Resistances conferred by Sr2 and Fhb1 are considered important in the control of stem rust and Fusarium head blight (FHB), respectively, but these genes on chromosome 3BS are known only to occur in repulsion. The objective of this study was to use a doubled haploid (DH) population of Carberry/AC Cadillac to seek a recombinant with the Sr2 and Fhb1 resistance alleles in coupling. Carberry expresses moderate resistance to FHB. AC Cadillac has marker alleles typically linked to the Sr2 resistance allele. Carberry has marker alleles associated with Fhb1. The DH population was genotyped with 578 DArT®, 55 SSR, 2 BAC-derived, 2 CAPS, and 1 STS markers. The parents and 261 DH lines were evaluated for adult plant stem rust response (Ug99) at Njoro, Kenya, and at Swift Current, Canada (Canadian Pgt races). Response to FHB was evaluated in nurseries near Portage la Prairie, Manitoba. Pseudo black chaff (PBC), known to be tightly linked to Sr2, was scored in nurseries when symptoms were expressed. Both cultivars have other Sr and Fhb resistance genes, and QTLs contributing to PBC on chromosomes other than 3BS. Using phenotypic and molecular marker data, and the very tight linkage or pleiotropic relationship of Sr2 with PBC, DHs were classified for presence of PBC and FHB response. Putative recombinant DH candidates were re-evaluated for symptoms of PBC, stem rust, and FHB in three international nurseries and genotyped with markers closest to Sr2 and Fhb1. The results will be presented.
Primary Author: DePauw, SeCan Association, Canada
Keywords: pseudo black chaff, Sr2, fhb1
Epidemics of stripe (yellow) rust on wheat and triticale fields of Algeria in 2016. Wheat and triticale fields in 69 localities from the eastern regions of Algeria were assessed for epidemics, which started in early march to late may corresponding to booting stage up to early dough stage of the alternative type crop. The infection had incidences ranging from 30 to 100% and severities of 30 to 70%. The newly released cultivar Ksar sbahi was infected up to 10%. The old improved durum cultivars HAR3116 (SHA7/KAUZ) and HAR1407 (COOK/VEES//DOVES) were rust-free at a number of locations. In the Amhara region, the wheat cultivars were at stem elongation to flowering with disease incidences of 50-100% and severities of 30-90%. The oldest cultivar ET 13 A2 was severely infected in the north Shewa zone of Amhara region. Triticale cultivar Logaw Shibo was susceptible at elevations above 2700 m and showed trace reactions at elevations below 2500 m. The local bread wheat cultivar grown in all wheat growing areas was only slightly affected by the disease. Yellow rust was rarely recorded in the Tigray region. Severe epidemics were recorded in the highlands and even at lower elevations where it is not commonly found on wheat.
Primary Author: DERBAL, Laboratoire de Biologie, Eau et Environnement, département d'écologie,university of 8 mai1945 Guelma, Algeria
When environmental stress develops during reproductive phases of growth, wheat plants have to rely increasingly on remobilisation of previously stored assimilates to maintain grain filling. The present study was undertaken to determine the effect of several peduncle (the uppermost stem internode) morpho-anatomical and biochemical traits on grain weight, and to assess the contribution of the peduncle water-soluble carbohydrate (WSC) reserves shortly after anthesis to its variation. In 2-year field trials, 61 wheat genotypes were used (27 F4:5 families, 17 parents used for the crosses and the 17 current best standards) comparing intact control plants (CP) with plants that were defoliated (DP) by cutting off all leaf blades 10 days after anthesis to simulate terminal stress. Estimated contributions of peduncle assimilate reserves to grain weight/spike were from 0.06 to 0.31% and from 0.11 to 0.45% in CP and DP plants, respectively. High peduncle reserve mobilization efficiency, a longer exposed part of the peduncle and larger peduncle storage capacity (through higher parenchyma and/or lower lignified area) were of specific benefit for maintaining grain weight in defoliated plants. There was a large difference in compensation of grain yield loss by dry matter remobilization within studied genotypes (in average 1.2-36.1%). Although compensation of yield loss might be improved through breeding process (our F4:5 families had slightly higher mean compensation effect than their parents under moderate stress), it does not mitigate the effect of post-anthesis drought in great extent (up to 38.4%).
Primary Author: Dodig, Maize Research Institute Zemun Polje
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.
