BSPP News 31 Autumn 1997 - Online EditionThe Newsletter of the British Society for Plant Pathology
Number 31, Autumn 1997
Reports on Meetings and Conferences
This Group began its existence almost ten years ago as the IACR/ADAS/Universities Cereal Root Pathology Group. Its original aim was to bring together government-funded researchers on take-all who would pool their experience and collaborate wherever possible. Now less formal, the Group includes participants from commercial organisations or with interests in root or stem-base pathogens such as Fusarium spp. that are associated with root disease.
Two meetings are held in most years, an indoor meeting in the spring to exchange information on current research and discuss any joint activities, and a field trip in the summer.
The 1997 indoor meeting, held at Birmingham University, was an assembly of 21 participants hosted by Chris Caten, who also chaired the morning session. This began with a report from David Hornby on progress on the new book ("Take-all of Cereals: a Regional Perspective"), a major undertaking that was an initiative of the Group to which several members have contributed. David, who is the leader of the project, expects the manuscript to be with the publishers by the end of the summer. (You can order your copy through CABI now.)
This was followed by short research presentations from Rothamsted on fungal communities on wheat roots in relation to stages in take-all epidemics (Geoff Bateman) and fungicides (Will Dawson), and on take-all in wheat after long-term barley in the Rothamsted "Classical" experiment known as "Exhaustion Land" (Richard Gutteridge). Neil Paveley (ADAS) updated us on effects of take-all on optimum N amounts and yield and Doug Bailey (Cambridge University) described his microcosm work aimed at understanding primary and secondary infections of take-all and the spread of bacterial biological control agents.
David Yarham, the Group's chairman, chaired the afternoon session, which included further research from ADAS, John Spink summarising results from an HGCA-funded experiment on effects of rotational position on wheat cultivars. We also heard about research at the Sainsbury Laboratory (John Innes Centre) on the root microbiology of avenacin-producing and non-producing oats (Jon Carter) and on measuring differential gene expression in the take-all fungus during infection (Paula Garosi). Take-all has so far not been amenable to control by fungicides, but Patrick O'Reilly (Monsanto) accepted an invitation to talk about the background to developments that may change all that.
We then moved away from root disease to hear about some highly relevant developments in techniques. Simon Edwards (Harper Adams) talked about his work on detection and PCR-quantification of Fusarium in seed, and Paul Nicholson (John Innes) described his multiplex PCRs for detecting stem base pathogens and their application in a new project for HGCA.
This year's field trip, in early June, was a visit organised by David Yarham to a farm in east Suffolk where he had identified rhizoctonia patch in winter barley. The obliging farmer kindly escorted us over his fields, allowing us to trample his crops in the interests of science. The symptoms of this root disease were unfamiliar to most of us, making the long journey particularly worthwhile, though in the same crops we were able to recognise take-all and other components of a disease complex. Early risers found they even had time to take in a Suffolk castle or two.
The cereal root pathologists' visit to Orford, Suffolk: Richard Gutteridge (IACR-Rothamsted, left), John Grimsey, the host farmer (centre), Edmund Brown, the farm's crop consultant (right) and part of David Yarham (foreground), examining the soil profile
Anyone wishing to have further information on the Group should contact its secretary, Anne Osbourn, at the John Innes Centre, Norwich (firstname.lastname@example.org).
The meeting took place in the University of Wales Conference Centre, Gregynog, near Newtown in Wales. The house was a mock Tudor mansion with black and white timber painted onto a concrete facade: Gregynog, we were later to discover, had among its many distinctions been the birthplace of concrete. The grounds to the house were extensive, including formal gardens, lawns for croquet and bowls and woodland stretching into farmland. A more ideal location could not have been found for what was a relaxed and informal, but extremely informative meeting. Over 120 delegates attended from throughout the UK and from Denmark (the sole European contingent). The meeting focused around four sessions of short talks presented mainly by Ph.D. students, an afternoon of discussion and ample opportunity for informal exchange of ideas over meals and in the bar.
