All BGRI Abstracts

Displaying 71 - 80 of 197 records | 8 of 20 pages

Nutrient uptake in rust fungi: How sweet is parasitic life?

BGRI 2010 Plenary Abstract
Ralf T. Voegele Fachgebiet Phytopathologie, Institut für Phytomedizin, Fakultät Agrarwissenschaften, Germany
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A better understanding of the fundamental principles of host-pathogen interactions should enable us to develop new strategies to control disease and to eliminate or at least manage their causative agents. This is especially true for obligate biotrophic parasites like the rust fungi. One vital aspect in the field of obligate biotrophic host-pathogen interactions is the mobilization, acquisition and metabolism of nutrients by the pathogen. This includes transporters necessary for the uptake of nutrients as well as enzymes necessary for their mobilization and metabolism. In a broader sense effector molecules reprogramming the host or triggering the infected cell into metabolic shifts favorable for the pathogen also play an important role in pathogen alimentation.

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Role of Berberis spp. as alternate hosts in generating new races of Puccinia graminis and P. striiformis

BGRI 2010 Plenary Abstract
Yue Jin USDA-ARS, Cereal Disease Laboratory
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The common barberry and several other Berberis spp. serve as the alternate hosts to two important rust pathogens of small grains and grasses, Puccinia graminis and P. striiformis. Barberry eradication has been practiced for centuries as a means to control stem rust. Diverse virulence variations have been observed in populations of P. graminis f. sp. tritici that were associated with susceptible barberries in North America. Barberry likely has played a role in generating new races of P. striiformis f. sp. tritici in some regions in the world. Several North American stem rust races, namely races 56, 15B and QCC, initially originated from barberry, were subsequently responsible for generating large-scale epidemics. Thus, sexual cycles on Berberis spp. may generate virulence combinations that could have serious consequences to cereal crop production.

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Characterization of two new wheat stem rust races within the Ug99 lineage in South Africa

BGRI 2010 Plenary Abstract
Botma Visser Department of Plant Sciences, University of the Free State, South Africa
View visser_2010.pdf (240.73 KB)

Two new races of the wheat (Triticum aestivum L.) stem rust pathogen, representing the fifth and sixth variants described within the Ug99 lineage, were detected in South Africa. Races TTKSP and PTKST (North American notation) were detected in 2007 and 2009, respectively. Except for Sr24 virulence, race TTKSP is phenotypically identical to TTKSF, a commonly detected race of Puccinia graminis f. sp. tritici (Pgt) in South Africa. PTKST is similar to TTKSP except that it produces a lower infection type on the Sr21 differential and has virulence for Sr31. Simple sequence repeat (SSR) analysis confirmed the genetic relationship amongst TTKSF, TTKSP, PTKST and TTKSK (Ug99). TTKSK, PTKST and TTKSF grouped together with 99% similarity, while sharing 88% genetic resemblance with TTKSP. These four races in turn shared only 31% similarity with other South African races. It is proposed that TTKSP arose locally as a single step mutation from race TTKSF, whereas PTKST probably represents an exotic introduction of Pgt to South Africa.

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Surveillance and race analysis of stem rust in Kenya for the years 2008 and 2009

