Saturation of the Yr34 region of wheat chromosome 5AL to identify closely linked SNP markers
The University of Sydney Plant Breeding Institute, Australia
Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is a major threat to global food security. Although stripe rust was detected for the first time in Eastern Australia in 1979, Western Australia (WA) remained free from stripe rust until 2002. The Pst incursion in WA was pathotyped as 134 E16A+ and differed from the most widely virulent pre-2002 group by combined virulence to Yr8 and Yr9 and avirulence for Yr3 and Yr4. An advanced breeding line, WAWHT2046, expressed resistant to moderately resistant (R-MR) response to 134 E16A+ under field conditions, and infection type (IT) 23C - 3C at the seedling stage. The resistance gene Yr34 that controlled stripe rust in WAWHT2046 was 12.2 cM distal to the awn inhibitor B1 in chromosome 5AL (Bariana et al. 2006; Theor Appl Genet 112:1143-1148) based on a Carnamah/WAWHT2046 doubled haploid (DH) population. The present investigation was planned to identify SNP markers closely linked with Yr34. Eight homozygous resistant and eight homozygous susceptible lines from the Carnamah/WAWHT2046 DH population were used for selective genotyping using SNP markers. Twenty four SNP markers were associated with resistance. Kompetitive allele-specific primers (KASP) were designed and SNP markers were genotyped on the DH population. SNP marker IWB80451 mapped 1.7 cM proximal to Yr34.
Segregation for avirulence/virulence in Puccinia striiformis based on an experimental genetic system using Berberis vulgaris
Department of Agroecology, Faculty of Sciences and Technology, Aarhus University, Denmark
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An experimental genetic system for Puccinia striiformis was recently developed using the alternate (sexual) host, Berberis vulgaris. Selfing of an aggressive Pst isolate resulted in an S1 generation of 16 progeny, which were confirmed by segregating SSR markers. We analyzed the inheritance of avirulence/virulence in the S1 generation using wheat genotypes representing 21 Pst resistance genes. All S1 progeny were virulent for 14 of 15 Yr genes where the parental isolate was virulent. No segregation was observed for 5 of 6 host genes for which the parental isolate was avirulent. Segregation was observed with respect to Yr8 where the parental isolate gave infection type (IT) 0, and to Yr17 where the parental isolate gave IT 5-6 (0-9 scale). Avirulence/virulence to Yr8 (Compair and AvS+Yr8) was represented by two phenotypes, and avirulence/virulence to Yr17 (VPM1, AvS+Yr17, and Baltimore) was represented by three host phenotypes. On both Yr8 host genotypes, some progenies produced IT 0 and others produced IT 1-2, suggesting that the parental isolate was heterozygous for two different Avr8 alleles resulting in different, but clearly avirulent phenotypes. On the Yr17 genotypes, two distinct phenotypes, IT 2-4 and 5-6 (occasionally 7), were observed, the latter being similar to the parental isolate. None of the progenies was considered virulent (IT 7 to 9), as observed for Yr17-virulent reference isolates. This unusual segregation pattern could be explained by the presence in the parental isolate of a heterozygous modifier gene influencing the phenotypic expression of avirulence. In order to resolve the genetics in detail, additional progeny are being produced from the parental isolate, and selfings of additional Pst isolates with divergent levels of aggressiveness are in progress.
Complementary resistance genes in wheat selection Avocet R conferring resistance to stripe rust
The University of Sydney, Plant Breeding Institute, Australia
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.
Phenotypic and genotypic analysis of stripe rust, leaf rust and stem rust resistance genes in Tajik wheat varieties
Tajik Agrarian University, 146, Tajikistan
The objective of this study was to characterize seedling and adult plant resistance to all three rusts in a set of 40 bread wheat varieties currently cultivated in Tajikistan. Gene postulation based on multi-pathotype seedling test data and adult plant responses identified Yr2, Yr9, Yr17 and Yr27; Lr10 and Lr26; and Sr5, Sr6, Sr10, Sr11, Sr31 and Sr38. The effects of slow rusting, adult plant, pleiotropic resistance genes Lr34/Yr18/Sr57 and Yr30/Lr27/Sr2 were observed in the field and confirmed with molecular markers. Furthermore, molecular markers diagnostic for Yr9/Lr26/Sr31 and Yr17/Lr37/Sr38 were assessed on all varieties. Genes Lr34/Yr18/Sr57, Yr9/Lr26/Sr31 and Yr27 were identified in varieties Sarvar, Vahdat, Oriyon, Isfara, Ormon, Alex, Sadokat, Ziroat-70, Iqbol, Shokiri, and Safedaki Ishkoshimi based on phenotypic and genotypic results. Some lines were highly resistant to stripe rust (4 varieties), leaf rust (5) and stem rust (9), but the genes responsible could not be identified. They may possess new resistance genes. We thus identified combinations of major and minor rust resistance genes in Tajik wheat varieties. These varieties can now be used by breeders in Tajikistan as crossing parents to develop new varieties with durable resistance to the rusts.
