BSPP News Spring 2001 - Online Edition

The Newsletter of the British Society for Plant Pathology
Number 38, Spring 2001 

Conference and Travel Reports

15th International Congress on the Science and Cultivation of Edible Fungi
Maastricht, The Netherlands : 15 -19 May, 2000.

The first of this series of Congresses was held in Peterborough, England in 1950. At that time there was considerable secrecy within the mushroom industry and one of the aims of the first Congress was to break down barriers and exchange information on all aspects of the production of the button mushroom (Agaricus bisporus). Thirty papers were given and forty delegates attended from a number of European  countries and  the USA.  The organisers of that meeting would have been amazed and would have felt that their objectives had been well and truly achieved had they attended the 15th Congress. Over 400 delegates from 38 different countries were present. In addition the Congress was run in conjunction with the Dutch mushroom exhibition of equipment and sundries associated with the industry.

The International Congresses are now organised under the aegis of the International Society for Mushroom Science. At Maastricht the Society combined with the Netherlands Mushroom Growers Cooperative under an organising committee chaired by Dr Leo van Griensven, Head of the Mushroom Research Station at Horst. This Congress, like the first, included all aspects of the production of button mushrooms but in addition, there were details of the cultivation of a number of other fungi. There is also a growing interest in the health promoting aspects of edible mushrooms as well as on the development of neutriceutricals. This Congress, for the first  time, included a keynote lecture on medicinally important fungi  as well as eight other papers on this subject.  The science of mushroom production is, like all branches of biological science, becoming more and more complex and unless one is familiar and up-to-date with the literature and the jargon it is not easy for the layman to follow. In this respect the International Congresses have become less grower orientated although there was plenty for growers to learn both at the Congress and the exhibition.

Annual consumption of mushrooms in Europe is about 3kg per head per year we were told in an introductory paper by Hans Megens from Rabobank International. What always surprises me is that in France and Germany, the largest consumers,  over 50% of the consumed product is processed whereas in the UK, Belgium and the Netherlands fresh mushrooms are preferred. The white button mushroom is still the most popular accounting for over 90% of mushroom sales in Europe although the situation is very different in the far east. There has been a very slow increase in the consumption of oyster mushrooms (Pleurotus ostreatus ) and shii-take (Lentinus edodes). The demand for organically produced mushrooms has also increased but still accounts for less than 1% of the total production. One of the limitations is the availability of organic straw and although the financial return can be up to 40% greater the yield is considerably less.  One of the major limitations to organic production is the control of pests and diseases.

A major challenge for button mushroom producers is the ever increasing power of the supermarkets who, in Western Europe, are the main retailers of the crop. They continually demand higher quality for lower costs. This is resulting in increasing competition between countries and giving an advantage to those countries where the costs of production are lowest (40% of the cost of production is wages). China has become a major exporter and in Europe both Poland and Hungary have experienced tremendous growth in their exports over the last decade.

The  mushroom industry in Europe appears to have reached a point where major changes are inevitable. France and the Netherlands are still the main producers with the UK third, but commercial pressures may soon bring about  changes. Countries with lower labour costs will go on increasing their production.  It is difficult to see how the present  main producers, such as the Dutch, can either increase yields or reduce costs further. When the first Congress was held in Peterborough a yield of 1 to 1.5 lbs of mushrooms per square foot of cropping area would have been enough to keep a business viable and make a modest profit. Now 6lbs is needed.

It is against this background that the control of pests and diseases must be considered. Yield losses are not acceptable and consistent yield losses result in bankruptcy. It is not surprising therefore that a whole section of the Congress was devoted to diseases and  pests with a total of four sessions (surprisingly only one paper in the whole of these was on pests).

Papers on fungal diseases included host pathogen relationship with Mycogone perniciosa,  the use of siderophore-producing pseudo-monads as biocontrol agents, the liberation of the conidia of cobweb (Cladobotryum mycophilum) and cell wall degrading enzymes produced by Verticillium  spp. and their relationship to infection in Agaricus bisporus.

The  Mycogone  paper by Ulmar, Geels and van Griensven on the morphology and pathology of disease is one of the first on the subject of fungal/ fungal host parasite relationships.  It included detailed morphological  studies and concluded that this combination is ideal for the study of fungal infections of a macrofungus. Apparently M. perniciosa  is able to affect the physiological state of the host cells and tissues from a distance. Intrahyphal growth has been observed and the authors believe that this may have important consequences especially if the host is also virus infected or harbours other transmissible factors such as mycoplasma or plasmids.

Two papers from India (not presented but in the Proceedings) on the use of siderophore-producing fluorescent pseudomonads demonstrated the possibility of using pseudomonads from mushroom casing as biocontrol agents. Some promising results were obtained although some bacterial isolates were more effective against one pathogen than another. Verticillium fungicola, probably the most important fungal pathogen wherever the crop is grown, was fairly well controlled with one bacterial isolate. Such methods of disease control will need to be developed if widescale organic production is to be a possibility.