BGRI 2010 Poster Abstract
Ruth Wanyera KALRO-Njoro, Kenya

Limited but targeted stem rust race characterization was undertaken in Kenya in 2004 and 2005 which led to the detection of Ug99 present in Kenya and designation of Ug99 as race TTKS (based on North American stem rust race nomenclature system). Further surveillance in 2006 and 2007 detected variants of TTKS with virulence on Sr24 (TTKST) and Sr36 (TTTSK), respectively. Stem rust surveillance was undertaken at an extended level in 2008 and 2009 within predominant wheat growing regions of Kenya. Three hundred and sixty farms were surveyed from regional districts of Naivasha, Narok, Nakuru, Laikipia, Meru, Uasin-Gishu, Nandi, Elgeyo and Trans-Nzioa, during 2008 main season (May to September and December). The information from farmers indicated that more than 95% of these farms were sprayed with fungicides. Despite the use of fungicides, stem rust was detected in 67% of the surveyed farms. Stem rust ranged from trace amount -100% in severity with minimum infection in Naivasha district (40%) and maximum in Narok district (90%). Yellow rust was detected in 22% of the farms. Out of one hundred and twenty-six stem rust samples collected, 37 and 39 (a total of 76 ) samples were sent to Cereal Disease Laboratory (CDL) Minnesota, USA and Cereal Research Laboratory of Agriculture and Agri-Food Canada respectively, for race typing using the respective differentials used by these labs. From the 39 collections sent to Canada, 17 (43%) survived, of which majority were typed to TTKST (65%) followed by TTKSK (18%), PTKST (12%) and mixture of TTKST and TTKSK (5%). The CDL typed vast majority of pathotypes as TTKSK (84%) followed by TTKST and TTTSK (7% each). The combined results of two labs indicated that predominant frequency in Kenya in 2008 was TTKSK (51%) followed by TTKST (31%), PTKST (6%) and TTTSK (6%). The frequency of TTKST significantly increased in 2008 compared to 2007 which is not surprising, given that Sr24 carrying wheat cultivar KS Mwamba is cultivated on large acreage in Kenya. In 2009, 262 farms were surveyed from regional districts of Narok, Laikipia, Nyandarua, Meru, Uasin-Gishu, Nandi, Elgeyo and Trans-Nzioa. The 2009 season experienced heavy drought in many areas. Nevertheless, stem rust was detected in 79% of the farms with disease severity ranging from trace to 100%. Yellow rust was detected in 15% of the farms. Stem rust infection ranged from 0 to 100% with minimum infection in Nyandarua (18%), Laikipia (42%) and maximum in Uasin-Gishu and Elgeyo (100% each). Out of seventy-four stem rust samples collected, 55 samples were sent to Canada for race typing. Only 20% of the samples survived, of which majority were typed to TTKST (50%), PTKST (34%) and PTKSK (16%). Borlaug Global Rust Initiative 2010 Technical Workshop / Poster Abstracts 7 The 2009 results did not depict real situation of predominance of pathogenic variability because of small sample size, however it provided fair indication that race TTKST is still the most prevalent. This information generated on the distribution of stem rust races, and the incidence of stem rust is important for anticipatory breeding and release of cultivars with effective sources of resistance in Kenya, and at same time mitigating global threat of stem rust by reducing intensity of stem rust inoculum in East Africa.

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Association mapping of rust resistance in pre-green revolution wheat accessions

BGRI 2010 Poster Abstract
Urmil Bansal The University of Sydney, Plant Breeding Institute, Australia

Association mapping detects correlations between genotypes and phenotypes in a sample of individuals based on the linkage disequilibrium and can be used to uncover new genetic variation among germplasm collections. Two hundred and five landraces collected by the English botanist A. Watkins in the 1920s were screened for rust response variation under field conditions during three crop seasons. An integrated map of 350 polymorphic DArT markers was developed. Association mapping identified the involvement of several genomic regions in controlling resistance to three rust diseases. Seven, eight and nine genomic regions, respectively, appeared to carry yet uncharacterized leaf rust, stripe rust and stem rust resistance. Three dimensional analyses indicated genetic association of leaf rust and stripe rust resistance in some accessions, whereas no such association was observed between stem rust resistance and resistance to either of the other two rust diseases. A new stripe rust resistance locus, Yr47, has been named. 

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Genetic map of stem rust resistant gene Sr35 in T. monococcum

BGRI 2010 Poster Abstract
W. Zhang Department of Plant Sciences, University of California-Davis, USA

With the TTKS family of races virulent on most genes currently providing protection against stem rust worldwide, identifying, mapping, and deploying resistance genes effective against these races has become critical.  We present here a genetic map of Sr35.  Both parents of our diploid mapping population (DV92/G3116, 142 SSD lines) are resistant to TTKSK, but the population segregates for resistance to TRTTF (Yemen) and RKQQC (US). Race analysis suggests that G3116 carries Sr21 and DV92 both Sr21 and Sr35.  Resistance to TRTTF and RKQQC was mapped to a 6 cM interval on chromosome 3AmL between markers BF483299 and CJ656351.  This interval corresponds to a 178-kb region in Brachypodium which contains only 16 annotated genes and exhibits a small inversion (including 2 genes) and a putative insertion (2 genes) relative to rice and sorghum.  This map contains closely-linked markers to Sr35 and provides the initial step for this gene's positional cloning.

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Screening for stem rust resistance in East Africa

BGRI 2009 Plenary Abstract
Davinder Singh The University of Sydney, Plant Breeding Institute, Australia
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The East Africa program of the Borlaug Global Rust Initiative (BGRI) was launched to reduce the scale and scope of wheat stem rust epidemics in Kenya and Ethiopia, and to mitigate the global threat of virulent and dangerous rust races originating from this region. Since the launch in 2005, the screening facilities in Kenya and Ethiopia have helped to determine the extent of the world’s vulnerability to stem rust race Ug99 and its variants, identify diverse sources of resistance including adult plant resistance based on minor genes, and catalyze a comprehensive global response, leading to expanded awareness, expanded research and breeding activities, and resource mobilization. This paper reviews the role and achievements of the eastern African screening facilities along with the opportunities and challenges faced by the facilities during the ongoing global response to the emergence of Ug99 and its variants.

