BSPP News Autumn 1998 - Online EditionThe Newsletter of the British Society for Plant Pathology
Number 33, Autumn 1998
Sixth International Workshop on Allium White Rot
Irapuato, Guanajuato, Mexico : 2-5 March 1998
White rot (Sclerotium cepivorum), a serious soil-borne disease of onion and garlic, has its own specialist group started in 1979 and affiliated to the ISPP. One objective of the group is to hold Workshops every 4 years. The present Workshop was organised almost entirely by email, a demonstration of the improvements in communication in the last few years.
Arriving in Irapuato a few days early to help with arrangements, it was soon evident that the Workshop was receiving a great deal of support from the University of Guanajuato, the Centro de Investigacion y de Estudios Avanzados (CINVESTAV), and the City and the State governments. Irapuato is a thriving industrial city, famous for its strawberry production and shoe manufacture, and located on the central altoplano at a height of 1,800 m. The city centre has some fine old buildings and, in common with many Mexico towns and cities, marimba bands join in a bustling street life.
Mexico is one of the top eight world producers of garlic with an annual production of 65,000 tonnes from 8,000 h, of which 60% is in Guanajuato State; onion production is 650,000 tons from 35,000 ha. White rot was introduced relatively recently into Mexico, possibly by vegetative planting material, and is now widespread and seriously damaging production.
The Workshop programme opened formally with representatives from Guanajuato University, CINVESTAV, the Garlic Growers Federation, and the Guanajuato State Government. There followed four days of sessions structured around geographical distribution, epidemiology, fungicide, biological and integrated control and field visits. Sclerotium cepivorum is soil-borne with no sexual stage and produces sclerotia as the only propagule. Sclerotia germinate in response to host root exudates and there is a cycle of depletion of `old' inoculum followed by replenishment by `new' sclerotia produced on the host stem base. Control measures centre on avoidance, eradication of sclerotia and fungicidal control. I have selected the following topics:
1. Use of germination stimulants to eradicate sclerotia. Based on the host specific germination response of S. cepivorum sclerotia to host exudates, treatment with diallyl disulphide or garlic oil gives marked reductions in sclerotial populations and a promising degree of white rot control. At other times, there is less effect apparently due to differences in sclerotial dormancy, sub-optimum soil moisture content, high soil temperature and low rates of active ingredient. The method offers great promise providing the reasons for the failures can be understood and rectified.
2. Variability in the pathogen. S. cepivorum has previously been thought of as "remarkably uniform" in germination response, cultural morphology, temperature response and fungicide sensitivity. This view appears set to change following reports of variability in genetic composition (RFLP), new mycelial incompatibility groups, field resistance to fungicides, higher than expected sensitivity to temperatures of >28oC, and a reduced capacity of some sclerotial populations to remain viable and to survive. Pathogen variability may be a factor in the variable expression of disease and of control measures.
3. Variability in the effectiveness of control treatments. Wide variations in the effectiveness of fungicide and soil fumigant treatments are common but not understood. Factors likely to be involved are the actual versus the target field dose achieved; the dispersal and persistence of active ingredient; soil environmental conditions mainly soil structure, temperature and moisture; and the biological properties of the sclerotial population.
4. Genetic control. Luis Perez Moreno, in the early 1990s, irradiated garlic to generate mutants that were resistant to white rot. The garlic selections continue to show differences in white rot response and there is the need to transfer the resistance to commercial cultivars with better agronomic characteristics e.g. fewer, larger cloves. There was great interest in the mechanisms of the resistance e.g. increased root tissue resistance, reduced rates of mycelial development in the root system, or production of fewer sclerotia on infected plants.
5. Spread of the disease to new areas. S. cepivorum is not a normal component of the soil microflora and white rot only occurs following introduction by infected vegetative planting material, infected plant waste or soil. In one sense this is a "man made" disease. It is crucial for the future economy that further disease spread is stopped. Preventative strategies could be the use of garlic "seed" from farms certified free of the disease, the exclusion of infective material carried by vehicles or irrigation run off, and sanitation of infected waste on the farm. The difficulties of implementing such measures at the farm level should be evaluated against the direct and indirect costs arising from the introduction of the disease.
On a scorchingly hot day, we visited the Instituto Ciencias Agricolas, University of Guanjuato, and Rancho Colorado, Celaya, to see trials of genetically resistant garlic selections, fumigants, germination stimulants and fungicides. Later, we were invited to a "typical Mexican lunch" - courtesy of the garlic producers - complete with a mariachi band of violins, trumpets, guitars and singers all dressed in ornamented close-fitting uniforms; tequila helped to cement local and international relationships!