The meeting began in the afternoon of the 16th July. Kirsten Nielson was the first to present her work on the development of a transient expression system for anti-fungal genes. Next, Paola Garousi discussed analysis of the expression of infection-induced genes in Gaeumannomyces graminis. K. Emami then talked about xylanase genes in Cochliobolus sativus. Sarah Perfect ended the session by describing her work on the isolation and characterisation of a biotrophy-related gene in the facultative pathogen Colletotrichum lindemuthianum.
There followed a brief history of the house at Gregynog given by the warden during which we learnt that, among other identities and owners, the house had formerly been devoted to the Arts and Crafts movement leaving a legacy of many fine paintings and prints, one of which (attributed to Velazquez), the warden pointed out, showed a figure with an uncanny resemblance to `Mr Bean'.
The next day opened with talks by Pascal Baladhere, Amanda Carlile, K. Wake and Katy Davies following the theme of pathogenicity determinants in plant pathogenic fungi. Pascal Baladhere had taken the shotgun approach to identify novel pathogenicity determinants of Magnaporthe grisea by REMI mutagenesis, whereas the other three speakers had focused on defined pathogenicity factors: a protease, avenacinase, and cutinase respectively. After a pause for coffee and to admire the carved panels in the Blaney Room, Andrew Payne talked about the isolation of a repetitive element from Erysiphe graminis.
This was followed by a series of talks which broadly spanned the topic of fungal metabolism with respect to pathogenicity. First, Kerry Blisset described primary metabolism in Cladosporium fulvum, concerned particularly with mannitol and osmo-regulation. Sally Wither then looked at arginine biosynthesis in Venturia inequalis. Next, Kirsty Howard described her efforts to disrupt the nitrate reductase gene in Stagonospora nodorum with a view to assessing the importance of this gene in fungal pathogenicity. Finally Gareth McKay described the detection in fungi of resistance to the fungicide benzimidazole.
There followed lunch and a free afternoon during which two workshops were held. One workshop discussed the molecular diagnostics of fungal pathogens and the other, under the nominal title `A Model System' provided a forum for the discussion of new ideas to promote research into molecular plant pathology. Many people also took the opportunity to walk around the grounds, play football or just sit out in the sun.
The final session of the day began with Katherine Steele talking about the isolation of a transposable element from yellow rust and its potential role in the promotion of genetic variation. Suzanne Baker then turned the focus to the plant side of the fungal-pathogen interaction by describing her work on the role of water stress in the temporary breakdown of mlo resistance in barley to Erysiphe graminis. Bleddyn Hughes described his work in generating antibodies to spore surface proteins of Colletotrichum lindemuthianum. Then, Katherine Dixon described the isolation of a MAP kinase homologue in Magnaporthe grisea and discussed its role in generation of turgor during appressoria-mediated penetration of the plant cuticle. To end the day of talks, Andrew Purvis discussed somatic hybridisation in Phytophthora infestans.
The evening began with a drinks reception followed by a `banquet' dinner of five courses and countless bottles of wine. As the wine flowed, discussion generated wackier and wackier ideas - who knows what innovation came out of that evening
The next day attendance at breakfast was noticeably sparse. Nevertheless, the morning session began with several talks with the theme of the development of PCR methods for diagnosis of fungal pathogens. First, Mariola Pedrajas described the use of nested SCAR (sequence characterised amplified region) primers to detect different pathotypes of Fusarium oxysporum. Next, Beth Stevens, S. Sreenivasaprasad and Duncan Simpson talked about the development of a PCR-based methods for the detection of Pyrenophora graminea, Colletotrichum spp. and Microdochium navale respectively.
After coffee, Andy Bailey described the importance of polyamines in fungal pathogens and the potential of disruption of the polyamine synthetic pathway to prevent pathogenesis. The final talk of the meeting was given by Chris Ridout, who described progress in the development of a genetic map of the Erysiphe graminis genome, focusing on several avirulence genes. This was an optimistic note on which to end the meeting as he described prospects of cloning avirulence factors from an obligate biotroph.