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Developing and optimizing markers for stem rust resistance in wheat

BGRI 2009 Plenary Abstract
Long-Xi Yu Department of Plant Breeding, Cornell University
View yu_2009.pdf (1.95 MB)

High quality molecular markers that are closely linked, codominant, and high throughput are critical for developing varieties with durable rust resistance. We are using a combination of microsatellite, sequence tagged site, and Diversity Array Technology markers for haplotyping, pyramiding, and mapping stem rust resistance genes. The primary goal of our research team is to identify and optimize markers for previously characterized and novel stem rust resistance genes in wheat. The specific objectives are to: 1) optimize markers for previously characterized stem rust resistance genes to maximize efficiency of the breeding programs, 2) haplotype uncharacterized rust resistant genotypes to infer novelty and to plan new mapping experiments, 3) pyramid novel sources of rust resistance, and 4) map novel sources of rust resistance, including adult plant resistance. To date, we have evaluated 58 markers associated with 21 stem rust resistance genes and used 20 for haplotyping 318 wheat lines and varieties for 15 Ug99 effective resistance genes. This germplasm panel is also being DArT genotyped. For tetraploids, the pyramiding includes Sr2, Sr13 and Sr25 in the breeding line UC1113 which is a high yielding semi-dwarf durum variety with the high-grain protein content gene Gpc-B1 and the non-race specific stripe rust resistance gene Yr36. The Australian group is developing markers for the stem rust resistance genes Sr33 and Sr45 that come from Aegilops tauschii and are located on wheat chromosomes 1DS. Diagnostic, codominant markers for Sr25 and Sr26 have been developed and are being pyramided into CIMMYT breeding lines. Three new sources of race-specific resistance in CIMMYT-derived spring wheat have been mapped and are designated SrA, SrB, and SrC. SrA mapped on 3DL, SrB on 3BS and SrC on 5DL. These genes provided moderate levels of resistance to stem rust at the seedling stage and acceptable to moderate levels at the adult plant stage.

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History and status of the wheat rusts

BGRI 2009 Plenary Abstract
Robert McIntosh The University of Sydney, Plant Breeding Institute, Australia
View Mcintosh_2009.pdf (273.55 KB)

The rusts have been ongoing problems for wheat production probably since domestication of the crop about 8,000 years ago. Epidemics vary in size and frequency with host genotype and environment, wet years being ‘rust’ years. Although partial control in modern agriculture was achieved with resistant varieties, conditions favoring epidemics were made worse with the intensification of production and greater resistance gene uniformity in the host. The current Ug99 incident illustrates the situation of very widely adapted successful genotypes grown across huge areas in the presence of an ongoing threat from a recently emerged widely virulent and obviously highly aggressive pathotype of the stem rust pathogen. This paper addresses some of the history of cereal rusts and reviews underlying principles of host pathogen genetics, some of which are being neglected in the period of modern genetics.

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Using race survey outputs to protect wheat from rust

BGRI 2009 Plenary Abstract
Robert Park The University of Sydney, Plant Breeding Institute, Australia
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Race (pathotype) surveys of cereal rust pathogens have been conducted in many parts of the world since the early 1900s. The only way to identify rust pathotypes remains virulence testing in greenhouse tests using genotypes (“differentials”) carrying different resistance genes. Virulence determinations have rarely targeted genes conferring adult plant resistance because of the technical difficulties of working with adult plants under controlled conditions. Where pathotype surveys have been conducted in a robust and relevant way, they have provided both information and pathogen isolates that underpinned rust control efforts, from gene discovery to post-release management of resistance resources. Information generated by pathotype surveys has been used to: devise breeding strategies; indicate the most relevant isolates for use in screening and breeding; define the distribution of virulence and virulence combinations; allow predictions of the effectiveness/ ineffectiveness of resistance genes; and issue advance warning to growers by identifying new pathotypes (both locally evolved and introduced) before they reach levels likely to cause significant economic damage. To be most effective, pathotype surveys should also provide fully characterized isolates (defined pathotypes) for use in identifying new sources of resistance and screening breeding material. Although constrained to some extent by a lack of markers, particularly those not subject to natural selection, surveys have also provided considerable insight into the dynamics of rust pathogen populations, including the evolution and maintenance of virulence, and migration pathways, including periodic long-distance migration events.

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