British Society for Plant Pathology

BSPP Presidential Meeting 1997

Plant Pathology - Global Perspectives of an Applied Science

Offered Posters

The fungicidal properties of plant extracts and essential oils
Alefyah Ali & Avice M. Hall
Department of Environmental Sciences, University of Hertfordshire

The aesthetic, medicinal and antimicrobial properties of plant essential oils have been known since ancient times. Numerous studies on the fungicidal and fungistatic activities of essential oils have indicated that many have the power to inhibit fungal growth.

Several studies have been conducted within the university of Hertfordshire on the antimicrobial effects of the essential oils of basil (Ocimum basilicum), Coriander (Corriandum sativum), Lavender (Lavandula angustifolia), Neem (Azadirachta indica) and Thyme (Thymus vulgaris). Both in vitro and in vivo experiments were designed to find out the fungicidal, fungistatic and phytotoxic effects of the oils both as a contact and as a fumigant fungicide. The test organisms were a range of economically significant fungi (Alternaria sp., Aspergillus sp., Botrytis cinerea, Erysiphe graminis). Several techniques were evaluated to find the Minimum Inhibitory Concentration (MIC) of the oil needed to inhibit the growth of the fungi, these included the droplet technique, the borehole method and the disc diffusion method. Vapour chambers were constructed to evaluate the fungicidal properties of the volatile components of the oil.

Various degrees of inhibition were observed for all oils examined except Neem oil, which did not show any fungicidal properties. Thyme oil proved to be extremely effective as a fumigant as well as a contact fungicide. The findings emphasise the fungitoxicity of various oils and pave the way for further studies and for their adoption as effective fungicides in the horticulture and agriculture industries.

The history of fireblight in England in relation to weather
Eve Billing
4 Fromandez Drive, Horsmonden, Tonbridge, Kent TN12 8LN

Movement of diseased plant material was an important factor in the spread of fireblight across England but, the amount of disease in different seasons on different hosts and cultivars was largely weather dependent. Major outbreaks of fireblight since 1957 were as follows: pear secondary blossom (1957 - 1960, 1966, 1967); late apple primary blossom (1978, 1982); hawthorn blossom (1960, 1964, 1982); pyracantha and cotoneaster blossom (1960, 1966, 1967 and some later years). Significant shoot blight on two or more hosts was associated with stroms (1968, 1969, 1982, 1994). In 1982, disease was widespread and severe on all hosts except pear. Since then, outbreaks on pear, apple and hawthorn have been sporadic but rarely severe. Weather patterns associated with outbreaks will be shown and problems of cross-infection between hosts described. The importance for risk assessment of good flowering records for each host and of storm records is emphasised.

Field Resistance of Wheat Varieties to Isolates of Mycosphaerella graminicola.
 JK M Brown1, H-R Forrer2, G H J Kema3, L S Arraiano1, P A Brading1, E M Foster1, E Jenny2, A Hecker2 and E C P Verstappen3
John Innes Centre, Colney Lane, Norwich, NR4 7UH, England
2 Swiss Federal Research Station for Acroecology and Agriculture, Reckenholzstrae 191/211, 8046 Zrich-Reckenholz, Switzerland
3 DLO Research Institute for Plant Protection (IPO-DLO), P O Box 9060, 6700 GW Wageningen, The Netherlands

Field trials of the resistance of 69 wheat varieties to single-pycnidium isolates of Mycosphaerella gramincola were carried out in England, Switzerland and the Netherlands in 1995, 1996 and 1997. These included varieties and breeding lines from the Czech Republic, England, France, Germany, the Netherlands, Portugal, Sweden and Switzerland, varieties from Europe and America which are parents of precise genetic stocks held at the John Innes Centre, and Veranopolis and Kavkaz-K4500, which have been identified as possible sources of resistance.

There was great variation among the varieties in their resistance to M. graminicola. A Czech breeding line was the most resistant, followed by Veranopolis, but several varieties which have been grown widely in the UK also had very good resistance. This indicates that there is considerable potential for UK breeders to improve the general level of resistance using well-adapted germplasm but further improvements in resistance may be obtained by introgression from exotic varieties.

There was also considerable specificity in interactions between varieties and isolates. In particular, a number of lines were resistant to IPO323 but susceptible to other isolates; these include parents of JIC precise stocks from countries throughout western and eastern Europe and from the United States. Varietyisolate interaction must therefore be taken into account in wheat breeding, because the evolution of specifically virulent M. gramincola populations presents a threat to the durability of varietal resistance. Although very little is currently known about the frequencies of specific virulences towards wheat varieties, the trials gave a hint that there may be regional differentiation between sub-populations of M. graminicola from different parts of Europe, since varieties which are used as resistant parents in Portuguese wheat breeding programmes were very susceptible to several Dutch isolates.

Effects of meteorological conditions, sclerotial position and cropping practice on Sclerotinia in field-grown lettuce
J.M. Ll Davies1, C S Young2, J M Whipps3, S P Budge3, L C Hiron1, J A Smith2, W J Stevenson2 and M. Watling1
ADAS Terrington, Terrington St. Clement, Kings Lynn, Norfolk. PE34 4PW
2 ADAS Wolverhampton, "Woodthorne", Wergs Rd, Wolverhampton. WV6 8TQ
3 Horticulture Research International, Wellesbourne, Warwick CV 35 9EF