Before departure, the future of the meeting was discussed: the number of attendees has increased from tens to over a hundred in the history of the meeting, and is predicted to reach over two hundred delegates next year. The nature of the meeting has also changed: with greater numbers, the chance to talk to everyone has disappeared and the feeling was that maybe the meeting had outgrown the size of Gregynog - this year many delegates were forced to find accommodation away from the house and others were turned down. Next year, plans are underway for the meeting to take place in Birmingham, a more practical if less picturesque location. Moreover, in order to keep the bias towards young researchers, the idea of limiting places for `oldies' was mooted !
Overall, the meeting focused on the application of molecular biological techniques to both the dissection of features of the fungal pathogen-plant interaction and the development of diagnostic and analytical procedures. The growing size of the meeting is surely a reflection of the growing importance of this field of research to the development of durable resistance to plant pathogenic fungi. The meeting provided an informal atmosphere in which to discuss research and, most importantly, an unique opportunity for many PhD students and young researchers to present their work to a sympathetic audience. This was an invaluable meeting for anyone emerging into the savage world of research!
Alison Hall (D.Phil student)
Department of Plant Sciences, University of Oxford
The setting for this large meeting was the picturesque Asilomar Conference Grounds in Pacific Grove, California. Arriving early allowed participants to visit nearby Cannery Row of Steinbeck fame with its wonderful aquarium, clam chowder restaurants and dropin massage parlours. The Conference ran from the afternoon of March 18 to noon of March 23, 1997 and was attended by some 660 delegates from a diverse range of disciplines, but all sharing a common interest sunnier climes! (some delegates happened to share an interest in fungi as well).
Taking the advice of colleagues who had attended previous meetings at Asilomar in March, many weatherhardened Brits (ourselves included) packed plenty of warm clothes, electric blankets and hot drinks, not wishing to appear unprepared when we arrived in the USA. Imagine, therefore, our surprise to find that the organisers had even arranged for glorious sunshine and soaring temperatures at no extra cost.
The meeting consisted of four plenary sessions and four sessions devoted to concurrent workshops, starting at 8.30 am every morning and ending, for the diehards, near to midnight. Even for two of us, it would have been impossible to attend all of the 200 (or thereabouts) scheduled talks, and should we have made this effort, we would have probably been vegetables in the end. One was also spoilt for choice with the disparate variety of high quality posters; in fact, three poster sessions had to be arranged throughout the week so that more than 400 posters could all be displayed. Unfortunately, this made for three very rushed afternoons running from venue to venue in an attempt to visit every relevant poster. Originally, abstracts and other information regarding the Conference were to be published in a supplement to the Fungal Genetics Newsletter (1997) 44; instead, an online version was opted for (sign of the times, eh?), the Web site for which is: http://kumchttp.mc.ukans.edu/research/ fgsc/asilomar/firstno1.html
Because of the broad areas covered by the meeting, we have decided to focus on discrete research themes which will hopefully be of interest to many. Following registration and a social reception on the Tuesday evening, it was down to work early on the Wednesday with a full day of activities. The opening plenary session, Gene Regulation and Metabolism, established a theme apparent throughout the meeting: the identification and analysis of components of signal transduction pathways. The work presented included maintenance of internal pH, the effects of external pH on catalase activity, and the effect of light on cell development and division. The roles of Gproteins, protein kinases and transcription factors were described. An interesting feature to emerge from much of this work is that unrelated functions may be regulated by common signal transduction pathways. Also, while the downstream components of the pathways are being identified, the receptors of the environmental signals remain, by and large, conspicuously elusive.
standing room only for latecomers: an indication of the increasing significance of fungal pathology at this meeting. The multiple roles of melanin were discussed with the focus on the importance of melanin in penetration. Data were presented for Gaeumannomyces graminis f.sp. tritici mutants with increased melanin content, which showed reduced protein secretion and pathogenicity (Joan Henson). Clare Kelly, University of Birmingham, has generated G. graminis f.sp. tritici mutants with altered melanin production which lack the characteristic brown melanin pigmentation and are nonpathogenic. Genetic studies suggested the mutation occurs in one gene. Large groups from Japan and USA have cloned and expressed many of the genes in the melanin biosynthetic pathway from both Colletotrichum lagenarium and Magnaporthe grisea. Much interest clearly lies in finding potential fungicide targets, with DuPont putting much effort into these studies.