Following the epidemic development of cobweb disease in the UK and Ireland in the early 1990s work by Adie and Grogan has shown that the conidia of the pathogen (Cladobotryum mycophilum was used in the work but C. dendroides  is probably the most common cause) are very readily airborne and the simplest of cultural operations can result in the dissemination of the pathogen. For instance the commonly used practise of covering disease mushrooms with salt was shown to be a major factor in the dissemination of spores.

Relationships between  72 isolates of Verticillium  spp. were  examined by RFLP, RAPD and sequence analysis by Mills et al. They identified  and quantified a range of enzymes which they think could be partially correlated with symptom production. Ultimately it is hoped that this work will help in the identification of breeding material from the Agaricus Resource Program (ARP) which will enable disease resistance to be bred into commercially available strains.

Two sessions were devoted to Trichoderma diseases, mainly those caused by compost colonising species and strains. Since 1987, T. harzianum  has been a major cause of crop loss, firstly in Ireland and the UK, and subsequently in Canada, USA, France, Spain and most recently Iran. A similar problem has also occurred in Australia. The relationship between Trichoderma  spp. and A. bisporus  is poorly understood as is the role of a number of other fungi (weed moulds) that frequently occur in mushroom cultivation. A paper by Grogan et al. found that the levels of moulds in mushroom composts could be related to the yields obtained; those with the highest populations generally yielding less well. Work on the biotypes of T. harzianum involved in the compost mould problem shows that the same biotype (Th-2) is associated with the problem in Ireland, UK, and France whereas in Canada and the USA the biotype (Th-4) is not the same, although the disease is identical. In Australia  neither  the European or North American biotypes are found and the same disease symptoms are caused by a number of different Trichoderma species. French work (Mamoun  et al.)  demonstrated that some spawn strains are not as severely affected as others but contrary to previous work, no difference was found between brown and whites strains. Some bacterial antagonists  of T. harzianum  were identified.  In contrast Anderson, Beyer and Wuest reported that brown strains showed losses of 8-14% compared with hybrid white strains where losses were 96%.

Goltapeh studied the interactions between A.bisporus  and various Trichoderma  species. He reported no interaction in a nutrient-rich medium but where the nutrient status was low coiling and hyphal lysis occurred. T. harzianum  and T. longibrachiatum  produced the most severe reaction and this was attributed to the lytic enzymes these species produced. Volatile metabolites were not found in any of the species studied.

A paper by Gaze et al. (HRI) and Romaine (Penn State University) described a new disease of  A. bisporus which has been seen in England since 1996. It is characterised by non-cropping patches  with normal mushrooms around the edges or by lines and swirls of normal mushrooms in otherwise barren areas of the bed.  Once present on a farm it is very difficult to eliminate. Analysis of samples from affected crops has failed to demonstrate virus particles or the ds RNA bands of the well known La France virus disease.  Symptoms have been reproduced using affected mycelium and spores from affected mushrooms.  The indications are that this new disease may be caused by a virus or virus complex as a number of ds RNA bands have been consistently found in extracts from affected mushrooms although they are not the same bands as those associated with La France disease.

Bacterial diseases of the crop are common. Work in France (Mamoum et al.) is aimed at the development of strains resistant to bacterial blotch (Pseudomonas tolaasii ).  A series of 5-6 standard tests are required before reliable results of strain susceptibility can be obtained. Perhaps overall the congress was notable for the increasing emphasis on the medicinal value of mushrooms and also for the report from the Dutch Mushroom Research Station on further developments in the use of Agrobacterium  to transform A. bisporus.  Mikosch and co-workers have shown that transformation is possible both with basidiospores and fragments of mycelium. This work opens the door to studies of gene functions and also to the possibility of introducing genes which will enhance the characteristics of the mushroom.  The vexed question of whether the public will be prepared to eat transformed mushrooms remains to be seen. The final day was spent visiting two mushroom farms, one in Germany,  the other in the Netherlands. The modern state of the industry was on display at both sites with large investments in capital equipment. The Dutch farm was an extreme example, producing 80,000 lbs of mushrooms per week but employing only four people, largely because of mechanical harvesting. This must be the ultimate in reducing cost of production but how often has the mushroom industry thought that!

For the pathologist, the mushroom crop offers many challenges and many of these were on display at the Congress. From the  molecular,  to epidemiology, host parasite relationships, the role of various fungi in the cultivation of the crop, the taxonomy of the main pathogens, the triggering  mechanisms of disease with the ds RNA viruses and the control of the diseases. These are all areas where further work is needed. Internationally there are very few research centres but perhaps an increasing interest in the medicinal properties of edible fungi will see more funds going into research.

