Scientific and practical aspects of the eradication programme against Xanthomonas axonopodis pv. citri in Florida
In a letter addressed to the editor of Phytopathology, Gottwald et al. (2001) described the scientific and practical aspects of the eradication programme against Xanthomonas axonopodis pv. citri in Florida (US). It is acknowledged that the significant increase of international travel and trade has dramatically increased the risk of introducing dangerous plant pests. The introduction of citrus canker has had a considerable political, social and economic impact in Florida, which has forced the authorities to establish an eradication programme. If established, the disease would have a direct effect on citrus production (debilitation of trees, losses in fruit quality and yield), but the main difficulties would be the restrictions or prohibitions on interstate and international fruit trade. The Florida citrus industry is mainly concentrated in the southern half of the state, close to rapidly expanding urban population centres. As the outbreaks of citrus canker originated from urban areas, eradication did not only affect producers but very large numbers of urban home-owners who possess citrus for ornamental purposes or garden fruit production. The importance and difficulties in obtaining sound scientific data for the establishment of eradication programmes were illustrated in this letter. Initially, based on data from Argentina, it was considered that the bacterium spreads up to 32 m during rainstorms. Therefore, it was decided in Florida to destroy all infected trees, as well as susceptible citrus trees located within a radius of 38 m. Despite this measure, the disease continued to spread. Research studies were then carried out and showed that this distance had to be increased to 580 m. In addition, a sentinel grid (1.6 x 1.6 km) was established to organize regular surveys. All susceptible hosts were located on this grid and regularly surveyed (every 30 days). The practical difficulties in implementing this eradication programme were explained, such as the strong refusal of owners and growers when their trees are destroyed (personal threat, law suits brought against the state by residents and municipalities, etc.), and the question of finances on how to fund the programme itself and the compensations paid to owners and growers. It was recognized that it is extremely difficult to eradicate completely a pathogen like X. axonopodis pv. citri which has spread to the extent observed in Florida, and which is likely to be re-introduced in the future. However, it is stressed that the magnitude of response to the current epidemic of citrus canker in Florida is unprecedented in plant pathology and represents a scale of public attention and governmental effort that would normally be devoted to eradication of a newly introduced human or livestock disease. Debate is taking place on the concept and feasibility of eradication, and many questions arise reflecting different views among researchers, growers and private owners such as ‘Can we live with citrus canker?’, ‘Can we afford not to protect our agriculture?’, ‘How to allocate adequate resources to simultaneous battle fronts? (as other
pathogens like Plum pox potyvirus or Xylella fastidiosa are also causing problems in other parts of USA).
Sources
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Gottwald, T.R.; Hugues, G.; Graham, J.H.; Sun, X.; Riley, T. (2001) The citrus canker epidemic in Florida: the scientific basis of regulatory eradication policy for an invasive species.
Phytopathology, 91(1), 30-34.
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