Despite the intensive nature of the scientific programme, there was time for socialising. At a civic reception at Irapuato museum we saw the extensive collection of guns, swords and spears from the time of the Spanish Conquest, reminding us of the sometimes violent history of Mexico. The following evening we visited Guanajuato City, famous for its gold and silver mines, its large colonial style buildings and the museum of mummies. We joined in a callejoneada, strolling along the narrow, steep streets led by a group of university students playing string instruments and singing to a very high standard. Very romantic.
The four days passed all too quickly and the Workshop ended with la clausure providing us with an opportunity to thank the local committee and other organisations for their support, hospitality and courtesy in supporting the Workshop. About 100 scientists, technologists, producers and consultants from seven countries attended, the large numbers of producers reflecting the importance of the disease to them. The Workshop was a great success and the local committee is to be congratulated.
Muchisimas gracias a todo y esperamus regresar pronto.
I would also like to thank the British Society of Plant Pathology for a Travel Grant that enabled me to attend the Workshop in my position as Secretary to the Allium White Rot Group.
European Association for Potato Research
Pathology Section Meeting
Umeå, Sweden : 31 March - 4 April 1998
The 1998 EAPR Pathology Section meeting was held in Umeå, Sweden. Being just below the Arctic Circle, an hour's flight North of Stockholm, Umeå was snow-covered and enjoying temperatures of around 9ºC in early April. The meeting, which attracted delegates from 12 countries, all with a common interest in potato pathology, began on Tuesday evening with opening words from the Chairman of the EAPR Pathology Section and organiser of this meeting Ulla Bång. This was followed by introductions to the county of Västerbotten, and to potato production in Sweden, which has a potato growing area of approximately 36,600 ha.
The first session on Wednesday morning, chaired by Karin Nordin was devoted to quarantine bacteria, with talks covering the surveillance, monitoring and indexing of the ring rot and brown rot pathogens Clavibacter michigan-ensis and Ralstonia solanacearum in France, Sweden and Canada. Ineke Mastenbroek then chaired a session on certification and seed potato quality, in which we heard about the different strategies employed in Sweden (Karin Nordin), Finland (Hanna Kortemaa) and Latvia (Ilze Skrabule), and the problems of silver scurf contamination in Poland (Józefa Kapsa).
Thursday morning began with a session on Streptomyces chaired by Hans Bång. The first speaker, Jari Valkonen, discussed the presence of new pathogenic Streptomyces species in potato under Finnish conditions and showed that by analysis of 180 strains of scab causing Streptomyces using various methods, at least four pathogenic species could be identified.
The second speaker, Karima Bouchek-Mechiche also spoke about analysis of Streptomyces strains, the aim of her work being to investigate the phenotypic and genomic diversity of the causal agents of common and netted scab in France. Finally in this session, Claudine Pasco, spoke of methods for screening for resistance to common scab in the glasshouse using artificial soil inoculum.
Following coffee, Leslie Dowley chaired a session on Phytophthora in which, evidence of sexual reproduction of Phytophthora infestans in a potato crop which had been artificially inoculated with two isolates of the fungus was given (Anita Strömberg). Trials showing that less fungicide was needed to control disease using the NegFry method of predicting disease risk, which, from biological and meteorological data, calculates the date of the first fungicide application and subsequent spraying intervals were discussed (Björn Andersson). The conclusions of a working group set up to produce European guidelines for assessing the foliage blight resistance of genotypes which might be included in a National List, and the assessment of resistance to storage diseases in combined tests, were also presented.
The final day of the meeting concentrated on fungal pathogens, and proved to be most relevant for us, with sessions entitled `Verticillium, Colletotrichum and Helminthosporium' and `Control of Tuber Diseases'. Talks included an examination of resistance to Verticillium dahliae in different cultivars (Sally Monnington), a very interesting assessment of the importance of the contribution by Colletotrichum coccodes to Potato Early Dying, caused predominantly by Verticillium dahliae, in Israel (Leah Tsror), the assessment of resistance to silver scurf and variation in the pathogen population (Helen Stewart) and the development of a PCR assay for the detection of Helminthosporium solani (Catherine le Cornet-Depays). Stuart Carnegie and Ulla Bång covered the control of tuber rot and skin blemish diseases using various fungicides, and natural substances, respectively.