The Congress was excellently organised by Prof. van Griensven, Jan Pijnenborg and their committee. The Congress dinner at Kasteel Vaalsbroek in the foothills of the Ardennes was absolutely splendid.  This together with an open air concert in the centre of the beautiful city of Maastricht and the excellent facilities of the International Conference Centre made the Congress memorable and very worth while. I am most grateful to BSPP for awarding me a travel grant which made attendance  possible.

John Fletcher
Godmersham, Canterbury

XIIth International Botrytis Symposium
Reims, France: 3 - 7 July, 2000

The XIIth International Botrytis Symposium was held in Reims. Botrytis affects a wide range of crops including the local vines of the Champagne region, giving us an excuse to sample the product itself.  Our first night in the city was memorable as we joined the street revelry after watching France's victory in Euro 2000 - the perfect antidote to our twelve hour journey from Aberdeen! 

Barrie Seddon and Eftihia Tsomlexoglou in celebratory mood.

On the first day of the congress, we were introduced to the "Structuration of the genus Botrytis and Plant Pathogen Interactions".  E. Fournier described genetic differences between B. cinerea Transposa and Vacuma.  The concept, that B. cinerea  is a complex of species including Transposa and Vacuma, was to be a recurring topic throughout the symposium.  Andreas Von Tidemann described differences in pathogenicity between strains of B. cinerea and concluded that B. cinerea is a collection of necrotrophs that vary in pathophysiology (particularly polygalactouronase activity or suppression of hydrogen peroxide scavenging systems of the plant).

Topics covered on the second day of the Symposium included: Phytohormones, Active oxygen species, Secondary metabolites and Cell walls.  Kris Audenaert described how abscisic acid (ABA) appears to negatively modulate salicylic acid-dependant defence in tomato - ABA negative plants are much less susceptible to B. cinerea than wild type plants.  Later, Brian Williamson described markers of oxidative stress associated with Botrytis infection and noted a drop in ABA in leaf tissue surrounding lesions on French bean and, through EPR spectroscopy, showed that rotten tissue lacked the free radical signal associated with photosynthesis.  Yigal Elad further discussed the interactions of ethylene, active oxygen species and antioxidants in B. cinerea infection.  The importance of iron in Botrytis infection was explained by Paul Wood who described how the Fenton reaction resulting from solubilisation of iron by oxalic acid secreted by Botrytis interfered with the plant's defence response.

In the Epidemiology session of the third day, Monika Walter presented a lively discussion of garden floor management in Boysenberry for control of B. cinerea.  Botrytis infection was reduced when garden floor litter was mixed with organic and inorganic compost amendments and when litter was piled rather than being scattered as is standard practice.  Gustav Holtz investigated the infection pathways of B. cinerea on grapes and deduced that the pedicel is the most important infection route, especially in latent infection and that disease tended to initiate on berry cheeks only after damage.  The rest of the day was devoted to Biocontrol in which Aberdeen University featured prominently.  Barrie Seddon discussed the development of biocontrol with Brevibacillus brevis, highlighting very promising results in greenhouse trials both in the UK and Greece and showing how B. brevis can be effective in a range of crop situations due to its two modes of antagonism (it produces a biosurfactant and an antifungal compound).  Eunice Allan introduced a less conventional approach to biocontrol through the use of L-form (cell wall-less) bacteria which, when associated with plants, induce production of chitinases which can break down fungal cell walls.  She showed that development of B. cinerea is delayed in L-form associated plants.  Jurgen Köhl explained promising results of field trials using Ulocladium atrum in a range of crops, with disease reduction of around 70%.  Ioannis Saligkarias then presented results of tomato stem assays where the yeast, Pichia guillermondii reduced B. cinerea infection by as much as 80% and Aled Dik exulted the potential of another yeast, PBGY1, which is now being developed for commercialisation as it is effective in a range of crops and diverse environmental conditions.

 "Chemical Control" was discussed on the final day of the Symposium.  Pierre Leroux described patterns of cross resistance in strains of B. cinerea collected from French vineyards.  A more positive picture of chemical control was presented by G. Haenssler who told us that fenhexamid has maintained efficacy for the past eight years.  The necessity for effective control in protected ornamentals in the UK was explained by Tim O'Neill.  The loss due to B. cinerea currently stands at £6m and he described the results of novel fungicide programmes which will be integrated with cultural and environmental control in future trials to develop economic and effective control systems.  In the "Integrated Control" session, Phillipe Nicot took us through the combined use of less susceptible varieties of crop plants, low toxicity fungicides, climate management and BCAs.  Jan van den Ende described BoWaS, a warning system developed for Botrytis leaf blight in bulb crops, based on leaf wetness and temperature, which can reduce fungicide use by up to 80%. This theme was continued by Jim Lorbeer who discussed BLIGHT-ALERT, a weather based forecast system for B. squamosa which reduced fungicide applications to onion crops by around 30%.

