All BGRI Abstracts

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Durable rust resistance - Understanding “R” and “APR” in cereal hosts

Zhang National Research Council of Canada, Canada

Leaf rust is the most widely occurring disease of wheat worldwide. Resistance is the most practical and effective way to control the disease. Most leaf rust resistance genes are race-specific (“R”, qualitative resistance) and a relatively few are adult plant resistance genes, some of which have been described as slow rusting (“APR”, quantitative resistance). Due to limited knowledge, most resistance genes have been deployed in cultivars by an inefficient “blind” approach. This results in the well known “boom and bust cycle” (resistance followed by susceptibility) because the pathogen evolves rapidly and migrates over long distances. Therefore, a breeding-by-design approach is needed to achieve durable resistance. Pyramiding multiple R, APR or APR+R genes has been used successfully over many years to achieve durable resistance to leaf rust in Canada and some other countries. To further enhance this strategy we seek to understand the molecular mechanisms underlying key resistance genes. To identify the molecular mechanisms underlying rust resistance conferred by major R and APR genes, we performed an integrated systemic transcriptome analysis via RNA-seq on the Thatcher NILs with Lr16, Lr22a, Lr21, Lr34, Lr34+Lr16, and Lr67 challenged with Pt race BBBD. Sampling was conducted over a time series during the infection process of both seedlings and adult plants. Through RNA-seq we were able to capture the dynamic interactome of host-pathogen interactions conferred by these R and APR genes. Preliminary results revealed that resistance reactions conferred by R gene Lr21 and APR gene Lr67 were significantly different compared to other R and APR genes. Significantly, the Thatcher NIL line with Lr34+Lr16 showed the combines defense reactions of Lr16 and Lr34.     

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Avirulence/virulence phenotypes of Puccinia striiformis f. sp. tritici samples collected from wheat in Ecuador, 2001-2014

Ordonez Pontificia Universidad Católica del Ecuador, Ecuador

Stripe rust is the most important disease of wheat in Ecuador. Knowledge of race diversity of the pathogen population is limited. Here we present avirulence/virulence phenotypes found in Pst samples collected from wheat between 2001 and 2014. A total of 30 isolates from the Ecuadorian highlands were tested on 15 near-isogenic wheat lines carrying single resistance genes; 21 races were identified. Lines with Yr2, Yr3, Yr26 and Yr27 were not tested in some years. Virulences to Yr1, Yr6, Yr7 and Yr9 were the most frequent (over 70%) in all years, followed by virulence to Yr17 (67%) and Yr27 (53%). Virulence to Yr8 was not found in 2013 and 2014. Virulence to Yr24/Yr26 was present in each year except 2014, although at a low level. Virulence to Yr10 was low. There were some unconfirmed discrepancies from a perfect association of virulences to Yr24/Yr26 and Yr10. Virulence to YrSP increased up to 2013, but was absent in 2014. There was no virulence to Yr5 and Yr15. Despite limited sampling, a diverse population of Pst seems to be present in Ecuador, with virulence for most resistance genes being present. Based on these analyses resistance to Pst in Ecuador could be achieved with Yr5 and Yr15, together with Yr24Yr26, and perhaps YrSP. One possibility for the high pathogenic variation might be sexual recombination on one or more of the 32 Berberis species reported in Ecuador. This needs to be examined along with more intensive sampling from wheat and analysis of the actual resistance genes present in current cultivars.

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Distribution resistance genes and strategies for sustainable control of wheat stripe rust in China

Zhou State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, P.R. China

The appearance and spread of new Pst races are common consequences of the widespread use of single resistance genes in one or more widely grown cultivars, with epidemics occurring some time later. Based on the geographical situation in China, epidemiology of stripe rust can be divided into three major zones, namely autumn sources of inocula, spring sources of inocula, and the spring epidemic areas. About 67 stripe rust resistance genes (Yr1 Yr67) and some temporarily designated genes have been catalogued in cultivated wheat varieties. Many of the genes have unique linked markers that enable their transfer by marker assisted selection (MAS). We recommend firstly that wheat breeders, rust geneticists and pathologists work in together in evaluating the effectiveness of resistance in multi-pathotype seedling tests in the greenhouse and in field trials at hot-spot locations to identify the genes conferring stable resistance across environments; and secondly to apportion the available resistance genes to the different epidemiological regions. We expect that such regional diversity of resistance genes will provide strong barriers to seasonal spread between regions.