As chairpersons of the Update on Pathogenicity Factors workshop, Hans van Etten and John Hamer employed a novel method to ensure that speakers did not talk for too long a 6 foot long hook! However, they had clearly not counted on the 7 foot tall Nick Talbot who talked about infection structure formation in the rice blast fungus, M. grisea, and other pathogenic fungi. In Magnaporthe, Nick's research has demonstrated that a variety of solutes, including glycerol, are accumulated at high concentrations in the developing appressoria. This results in the generation of an internal physical pressure of about 8 MPa (equivalent to 43 times the pressure in a car tyre) which facilitates penetration of the rice leaf surface by an infection peg.
Kate Dixon is attempting to further characterise a signal transduction pathway thought to be involved in regulation of glycerol accumulation, and to this end has identified a mitogen activated protein kinase encoding gene, HOG1, in the fungus. In the same workshop, John Hamer provided an update on the use of differential expression and related techniques to identify putative pathogenicity genes. He pointed out that many groups were now using these methodologies, and examples could be found in the poster abstracts.
Anne Osbourn talked about the methods employed in the detoxification of phytoanticipins (a term first suggested by Hans van Etten in the 7th International Symposium on Molecular PlantMicrobe Interactions, Edinburgh, 1994 to describe low molecular weight antimicrobial compounds found in plants before infection or produced after infection from existing compounds) and phytoalexins (antimicrobials synthesised de novo). In particular, she considered the widespread common mechanisms of saponin detoxification in various phytopathogenic fungi such as G. graminis, Septoria avenae and S. lycopersici.
Barbara Valent opened Thursday's proceedings with a general overview ofplant pathogenesis. She outlined DuPont's strategy to identify putative pathogenicity genes in the rice blast fungus by using restriction enzyme mediated insertional (REMI) mutagenesis to randomly disrupt genes, and described the large, and often laborious, programme aimed at characterising the hundreds of isolated genes. One such gene, PTH11, was identified twice in such a mutant-hunt based on REMI, mutants of which form few appressoria on hydrophobic surfaces in vitro and on plant surfaces. Since mutants form wild type levels of appressoria on other surfaces, it was speculated that the gene is possibly involved in surface recognition.
The current intensive research effort into microtubules was reflected in Berl Oakley's description of the complex regulatory and structural role of tubulin in microtubule organisation. tubulin is able to assemble microtubules in vitro, and has been shown to be essential for nuclear division, MG1 transition and assembly of the mitotic apparatus. The "superhighway" function of microtubules was discussed by Mike Plamann in his presentation of research on dynein and kinesin motors. These proteins are involved in the ATPdependent movement of vesicles and organelles along microtubules.
The evening workshop on Gene Regulation and Cell Biology included an overview of carbon and nitrogen control in fungi by Matt Sachs. George Marzluf discussed the importance of proteinprotein interactions in nitrogen gene regulation, with special reference to the action nit2 and nit4 gene products on the nitrate reductase gene, nit3, of Neurospora crassa.
Researchers in nonmedical fields are often a little jealous of their wellfunded and highimpactrated counterparts in medical departments. A visit to the Medical Mycology workshop was, therefore, particularly rewarding. Many organisms of interest in this field, including Cryptococcus neoformans and Pneumocystis carnii, have poorly understood clinical lifecycles and virtually unknown modes of infection. The obligate pathogens, such as P. carnii, provide particular problems, which plant pathologists working with rusts or mildews may only imagine (with some pleasure!). These problems are leading workers to concentrate initially on closely related model organisms (Aspergillus nidulans instead of A. fumigatus, for instance), transferring effort to the pathogenic species at a later stage. Logically, discussion of this approach led to a "heated" debate surrounding genomics, another significant theme of the meeting. Completion of the sequencing of the yeast genome has excited interest in sequencing the genome of a filamentous fungus. The arguments surrounding sequencing the genome of a filamentous fungus are well presented by Lisbeth Hamer (Fungal Genetics and Biology (1997) 21:810).