Posters were on display throughout the conference and daily poster sessions were arranged so as to coincide with oral presentation topics.  I was particularly pleased to see a large contingent of Biocontrol posters and enjoyed having the opportunity to present my own poster and discuss my work.

The deterioration in weather throughout the week failed to dampen spirits, even when ferocious thunder storms took hold on the day of our excursion to champagne producers Mailly and Moet & Chandon.  We learned about the fascinating process of champagne production as we strolled in the cool damp limestone cellars and enjoyed delicious food washed down with several varieties of champagne.

I am grateful to BSPP for providing a Travel Grant which helped fund my attendance at the  Symposium.  Not only did I benefit from the high quality presentations, but I also enjoyed the conference very much and I'm sure everyone who attended is looking forward to the 13th International Botrytis Symposium in Turkey in 2004.

Rosalind McHugh
University of Aberdeen

XIIth International Botrytis Symposium
Reims, France: 3 - 7 July, 2000

Over seventy years ago Brierly (1921) stated that "Botrytis cinerea is perhaps the commonest and best known fungus and has been a centre of mycological research since the time of de Bary". Since then, despite the thorough studies by so many able investigators and the resulting extensive literature, Botrytis diseases are probably still the most common and widely distributed diseases of greenhouse crops and vegetables, ornamentals, fruits, and even field crops throughout the world, causing considerable losses of yield and quality.

The  Symposium was held in Reims, the city of champagne and the smiling angel.  This well established series of symposia attracted over 100 participants from more than 22 different countries. The organising committee, along with the scientific advisory committee including the world's Botrytis experts, organised an interesting meeting. The event took place at Reims Congress Centre (walking distance from the town centre) which, despite its state of the art technology and excellent auditoria, managed to upset a couple of speakers due to continuous failure of the projector. The symposium consisted of 80 posters and 42 oral presentations on most of the important aspects on Botrytis, including plant-pathogen interaction, epidimiology, biological and chemical control and ABC transporters.

Among the posters the announcement by Dr Frances Molly Dewey of a new panel of monoclonal antibodies to B. cinerea which can be used to quantify the pathogen in juice of infected grapes with three different assay types was one of the most interesting, allowing quick and early detection of Botrytis. A similar colorimetric immuno-PCR based detection system was also announced by Dr Carlos Figueroa.

The evidence that the latency of B. cinerea pathogen in grapevine may be regulated primarily by the pedicel and not by the berry "cheeks" was a surprise, as many were confident until now that B. cinerea gained access to the berries only through the cheeks. The subject was raised by Dr. Gustav Holz and was extensively discussed at a later workshop.

Pest management and particularly the biological control part chaired by P. Nicot was one of the most interesting for me. The session comprised 7 oral and 10 poster presentations each proposing a different approach to the biocontrol of B. cinerea. It started with Bacillus brevis and Dr B. Sedon, followed by a talk on L-form bacteria and the induction of pathogenesis related proteins given by Dr Eunice Allan. The filamentous fungi approach (such as Ulocladium sp.) was presented by both Dr Steward and Dr Jürgen Köhl. The session closed with a presentation by Dr Aleid Dik on the use of epiphytic yeasts as biocontrol agents.

On behalf of myself and my supervisors (Dr HAS Epton, Univ. Manchester, UK and Dr FT Gravanis, Technological and Educational Institution of Larissa, Greece), I gave an oral presentation entitled "The effect of timing and concentration on the biocontrol activity of yeast Pichia guilliermondii strains US-7 & 101". I was really impressed by the positive feedback and the ideas I got for future work and discussion.

The pest management session closed with chemical control where some of the audience found themselves lost in different active ingredients and different types of resistance present on different crops. An presentation was given by Dr Nicot on the integrated approach for the control of B. cinerea in greenhouse tomato where he pointed out the effect of all factors (humidity, temperature, pruning etc.) on disease incidence.

The meeting closed at Mumm Perrier Jouët cellars, with an enjoyable dinner served after listening to a University choral society (Vox Remensis). The post-symposium tour included visits to the world's most famous champagne cellars and "The Champagne Information Bureau" at Epernay, where the participants had the opportunity to get a lot of scientific and technical information regarding Champagne production including Botrytis problems.

The symposium gave me the ideal opportunity to share my experience and knowledge with other scientists, to make a number of useful contacts with other research groups and also benefit from a very valuable learning experience. I am grateful to the BSPP for providing me with the financial assistance that made it possible to attend.

Ioannis Saligkarias
University of Manchester