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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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.
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.
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.
Bangladesh Agricultural Research Institute (BARI)
Leaf rust is most common wheat rust in Bangladesh. Late planted wheat crops are more likely to be affected. Yellow rust occurs occasionally with sporadic infection in the northern parts and stem rust was observed after three decades in 2014, but Ug99 races were not detected. The Wheat Research Centre in Bangladesh works in collaboration with CIMMYT and BGRI to develop high yielding rust resistant wheat varieties. Advanced lines and breeding materials are screened every year at KARLO, Kenya, and EARI, Ethiopia, for resistance to Ug99. Rapid multiplication of pre-released and newly released rust resistant varieties is given top priority for quick replacement of rust susceptible varieties. Currently, about 60% of the wheat area is covered by leaf rust resistant varieties released in the last five years, including around 20% of the area covered by varieties with adult plant resistance to Pgt race Ug99. About 40% of the wheat area is still covered by older varieties such as Prodip. Another Ug99 resistant variety (BARI Gom 29) released in 2014 is undergoing seed multiplication. Large scale seed multiplication of Ug99 resistant varieties is part of a broader strategy to mitigate the potential threat. In the last four years, about 125 tonnes of breeder seed and more than 50 thousand tonnes of certified seed of rust resistant varieties were produced and distributed to seed production agencies and to farmers. Rust surveillance is conducted on a regular basis in the major wheat growing areas. About 50% of the sites surveyed in 2014 had moderate to high severities of leaf rust, but in 2015 severities were much lower. These efforts have been very useful for sustaining and enhancing wheat productivity and production in Bangladesh.
Ethiopian Institute of Agricultural Research (EIAR)
Wheat rusts can be controlled by host resistance or chemicals. Ethiopian farmers are not widely experienced with chemicals. Sixty seven (49 bread wheat (BW) and 18 durum (DW)) non-replicated varieties were planted on 0.4 m2 plots at 22 rust hotspot locations in 2014. Kubsa and Digalu were used as susceptible checks for YR and SR, respectively. Rust severities were scored according to the modified Cobb scale. Ten YR and 12 SR hotspot locations with mean rust severities of ≥40% were used in data analyses. Kubsa had a mean 59% YR severity and Digalu, a 73% SR severity. Rust severity levels were divided into three categories, viz. low (≤35%), moderate (36-40%) and high (>40%), across locations for both diseases. The frequency of varieties with low YR severities in the BW group was 26.5%, medium 18.4% and high 55.1% compared to DW varieties at 61%, 28% and 11%, respectively. In the case of SR, both BW and DW had large proportions of entries in the high severity category at 69.4% and 72.2%, respectively. The medium and low SR severity groups were represented by 20.4% and 10.2% for BW, and 11.1% and 16.7% for DW, respectively. In summary, the top 10 widely cultivated BW and a few DW varieties categorised in the medium and high severity groups for both YR and SR, would definitely require fungicides in rust-prone areas for optimum disease control. Many cultivars released after 1974 are still cultivated indicating that susceptible varieties are only slowly replaced. Hence, development and distribution of resistant cultivars, replacement of susceptible cultivars, and training industry workers and farmers on effective field scouting and fungicide use will be paramount for sustainable wheat production in Ethiopia.
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.
Universidad de las Américas, Ecuador
Identifying and tracking new races of wheat rust pathogens in a timely manner is important for early warning of disease potential in wheat-growing regions. Ecuador, located in northwestern South America, serves as a strategic monitoring location for rust fungi between the wheat production areas of North and South America. New races are likely to occur more often when the fungus is in the proximity of the alternate Berberis species host. More than 30 Berberis species have been reported in Ecuador, most of them endemic. However, most herbarium collections correspond to types, have only been found once, and/or date back 20 years or more. Therefore, the current status of diversity in Berberis spp. in Ecuador is largely unknown. Our goal is to collect Berberis species in Ecuador, document their distribution, prepare herbarium specimens, and identify the species morphologically and genetically. We will use this information to establish the relationships of neotropical Berberis species with Berberis in other parts of the world, and determine the pathogenicities of various rust fungi associated with them. Preliminary results show that the Ecuadorian Berberis spp. are phylogenetically distinct from those of Argentina and Brazil. To date, the rust fungi on Ecuadorean Berberis do not infect wheat. We have identified three potentially new rust fungal species based on DNA analysis.