust resistance genes Lr1, Lr3a, Lr13, Lr14a, Lr16 and Lr20 were postulated either singly or in various combinations. A high proportion of cultivars were identified to carry Sr15/Lr20 presumably due to earlier selection, or fixation, of Pm1 in breeding populations. Seedling test data using five Pst pathotypes did not allow postulation of genes present in a many cultivars because of a widely effective single gene or overlapping effectiveness of two or more resistance genes. Stripe rust resistance gene Yr27 was postulated in five cultivars. The presence of Yr1 in one cultivar was predicted by amplification of the linked marker allele. Eighteen, 47 and 32 cultivars showing seedling susceptibility, respectively, to stem rust, leaf rust and stripe rust were tested under field conditions to identify sources of adult plant resistance (APR). Cultivars possessing APR to all three or to two rusts were identified. Molecular markers linked to APR genes Lr34/Yr18/Sr57, Lr68, and Sr2 detected the likely presence of these genes in some cultivars.

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Leaf rust on triticale in the Czech Republic

Hanzalova Research Institute of Crop Production, Czech Republic

farming because of lower demands for pesticide applications. Triticale as a hybrid of wheat and rye may possess disease resistances derived either or both from wheat and rye. In the Czech Republic the leaf rust pathogen isolated from triticale is Puccinia triticina. Triticale is usually resistant to the rye leaf rust pathogen (P. recondita). Limited information is available comparing P. triticina isolates collected from wheat and triticale. Manninger (2006, Acta Phytopathologica and Entomologica Hungarica 41: 93-100) pathotyped 82 isolates collected from wheat and triticale on 15 Thatcher NILs. More than 50% of isolates from wheat were virulent to Lr2b, Lr2c, Lr3, Lr11, Lr17, Lr21 and Lr26. Of 12 isolates from triticale 9 were virulent only to Lr2b and Lr2c and the other 3 isolates were virulent to Lr2b, Lr2c and Lr11. We inoculated 15 NILs and 7 triticale cultivars with 36 Pt isolates from wheat and 36 isolates from triticale. Characteristic differences between the reactions on NILs of isolates from triticale and wheat were not found except that virulence to Lr1 was much more frequent in isolates from wheat. Whereas isolates from triticale were virulent to all 7 tested triticale cultivars, isolates from wheat were virulent to only 3 triticales. In another experiment isolates from wheat and triticale were collected at four locations. Although paired isolates came from the same locations the responses of the NILs were different. Isolates from triticale for all four locations were virulent to a higher number of triticale cultivars than those from wheat. It seems that P. triticina races infecting triticale have changed over the last decade from having a narrow virulence range on bread wheat to the current situation of typical bread wheat races becoming specialized on triticale.

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Genetic variation in Puccinia striiformis f.sp. tritici populations on wheat in Iraq

Al-Maaroof Sulaimani University, Iraq

This study was conducted to detect new races of Puccinia striiformis f. sp. tritici in Iraq. Trap nurseries were planted in different locations throughout the main wheat growing areas. Stripe rust severities and infection types on each genotype were recorded at different stages of crop development. Yellow rust samples collected from commercial wheat fields at different locations were sent to the Global Rust Center for race analysis. Local adult plant tests indicated virulence for host genes Yr2, Yr6, Yr7, Yr9, Yr18, YrA, Yr20, Yr21, Yr27, Yr28, Yr29, and Yr31 at the adult plant stage in Sulaimania, and virulence to Yr2, Yr6, Yr7, Yr9, YrSD, YrSP, YrA, Yr21, Yr27, Yr28, and Yr31 at Nineveh. Virulence on lines carrying Yr5, Yr6, Yr7, Yr9, Yr20, Yr21, Yr27, Yr28 and Yr31 were recorded in Babylon and to Yr2, Yr5, Yr6, Yr7, Yr9, Yr18, YrA, Yr20, Yr25, Yr28, Yr29, and Yr31 at Diyala. Of 21 YR samples sent to GRRC for race analysis, cultures were recovered from ten. Two Pst pathotypes (races) were identified; one was virulent to Yr2, Yr6, Yr7, Yr8, Yr9, Yr27, and AvS whereas the other had additional virulence to Yr25 (Strubes Dickkopf). None was virulent for Yr5. Both pathotypes were aggressive based on Milus et al. measures.

