SESSION 2 - Development – understanding the pathogen
Problems of scale and inference: how good can our epidemiology be?
Dr Mike Shaw, University of Reading, UK
Decision support can be quite good in the total absence of a correct or mechanistic understanding of disease, in part because "optimal" decisions are often rather forgiving. But decision support and disease management will surely be better the better we understand disease processes in populations. The commonest routes to understanding are to build up predictions of population change from knowledge of the environmental relations of a pathogen, and to look for direct relations between environmental and host factors and disease in crops without assuming detailed mechanisms in advance. I argue through a series of examples that critical tests of predictions at population scales based on laboratory work are quite hard. This means mechanistic work may not look at factors important at the population level; that we accept some remarkably bad predictions in consequence; and that the promise offered by molecular biology methods need to be better coupled to classical ecology and detective methods if we are to really improve our ability to predict the consequences of management actions.
Wheat archive links long-term fungal pathogen population dynamics to air pollution
Sarah Bearchell*†, Bart Fraaije†, Michael Shaw* and Bruce Fitt†
* University of Reading, Whiteknights, Reading, Berks, RG6 6AS, UK
† Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
Quantitative polymerase chain reaction (PCR) was used to study the presence of the two septoria pathogens, Phaeosphaeria nodorum (glume blotch) and Mycosphaerella graminicola (leaf blotch) in wheat leaf/stem samples archived each year at harvest of the long-term Broadbalk experiment at Rothamsted, which was started in 1843. The data were used to construct a time-series of the relative abundance on these tissues of the two pathogens over the 160-year period. The relative abundance of DNA of these pathogens in the Broadbalk experiment has reflected the relative abundance of the two diseases on upper leaves of winter wheat at grain filling (GS 73-75) in England and Wales disease surveys over the last 30 years (R2, 71%, P<0.001). Unexpectedly, changes in the ratio of the two pathogens in the Broadbalk experiment over the 160-year period were very strongly correlated with changes in atmospheric pollution, as measured by SO2 emissions (R2, 92%, P<0.001). By contrast, the changes in the ratio were not well correlated with changes in many of the agronomic or environmental factors previously suggested as causes of the change in the predominant disease on leaves of winter wheat in the early 1980s from septoria glume blotch to septoria leaf blotch. These results suggest that long-term changes in pathogen populations can be influenced by anthropogenically induced environmental changes.
Survival and dissemination of Leptosphaeria maculans (blackleg, phoma) in south-eastern Australia
S.J. Marcroft1,5, S.J. Sprague2, P.A. Salisbury1,3 and B.J. Howlett4
1Department of Primary Industries, Horsham, Vic. 3401, Australia, 2CSIRO Plant Industry, Canberra, ACT 2601, Australia, 3Institute for Land and Food Resources, The University of Melbourne, Melbourne Vic. 3010 Australia, 4 School of Botany, The University of Melbourne, Melbourne Vic. 3010, Australia, 5 Joint Centre for Crop Innovation, Horsham, Vic. 3401, Australia.