During the 4 days of the meeting, visits were made to the Västerbotten museum, where we learned about the history of Umeå and the surrounding area, and to two departments of the Swedish University of Agricultural Sciences, Forestry, and the department of Agricultural Research for Northern Sweden. There we were shown work to determine the active ingredient in garlic extract that has been shown to be effective in the control of several tuber diseases that develop during storage. We also heard about potato seed production and certification, and visited the seed production company IVK Potatis AB's seed store and laboratory where we were shown methods of detecting the incidence of the blackleg and storage rot pathogens on seed tubers. An enjoyable final day of the conference was spent on a snow-scooter safari that enabled us to see some of the surrounding countryside and experience riding on a dog-sleigh.
The specialised nature of this meeting and its relatively small size (40 delegates) was ideal in terms of promoting friendly discussion between all the participants and allowing useful contacts to be made. We are therefore grateful to BSPP, and to the British Potato Council for providing the financial assistance that allowed us to attend this meeting.
Alison Lees and Helen Stewart, Scottish Crop Research Institute
The IV International Bioherbicide Workshop
University of Strathclyde, Glasgow, Scotland : 6-7 August 1998
The weather was brilliant on arrival but, as one would expect of a Scottish summer evening, it was pouring with rain before long! The University Halls of residence (particularly Murray and Chancellor's) were not disappointing. Not only were the rates reasonable, but the accommodation proved to be comfortable and ideally located so that the Lord Todd building was just round the corner, where a hearty breakfast was served each morning.
The talks were held in a small lecture room in the McCance building which was conveniently located within walking distance of the Halls. Seventeen posters were displayed in a conservatory area adjacent to the lecture room, where hot cups of tea or coffee and delicious light lunches were served between sessions. Mushrooms were suspiciously evident in some of the meals.
There were 54 participants in total. Alan Watson, who was unable to attend, will be the new International Bioherbicide Group (IBG) Chairman, taking over from Bruce Auld. Maurizio Vurro (Consiglio Nazionale Delle Ricerche) is the new Newsletter Editor replacing Louise Morin, who was also absent! A repertoire of speakers from as far as Canada, the USA, South Africa, New Zealand, Australia, Japan, etc. were at hand to enlighten the participants on various aspects of their work.
The first session covered various aspects of classical control and terminology. Bertie Henneche discussed the combination of classical and mycoherbicide approaches for the leaf pathogen Phloeospora mimosae-pigrae as a biocontrol agent for Mimosa pigra in Australia, a subject particularly close to my heart.
Biocontrol work was initiated in 1979; 9 insects and 2 pathogens were tested. In his work, methyl-cellulose was used as a sticker with P. mimosae-pigrae. Herbicides normally used on M. pigra did not affect the efficacy of the pathogen. The leaves died-back towards the base but, new foliage resprouted after a while. Cultures were grown in 20% V8 juice (liquid media) placed on orbital shakers for 10 days. Unfortunately, the percentage germination was lost 2 days after conidial production, therefore there was a need to look at better storage techniques.
Graham Ash continued the Australian theme with a lively discussion on the implications of genetic diversity on the biocontrol of saffron thistle, a thorny endemic weed which causes up to 70% yield loss in cereal, legume and lucerne areas. Some of the plants grown under the same conditions in the glasshouse were very different morphologically; there was a great genetic variation between the plants. A Phomopsis sp. was formulated as a mycoherbicide (inundative), whereas a classical approach was used with Puccinia sommieriana and a Septoria sp. In all, 45 Phomopsis spp. were tested on 55 plants.
Anthony Caesar gave a few pointers to the successful biocontrol of perennial weeds. Fungal species (including a Rhizoctonia sp.) were isolated from Aphthona flava and A. nigriscutis and Centura diffusa and C. maculosa. Death occurred within 10 days in some species, in combination with the insect, due to synergism. against leafy spurge. The pathogen took advantage of the damage caused by the insect on the leaves and larvae on the roots. These pathogens included Rhizoctonia solani, Fusarium oxysporum and Pythium spp.
If some of the participants were looking at their watches by this time, longing to sip a soothing beverage, it was not because they were not enjoying the session, but rather the fact that the air conditioning was off from the start of the session! Fortunately, they were momentarily distracted by the next speaker, Nigel Crump, who initiated a controversial debate, which kept the rest of the Workshop buzzing! Definitions. How brave. It took this aggressive researcher a few minutes to raise the hackles of the most tame. "Biopestistat" was in; "biopesticide" was out? Where a weed is suppressed, not killed, one cannot use the latter. We happily use "mycoherbicide", so why not use a suitable prefix regarding bacteria and viruses as well? Intriguing.