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Yellow rust in Georgia in 2010-2013

Natsarishvili Institute of Phytopathology and Biodiversity, Batumi Shota Rustaveli State University,Georgia

Stripe rust is a worldwide constraint to wheat production. The rust pathogens are assumed to have originated in the Caucasus, from which they disseminated into Western Europe and Asia (Zhukovsky 1965, Euphytica, 14; Stubbs 1985, The Cereal Rusts II). Rust surveys are a useful means to provide information on distribution. More than 400 wheat fields were monitored for rust incidence and severity and for collection of samples at 20 locations in Georgia during 2010-2013. The majority of wheat fields were occupied by Russian cultivars and Bezostaya-1 was the most common, followed by Copper and American cv. Jagger. Yellow rust was the most widely distributed rust, with>65% of fields showing its presence. In 2009 yellow rust incidence was moderate to high. Abundant overwintering inoculum, susceptible cultivars and favorable conditions resulted in severe epidemics in late May and early June 2010. Mean field incidence and severities were 74.8 and 84.6% in the Kakheti zone, and 70 and 68.2% in Kvemo Kartli. Incidence was lower in the following years due to drought and high late spring temperatures. Bezostaya 1 and Jagger showed moderately susceptible reactions to all three rust, but Copper was moderately resistant. Accessions of Georgian endemic species T. carthlicum, T. timopheevi, T. macha, T. georgicum and T. monococcum were resistant to all three rusts.

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Association mapping of resistance to stripe rust in a globally diverse panel of wheat accessions

Ng The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, Australia

Effective control of stripe rust (YR) requires deployment of resistant cultivars. Adult plant resistance (APR) is preferred over all-stage resistance because of its putatively durable nature. Discovery of new sources of resistance is a priority to combat rapidly evolving Pst races. Genebanks contain untapped genetic diversity that likely harbor novel resistance genes. We examined a diverse panel of 300 lines sourced from the Vavilov Institute, including landraces, cultivars and breeding lines from 28 countries. The most virulent Pst pathotype in Australia (134 E16 A+,Yr17+,Yr27) was used for all experiments, where YR reactions were determined on seedlings in a greenhouse and on adult plants in a field disease nursery. A total of 54% of accessions displayed all-stage resistance and 33% displayed moderate to high levels of APR. Accessions were genotyped using the DArTseq genotyping platform and using an association mapping approach we identified genomic regions associated with YR resistance. These were aligned with previously reported QTL and cataloged resistance genes on a consensus map. This enabled identification of novel genomic regions. Accessions carrying high levels of APR were screened using markers linked to well-known APR genes (i.e. Yr18, Yr29 and Yr46). Twenty two accessions carrying potentially novel sources of APR to YR were identified. Our current efforts are aimed at further characterizing and validating these genetic resources against a wide array of pathotypes and environments around Australia.

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Genetics of stem rust resistance in tetraploid wheats (Triticum turgidum ssp.)

Olivera Department of Plant Pathology, University of Minnesota, USA

Our research objective is to identify new resistance genes in cultivated and wild tetraploid wheats that are effective against race TTKSK and other Pgt races, and could be utilized in durum breeding. We characterized 7,000 durum and 360 emmer accessions for field resistance at Debre Zeit, Ethiopia, and Saint Paul, Minnesota. Accessions with resistant to moderately resistant responses in multiple field evaluations were characterized at the seedling stage for resistance to races TTKSK, TRTTF, TTTTF, JRCQC, TKTTF, and an additional six representative U.S. races. We identified 208 durum and 28 emmer accessions resistant to moderately resistant in all field and seedling evaluations. A search for resistance through seedling evaluations was also conducted on wild emmer (840 accessions) and four cultivated tetraploids (Persian, Polish, Oriental, and Pollard wheats, 560 accessions). About 20% of the accessions were resistant to race TTKSK. Thirty-six resistant accessions of cultivated and wild tetraploids were selected to investigate the genetics of TTKSK and TRTTF resistance. Results from evaluating F2 and F2:3 generations from biparental crosses revealed that resistance to race TTKSK in various subspecies of T. turgidum was conferred mostly by one or two genes with dominant and recessive actions. Additional resistance genes were identified when populations were evaluated against race TRTTF. A bulk segregant analysis approach is being used to map the resistance genes in selected resistant parents using the 90K SNP platform.

