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SESSION 1 - Discovery - New horizons in plant pathology - page 19 / 65





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how strategic is plant disease control currently? All too often, plant disease management is still thought on a 'pesticide' mode, i.e. as tactical operations with one type of tool (xenobiotics, biocontrol agent, or plant resistance) used alone. Repeated experience shows that this approach is essentially non-durable. Sustainable disease control therefore imposes that pest management be part of the strategic choices every grower makes. This in turns requires the scientific management of interacting components in complex systems, an area still in its infancy.


are we aiming at the right targets? Any R & D institute can cite plenty of examples of technically efficient strategies that never made it to the growers' fields. I think a major reason for that limited implementation is that these technologies did not take the actual limiting factors of the production system itself, such as market requirements, labour organisation on the farm, cost analysis, contract policy, etc…, into account from the start. As a consequence, many of them are developed with the grower in mind, when more often than not he is no more the actual decision maker.

Therefore, at least three challenges lie ahead for an improved, more widespread use of cultivar resistance: gathering more knowledge on pathogen response to selection; understanding the possibilities for complementation between resistance and crop production operations for disease management; and designing integrated crop production strategies that match the end-user, decision-maker requirements.

Two distinct variants of Wheat dwarf virus infect barley

Jon Ramsell1, Gassan Köklü2, Klas Lindsten3, Margaret Boulton4, Anders Kvarnheden1

1Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences (SLU), P.O. Box 7080, SE-750 07 Uppsala, Sweden; 2Department of Plant Protection, Faculty of Agriculture, Trakya University, 59030 Tekirda─č, Turkey; 3Department of Ecology and Crop Production Science, SLU, P.O.Box 7043, SE-750 07 Uppsala, Sweden;4Department of Disease and Stress Biology, John Innes Centre, Norwich NR4 7UH, UK. Email: anders.kvarnheden@vbsg.slu.se

Wheat dwarf virus (WDV) is a single-stranded DNA-virus (family Geminiviridae, genus Mastrevirus) transmitted by the leafhopper Psammotettix alienus. The host range includes wheat, barley, oats and many grasses. WDV is causing disease in wheat and barley in many parts of Europe. Characteristic symptoms of disease are dwarfing, yellowing and reduced heading. Two different forms of WDV exist: a wheat-infecting form and a barley-infecting form. Barley-infecting WDV is serologically similar to wheat-infecting WDV, but does not infect wheat. The complete sequences have been published for four wheat-infecting isolates of WDV from different parts of Europe, but not for any barley-infecting isolates. Sequence analysis of a partial clone for a barley isolate from Hungary (WDV-Bar[HU]) showed that it differed with 16% from the wheat isolates, while the divergence among the wheat isolates was less than 3% (Kvarnheden et al., Arch Virol 147: 205-216, 2002). Sequence determination of the complete WDV-Bar[HU] genome revealed that it consists of 2734 nucleotides (nt), which is shorter than the wheat isolates (2749-2750 nt). Among the open reading frames (ORFs), the movement protein (MP) was least conserved between the wheat and barley strains (81% amino acid identity). The cloned DNA of WDV-Bar[HU] was shown to be infectious on barley using agroinoculation. This clone will be used to study plant-virus-interactions. Two barley-infecting isolates from the Trakya region of Turkey were also characterized. The sequenced region of 1158 nt contained the complete long intergenic region (LIR), and the 5’ ends of the Rep and MP genes. Interestingly, the nt sequence for the barley isolates from Turkey differed by 6% from WDV-Bar[HU] and 16% from the wheat isolates. In a phylogenetic analysis, the barley isolates formed a distinct clade well separated from the wheat isolates. The complete sequence is now being determined for one of the Turkish barley isolates. The WDV isolates infecting barley or wheat seem to represent two differentiated strains. The barley-infecting isolates could be divided into two different subtypes based on the sequence divergence. Further characterization of WDV isolates from different hosts and geographic origins are necessary to obtain a complete understanding of the viral diversity.

A phylogeographical history of Mycosphaerella graminicola on wheat

Søren Banke and B.A. McDonald.

Institute of Plant Sciences, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.

Where do plant pathogens originate and how do they evolve? What processes define their evolutionary past and possible evolutionary future? Can we predict future evolutionary trajectories by understanding past evolutionary history? Answers to these questions can orient the search for sources of resistance in agricultural crops, because host resistance is most likely to occur at the center of origin of the pathogen. An understanding of the paths of recent pathogen

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