All BGRI Abstracts

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Genetic diversity among Puccinia graminis f. sp. secalis and winter rye populations

Flath Julius Kuehn-Institut, Institute of Plant Protection in Field Crops and Grassland, Germany

Rye stem rust (caused by Puccinia graminis f. sp. secalis, Pgs) causes considerable yield losses in rye crops grown in continental climates. In Germany, stem rust resistance in rye has attracted little attention until now. In order to implement resistance breeding, it is of utmost importance to (1) analyze Pgs populations in terms of diversity and pathotype distribution, and (2) identify resistance sources in winter rye populations. Within a three-year research project, we analyzed 389 single-pustule-isolates, collected mainly from German rye-growing areas, on 15 rye inbred differentials with different avirulence/virulence patterns; among them, 226 pathotypes were identified and only 56 occurred more than once. The majority of isolates infected 5-6 differentials. This high diversity was confirmed by a Simpson index of 0.99, a high Shannon index (5.27) and an evenness index of 0.97. In parallel, we investigated stem-rust resistance among and within 122 genetically heterogeneous rye populations originating from 19 countries across 3 to 15 environments (location-year combinations) in two replicates. While 7 German commercial rye populations were highly susceptible, 11 non-adapted populations, mainly from Russia, Austria and the USA, were highly resistant, harboring 32-70% resistant stems on plots averaged across 8 to 10 environments. Selections for low disease severity at the adult-plant stage in the field also displayed resistance in leaf-segment tests (r=0.86, P<0.01). In conclusion, rye stem rust pathogen populations are highly diverse and the majority of resistances in rye populations are race-specific. The new Pgs isolate set firstly developed within the project covers the current spectrum of virulences and can be used to assess the effectiveness of stem rust resistance genes or sources. New pathotypes can be detected using this differential set and farmers and industry can be alerted to circumvent economic damage. In the long term, resistances from non-adapted populations should be introgressed into commercial rye cultivars.

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Chromosomal locations of stem and leaf rust resistance genes from Ae. caudata, Ae. searsii and Ae. Mutica

Dundas School of Agriculture, Food and Wine, The University of Adelaide, Australia.
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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.

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

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

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.

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Supercharging the radars for pathogen surveillance

Saunders National Institute of Agricultural Botany, UK

Emerging and re-emerging diseases of humans, animals and plants pose a significant hazard to public health and food security. With recent advances in sequencing technology, bacteriologists and virologists are now integrating high-resolution genotypic data into pathogen surveillance activities. However, the application of genomics to emerging filamentous plant pathogens has lagged. To address this, we developed a robust and rapid “field pathogenomics” strategy. We applied this method in 2013 to the wheat yellow rust pathogen Puccinia striiformis f. sp. tritici (Pst), using gene sequencing of Pst-infected wheat leaves taken directly from the field to gain insight into the population structure of a re-emerging pathogen. Our analysis uncovered a dramatic shift in the Pst population in the UK and supports the hypothesis that recent introduction of a diverse set of exotic Pst lineages may have displaced the previous population. Gene sequencing of infected host tissue can also be leveraged to assess the genotype of the host, rapidly confirming whether previously resistant wheat varieties have indeed been overcome. We have now expanded this study to analyze Pst-infected plant samples from across Europe and beyond and will provide an update on the insights we have gained regarding Pst population dynamics. Working with cross-institutional and industrial partners we are now developing this technique further to reduce cost so it can be applied routinely within the U.K. cereal disease surveillance program.

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Genetic analysis and molecular mapping of resistance in barley to the heterologous rust pathogens Puccinia graminis f. sp. avenae and P. triticina

Haghdoust The University of Sydney, Plant Breeding Institute, Australia

Stem rust is considered one of the most important threats to world cereal production. The appearance and spread of the wheat stem rust pathogen [Puccinia graminis f. sp. tritici (Pgt)] race Ug99 has caused great concern for global wheat production. Barley is a host to different specialized pathogen species such as Pgt, but is characteristically a near nonhost to most non-adapted (heterologous) rust pathogens such as the wheat leaf rust pathogen [P. triticina] and oat stem rust pathogen [P. graminis f. sp. avenae (Pga)]. The barley research line SusPtrit, developed for susceptibility to heterologous rust pathogens, is a useful resource to study the genetics of nonhost resistance and to clone the genes involved, particularly due to the recent availability of the genome sequence. Studies in wheat suggest that resistance genes that are effective against multiple rust pathogens (pleiotropic) such as Lr34/Yr18/Sr55, confer durable disease control. We intercrossed the sequenced barley genotype Morex with SusPtrit to determine the inheritance of resistance to the wheat leaf rust and oat stem rust pathogens. The F2 population segregated for a single dominant resistance gene in response to both heterologous pathogens Pga and Pt. Subsequent progeny testing and genetic analysis of the segregating F3 population will be performed to map and determine the relationship between the resistance genes. Large F2 populations were developed to fine map and clone the genes, and ultimately to transfer them into related crop species as an alternative approach for crop protection.

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Cytogenetic analysis and molecular mapping of inheritance of resistance in barley to Puccinia striiformis

Elmansour The University of Sydney, Plant Breeding Institute, Australia

Plants are generally non-hosts to most diseases. Barley is a host to Puccinia striiformis f. sp. hordei, but is a near non-host to P. striiformis f. sp. tritici (Pst) and to P. striiformis f. sp. pseudohordei (Psp), which cause stripe rust on wheat and barley grass (Hordeum murinum, H. leporinum), respectively. This study was carried out to determine the inheritance of resistance in barley line 81882/BS1 using the mapping population: 81882/BS1/Biosaline-19. 81882/BS1 is a H. vulgare derivative of cv. Vada, carrying an introgression from H. bulbosum on chromosome 2HS, and Biosaline-19 is susceptible to both Pst and Psp. Phenotyping of F3 lines with Psp culture 981549 and Pst pathotype 134 E16 A+ showed that 81882/BS1 carried two genes for resistance to Psp, and three genes for resistance to Pst. Cytogenetic analysis and molecular mapping were performed to further characterize the resistance of 81882/BS1 to Psp. Joint phenotypic and cytogenetic analysis indicated that at least one of the genes for resistance to Psp was associated with the H. bulbosum introgression previously located on chromosome 2H (Zhang unpublished). Preliminary molecular mapping of 15 non-segregating resistant and 15 non-segregating susceptible lines using >10K DArTseq molecular markers located the second gene on chromosome 1H. This gene was probably contributed by Vada. Further studies are underway to confirm the locations of these two loci by fine mapping.

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