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Breeding strategies to decrease stripe rust epidemics in Uzbekistan

Ziyaev Kashkadarya Branch of the Grain and Leguminous Research Institute, Uzbekistan

Winter wheat production in Uzbekistan is threatened by yellow rust and leaf rust. Both rusts are capable of causing substantial economic losses, but their incidence varies due to different ecological requirements. Yellow rust caused significant yield losses in 2009, 2010, 2013, and in some regions, also in 2014. Several stripe rust resistant lines with high grain yield and desirable agronomic characteristics are being introduced through the International Winter Wheat Improvement Program (IWWIP) and submitted to the State Varietal Testing Commission. A number of new yellow rust resistant varieties were released for specific epidemiological areas of Uzbekistan. These varieties planted on about 200,000 ha are helping to reduce inoculum buildup and spread of rust in farmers’ fields. The objective of the present work was to identify locally adapted yellow rust resistant wheat lines in international nurseries. In 2014 448 winter wheat lines were evaluated for response to the prevailing Pst population under controlled conditions at the Plant Industry Research Institute and field conditions at the Kashkadarya Branch of the Grain and Leguminous Research Institute. Eighty lines were immune and 73 lines showed moderate to high levels of resistance in the field. Following agronomic assessments 55 lines were promoted to advanced multi-site yield trials. A set of selected lines was also distributed to other wheat research institutions within the country. It is expected that this process will lead to the release and deployment of more resistant winter wheat varieties in Uzbekistan.

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Progress in simultaneous selection for stable, high yielding, rust resistant wheat genotypes for Kenya

Macharia Kenya Agricultural and Livestock Research Organization, Kenya

In the past decade Pgt race Ug99 and its variants have been a challenge to wheat production in Kenya. Towards identifying suitable varieties, 37 lines selected from rust screening nurseries and 3 checks were tested for yield and adult plant reaction to natural stem rust epidemics across 11 diverse Kenyan environments in 2013 and 2014. Trial locations were chosen to mainly represent key wheat growing areas as well as three new sites. Evaluations based on the AMMI linear-bilinear model indicated significant (P≤0.01) genotype (G), environment (E), and GE interactions with the first three principal components (PC) explaining ~70% of the observed variation. With a contribution of over 90% to total sum of squares, environment was the predominant source of variation and the genotypic effect was approximately twofold higher than the GE effect. Based on biplot projections, clusters of lines were most closely associated with specific environments. Biplots also pointed to at least five environments, clearly those in traditional wheat growing areas that were highly correlated and associated with positive PC suggesting a similar ability to discriminate genotypes. Each non-traditional testing environment was associated with negative PC and was uncorrelated in its discriminatory ability. Combined yield and stability results achieved through classifying genotypes based on Shukla’s stability variance and Kang’s stability rating, revealed four genotypes (R1357, R1362, R1372, and R1374) as desirable candidates. The hitherto popular variety Robin, used as the ‘best check’ for yield, posted an at least 10% lower yield relative to the highest yielding genotype (R1357). Moreover, Robin which was released as a high yielding variety with adult plant resistance in 2009, was not stable in performance across environments, perhaps due its current susceptibility to a new Pgt race (TTKTT) within the race Ug99 group, that is virulent to the SrTmp-based resistance.

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Pst pathotypes and Yr gene postulation in Tunisian wheat