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Wheat Gene Expression Differences Induced by Six Races of Puccinia triticina

Neugebauer Department of Plant Pathology, Kansas State University, USA

Puccinia triticina, the causal agent of wheat leaf rust, is a devastating disease that can cause up to 40% yield loss. During fungal infection the host plant recognizes pathogen effectors, which trigger a host defense response. Changes in the pathogen effectors due to host selection pressure are responsible for the rapid development of new rust races and make durable resistance hard to obtain. The objectives of this study are to identify and characterize wheat genes that are utilized by races differently throughout infection and to understand functions of these genes using gene silencing. Six races of leaf rust were inoculated on a susceptible wheat variety and tissue was collected at six days post inoculation. RNA was sequenced and 63 wheat genes were identified that showed varying expression in response to the six races. 54 of these genes were evaluated in a time course study from zero days to six days post inoculation with the same six races. Real-time PCR was then used to analyze the timing of expression during early infection. The characterized genes have proposed functions involved in plant defense and stress, energy and metabolism, protein transport, replication, and RNA binding. Majority of the candidate genes showed three main expression patterns. However, race specific expression was found in three wheat genes that are affected by race shifts on Lr2A, Lr2C, and Lr17A. Sixteen potential susceptibility genes were also identified. Host susceptibility genes could be altered to provide durable resistance. RNAi was used to silence seven wheat genes to further understand their roles in leaf rust infection. T0 and T1 plants have been obtained and confirmed for the gene of interest. T2 plants were inoculated and observed for changes in susceptibility.

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Adult plant resistance to leaf and stripe rusts in landraces

Rehman International Maize and Wheat Improvement Center (CIMMYT) Pakistan Office
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A set of 63 wheat landraces obtained from Institute of Agri-Biotechnology and Genetic Resources, NARC-Islamabad was screened for adult plant resistance (APR) at two inoculated locations during the 2012-13 cropping season, i.e. Wheat Research Institute (WRI), Faisalabad, for leaf rust and Cereal Crops Research Institute (CCRI), Pirsabak, for stripe rust. Responses based on coefficients of infection (CI) were recorded. Five landraces were susceptible (CI >60) and 39 were resistant to both rusts at the adult plant stage; 47 lines were resistant to leaf rust and 51 were resistant to stripe rust, with CI values of 0-20. Four landraces had moderate levels of APR (CI 21-40) to both rusts, 12 to leaf rust and 8 to stripe rust. Only two landraces (accessions 10975 and 11029) showed MR/MS reactions, and one (11438) had an MS/S reaction; the remaining produced S reactions to leaf rust at WRI. At CCRI Pirsabak, the majority of lines responded with MR/MRMS reactions, the remaining lines were susceptible. The 39 landraces identified to have resistance to both diseases may carry new APR gene(s) to one or both rusts, but must be further characterized prior to use as parents in national wheat breeding programs.

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Research for development (R4D) approaches to minimize the threat of new Pgt races to wheat production in Ethiopia

Badebo CIMMYT-Ethiopia

Recurrent outbreaks of rusts debilitated mega wheat varieties in major production areas in Ethiopia. Projects to accelerate seed multiplication of rust resistant varieties funded by USAID, BMGF and others contributed to the replacement of the widely grown susceptible varieties Kubsa and Galama. In 2013/14, a new Pgt race (TKTTF) - unrelated to Ug99 - caused 100% yield losses on bread wheat variety Digalu. The continuing epidemic calls for fast replacement of the now susceptible varieties by accelerated seed multiplication to scale-up new varieties with durable rust resistance, and demonstrations to promote their adoption. In 2014, CIMMYT initiated a short term R4D project ‘Emergency Seed Support and Demonstration of Rust Resistant Wheat Varieties in Stem Rust Affected Areas of Ethiopia’. The project was financed by USAID and implemented in collaboration with EIAR, regional agricultural research institutes, and the Oromia Bureau of Agriculture. In collaboration with DRRW, CDL, and WSU, technical assistance was given to research centers to phenotype and genotype their breeding lines and commercial cultivars. A total of 352 Development Agents (15% female) were trained in rust identification, seed technology and crop management. Eight rust resistant varieties were demonstrated on 430 model farms in 16 districts in Oromia, Amhara and SNNPR. Awareness was created through field days organized by the Kulumsa and Sinana research centers in Arsi and Bale, respectively. Technical and financial support was given to four federal (Kulumsa, Werer, Debre Zeit, and Holetta) and three regional (Mekele, Sinana, and Adet) research centers for early generation seed multiplication. A total of 2,000 resource-poor farm households (10% female headed) selected on the basis of having suffered heavy losses to stem rust in the previous season, received technical assistance and 165 tonnes of seed of rust resistant varieties. Assisted farmers recorded above average zonal yields in 2014/15.

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