stripe rust

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Reactions of spring wheat genotypes in crossing block nursery to stem, leaf, and stripe rust

Rusts (Puccinia spp.) are the most significant disease affecting wheat yield and quality in Turkey. Knowing the resistance status of wheat genotypes in crossing program is an important issue for breeding programs. The aim of the study was to determine of the resistance of the 106 wheat genotypes consisting of Crossing Block Spring Wheat (CBSW) nursery developed by the International Winter Wheat Improved Project (IWWIP). For this purpose, adult plant and seedling test were conducted for yellow rust while only seedling test were conducted for leaf and stem rust. Evaluations were carried out at the research facilities of CRIFC at İkizce and Yenimahalle in Ankara in the 2014 season. For adult plant reactions; the genotypes were inoculated with local Pst populations (virulent on Yr2,6,7,8,9,25,27,Sd,Su,Avs). Stripe rust development on each entry were scored using the modified Cobb scale when the susceptible check Little Club had reached 80S infection severity in June, 2014. Coefficients of infections were calculated and values below 20 were considered to be resistant. For seedling test; the seedling was inoculated with local Pgt (avirulent on Sr24, Sr26, Sr27, and Sr31), Pt (avirulent on Lr9, Lr19, Lr24, and Lr28) and Pst populations. Stripe, leaf and stem rust development on each entry were scored after 14 days with 0-4 and 0-9 scale for leaf-stem rust and yellow rust, respectively. In seedling stage, thirty nine (37%), 47 (44%), and 20 (19%) genotypes were resistant to local Pgt, Pt, and Pst populations, respectively. In adult plant test, 46 (43%) genotypes were resistant to Pst.  The resistance genotypes to stem, leaf, and stripe rust were determined with this research.

 

Mert
The Central Research Institute for Field Crops, Turkey
Primary Author Email: 
mert_zafer@yahoo.com
Poster or Plenary?: 
Poster
BGRI Year: 
2015
Abstract Tags: 
geographic_area: 

Complementary resistance genes Yr73 and Yr74 (YrA) in wheat selection Avocet R confer resistance to the non-adapted barley grass stripe rust pathogen Puccinia striiformis f. sp. pseudohordei.

This is the first study on the inheritance and genetic mapping of resistance to the barley grass stripe rust pathogen (Puccinia striiformis f. sp. pseudohordeiPsph) in bread wheat. Psph, commonly infects barley grass (Hordeum leporinum, H. murinum), but about 10% of commercial barley varieties are also susceptible. We tested over 500 diverse wheat accessions and determined that less than 20% were susceptible at the seedling stage suggesting wheat is an ‘intermediate’ host to Psph. The Australian variety Teal is highly susceptible to Psph at the seedling stage, whereas selections Avocet S and Avocet R are highly resistant and resistant, respectively. We used the Teal/AvocetR doubled haploid (DH) population to characterize the resistance of Avocet R to Psph and determine whether the complementary genes Yr73 and Yr74 (YrA resistance) in Avocet R conferred resistance to Psph. Phenotypic comparison of the Teal/AvocetR DH lines in response to both Psph and Pst showed that all DH lines carrying YrA were also resistant to Psph; however, fewer DH lines were susceptible to Psph suggesting additional resistance genes. Marker-trait association analysis detected three DArT-Seq markers significantly associated with resistance to Psph, two mapping to chromosomes 3DL and 5BL in the same regions as Yr73 and Yr74 and the third mapping to chromosome 4A. Single gene stocks with the 4A gene and combinations of the 5BL and 3DL genes will be used for monitoring avirulence/virulence within Australian Psph population. Genetic analysis of seedling-susceptible T/AvR DH lines as adult plants in the greenhouse determined that Teal and Avocet R each carried at least one APR gene effective against Psph.

Dracatos
The University of Sydney, Plant Breeding Institute, Australia
Primary Author Email: 
peter.dracatos@sydney.edu.au
Resistance Gene Tags: 
Poster or Plenary?: 
Poster
BGRI Year: 
2015
Abstract Tags: 

The Stubbs Pst Culture Collection: Recovery, avirulence/virulence phenotyping and past population structure at a global scale