Primary Author: Dracatos, The University of Sydney, Plant Breeding Institute, Australia
Keywords: stripe rust, resistance, avocet
This is the first study on the inheritance and genetic mapping of resistance to the barley grass stripe rust pathogen (Puccinia striiformis f. sp. pseudohordei – Psph) 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.
Primary Author: Dracatos, The University of Sydney, Plant Breeding Institute, Australia
Keywords: stripe rust, barley, Yr73, Yr74, avocet
Stripe rust (Puccinia striiformis f. sp tritici) (Pst) infected wheat samples collected from three Egyptian Governorates (Alexandria, Beheira and Kafr-El Sheikh) were processed for race analysis to determine the race identity among the current populations of the stripe rust fungus. Single uredinial isolates were inoculated to a core set of the 17 World/European differential hosts along with wheat lines with Yr17, Yr25, Yr32. Based on virulence phenotyping, the data revealed that the current populations of Pst belong to three races: Triticale aggressive (virulent to Yr2, Yr6, Yr7, Yr8, Yr10); PstS3 (virulent to Yr2, Yr6, Yr7, Yr8, Yr25); and PstS2 (virulent to Yr2, Yr6, Yr7, Yr8, Yr9, Yr25, Yr27). No collections were found with the Warrior race, that has virulence to Yr1, Yr2, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr25, Yr32, YrSp).
Primary Author: Draz, Wheat Disease Research Department, Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
Keywords: stripe rust
The wild relatives of wheat represent a vast resource of potentially useful genes for agriculture. The genus Aegilops has provided several rust resistance genes used in commercial cultivars. Here we report progress on mapping of potentially new stem and leaf rust resistance from Ae. caudata, Ae. searsii and Ae. mutica (Amblyopyrum muticum). Addition lines derived from the amphiploids Alcedo/ Ae. caudata, TA3368, CS/ Ae. mutica, TA8024 (both from Wheat Genetics Resource Center, Kansas State University, USA) and CS/ Ae. searsii TE10 (kindly provided by Dr Moshe Feldman, Weizmann Institute, Rehovot, Israel) were produced after backcrossing the amphiploids with Australian cv. Angas or Westonia. Backcrossed generations were screened for stem rust and leaf rust responses and both resistant and susceptible plants were sampled for DNA marker analysis. Stem rust resistant plants derived from the Ae. caudata amphiploid and leaf rust resistant plants derived from the Ae. searsii amphiploid showed the presence of non-wheat marker bands after hybridizing restricted genomic DNA with the Triticeae group 5 RFLP probe PSR128, and after PCR using EST-based primers specific for Triticeae group 5. Susceptible plants did not show those non-wheat molecular markers. Hence, stem rust resistance from Ae. caudata was allocated to chromosome 5C, and the resistance gene is temporarily named SrAec1t. Leaf rust resistance from Ae. searsii was allocated in a similar manner to chromosome 5Ss, and is temporarily named LrAesr1t. Leaf rust resistance transferred from Ae. mutica was traced to a 6T chromosome after associating resistance with the presence of Triticeae group 6 RFLP probes (including BCD001, BCD269, BCD276, BCD1426, CDO772, CDO1380, WG933) and that gene is temporarily named LrAmm1t. The addition lines involving the 5C, 5Ss and 6T chromosomes were crossed with Sears’ ph1b mutant to induce homoeologous recombination with related wheat chromosomes.
Primary Author: Dundas, School of Agriculture, Food and Wine, The University of Adelaide, Australia.
Keywords: wild relatives, resistance genes, stem rust, leaf rust, land races
Bread wheat (Triticum aestivum L.) being the world's most popular edible cereal, plays a major role in global economy. Rust in wheat leaves, caused by Puccinia triticina, affects grain quality and severely retards its production worldwide. Micro(mi)RNAs are considered major components of gene silencing and so have a great role to play during stress. The present study focuses on identification of miRNAs, produced by host to suppress pathogen as well as delivered by pathogens to encounter host defence mechanism. Therefore, these miRNAs may be called as leaf rust responsive microRNAs. Small RNA and degradome libraries were prepared from a pair of near isogenic lines of wheat (HD2329, HD2329+Lr24), one set was mock inoculated while the other set was inoculated with urediniospores of leaf rust pathogen. Using these libraries as input a vast number of miRNAs rather a population of miRNAs were identified derived from wheat that were targeting genes mostly involved in functions like defense response, signal transduction, development, metabolism, and transcriptional regulation.
