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European Whitefly Symposium, Cavtat, Croatia
In October 2004 I attended the 2nd European Whitefly Symposium, held in Cavtat, Croatia. This second symposium followed the inaugural symposium held three years earlier in Ragusa, Sicily and followed on from its success. The conference, which lasted for four days, attracted over 150 delegates from far and wide and we welcomed many from the Far East and the Americas to join us under the European banner of the meeting. The conference itself was held in the beautiful coastal resort of Cavtat, which was almost as close to the airport as I live from Heathrow, but without the accompanying 36 second interval plane arrivals.
Delegates were mainly accommodated in two hotels, the larger of which, The Hotel Croatia, was the venue for the symposium. With almost two days free before a Tuesday start to the meeting many of the delegates got themselves into a relaxed mood for the upcoming presentations and renewal of friendships and collaborations.
Because of the nature of the subject matter of the meeting the overall theme was naturally multidisciplinary covering everything whitefly-related including faunistics, systematics and ecology, chemical and physical controls, integrated pest management and biological control, whitefly-natural enemies and whitefly-transmitted viruses and epidemiology. The latter is my specialist topic but this did not prevent my attendance or interest in a wide-ranging programme of talks on these topics.
The symposium began with an official opening ceremony that included short speeches from representatives of regional government (the county of Dubrovnik & Neretva and the Konavli region) and the Croatian Ministry of Agriculture, Forestry and Water Management. Once the formalities of the opening ceremonies and welcome to Croatia by our fine hosts from the Institute for Adriatic Crops and Karst Reclamation headed by Dr Katja Zanic were behind us it was full-speed ahead to three full days of scientific presentations, including over 30 oral presentations and some excellent posters. The enormous diversity of whiteflies and their global movement, assisted by man, air travel and climate change together with their impact on plants either as pests or vectors of virus disease set an ideal backdrop as to what was to follow on all of the above aspects.
In terms of whitefly-transmitted viruses the presentations fell squarely down the middle and concerned the DNA-containing Geminiviruses, which contain one of the smallest plant virus genomes, and the RNA-containing Criniviruses, which are members of the closterovirus family and contain the largest plant virus genomes. There are a number of other viruses that are whitefly-transmitted but these were not mentioned in detail. An excellent review by Stephan Winter from Germany of the worldwide distribution and agricultural impact of all whiteflytransmitted viruses, together with known details of their biology, molecular biology and epidemiology set the scene for the day’s proceedings. The current status of cassava Begomoviruses, the most serious constraint to the production of cassava, a major staple food crop in sub-Saharan Africa, was reviewed in relation to their distribution, effects, aetiology, and epidemiology. The dynamics of the exquisite relationship between the whitefly vectors and the viruses they transmitted was the theme for several of the talks which illustrated that a subtle balance existed to determine which whitefly vector species, whether it be Trialeurodes vaporariorum or Bemisia tabaci of differing biotypes, predominated in any one particular geographical location.
Subsequent virus infection could then be transient and managed by the introduction of better phytohygenic practice or resistant/tolerant cultivars, as illustrated by Herve Lecoq in France and in California or variable in terms of the predominant whitefly species, as shown by several laboratories in Almeria, Spain where the displacement of Trialeurodes vaporariorum and its replacement by Bemisia tabaci meant the elimination of one virus, Beet pseudo-yellows virus and the appearance of another, Cucurbit yellow stunting disorder virus, which in turn has been replaced by another virus, Cucumber vein yellowing virus which is transmitted by a different biotype of Bemisia tabaci.
Geminiviruses then moved centre stage and new descriptions of the potential movement of Old World and New World types in both directions only confirmed just how mobile these diseases and their whitefly vectors are.
The enormous variety and number of geminivirus isolates described only served to illustrate that if you look hard enough there are many more viruses than you thought and the possibilities of synergism and silencing in multiply-infected plants, emphasised by more than one speaker, illustrated the dramatic effects that may ensue.
The contribution of the DNA beta satellite molecules to the pathogenicity of unipartite Begomoviruses was excellently described in talks from John Stanley and Rob Briddon. Here results on the biology of this intriguing phenomenon ranged from field observations to sophisticated molecular analysis.
As is normal for any meetings involving virologists and epidemiologists the week would not be complete without the mandatory visit to view infected plants in a field situation and this symposium was no exception. However this was no ordinary field trip as it involved visiting a massive valley devoted in October and through until Christmas to the production of mandarin orange.
We saw the whole process through from field to supermarket and then experienced at first hand how most of the oranges reached the processing area via river and sampan. Following a 30 minute journey when I anticipated meeting Charlie Sheen at any moment we reached our lunch venue where we feasted on frogs legs and eels, well some of you did! But prior visits to screen houses growing a variety of salad crops illustrated the importance of this agriculture to the growing Croatian economy.
Despite many of the delegates searching both crops and indigenous weeds, we only found very low numbers of whiteflies during the day. However, their presence, especially Bemisia tabaci, which is the vector of so many plant viruses, should be noted and carefully monitored. The situation experienced in southern Spain over the past decade demonstrates how rapidly this whitefly species can become a serious agricultural problem.
Following the final days session which culminated in a visit to the future by Henryk Czosnek, who invited all of us to join him and Judy Brown to collaborate and push forward the genomics of Bemisia tabaci in an effort to understand more of its biology and virus-transmission capabilities, we repaired to the walled city of Dubrovnik for the conference dinner which was as fine affair as were all of the other social functions throughout the meeting.
Many congratulations to Ian Bedford, Liz Robertson and David Oliver and their Croatian counterparts for organising an excellent meeting. They will be a hard act to follow in wheresoever the next meeting occurs in 2007. At the end of the meeting numerous enticing possibilities were offered to host the next symposium encouraging further global gallivanting.
I am indebted to the BSPP travel fund for financially supporting my attendance in Croatia.
Bob Coutts Imperial College London