Until recently, the lack of repetitive DNA elements was regarded as a characteristic of filamentous fungi. MarieJosé Daboussi's overview (during Friday's plenary session) of the wide variety of transposable elements now known to be present in fungal genomes illustrated how our knowledge of the genome architecture of fungi has increased. Her discussion of the role of mobile DNA was with particular reference to the variability of fungi, especially among plant-pathogenic fungi. It is clear that much work remains to be done before the implications of the presence of these elements in fungal genomes become well defined.
The complexities of Fusarium phylogenetics were presented by Kerry O'Donnell; a new phylogeny was described which seemed to continue the historical trend for ever more Fusarium species. The evolutionary impact of mutation, gametic disequilibrium and pseudohomothallism were also discussed, after which your reporters were free to set up their posters.
Following the previous evening's ad hoc yeast biotechnology workshop at Doctor Thirsty's Surgery, participants looked forward to a Saturday morning of stimulating, fungal sex. The presentations concentrated on what happens when mating, or the outcome of mating, goes wrong. This was illustrated with slides of some very sorrylooking mutants. Regine Kahmann described her work on the dimorphic fungus Ustilago maydis. The haploid sporidia, which grow in a yeastlike fashion, are nonpathogenic, while the dikaryon grows filamentous and is pathogenic. The switch from the haploid state to the dikaryon is mediated by a pheromone response between two mating types. Interestingly, components of the pheromone response pathway have also been implicated in pathogenic development.
The excellent farewell banquet on Saturday evening was completed with a highly entertaining invited lecture by Lorna Casselton entitled "Sex and Sexuality". The talk described many years of research and could have probably been renamed "Everything you wanted to know about Coprinus mating type, but were afraid to ask". Exactly how she managed to incorporate a slide of the popstar Michael Jackson into her talk is still a mystery and will probably remain so (must have been all the free wine dulling the senses!). The Conference was concluded by a party which carried on well into the night. Many an eminent scientist was seen "boogying the night away" and the general feeling was that the meeting had been a huge success.
Due to the everincreasing numbers attending the Asilomar congress, the organising committee proposed that the 1999 meeting be held at a different venue. However, a show of hands suggested that this was not a viable option, and that in the future, numbers would probably need to be restricted. One possible solution recommended is to limit graduate students to those in the final stages of study. In addition, it may be necessary to limit the number of delegates from very large research groups; these are clearly issues for the next organisers to deliberate over.
We would like to thank the Society for financial assistance enabling us to attend the Conference and present some of our work in the poster sessions. At a time when it seems to be getting harder and harder to obtain travel grants, the BSPP has provided us with the opportunity to broaden our outlook and meet many of the world experts in our respective fields.
University of Birmingham
IACR Long Ashton
One hundred and one years ago Erwin F Smith described a bacterial wilt disease of solanaceous crops, caused by the bacterium now known as Ralstonia solanacearum. The Second International Bacterial Wilt Symposium, held in June on the island of Guadeloupe, brought together around 120 researchers from over 30 different countries to discuss the latest research on the disease. The meeting opened with an address by Arthur Kelman, one of the longest-serving members of the bacterial wilt research community. Dr Kelman surmounted the monumental task of summarising the last century's research on bacterial wilt by drawing on some of the landmark achievements accomplished during that time.
Diversity and diagnosis
One of the most extraordinary characteristics of R. solanacearum is the enormous diversity within the species. With the possible exception of Agrobacterium it infects more plant species than any other bacterium. The first session of the meeting, and the following poster session, discussed the diversity of R. solanacearum, with particular emphasis on the molecular methods now available to characterise genetic variation. Several papers explored the use of RFLP, DNA sequencing and PCR-based methodologies and their relevance to the more traditional classification of the bacterium based on host range and biochemical characteristics. I was able to present my results on molecular characterisation of R. solanacearum by PCR in the accompanying poster session.