The second session focused on projects in late stages. Sarah Green explained how the application of a pathogen (0.2 g/plant) could kill the dandelion after 14 days, causing rot right down to the base. The pathogen could not be named at this stage.
Seiko Imaizumi spoke about a host specific bacterial isolate which has been developed against annual bluegrass. The bacterium is xylem-limited with an optimum of 28-32ºC and plant death can occur after 7 days, However, the weed has an optimum of 17ºC, therefore the pathogen does not perform efficiently in the winter. A frozen capsule formulation (2 x 1011 CFU/ml) was prepared with a shelf life of 18 months at -35ºC.
Simon Shamoun talked about the use of Chondrostereum purpureum against hardwood weeds in conifer reafforestation sites and utility rights of way. The fungus is applied to a girdled plant and the area on the stem is covered with parafilm. They are trying to incorporate this technique with manual brushing and so far have managed to control deciduous resprouting as efficiently as chemical herbicides. The fungus is grown for 14-21 days and a clay-talc formulation prepared and stored at 4ºC.
The last three sessions focused on chemical adjuvants to mycoherbicides. Susan Boyetchko evaluated the deleterious rhizobacteria for the biocontrol of grassy weeds. Root suppression, delay in germination and root necrosis occurred when some deleterious bacteria were tested on grassy weeds. These bacteria and their secondary metabolites provide some opportunities for weed management. The bacteria can control both resistant* and susceptible grassy weeds (* resistant to certain herbicides). Peat prills were most suitable for delivery of the bacteria; release was slow and a shelf life of 3 months was possible. The bacteria is effective at several temperatures.
Silke Brebaum worked on Phoma herbarum in liquid formulations (especially with adjuvants and surfactants) against the dandelion. Various treatments using guar gum, gluten flour, NatipiderII, pectin and durum semolina were evaluated under field conditions. Using mycelia was more effective than using spores. Disease severity increased when the fungus was formulated with guar gum, gluten flour or durum semolina and reduced dandelion populations with no detection of phytotoxicity.
Continuing with the dandelion theme, Parry Schnick explained how the application of 2,4-D, diquat and glyphosate could predispose the dandelion to potential mycoherbicides such as Phoma herbarum, Curvularia inaequalis and Plectosphaerella cucumer-ina. A combination of P. herbarum and diquat were very effective. Pathogens combined with sublethal herbicide treatments may create positive interactions, potentially increasing weed control and reducing costs sufficiently to permit commercial production.
Having the responsibility of assisting with the organisation of the Workshop, Doreen Main had a lot on her plate yet she managed to deliver a soft-spoken talk quite well. She explained how Ascochyta pteridis could control bracken, when applied in invert (water-in-oil) emulsion formulations containing low doses of chlorsulfuron or ioxynil. Ioxynil gave the best results in treatments in which the propagules were suspended in emulsion, causing the most damage to the rachis. Some of the plants developed necrotic lesions, but the plants outgrew the disease after a while. Using an application volume of 50 L ha-1, 75% necrosis was achieved in some areas.
Richard Ostrowski explained how dodder plants smother some cranberry sites, resulting in poor harvests. Foliar and granular formulations of Alternaria spp. were tested with encouraging results. In another project, onions and garlic exudates were examined for their stimulatory effect on sclerotia germination (specific to Sclerotium cepivorum which prefers cool temperatures). The rather smelly diallyl disulphide was identified as the main active ingredient extracted from ground up onion and garlic roots.
Hamed Abbas talked about how different Xanthium struma-rium biotypes could be controlled by Alternaria helianthi and Pseudomonas syringae pv. tagetis. The multiple seeded biotype was most susceptible to the fungus. When 0.1% Silwet L-77 was added, the level of infection increased, and 100% mortality was achieved with 0.1% Silwet L-77 and unrefined corn oil. The bacterium, in an aqueous suspension with 0.1 or 0.2% Silwet L-77, caused chlorosis of leaves and petioles, necrosis, apical curl and biomass reduction.
Last, but not least, Bruce Auld explained how Colletotrichum orbiculare was being developed as a bioherbicide against Xanthium spinosum. The fungus could be grown on submerged culture and formulated as dried spores with kaolin, with a shelf life of 12 months. Fungi from Argentina, Erysiphe cichoracearum and Cercospora xanthicola were also evaluated. The Argentinean isolates were no better than the Australian ones.
