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12th International Plant Virus Epidemiology Symposium, Arusha, Tanzania 28th January – 1st February 2013 “Evolution, Ecology & Control of Plant Viruses”
This meeting was arranged on behalf of the Plant Virus Epidemiology Committee of the International Society of Plant Pathology (ISPP). The Committee was authorised by the ISPP Council during the International Congress of Plant Pathology held in Munich in 1978. It was founded as a direct consequence of a UK initiative, with the intention of fostering and promoting epidemiology.
The concern at the time was that this topic and other “biological” aspects of Plant Virology were in grave danger of being almost totally subsumed by the biochemical approach which was becoming increasingly prominent.
The first Symposium was held in Oxford in 1981 and was arranged jointly by the Federation of British Plant Pathologists (forerunner of the BSPP) and the Entomology/Plant Virology groups of the Association of Applied Biologists.
There have since been eleven other symposia and five have been held in Europe, three in the Americas, two in Asia and one in Australia. The latest was held in a large tourist hotel in Tanzania near the Arusha National Park.
Some of the fellow guests were en route to Kilimanjero. Several were travelling with enormous packs carrying hang gliders in order to take advantage of the annual two-week “window” when they can be used for a rapid (and hopefully controlled) descent of the mountain!
From the outset, successive symposia organisers have been encouraged to adopt a very liberal approach in their interpretation of the term “epidemiology”. This means that a very wide range of topics has been included in previous meetings and in the ensuing publications. The Arusha meeting was no exception and attracted a very large number of participants from different countries and continents. As to be expected, many of the participants were from International Centres and organisations and from African Universities or National Agricultural Research Services, including postgraduate students and their supervisors from Europe or North America. There were also researchers involved in donor -funded projects and a strong representation led by Sue Tolin from the US Col laborative Research Programme on Integrated Pest Management.
The 4-day formal programme at Arusha included both plenary and concurrent sessions. There were also poster displays and field excursions when participants could opt to see agricultural export projects or visit an international seed company located near Arusha.
Others travelled further afield to see and photograph wildlife in one of the spectacular National Parks. Several groups took the opportunity to stay on after the main symposium for ancillary meetings. So many papers and so much information was presented during the week that it is impossible to provide a comprehensive review, especially as your correspondent was operating inefficiently for much of the time due to a very UK chest complaint incubated on the over-night plane from London!
As at previous meetings considerable attention was given to current problems of topical interest. In Arusha these included Maize lethal necrosis which has been associated with Maize chlorotic mottle virus and Sugarcane mosaic virus. The disease was first reported in parts of Kenya in the latter part of 2011. It has since become prevalent there and poses a serious threat to neighbouring countries. Banana bunchy top is another disease attracting increased attention in many African countries including Democratic Republic of Congo (DRC), Malawi, Zambia, Burundi and elsewhere in the Great Lakes Region. Several contributors reported progress in developing virusfree planting material and there was an important paper on the biology of the aphid vector Pentalonia nigronervosa.
Viruses of cassava have attracted much attention in Africa in recent years following the first reports of a damaging epidemic of cassava mosaic disease (CMD) in Uganda in 1988. There have since been many reports of the progress of the epidemic into a major regional pandemic affecting much of East and Central Africa. In Arusha there were several reports of disease mitigation projects based on the selection and deployment of varieties with conventional forms of resistance.
These have led to a considerable improvement in the overall situation in several countries. Detailed disease distribution maps were featured in one poster and work was presented on mapping resistance genes and on the big increase in whitefly vector populations and changes in biotype that have occurred since the pandemic began.
The marked decline in the importance of CMD has been accompanied by a big increase in the prevalence of cassava brown streak disease (CBSD). This has been known since the 1930s but for many years appeared to be restricted to lowland coastal areas of Eastern Africa and parts of Malawi. It has since become prevalent in mid-altitude areas of Uganda, Kenya and Tanzania and more recently in Burundi, Rwanda and eastern DRC. New information was presented in Arusha on many aspects of CBSD including epidemiology and transmission by the whitefly vector.
Both CMD and CBSD were considered by Claude Fauquet in his “declaration of war” on cassava viruses in Africa. This was discussed in more detail in a later May 2013 meeting at the Rockefeller Conference Centre in Bellagio, Italy which was arranged to develop a comprehensive “action plan” to submit for donor funding.
It has long been known that plant viruses can have direct or indirect effects on the fecundity and behaviour of their vectors. However, the full significance of these effects is not fully appreciated. Additional information on this topic was presented at the Cornell Symposim in 2010 and further papers featured in the Arusha programme. For example, Alberto Fereres (Spain) described a mutualistic-type of relationship by which both persistent and non-persistent viruses can influence the flight, settling and probing behaviour of their aphid vectors such that virus transmission and spread are optimised. In other studies with other aphid-borne viruses, Nilsa Bosque-Perez (Idaho) demonstrated a shift in preference from infected to un-infected plants following virus acquisition which facilitates virus spread. Stewart Gray (Cornell) used a very different and novel approach in studies on “the carefully tuned orchestra of virus, vector and host proteins” that influences the transmission of circulative, non-propagative aphidborne viruses.
Genetically engineered resistance first featured in the programme of the Montpellier symposium in 1989 when there were contributions from Roger Beachy, Claude Fauquet and Monsanto scientists. The ear ly opt imism suggesting that this approach would soon become a universal panacea has not been realised. Nevertheless, research continues and in Arusha there were reports of field trials in Hawaii on transgenic banana with resistance to Banana bunchy top virus and on transgenic plum, sweet potato, Arabidopsis, tobacco, cucumber and melon. Two groups have engineered cassava with resistance to Cassava brown streak viruses (CBSVs). In the absence of conventional resistance to CBSVs this could provide a powerful incentive to overcome the formidable obs tac les to the release and deployment of transgenics.
During the week there was a brief business meeting when a new committee was elected and a decision was taken to hold the next meeting in Avigno, France in 2015 or 2016. An innovation at Arusha was an Awards Ceremony when presentations were made to previous Chairmen and longserving members of the committee including Mike Irwin (USA), Benny Raccah (Israel), Roger Jones (Western Australia), Herve Lecoq (France), Alberto Fereres (Spain) and Mike Thresh (UK). The well known American virologist Karl Maramorosch (long-time editor of Advances in Virus Research and other Elsevier/Academic Press publications) celebrated his 97th birthday in Arusha and took the opportunity to give an account of his 1953 visit to Radcliffe Nathan Salaman in Cambridge. Salaman was a former medic who was advised to take up less exacting pursuits when affected by tuberculosis. He became the first Professor of Plant virus Diseases and included K M Smith and F C Bawden among his students who worked on virus diseases of potato.
Lava Kumar and colleagues at the International Institute of Tropical Agriculture are to be congratulated on arranging such a successful conference and for attracting such substantial funding. I am grateful to the organisers for their hospitality and to BSPP for the generous travel grant.
Michael Thresh Formerly Natural Resources Institute, University of Greenwich