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.
The University of Agriculture, Peshawar, Pakistan
The Himalayan and near Himalayan region of Pakistan, China and Nepal was recently identified as the center of diversity of Pst. The Pakistani Himalayan populations were shown to be recombinant and possibly maintained through sexual reproduction on the alternate host, Berberis spp. To examine the role of Berberis spp. in supporting Puccinia spp. in the Himalayan region of Pakistan, 274 pycnial/aecial-infected Berberis leaves and 16 grass samples with uredinial infections were collected in the region from 2012 to 2014. Amplification of infected grass and Berberis spp. samples with EF, ITS region, and β-tubulin primers and subsequent species identification based on comparisons of the sequences to sequences in GenBank identified at least five Puccinia spp. viz., P. brachypodii, putative P. coronata-loli and P. coronati-agrostis, P. striiformis f. sp. dactylis (P. striiformoides), and P. striiformis on Berberis and grasses. This infers a role of Berberis as alternate hosts to Puccinia spp. in the Himalayan region of Pakistan, and in contributing to the overall diversity of these species in the region. Microsatellite characterization of Pst samples collected on wheat in 2013 and 2014 indicated an overall high diversity and recombinant population structure in the region. However, the low frequency of wheat-infecting P. striiformis isolates obtained from Berberis spp. necessitates ongoing investigation.
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.
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.
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.
International Maize and Wheat Improvement Center (CIMMYT) Pakistan Office
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Resistance has been an environmentally friendly and proven means of controlling stem rust for more than a century; the problem is that resistance has not been durable. A collection of 100 wheat landrace accessions from the Institute of Agri-Biotechnology and Genetic Resources, NARC-Islamabad, was tested at the seedling stage for response to 11 of Pgt races with multiple virulences, including TTKSK (from Kenya), TRTTF (Yemen), TTTTF (USA), and RRTTF (Pakistan). Six accessions were resistant (IT 0; to 2) to race TTKSK, 11 to race RRTTF, and 9 to races TRTTF and TTTTF. Further tests with US races QTHJC and TPMKC indicated that the majority of these landraces were susceptible. The resistant landraces could be used as donor parents in crossing programs to broaden the genetic base for stem rust resistance in Pakistani wheat varieties.
Bahri Dağdaş International Agricultural Research Institute, Turkey
The International Winter Wheat Improvement Program (Turkey-CIMMYT-ICARDA) conducted a national inventory of wheat landraces in Turkey from 2009-2014. The material in this study were landraces from 10 provinces (Afyon, Aksaray, Burdur, Eskişehir, Karaman, Konya, Kütahya, Nevşehir, Niğde and Uşak) collected in 2009-2010, head-rowed and increased for evaluation in a yield trial in 2012-2013 in Konya province (200 entries, 2 replicates). Drought tolerant cultivars Karahan-99 and Gerek-79 served as checks, each repeated 8 times. The average yıeld of selections from the landraces was 2.95 t/ha compared to 3.7 t/ha for Karahan-99 and 2.8 t/ha for Gerek-79. The mean yıeld of the ten best landrace selections was 3.9 t/ha. In separate disease tests 5% and 11% of selections from the landraces were resistant and moderately resistant to stripe rust, respectively. Four landraces selections (Sahman-Aksaray, Kırmızı Buğday-Uşak, Kobak-Kütahya, Koca Buğday-Burdur) had higher grain yield than Karahan-99 and Gerek-79 and were resistant to stripe rust. There is some likelihood that this resistance is of a durable nature. The selected lines can be used in breeding programs targeting improved dryland performance while improving durability of stripe rust resistance in modern cultivars.
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.
Department of Plant Pathology, University of Minnesota, USA
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Berberis holstii, native to the highlands of East Africa, is susceptible to Puccinia graminis and P. striiformis in artificial inoculations. However, it is not known whether these pathogens complete their sexual cycles in the region. In an attempt to understand the role of B. holstii in pathogen variation and epidemiology of wheat stem rust and stripe rust, we investigated the functionality of B. holstii as an alternate host. Natural aecial infections on B. holstii were observed and sampled in August at Mt. Kenya and Narok (Kenya), and June to December at North Shewa (Ethiopia) from 2008. Aeciospores from the collections were inoculated to a panel of cereal species, including Line E and ‘Morocco’ wheat, 'Hiproly’ barley, 'Prolific' rye, and ‘Marvelous’ oat. For the majority of aecial samples, aeciospore viability was lost during shipment and storage; thus inoculations were not successful. Inoculations using relatively fresh samples collected at North Shewa in 2012 and 2014, resulted in stem rust infections on Line E, Prolific, Hiproly, and Marvelous. DNA assays using real-time PCR confirmed the presence of P. graminis in these samples. While it is likely that the pathogen infecting Line E, Prolific and Hiproly is P. graminis f. sp. secalis (Pgs), the inoculation and DNA assays did not provide sufficient resolution to distinguish Pgs from Pgt. Stem rust infections on Marvelous were assumed to involve Pg f. sp. avenae. Experiments are in progress to characterize isolates derived from these samples, and to determine if other rust fungi are present in these samples. Based on these preliminary data, we conclude that P. graminis completes its sexual cycle in Ethiopia. The contribution of the sexual cycle to the observed variation within the Pgt population in the region remains unclear.
CSIRO Agriculture Flagship, Australia
The Lr34 resistance gene from Triticum aestivum encodes a putative ABC transporter protein that confers broad spectrum, partial adult plant resistance to all three rusts species and powdery mildew. It has remained a durable source of resistance for over 100 years in which time no increased virulence towards Lr34 has been observed. This gene is located on chromosome 7D and consequently cannot be readily transferred to durum wheat by traditional breeding. A transgenic approach was used to transfer Lr34 to durum wheat cultivar Stewart by Agrobacterium transformation. Homozygous progeny from a number of independent Stewart lines expressing Lr34 under regulatory control of its endogenous promoter showed high levels of rust resistance at the seedling stage. A correlation between seedling resistance and transgene expression levels was observed in these plants. In contrast seedlings from a near isogenic line of hexaploid wheat cultivar Thatcher containing Lr34 showed only a minor difference in rust growth when compared with Thatcher seedlings, typical of this adult plant resistance gene in hexaploid wheat. Little is known about how the Lr34 gene product functions; however, the seedling resistance of these durum transgenics enables functional assays to be readily undertaken without the need for adult plant material. By infecting seedlings we have shown that day length has an effect on Lr34 resistance to leaf rust, with higher levels of resistance observed under long days (16 h light) compared with short days (8 h light). This study demonstrates that Lr34 provides strong and presumably durable seedling resistance to rust in durum plants that can be used to further understand how this gene confers resistance.