The "Stubbs Collection", began in 1956 by the late Dutch plant pathologist R.W. Stubbs, refers to a unique historic collection of urediniospore samples of Puccinia striiformis that had been stored in liquid nitrogen for decades. Since 2010 the collection has been maintained by the Global Rust Reference Center (GRRC) in Denmark. Part of the collection is now being in a study of past pathogen diversity. A subset of samples collected between 1958 and 1991 from 35 countries was investigated to assess recovery rate, race identity, and previously undetected virulences. A new method for recovery using an airbrush sprayer and NovecTM 7100 fluid as dispersal agent in inoculating host plants was highly successful, resulting in a 96% recovery from 231 isolates. Phenotyping on the World and European differential host sets and additional wheat genotypes revealed 181 apparently uniform isolates, of which race identities were confirmed for 102. Race identities were updated for additional isolates based on improved resolution due to updated and more informative differential lines. Additional virulences corresponding to Yr17, Yr25, and Yr27 were added, as these were not assayed earlier. The past population structure was investigated by genotyping 212 isolates using 19 multilocus microsatellites. Seven distinct populations were detected, including clonal populations and recombinant populations. These results were compared with recent studies and demonstrated an overall consistent population subdivision at the global scale with clear migration events between populations. The outcome of the study facilitates conclusions about long-term temporal dynamics and overall migration patterns within and among world-wide populations of Pst.

Thach
Department of Agroecology, Aarhus University, Denmark
Primary Author Email: 
tine.thach@agro.au.dk
Poster or Plenary?: 
Poster
BGRI Year: 
2015
Abstract Tags: 

The effector repertoire of Puccinia striiformis subdues host-plant immunity

Rust outbreaks cause severe yield lossespose a serious threat to global food security. As biotrophic pathogens, rust fungi produce effectors to suppress host immunity. In this study, we used a systemic approach to identify and characterize effectors in Puccinia striiformis f. sp. tritici. Among secreted proteins encoded by the Pst genome, we identified 150 putative effectors that are Cys-rich or up-regulated during hostinfection. A systematic screen showed that 14 of them suppressed programmed cell death (PCD) triggered by BAX and INF1 in Nicotiana benthamiana, and all have high intra- and inter-species polymorphisms at the protein level. Although these 14 effectors individually made only minor contributions to Pst virulence, delivery of them into wheat plants via a bacterial type-III secretion system efficiently suppressed PTI and ETI. Interestingly, three of them, Pst_4941, Pst_4884, and Pst_5578, triggered HR-like PCD in the AvSYr1NIL, but only Pst_4941 also caused PCD in the AvSYr7 NIL, suggesting that they may function as avirulence factors. This study suggests that Pst effectors function to suppress PTI and ETI.

Wang
State Key Laboratory of Crop Stress Biology for Arid Areas and College of Agronomy, Northwest A&F University, P. R. China
Primary Author Email: 
tclbad@163.com

Pathogenic variation in Puccinia striiformisf.sp.tritici(Pst) Following selfing on Berberis shensiana

Pst is highly variable, and new races that overcome newly released resistant cultivars are regular events. The widely virulent race V26 (virulent to Yr26) has a significant potential to cause epidemics in China. In this study teliospores from a single urediniospore isolate of V26 (No. Pinglan 17-7) produced on the Nanjing wheat line 92R137 (Yr26) were induced to germinate and infect Berberis shensiana as a sexual host. One hundred and eighteen single aeciospore (SA) selfed progeny and the V26 parent were typed for pathogenicity on a set of differentials comprising 22 Yrnear-isogenic wheat lines (NILs). Virulence phenotyping was conducted twice for all isolates, and similar results were obtained each time. The V26 isolate (No. Pinglan 17-7) was avirulent on differentials with Yr5, Yr6, Yr8, Yr15, Yr43, YrSp, YrTr1 and virulent on those with Yr1, Yr2, Yr4, Yr7, Yr9, Yr10, Yr17, Yr25, Yr26, Yr27, Yr28, Yr32, Yr44, YrV23, and YrExp2. The progeny were all virulent to Yr1, Yr2 (Kalyansona), Yr7, Yr9, Yr10, Yr17, Yr25, Yr26, YrV23 (Vilmorin 23) and YrExp2, and all avirulent to Yr5, Yr8, Yr15, and YrTr1, suggesting that V26 is homozygous at the corresponding pathogenicity loci. Various segregation ratios were apparent for other Yrgenes (P values ranging from 0.6to 0.09).These included3 avirulent: 1 virulent with respect to Yr6 and Yr43, 1 avirulent : 3 virulent forYr27 and Yr28, 1 avirulent : 15 virulent forYr4, Yr32, and Yr44,and 13 avirulent : 3 virulent for YrSp. Among the 118 progeny,27 of new pathotypes were identified as compared with the avirulence/virulence loci of the parent isolate. A study of the population based on markers and development of a molecular map is in progress.