Related to diversity is the issue of diagnosis. Many of the tests used to assess variation have been adapted as tools for detection of the pathogen and diagnosis of the disease. The session devoted to diagnosis was dominated largely by papers discussing the appearance of R. solanacearum in Europe, in the form of potato brown rot. The potentially serious threat which R. solanacearum poses to potato production has led European researchers to develop routine tests for infection of seed potatoes. Jape Janse of the Dutch plant protection service reported that last year 60,000 seed potato and 15,000 surface water samples were tested for the presence of R. solanacearum.
A round-table discussion held later on in the meeting provided another opportunity to examine the problem of brown rot in Europe. Delegates heard details of the disease management procedures implemented in Europe as well as the latest news on the spread of the bacterium. It was agreed that the priority for future research must be to gain a greater understanding of the epidemiology of bacterial wilt in Europe so that control measures may be improved.
While R. solanacearum is in the main only a potential threat to Europe, it is already a serious problem in tropical and sub-tropical areas. The problem of identification here is compounded by the fact that well-equipped laboratories are few and far between, so simple, cheap and effective means of identification are required. The last speaker in the diagnosis session, Rob Black, addressed this problem and described how diagnosis and detection methods had been adapted for use in such countries. Of particular interest to many was the BACTID system of biochemical tests, suitable for identifying plant pathogenic bacteria in less developed countries. This theme was continued in a round-table discussion, in which the problems of developing diagnostic tests more suited to less-developed countries were further discussed.
The second day of the meeting began with a collection of papers on the mechanisms of pathogenicity employed by R. solanacearum. A number of pathogenicity factors have been identified, which are subject to complex regulatory networks. Two of these factors, namely extracellular polysaccharide and pectin-degrading enzymes, along with their associated control systems were described in some detail by Tim Denny and Caitilyn Allen respectively. The role of some of the proteins encoded by the hrp genes of R. solanacearum was discussed by Frédérique Van Gijsegem.
The use of resistant plants is in the future likely to become increasingly important in the control of bacterial wilt. Two sessions were devoted to host resistance, exploring its mechanisms and possible use through breeding programs. Nigel Grimsley and Matthieu Arlat gave papers describing the mapping of resistance loci in tomato and Arabidopsis respectively. Other speakers elucidated in more detail the response of the plant to infection by R. solanacearum and explored possible sources of resistance in commercial crops such as tomato and potato. The day was rounded off by the congress party. Any misgivings about the local food on offer were soon forgotten when delegates were treated to a display of traditional (and shall we say, evocative) dancing.
The third day of the meeting was reserved for tours of the island, which provided both a break from the formal sessions and an opportunity to meet other delegates on a more informal basis. A number of tours were available, I chose to visit the fruit research station of the French international agricultural research organisation, CIRAD. The centre had a large collection of banana cultivars. Being involved in research on bacterial wilt disease of bananas I found this trip particularly enlightening.
The next day, back in the conference hall, biological control of R. solanacearum was discussed. A number of strategies were described, including the role of some rotational crops in reducing bacterial wilt incidence and the application of micro-organisms as biocontrol agents. Gerry Saddler of the International Mycological Institute described the development of hrp mutants of R. solanacearum for use against bacterial wilt of potato in Kenya. This paper highlighted one of the major issues inherent in biocontrol strategies of this type; the release of genetically modified bacteria into the environment. Many countries in which bacterial wilt occurs have no experience of such experiments and no legislation governing the use of genetically modified organisms.
The last session of the meeting saw papers from Latin America, the USA, Zimbabwe and Nepal on the management of bacterial wilt of various crops, notably potato and tobacco. Each of the papers highlighted the need for a greater understanding of the interaction between the pathogen, the host and the environment in order to develop suitable control strategies.
The only point of discussion then remaining was to decide on a venue for the next meeting. The third international bacterial wilt symposium will be held in the Republic of South Africa in 2002. The success of the meeting lay in the fact that it bought together researchers from a number of diverse disciplines, so by the end of the week one was left with a more holistic and enlightened view of the nature of the disease. I would like to thank the BSPP who's financial support, through the BSPP travel fund, allowed me to attend the meeting.
Natural Resources Institute