Hamza National Institute of Agronomy, Tunisia

Yellow rust is a widely distributed wheat disease, that is more damaging in cooler, temperate regions. Epidemics have increased worldwide due to spread of aggressive high temperature tolerant strains PstS1/S2 that reached North Africa and southern France in 2004 and the widely virulent exotic Warrior race that spread in Western Europe in 2011. Resistant varieties are effective solutions to reduce the use of pesticides. However, races of the pathogen quickly overcome resistance genes. Therefore, selection of varieties with durable resistance to yellow rust is paramount for protection of both bread wheat and durum. To conduct a genetic control strategy, it is essential to study the pathotype dynamics and the resistance genes in wheat. We identified the pathotypes using the European and world differential sets that discriminate between 23 avirulence/virulence factors as well as simple sequence repeat (SSR) diversity among 20 Pst isolates collected in Tunisia in 2014. In addition, we postulated resistance genes in 28 Tunisian varieties and accessions at the seedling stage in order to identify the resistance diversity. Race 239 E175V17 was involved in the 2014 epidemic in Tunisia. Genetic analysis revealed that this race is exotic and distinct from the Northwestern European and Mediterranean groups, previously present in Tunisia. Resistance gene postulation indicated the presence of Yr3, Yr6, Yr7, Yr9+Yr4, and Yr25 in Tunisian varieties and accessions. Durum varieties Khiar and Salim, and bread wheat variety Tahent, were resistant to the local Northwestern European and Western Mediterranean pathotypes as well as the Warrior race. These varieties are thus short-term measures to address the yellow rust problem in Tunisia. Gene identifications will be confirmed by molecular and pedigree analyses of the accessions.Yellow rust is a widely distributed wheat disease, that is more damaging in cooler, temperate regions. Epidemics have increased worldwide due to spread of aggressive high temperature tolerant strains PstS1/S2 that reached North Africa and southern France in 2004 and the widely virulent exotic Warrior race that spread in Western Europe in 2011. Resistant varieties are effective solutions to reduce the use of pesticides. However, races of the pathogen quickly overcome resistance genes. Therefore, selection of varieties with durable resistance to yellow rust is paramount for protection of both bread wheat and durum. To conduct a genetic control strategy, it is essential to study the pathotype dynamics and the resistance genes in wheat. We identified the pathotypes using the European and world differential sets that discriminate between 23 avirulence/virulence factors as well as simple sequence repeat (SSR) diversity among 20 Pst isolates collected in Tunisia in 2014. In addition, we postulated resistance genes in 28 Tunisian varieties and accessions at the seedling stage in order to identify the resistance diversity. Race 239 E175V17 was involved in the 2014 epidemic in Tunisia. Genetic analysis revealed that this race is exotic and distinct from the Northwestern European and Mediterranean groups, previously present in Tunisia. Resistance gene postulation indicated the presence of Yr3, Yr6, Yr7, Yr9+Yr4, and Yr25 in Tunisian varieties and accessions. Durum varieties Khiar and Salim, and bread wheat variety Tahent, were resistant to the local Northwestern European and Western Mediterranean pathotypes as well as the Warrior race. These varieties are thus short-term measures to address the yellow rust problem in Tunisia. Gene identifications will be confirmed by molecular and pedigree analyses of the accessions.

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Leaf rust on high yielding winter wheats in Chile

Madariaga National Institute of Agricultural Research [INIA], Chile

The physical environment and farming system in Chile are conducive to high yields from winter/alternate wheat cultivars. The national average yields for 2012-2014 were 6.5 t/ha for pasta wheat and 5.3 t/ha for bread wheat grown on 19,000 and 239,000 ha, respectively. The most efficient farmers obtain averages of 8-9 t/ha, and experimental plots at southern INIA sites are as high as 14 t/ha. The most important diseases are Septoria leaf blotch, stripe rust, powdery mildew, and BYDV. Recent increases of leaf rust on winter cultivars from near non-existence to the level of a major threat are a concern. Wheat cultivars such as Bicentenario INIA showed yield increases of 31.7% to reach 12.4 t/ha yield when sprayed twice with a mixture of strobilurin and triazol compared to 9.4 t/ha for the unsprayed control. Susceptible winter cultivars being introduced by private companies require complete chemical protection. In order to understand the virulences present in the pathogen population the Thatcher NILs were grown in 2014/15 under non-inoculated conditions in central [Chillan] and southern [Osorno] Chile. The Morocco check showed 100S, Thatcher 60S, TcLr1 40S, TcLr2b 30S, TcLr2c 40S, TcLr3a 30S, TcLr3ka 20S, TcLr3bg 30S, TcLr9 20S, TcLr10 60S, TcLr11 80S, TcLr12 60S, TcLr13 70S, TcLr14a 70S, TcLr15 50S, TcLr16 60S, TcLr17a 30S, TcLr18 20MR, TcLr19 0, TcLr20 30S, TcLr21 0, TcLr22a 0, TcLr23 70S, TcLr24 60S, TcLr25 0, TcLr26 60S, Lr27+31 80S, TcLr28 10MR, TcLr29 40MS, TcLr30 60S, TcLr32 70S, TcLr33 60S, TcLr34 70S, TcLr35 10MR–MS, Lr36 0, and TcLr37 0. The most significant differences (>40%) in response between the two locations were for TcLr2b, TcLr2c, TcLr11 and TcLr33. The Cereal Disease Laboratory (U.S.A.) tested 68 isolates from 55 samples from 2012/13 and identified 14 races, including one Triticum turgidum race (BBBQJ 26%). Significant breeding efforts are currently underway to address the leaf rust problem in Chile.

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