Kang
State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, P.R. China
Primary Author Email: 
kangzs@nwsuaf.edu.cn

Determining the breeding value of CIMMYT’s International Bread Wheat Nursery (IBWSN) entries for leaf, stem and stripe rust resistance

The quest for durable rust resistance in wheat is burgeoning with the emergence of new virulent races. Breeders challenged with this unceasing plant-pathogen arms race have to devise strategies for effective evaluation and exploitation of the rust resistance genes. Considering the likely presence of useful variation for rust resistance in CIMMYT’s international bread wheat screening nurseries (IBWSN), we implemented genomic prediction in the 45th and 46th IBWSN entries to determine their genomic estimated breeding values (GEBV’s) for leaf, stem and stripe rust resistance. The 350 lines (45th IBWSN) and 329 lines (46th IBWSN) were phenotyped in replicated trials over two to three years in El Batan, Mexico (leaf rust); Njoro, Kenya (stem rust) and Toluca, Mexico (stripe rust). The filtered genotyping data for these two nurseries comprised of 6,786 and 11,218 genotyping by sequencing (GBS) markers. Our objective was to compare the GEBV’s estimated by four different models: multiple linear regression (MLR) with QTL-linked markers as fixed effects; Genomic-best linear unbiased prediction (G-BLUP); G-BLUP mixed model which includes QTL linked markers as fixed effects and Bayesian least absolute shrinkage and selection operator (LASSO). We observed that the prediction accuracies (calculated using 10-fold cross validation) were the highest for stripe rust (0.52 to 0.61), followed by stem rust (0.42 to 0.65) and leaf rust (0.15 to 0.45). Among the models, the MLR gave the lowest prediction accuracies (0.15,0.42 and 0.52), while G-BLUP (0.45,0.59 and 0.59), mixed G-BLUP (0.38,0.65 and 0.62) and the Bayesian LASSO (0.45,0.58 and 0.61) yielded relatively higher and almost similar accuracies. Overall, our results are promising and indicate that using genome-wide markers is advantageous than including only significant QTL-linked markers. We hope that implementing genomic prediction in breeding programs, would help to achieve rapid gains from selection and revolutionize our efforts in combating the rust pathogen.

Juliana
Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, USA
Primary Author Email: 
fp228@cornell.edu

Breeding Studies of Resistant Varieties to Stripe and Stem Rust Diseases in West Transitional Zone of Turkey

The most serious wheat diseases affecting yield and quality in West Transitonal Zone of Turkey is rust diseases. Breeding resistant varieties is the most economic and confident way to struggle with these diseases. In this study, it was aimed to determine the genotypes which are resistant to stripe and stem rust diseases existing in our region and use these genotypes as material in breeding program. The study was carried out in 2014 at natural and artificial epidemic conditions in the experimental field of  Transitional Zone Agricultural Research Institute. The reactions of some wheat genotypes to stripe and stem rust diseases caused by the fungal agents P.striformis ve P.graminis were detected. For this purpose,  310 lines and  18 variety of  bread wheat belonging to Transitional Zone Agricultural Researh Institute were sown in a way 1 m x 1 row. The disease assessments were conducted in May-June 2014 according to the Modified Coob Scale. As a result of infection coefficient observations, it was determined that 49% of the material are resistant to stripe rust and 60% of the material are resistant to stem rust.

Belen
Transitional Zone Agricultural Research Institute, Turkey
Primary Author Email: 
savasbelen@gmail.com

Identification and validation of SNP markers linked to the stripe rust resistance gene Yr5 in wheat

Stripe rust (Puccinia striiformis f. sp. tritici) is a devastating disease of wheat production world-wide. Yr5 is a race-specific resistance gene effective to all races which have been identified in the U.S. Therefore, it has been increasingly used for cultivar development in the U.S.  The goal of this study was to identify “breeder friendly” SNP markers associated with Yr5 through linkage mapping in a spring wheat recombinant inbred line (RIL) population and validate these markers with an additional RIL population, Pacific Northwest (PNW) wheat elite breeding materials, and a world-wide collection of spring wheat. RIL populations were developed from a cross between moderately susceptible experimental line WA8149 and two elite Yr5 donors, S0900317 and S0900163. Seventy PNW spring and winter wheat lines either carrying Yr5 or not, and 3,040 hexaploid spring wheat lines from a world-wide collection were used to further validate flanking markers for Yr5. Seedling resistance response to isolates Pstv-37 and Pstv-51 was evaluated for these RIL populations. These RILs were genotyped with 46 KASP markers located on chromosome 2B in addition to previously reported Yr5 linked markers, wmc175 (Murphy et al. 2009) and TaAffix65234.1.S1_at (McGrann et al. 2014). Linkage mapping was conducted by MapDisto v1.7.5. A total 10 markers localized Yr5 within 0.7 cM chromosome region in the WA8149/S0900317 population of 300 RILs. The same set of markers also localized Yr5 within 3 cM chromosome region in the WA8149/S0900163 population of 274 RILs. Newly identified KASP markers were closer to Yr5 than wmc175 and TaAffix65234.1.S1_at in these two populations. These markers were further validated with PNW winter and spring wheat and a world-wide collection of spring wheat. These KASP markers flanking Yr5 reliably selected for germplasm carrying Yr5 and will assist in pyramiding different resistances into breeding lines to develop more durable stripe rust resistant cultivars.

