British Society for Plant Pathology

BSPP Presidential Meeting 1997

Plant Pathology - Global Perspectives of an Applied Science

Session IV - Assessing the risk

Plant disease - barrier to world trade
Mr Robert L. Griffin
Co-ordinator, Secretariat of the International Plant Protection Convention, Food & Agriculture Organisation - AGPP, Vialle Delle Terme di Caracalla, 00100, Rome, Italy.

Abating the introduction and spread of plant diseases through exclusion is a concept receiving greater attention in the dawning era of globalization. As the movement of people and goods accelerates geometrically with the liberalization of trade, the regulatory measures used to inhibit the spread of harmful plant diseases becomes increasingly more important. The basis for the placement and strength of such measures is key to determining whether they withstand international scrutiny. It is in this respect that regulators are strongly dependent upon the research community to provide scientific support needed to properly develop, evaluate, and challenge regulatory measures for plant diseases. A harmonized process of pest risk analysis (PRA) is the recognized means to provide a scientific foundation to regulatory decision making. Increasing the awareness and sensitivity of plant pathologists to trade issues and the needs of regulators, particularly in the area of pest risk analysis, is essential to strengthening the role of science in regulatory policy making and assuring that needed protection is provided without plant diseases becoming unjustified barriers to trade.


Bacterial brown rot of potato, caused by Ralstonia (Pseudomonas) solanacearum race 3, biovar 2 in Europe
Dr Jaap D. Janse
Plantenziektenkundige Dienst, Geerjesweg 15, Postbus 9102, 6700 HC Wageningen, The Netherlands

Race 3, biovar 2 of Ralstonia (Pseudomonas) solanacearum is adapted to cooler climates (optimum growth temperature 27C, unlike the tropical races 1 and 2 with 35-37C). Its origin, as it is for potato, is most likely South America, (where it occurs in the highlands and also resistance is present in wild potato) and spread with its main host, potato. It has a narrow host range (potato, tomato, some solanaceous weeds and exceptionally a few others like eggplant and pepper).

Race 3 was first observed in the Mediterranean area in the forties and adequately described from Portugal in 1947, where it caused severe outbreaks up to the sixties, but disappearing in later years. It was reported in Greece in 1951. In Egypt the disease became endemic and findings in early table potatoes exported to Europe were reported as early as 1962, but infections were also found in potatoes coming from Cyprus and Malta at that time. In subsequent years reports were mainly from Egyptian potatoes and recently also a few cases from Turkey.

An outbreak of brown rot in Western Europe was first reported from Sweden (1972) in ware potatoes, where an apparent link was found between waste for processing industry dumped into a river, infection of bittersweet (Solanum dulcamara) growing with its roots in water and irrigation with contaminated surface water of potato fields. In 1989 in Belgium and 1992 in Belgium, the Netherlands and the UK isolated cases in ware potatoes were reported. For the UK and Belgium epidemiological research established a link between contaminated surface water and bittersweet and not with seed. In 1995 a more severe outbreak was found in the Netherlands in both seed and ware potatoes. Here spreading of the disease could largely be explained by a heavily infected seedline (probably contaminated by the use of contaminated surface water), but in a number of cases irrigation with contaminated surface water appeared to be the cause and the relation with bittersweet was clearly established. In the same year (with an exceptional warm summer in Western Europe) the disease was also reported from France (possible links with contaminated surface water, also in outdoor and glasshouse tomato), Portugal (unexplained cases) and Italy (some perhaps connected with imported seed, others unexplained). In 1996 further findings occurred in the UK, the Netherlands (also one case of glasshouse tomato with a link to the use of contaminated irrigation water) and Spain (unexplained). In 1997 the disease was reported from Germany (unexplained), the UK (glasshouse tomato with a link to contaminated irrigation water), the Netherlands (contaminated irrigation water) and Italy (possible link to processing industry).

Ecological research performed so far, has established for most infected countries a possible link between industries using infected potatoes fro processing, contaminated surface water and, especially in Western Europe, bittersweet. Apparently soil seems not to play an important role in survival of the bacterium and perpetuation of the disease. Many aspects in the epidemiology are still unclear, however.

Possibilities for control like the use of healthy seed, testing of seed and imported table and processing potatoes, avoidance of use of irrigation water, decontamination of waste water, hygiene and measures for infected fields will shortly be outlined.


