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SESSION 1 - Discovery - New horizons in plant pathology - page 11 / 65

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PH Gregory Competition

Test tube evolution of the plant pathogenic fungus Mycosphaerella graminicola towards resistance against plant defense enzymes

T. Jürgens, S. Banke, and B.A. McDonald

Institute of Plant Sciences, ETH Zentrum / LFW, Universitätstrasse 2, CH - 8092 Zürich

Using yeast as a model system, Cowen et al. (Annual Review of Microbiology 56:139-165, 2002) recently evolved fungal strains towards drug resistance. The present study uses a similar experimental approach: the evolution of a plant pathogenic fungus towards resistance against enzymes that play a role in plant defense. The wheat pathogen Mycosphaerella graminicola was chosen for this serial passage experiment because it is in its yeast growth phase able to multiply as single cells. This makes it possible to cycle single cell lines for many generations. Selection pressure was kept high at all times by monitoring the increase in resistance on a regular basis (equaling increasing multiplication rates), and subsequently increasing the concentration of chitinase in the growth media. A total of four lines were cycled for 30 generations. For the most susceptible line, a steady increase in resistance over generation time was found. A transgenic wheat line was used to document the decreasing level of resistance on the host side.

Proteomic analysis of pea downy mildew infections

Richard Amey, Tanja Schleicher, Heather Macdonald, Steve Neill & Peter Spencer-Phillips.

Centre for Research in Plant Science and Bristol Genomics Research Institute,University of the West of England, Bristol, Coldharbour Lane, Bristol, BS16 1QY.

Downy mildew is the most common foliar disease of the pea crop (Pisum sativum) in the UK, with up to 55% losses in yield observed where plant resistance is ineffective. Control of the pathogen Peronospora viciae is achieved through the use of resistant cultivars and treatment with fungicides such as the phenylamides, which have systemic and curative activity. Resistance to these fungicides has been observed, so optimal application is required to prolong their effectiveness in controlling downy mildew outbreaks. This DEFRA-funded work uses two dimensional difference gel electrophoresis (2D-DIGE) and mass spectrometry to identify protein biomarkers that are up- or down-regulated during early stage pea downy mildew infection. The genes encoding the identified biomarkers are being cloned and expressed so that sufficient protein is available for the generation of specific antibodies against the proteins. It is proposed that the antibodies may be utilised subsequently in biosensor detection devices for the pre-symptomatic diagnosis, allowing fungicides to be applied more efficiently and effectively. A secondary aim of the project is to generate fundamental information on proteins specifically involved in this plant-pathogen interaction, which may be employed in novel control strategies for downy mildew diseases.

Yellow rust development in wheat mutants exhibiting enhanced adult plant resistance

James P.E. Melichar, Simon Berry, and Lesley A. Boyd

Department of Disease and Stress Biology, John Innes Centre, Norwich Research Park, Colney, Norwich, NR4 7UH, United Kiingdom

Puccinia striiformis f.sp. tritici is an asexual, biotrophic fungal pathogen. It is the causal agent of yellow rust in wheat, and a serious economic foliar disease of most temperate wheat growing areas of the world. It has a distinctive phenotype of intervenal-stripes of yellow pustules (uredia). Control in the UK is based on an integrated approach of resistance breeding with rotation of fungicides of differing modes of action. Mutagenised populations of the wheat varieties Guardian and Hobbit ‘sib’ have been screened in field tests, and mutant lines selected that give enhanced yellow rust adult plant resistance (APR). These include the Guardian-derived mutants M66 and M257 (Boyd and Minchin, 2001, Euphytica 122:361-368), and the Hobbit ‘sib’ mutant line I3-54 (Smith et al, in press, MPMI). M66 and M257 also show resistance to powdery mildew and brown rust (Boyd et al, 2002, Genome 45:1035-1040), while I3-54 is resistant to powdery mildew but not brown rust. The M66 mutant also shows evidence of spontaneous necrotic flecking analogous to the lesion mimics found in mlo barley lines. Pathology studies have been looking at pathogen development and plant resistant responses at three distinct plant growth stages: seedling (GS 12-13), tillering (GS 26-27), and heading (GS 49-51), in order to study the development and resistance phenotype of APR in these mutants. Preliminary histological examination of pathogen arrest in M66 and M257 suggests that the enhanced resistance is not due to an early, hydrogen peroxide mediated HR, with resistance operating just prior to sporulation. In contrast, I3-54 causes early pathogen arrest in the stomatal cavity, but again is not associated with a hydrogen peroxide mediated defence reaction.

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