Nauoka
Department of Crop and Soil Sciences, Washington State University, USA
Primary Author Email: 
yukiko.naruoka@wsu.edu

Current status of wheat rust and its management approaches in Nepal

Wheat is one of the three most important food crops of Nepal for which rusts (Puccinia triticina, P.striiformis and P.graminis) are major biotic stresses. Leaf rust is widespread and causes 14-20% yield losses and speculated that P.triticina over summer on self-sown wheat in hills of Nepal. Twenty two different pathotypes of P.triticina have been recorded while thirteen leaf rust resistant genes (Lr1, Lr3, Lr10, Lr13, Lr14a, Lr16, Lr17, Lr19, Lr23, Lr26, Lr27, Lr31 and Lr34) either singly or in combinations, impart resistance to wheat genotypes in Nepal. Yellow rust is also a major disease in mid and lower hills, river basin and valleys, causing 30-80 % grain yield losses. Twenty-nine pathotypes of P.striiformis have been recorded till now in Nepal while nine Yr genes (Yr2, Yr2 KSA, YrA, Yr6, Yr7, Yr9, Yr27, GA, and SU) have been postulated. Stem rust is a minor and sporadic disease in central, western, mid-western region late in the season. Nine Sr genes (Sr2, Sr5, Sr7b, Sr8, Sr8a, Sr9b, Sr11, Sr25 and Sr31) have been characterized. Vijay was the first Ug99 resistant wheat variety released for cultivation. Previous experiences show that Nepal served as a focal point of wheat rusts for further spread in the Gangetic plains of India due to presence of more than 25 species of Berberis in hills of Nepal. Efforts are underway to survey rusts infection on Berberis spp. Use of Tilt (Propiconazole), Triadimefon (Bayleton) and Indar (RH-124) was found effective to reduce leaf rust as well as foliar blight. Cultivation of resistant varieties in Nepal not only reduces rust severity in this country but also minimizes crop losses in other neighboring countries especially India. This demands the need for regional collaboration in South Asia to combat wheat rusts.

Mahto
Plant Pathology Division, Nepal Agricultural Research Council (NARC), Nepal
Primary Author Email: 
bnmahto_7@yahoo.com

Complementary resistance genes in wheat selection Avocet R conferring resistance to stripe rust

This study reports the inheritance and genetic mapping of YrA seedling resistance to stripe rust in a resistant selection of the Australian spring wheat variety Avocet (AUS20601). Genetic analysis was performed on F2 and F3 generation families derived from crosses between wheat genotypes previously reported to carry the YrA resistance and lines that lack the YrA resistance phenotype. Seedling tests with two Pst pathotypes (104 E137 A- and 108 E141 A-) avirulent with respect to YrA confirmed that the resistance was inherited as two complementary dominant genes. Ninety-two doubled haploid (DH) lines derived from a cross between the Australian cv. Teal (seedling-susceptible) and Avocet R were used to confirm the mode of inheritance of YrA and to develop a DArT-Seq genetic map to locate the components of the YrA resistance. Marker-trait association analysis based on 9,035 DArT-Seq loci mapped the two genes to chromosomes 3DL and 5BL. F2 populations derived from intercrosses of seedling susceptible DH lines that carried each gene (based on marker genotype) reproduced the YrA phenotype and specificity, confirming the complementary resistance gene model. The YrA resistance component loci were designated Yr73 (3DL) and Yr74 (5BL). Candidate single gene reference stocks will be permanently accessioned following cytological analysis to avoid a T5B-7B translocation in Teal relative to Avocet and Chinese Spring.

Dracatos
The University of Sydney, Plant Breeding Institute, Australia
Primary Author Email: 
peter.dracatos@sydney.edu.au

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