Quarantine strategies and new disease risks in Australia
Dr Peter Merriman
Institute for Horticultural Development, Knoxfield, Victoria, Australia

Primary industries have, for many years, benefited from Australia's geographic isolation and relative freedom from some of the most destructive pests and diseases which are common in other western agricultural systems. This status has long been recognised by Government and Industry, and quarantine barriers are generally considered to have been effective in minimising the risk of incursions.

In the past 10 years, increased tourism, business and movement of cargo have imposed greater pressure on services which may have contributed to more frequent breaches of the quarantine barrier, especially in plant industries. Papaya Fruit Fly, Race 4 of Fusarium oxysporum f sp. cubense, Mycosphaerella fijiensis and Erwinia amylovora are currently subject to eradication programs which are funded by the State and Commonwealth governments. Costs are substantial. Eradication of Papaya Fruit Fly in Far North Queensland is estimated at $30 M since Oct. 1995 and the program against Erwinia amylovora, which commenced May 1997, at $2 M.

The Commonwealth Government is responsible for the Australian Quarantine and Inspection Service (AQIS), and has responded to recommendations of a comprehensive review of AQIS ( Nairn review) by investing $76 M in strengthening the capabilities of operational and policy groups. Plant industries are major beneficiaries through the newly created Chief Plant Protection Officer with specific responsibilities for contingency planning and incursion management; and through the proposed Australian Plant Health Council which will commission projects to enhance plant protection programs. Increased resources are being provided for inspection at ports and mail centres, for pest risk analysis, for off shore eradication and containment of pests and pathogens on Australian islands in the Torres Strait, and for the development of more prescriptive contingency plans for exotic pests and pathogens at both generic and specific levels.

Funding for reference collections of pests and pathogens and diagnostic services in Australia is inadequate and a national review is seeking long term solutions for this issue, which undoubtedly will assume increased importance under the Sanitary and Phytosanitary agreement of the GATT Uruguay round concluded in 1993 (now WTO).


Pathogen risk assessment in the UK
Dr Claire E. Sansford
Central Science Laboratory, Sand Hutton, York, Y04 1LZ

The concept of risk analysis is not new. Examples of applications can be found in a wide-range of disciplines outside of plant pathology (e.g. finance and engineering), but the fundamental principal of risk analysis is that it provides a practical framework for decision making.

Pest Risk Analysis (PRA) (for "pest" read pathogen) is necessary to identify and assess risks to agricultural and horticultural crops and forestry, from economically damaging alien pests. The process of PRA includes not only the assessment of the risk of entry and establishment of the pest but also the economic and environmental damage which might result should the pest be introduced.

Until recently risks were assessed and plant health regulations were developed in an unsystematic manner. However, following the Uruguay round of the GATT (now WTO) an agreement on Sanitary and Phytosanitary Measures (SPS) was made which aims, amongst other things, for greater transparency of national policies and objectivity in the process of PRA. The intention is that phytosanitary measures that restrict trade should be applied only to the extent necessary to protect plant health, thus facilitating freer trade in plant material. The SPS agreement also aims to encourage the use of international standards. With respect to plant health any measures stricter than international standards must be scientifically justifiable and all new phytosanitary measures must be justified by an analysis of pest risk.

The development of risk analysis has been underpinned by developments in a number of other key areas, including: epidemiology - understanding the mechanisms of disease spread among plant populations; computer-based tools such as Geographical Information Systems which can help make more accurate predictions about events such as the likelihood of introduction of a new pest; improved techniques for surveillance and monitoring for the identification of pests, diseases and their vectors; and growth in international agreement and mutual understanding between trading nations about common standards for the assessment and management of risk.

National, European and international schemes for PRA are being standardised. The ultimate aim is to construct an effective system which can be used for a range of situations such as interceptions on imported plants/plant products, or requests for importation of plant material. Examples of pathogen risk analysis given in this paper include the risks associated with Tilletia indica Mitra, the cause of Karnal bunt in wheat; tospoviruses transmitted by the insect vector Thrips palmi Karny; Zoysia grass from the USA and Fusarium oxysporum f.sp. basilici on sweet basil.

At the end of the PRA process, decisions need to be made. Different interest groups have differing views on acceptable levels of risk. However, risk analysis aims to ensure that the decisions will be well informed, transparent and neutral.