When reads specifically produced under pathogen inoculation were taken as input with Puccinia triticina genome sequences as reference, only three putative miRNA precursor loci were detected and the molecules produced were called miRNA-like molecules as their precursors lacked one or two criteria essential for a true miRNA precursor. The identified miRNAs were targeting genes like F-box protein, MAP kinase, calmodulin and susceptible antioxidant protein. We further identified the presence of argonaute and dicer like domains in Puccinia proteome available at FungiEnsembl which strengthens presence of RNAi-like activities in Puccinia.
In addition, differential expression of wheat as well as Puccinia small RNAs using stem loop RT-PCR under varying time points of disease progression (0-168 hpi) revealed their direct connection with stress responses.
Primary Author: Dutta, Department of BioEngineering, Birla Institute of Technology, Mesra, Ranchi, India
Keywords: leaf rust
Stem rust of wheat caused by the fungal pathogen Puccinia graminis f. sp. tritici historically caused major yield losses of wheat worldwide. To understand the genetic basis of stem rust resistance in contemporary North American spring wheat, genome-wide association analysis was conducted on 250 elite lines. The lines were evaluated in separate nurseries each inoculated with a different P. graminis f. sp. tritici race for three years (2013, 2015 and 2016) at Rosemount, Minnesota. The lines were also challenged with the same four races at the seedling stage in a greenhouse facility at the USDA-ARS Cereal Disease Laboratory. A total of 22,310 high-quality SNPs obtained from the Infinium 90,000 SNPs chip were used to perform association analysis. Markers strongly associated with resistance to the four races at seedling and field environments were identified. At the seedling stage, the most significant marker-trait associations were detected in the regions of known major genes (Sr6, Sr7a and Sr9b) except for race QFCSC where a strong association was detected on chromosome arm 1AL. Markers presumably linked to Sr6 and Sr7a were associated with both seedling and field resistance to specific races. A field resistance QTL on chromosome arm 2DS was detected for response to races RCRSC and TPMKC. A QTL specific to field resistance was detected for QFCSC and TPMKC on 2BL. The markers that showed strong association signals may be useful to pyramid and track race-specific stem rust resistance genes in wheat breeding programs. We postulated the presence of Sr2, Sr6, Sr7a, Sr8a, Sr9b, Sr11, Sr12, Sr24, Sr25, Sr31, and Sr57 (Lr34) in this germplasm based on phenotypic and marker data. We found that combinations of genes conferring resistance to specific P. graminis f. sp. tritici races accounts for the prevalent stem rust resistance in North American spring wheat.
Primary Author: Edae, University of Minnesota
Keywords: stem rust, major genes
Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a significant disease limiting wheat yield in Ethiopia. Wheat varieties such as 'Digalu' with single major-effect stem rust resistance genes have not exhibited durable resistance in Ethiopia. Identifying wheat lines with adult plant resistance (APR) has been proposed as a strategy to select for durable resistance. Our objective was to test the hypothesis that APR to stem rust is non-race-specific. We selected 31 wheat lines (including 10 durum and 21 bread wheat lines) that were susceptible as seedlings to Pgt races TTKSK, TKTTF, and TRTTF. These 31 wheat lines and Digalu were evaluated in 2014 and 2015 at the Kulumsa Agricultural Research Center, Ethiopia. The lines were planted in 1 m rows and replicated twice in separate single-race-inoculated nurseries. The three single-race nurseries inoculated with Pgt races TTKSK, TKTTF, and TRTTF were separated by at least 100 m and included selective spreaders. Plot yield, thousand kernel weight (TKW), and visual disease responses were measured for each plot. We used a least-squared means test to detect differences in coefficient of infection and TKW of each line across paired race comparisons. Lines 'Park', 'CI11469', and 'CI12818' displayed significantly different coefficient of infections between races TTKSK and TRTTF. For CI11469 and CI12818, this difference was validated by significant differences in TKW. Significant differences in TKW were also detected between various race comparisons for 'ETHBW019', 'CI14798', 'CI15159', 'CI14618', and 'CI14094'. Our data demonstrated that APR in the selected germplasm was largely non-race-specific, but there were exceptions where race-specificity of APR was detected. These results have implications for resistance breeding and monitoring: testing of breeding material against prevalent Pgt races in target environments, not relying only on hotspot screening locations, and careful monitoring of deployed APR varieties are all warranted.
Primary Author: Edae, University of Minnesota
Keywords: Ethiopia, stem rust