The Workshop would have been incomplete without the excursion through the Queen Elizabeth Forest Park, Loch Lomond and the Trossachs: the Rob Roy experience. Most of the park lies within typical highlands. Bracken (Pteridium aquilinum) is the most conspicuous weed in the uplands. Others include Rhododendron ponticum, Cirsium arvensis, Senecio jacobea, Rananculus repens, Rumex spp., Avena fatua, Sinapsis arvensis, Chenopodium album, Chrysanthemum segetum, Epilo-bium angustifolium, Convo-vulus arvensis and Gallium aparine.
The history behind the Glengoyne Distillery was explored by viewing a video, sipping the whisky (10 and 17 years old) and touring the grounds. By the time we got to Ross Priory, where we were welcomed with the bag pipes, there was a distinct gleam in the eyes of those who had tasted the spirit of the Glen. Ross Priory dates back to around 1693 and stands in an unrivalled position on the south shore of Loch Lomond, with stunning views of the surrounding hills. It has been owned by the University since 1971. A fine meal awaited us, starting with the ceremonial cutting of the haggis, to the spiked coffee at the end.
I am grateful for a University of Reading Arthur Hosier travel grant and a BSPP travel award which enabled me to attend and present a poster at this very interesting meeting. And remember, the next time you pour a glass of Scotch whisky, impress your audience by giving a toast in Gaelic fashion ... Slainte! [to your health].
Irene Mutinda, University of Reading
The Future of Fungi in the Control of Pests, Weeds and Diseases
Southampton, England : April 1998
The symposium was held in the Bolderewood Conference Centre, Southampton University and organised by the British Mycological Society (BMS). The meeting was conceived by the BMS Special Interest Committee (SIC) on Fungus - Invertebrate Interactions, and was sponsored by BMS, EU COST-821 and EU COST-816.
The symposium was also the venue for one-day meetings of the nine BMS SICs. The meeting was attended by approximately 300 delegates, representing 28 countries. There was a total of 55 oral presentations and 88 posters presentations in a period of four days, covering a diverse range of research on Biological Control Agents (BCAs).
The oral and poster presentations were loosely based on eight themes:
1. Mechanisms of fungal pathogenesis
2. Improving virulence and ecological fitness of fungal BCAs
3. Ecology of fungal BCAs
4. Markers and monitoring of fungal BCAs
5. Mycorrhizal fungi
6. Production, formulation and application
7. Biocontrol fungi: progress, problems and potential
8. Risk assessment and registration
The president of BMS, Professor Alan Rayner, opened the symposium, introducing the first speaker Dr G. Riba (INRA, France), who gave a comprehensive overview about the future of entomogenous fungi as biocontrol agents of pests. Then two other presentations followed which discussed the use of fungi for biological disease and weed control.
The rest of the day was dedicated to `Mechanisms of Fungal Pathogenesis', a very informative set of papers about the factors that affect invasion and pathogenesis of fungi on their hosts. After dinner, a workshop on `Fungal Toxins' took place, chaired by Dr. Keith Charnley (Bath University).
The second day of the symposium started with the session on `Improving Virulence and Ecological Fitness of Fungal BCAs' in which genetic advances for improving BCAs were discussed.
The ecology of fungal BCAs was the topic of the next session, chaired by Dr David Chandler. Professor Mike Jeger (Wageningen Agricultural University, Netherlands) gave a particularly stimulating talk on the distribution and survival of fungal biocontrol agents. In the next session, the molecular marker methods for monitoring fungal BCAs were briefly discussed. The last session of the day was sponsored by COST 821 and was about the potential and commercial use of mycorrhizal fungi
The third day of the symposium was dedicated to the commercial use and production of the BCAs. The day started with a session on the production, formulation and application of BCAs. Speakers from UK, USA and South Africa presented papers on the progress, problems and potential of biological control. Extensive overviews on the future of BCAs were presented at the end of the session.
`Risk Assessment and Registration' was the major theme of the final day of the symposium. This session was sponsored jointly by COST 816 and BMS. In this session, speakers expressed their concerns about the risks associated with the use of BCAs.
After lunch more papers were presented on the registration procedures of biological pesticides. Is was good to hear that new bio-pesticides are going to be commercially available within few year which will certainly expand farmers arsenal in their fight against pests, weeds and diseases. In the evening, a workshop on the `Registration of Fungal Biocontrol Agents' took place, chaired by Dr Edgar Butts.
The symposium was really intensive, having presentations in the morning and in the afternoon and poster sessions or workshops in the evening but it was very interesting to meet and talk to people who are working in the same field as me. Overall, it was a most enjoyable and stimulating symposium, with much interesting discussion. I would like to thank BSPP for the student bursary which made it possible for me to attend the conference.
Polyvios Kyritsis, University of Reading