Central Science Laboratory, Sand Hutton, York Y04 1 LZ, UK

Background and objectives
Pest risk analysis (PRA) (note: 'pest' includes pathogens) is required to identify, assess and propose measures to prevent risks to crops from economically damaging alien pests. PRA includes an assessment of the risk of entry and establishment as well as the likelihood of economic and environmental damage. The 1994 World Trade Organization agreement on Sanitary and Phytosanitary Measures (SPS) states that risk assessment techniques should be employed when measures are imposed to protect plant health. This is to ensure that barriers to trade in plant material are justified. The FAO has led moves to standardize PRA procedures following scientific principles.

The development of risk analysis has been underpinned by advances in several key areas, including epidemiology - understanding the mechanisms of disease spread among plant populations; computer-based tools e.g. geographical information systems (GIS) which enable the preparation of maps highlighting areas at greatest risk from the introduction of new pests; and improved techniques for surveillance of pests or their vectors. The application of scientific principles within PRA results in better-informed decisions and a growth in understanding between trading nations concerning common standards for the assessment and management of risk.

This paper describes the results of evaluating a model predicting disease severity using a GIS to assess the risks of establishment of the pathogen Tilletia indica Mitra, the cause of Karnal bunt within the European Union (EU). Initial reports of infection of seed lots of durum wheat in the USA in 1996 triggered an assessment of the risks associated with EU trade in bread and durum wheat, rye and triticosecale from countries where the disease is known to occur. The key period of infection of cereal crops by the pathogen is between spikelet emergence and anthesis. Analysis of meteorological conditions known to be favourable for disease development in wheat during this period at weather stations within the area where the disease is prevalent in India, and a comparison of climatic conditions at weather stations in the cereal growing areas of the UK during the same phonological period, allowed a measure of the risk of establishment to be made [1]. As a result of this work, amendments to UK and EU plant health legislation were implemented to protect cereal production.

Materials and methods
In order to determine where T. indica may establish in the EU, and to map the areas at greatest risk, the meteorological factors known to determine the distribution and severity of Karnal bunt in India [2] were ascertained for the states in India where the disease is established and for cereal-growing areas in the EU. Calculations were made using a new 0.511 latitude by 0.50 longitude world terrestrial surface mean monthly climatology for 1961-90 provided by the Climatic Research Unit, Norwich, UK. The results were displayed in a GIS.

Results and conclusions
Information derived from the scientific literature, combined with comparisons of relevant meteorological factors between areas where Karnal bunt is established and those that are potentially at risk, showed that T. indica could establish over large areas if introduced into the EU. The application of scientific principles to assess the risk of establishment clearly indicates the threat presented by this pathogen to the cereal-growing areas of the EU.

1. Sansford CE, 1998. In Proceedings of an International Symposium on Smuts and Bunts of Wheat, North Carolina, USA, 17-20 August 1997 (in press).
2. Jhorar OP, Mavi HS, Sharma I et al., 1992. Plant Disease Research 7, 204-209.