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I had hoped to be reporting on this Symposium on returning from Japan but, for various reasons, the meeting was moved to Corfu, Greece. It is greatly to the credit of Prof. Tjamos (Chairman of the International Steering Committee) and his local committee that they were prepared to take on organising the Symposium at short notice and make a great success of it. As a result, over 80 participants from 14 countries came together to discuss all aspects of Verticillium wilts. Ninety one presentations spread over two plenary sessions, keynote talks and several oral and poster discussion sessions were given during three and a half formal days. Much informal discussion took place during a whole day trip to Meteora Monastery on mainland Greece and during a half-day tour of the beautiful island of Corfu.
Two species, Verticillium dahliae and V. albo-atrum, have traditionally formed the core of these meetings but this time their dominance was challenged by a new kid on the block – V. longisporum. This latter species is relatively newly named and takes in those isolates originally classified as V. dahliae var longisporum – these are genetically quite distinct (being amphihaploid while the other two species are haploid) and almost entirely confined to cruciferous hosts. A consortium of scientists in Germany, lead by Prof Gatz, has received major funding and are concentrating on host-pathogen interactions using V. longisporum– Arabidopsis as a model pathosystem. More than a dozen presentations discussed their mainly molecular studies in which are showing up both parallels and differences with other model systems. This work seems to me not yet well advanced enough for a clear overall understanding to have formed but it is exciting work.
Also on the basic research side, the other major advance was the announcement of genome sequences for haploid isolates of V. dahliae and V. albo-atrum. These were presented and discussed by Dr Klosterman on behalf of the consortium responsible. Again this work is too new to have yet brought about major advances but intensive analysis is ongoing and exciting new insights are going to emerge both from comparing these two species with themselves and with other vascular pathogens.
A perennial problem with Verticillium is the effective estimation of soil inoculum levels. Migrating slow conventional plating tests with variable accuracy to fast and reliable molecular tests is proving difficult. Several talks and posters were given and a number of groups, including my own, are interested in taking this forward. One very practical outcome of the Symposium is that we have formed a multi-laboratory information-sharing group which hopefully will lead to improved detection in soils.
As xylem limited pathogens, the plant pathogenic Verticillium sp. are difficult to control, especially with the loss of Methyl Bromide as a soil-sterilant. Biocontrol using various agents, ways of inducing increased resistance and alternative methods of reducing the soil inoculum remain important topics but progress seems piecemeal and slow. Certainly no “magic bullet” emerged from the discussions here but many groups continue to work at this coalface. Resistance is often touted as the best way to achieve effective control, but the only good example of major gene resistance actually deployed so far (the Ve gene) has already broken down and effective polygenic resistances have been hard to develop. A 15+year approach to developing durable resistance in Acer to V. dahliae was described, but generally resistance breeding remains a poor relation of studies on control. Other delegates described good applied pathology projects covering new outbreaks, better prediction of disease, the effect of agronomic factors on disease etc.
However, the Verticillium wilts remain important and widespread diseases which are difficult to control. I have no doubt there will be sufficient interest to support an 11th Symposium (slated to be held in Germany in 2012). I look forward to exciting new developments coming from the availability of genome sequences and the maturing of the major German V. longisporum-Arabidopsis effort. On the other hand, whilst I fully expect that good progress on control will be made before then, I suspect that the various Verticillium wilt diseases will still be with us as major practical problems when those of us interested in these diseases re-convene.
I am grateful to both the BSPP and the GCRI Trust for part funding my attendance at the 2009 Verticillium Symposium to present a keynote talk on mating type genes in Verticillium. The GCRI Trust promotes scientific research & education on cultivation of protected crops. It provides small travel grants to researchers involved in British horticulture and publishes technical reports of new/interesting items of potential value to UK horticulture. The Trust also sponsors student scholarships for related courses and a biennial seminar on international future trends.
Dez Barbara, Warwick HRI.