Divergent evolution of the Jackie pathotype of Puccinia striiformis f. sp. tritici between Australia and New Zealand
New South Wales Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Australia
Based on historical data, Australia and New Zealand (NZ) form a single epidemiological unit for cereal rusts. The dominant westerly wind pattern produces a one-way pathway of pathogen movement from Australia to NZ. Until 2002, pathotype analysis of cereal rust pathogens for NZ was conducted at the University of Sydney, Plant Breeding Institute. Over that time, windborne dispersal of members of the Pst 104 pathotype lineage to New Zealand was confirmed. Historically, pathotypes of Pst introduced to New Zealand have taken different evolutionary pathways to their Australian relatives, including a higher diversity of step-wise mutant isolates, often with different virulence profiles. A preliminary screen of Pst in NZ was conducted in January 2013 and a broader survey was conducted in 2014. Initial results confirmed that the Australian pathotype (pt.) 134 E16 A+ YrJ+ had crossed to NZ. The designation “YrJ+” was allocated to indicate virulence for an unidentified, probably rye-derived, resistance gene in the Australian triticale cultivar ‘Jackie’. The divergent evolution of this pathotype in NZ relative to Australia is of interest. In NZ, this pathotype subsequently acquired virulence for Yr10 to produce pt. 150 E16 A+ YrJ+. In Australia, Yr10 virulence had previously evolved in pt. 134 E16 A+, the progenitor of pt. 134 E16 A+ YrJ+. Only two mutational derivative pathotypes have evolved from pt. 134 E16 A+ YrJ+ in Australia. The first acquired virulence for an adult plant resistance gene in another triticale variety, ‘Tobruk’, and the second acquired virulence for Yr27. Despite being present in both Australia and NZ, pt. 134 E16 A+ Yr17+ has dominated the Australian Pst population whereas in NZ the predominant pathotype appears to be 134 E16 A+ YrJ+. Since the rust resistance genotypes of NZ varieties are poorly characterised, no conclusions can yet be reached as to whether this difference in dominant pathotype is due to selection or chance.
Diversity of Puccinia spp. on wheat, grasses and Berberis spp. in the Himalayan center of diversity of Puccinia striiformis f. sp. tritici
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.
Molecular cytogenetic characterisation of wheat lines carrying the YrA resistance to stripe rust
The University of Sydney, Plant Breeding Institute, Australia
Genetic analysis of YrA resistance in Avocet R confirmed two complementary resistance genes. Marker-trait association analysis on a doubled haploid (DH) population derived from Teal/Avocet R mapped one of the genes to chromosome 5BL. A DArT-Seq genetic map for the population indicated the presence of a T5B-7B reciprocal translocation. Fluorescence in situ hybridization (FISH) confirmed the translocation in the susceptible parent Teal relative to Avocet R. Additional FISH examinations on Cappelle Desprez (CD), Chinese Spring (CS) and Avocet S as controls indicated that the translocation in Teal was similar to that in CD. FISH studies also revealed additional polymorphisms in both chromosome 7B arms of Avocet R and Avocet S relative to CS, and that chromosome 5B in Avocet S lacked about 32% of the long arm relative to Avocet R and CS. It was postulated that complementary gene Yr74 was deleted with the missing segment. Australian cultivars Banks, Condor and Egret are also polymorphic for stripe rust response, and intercrosses in earlier studies between the S selections failed to confirm complementary genes. FISH analyses are currently underway to test the hypothesis that the S selections carry the deletion. Results will be reported in the poster.