Five sequential crops of lettuce were planted in 1996 and 1997, on a naturally infected site and a disease free site, in both Cheshire and East Anglia. Plots of single (normal) spaced plants and double spaced plants were artificially infested with sclerotia placed at specific positions relative to the plants. Meteorological stations were set up in 1995 to measure rainfall, air and soil temperatures in the winter months and, in addition, soil moisture, soil moisture tension, surface wetness, wind speed and solar radiation during the growing seasons. The maximum sclerotial germination observed per plot in 1996 and 1997, respectively, was 100% and 52% in Cheshire, and 34% and 16% in East Anglia. There was considerable variation in the timing and quantity of apothecial development between plantings and particularly between sites. Disease only occurred at the Cheshire site with maximum disease incidence per inoculated plot of 66% and 22% plants affected in 1996 and 1997, respectively. Disease was not related to the presence of apothecia directly beneath plants, which suggests that airborne ascospores may be responsible for infection. A qualitative examination of the meteorological data suggested that temperatures between 10 and 18oC and an increase in soil tension, i.e. a period of drying following a rain event appeared to stimulate the formation of apothecia in the field. Laboratory and glasshouse studies under controlled conditions are underway to confirm field observations of the key factors controlling apothecial production and lettuce infection.

The effect of the spore concentration of Verticillium albo-atrum and salt treatment on infection and disease progression in tomato plants
Murat Dikilitas & C. J. Smith
School of Biological Sciences, University of Wales Swansea, Singleton Park SA2 8PP

The pathogenic effects of virulence of Verticillium diseases on tomato plants was increased when they were inoculated with high spore concentration of the fungus in early stages of growth (for-week old seedlings). When plants were inoculated in later stages (five-week old) with a lower spore concentration the effect of pathogen on tomato plants was decreased (although it was still pathogenic to tomato).

The severity of the disease was higher in tomato plants treated with the fungus and salt solution, than in plants given either treatment separately.

Pathogenicity of lucerne (V1) and tomato (V2) isolates of Verticillium albo-atrum to salt-tolerant lucerne strains
Murat Dikilitas, C.J. Smith & J. M. Milton
School of Biological Sciences, University of Wales Swansea, Singleton Park SA2 8PP

The pathogenicity of lucerne V1 isolate and tomato V2 isolate to salt-tolerant lucerne strains (150, 200, 250 and 300 mol/m3) was investigated both under greenhouse and field conditions. Six week old salt-tolerant lucerne seedlings (Medicago media) were inoculated by the method of root dipping and wound inoculation. Height and symptom index were assessed one week after inoculation for a period of ten weeks. Isolate V2 caused mild symptoms under greenhouse conditions but did not cause any symptoms or height reduction under field conditions on salt-tolerant strains, while isolate V1 caused severe symptoms on the salt-tolerant plants both in the greenhouse and under field conditions. Susceptibility of salt-tolerant plants to the disease increased in both conditions when their level of tolerance to salt increased.

Assessing the Greening Effect of New Fungicide Chemistry on Winter Wheat
1Leonor Leandro1, Rosie J. Bryson2, W. S. Clark2 & J. Criagon1
Dept. of Environmental Sciences, Sutton Bonington Campus, University of Nottingham, Sutton Bonington. Leics. LE12 5RD
ADAS Boxworth, Battlegate Road, Boxworth. Cambs. CB3 8NN

Two new groups of plant protection chemicals, Strobilurin fungicides and plant activators, have been reported to have, apart from disease control, a 'greening' effect on treated plants, the leaves having a more intense green colour and staying green longer than controls. The main aim of this study was to test if the claimed greening effect was measurable on winter wheat (Triticum aestivum L.) with methods currently used to assess leaf colour. A secondary aim was to compare the performance of the available methods of detecting possible differences in greenness.

Chlorophyll content of the leaves was assessed by extraction in acetone and with a portable SPAD-502 chlorophyll meter. Spectral transmittance and reflectance were measured with a LI-COR LI-1800 spectroradiometer with an integrating sphere attachment. A high correlation was obtained for the calibration curve (R2 = 0.97) between SPAD readings and extractable chlorophyll. The relation between SPAD readings and the NIR/R ratio calculated from LI-COR measurements was also highly correlated (R2 = 0.92). both the SPAD meter and the LI-COR detected differences in greenness (P<0.01) between leaf layers, with the second leaf being the greenest in all treatments. Differences were also found (P<0.01) between untreated and fungicide treated plants. The top three leaf layers of the Strobilurin treated plants were shown to be significantly greener (P<0.05) than corresponding leaves of all other treatments, with a suggestion of a stronger effect on older leaves. This suggestion was further supported by the lower percentage (P = 0.017) of dead or very senesced fourth layer leaves found in this treatment. Transmittance spectra provided an indication that there was also an effect of the Strobilurin fungicide on internal leaf structure. No significant greening effect was found for the plant activator.

Foliar fertilisers can suppress Septoria tritici
Ruth L Mann, Peter S. Kettlewell & Peter Jenkinson
Crop and Environment Research centre, Harper Adams Agricultural College, Newport, Shropshire TF10 8NB

Septoria tritici is a widespread and damaging disease of winter wheat in he UK. It has been suggested that fertiliser application, particularly potassium chloride, to the foliage of wheat will suppress S. tritici.

A field experiment was set up to investigate the efficacy of potassium chloride compared to a conventional fungicide. Potassium chloride or epoxyconazole (opus, BASF) was applied tot the leaves of winter wheat, cultivar Consort, either at growth stage (GS) 31, or 39, or at both growth stages, or according to a disease threshold. The percentage leaf area infected with S. tritici was assessed visually at GS 71. Although not significant between timings, applications of potassium chloride were shown to significantly reduce the percentage area of leaf 2 affected with S. tritici, from 18.4% in unsprayed controls to between 10.3% and 12.3% in treated plots. A similar situation was observed following epoxyconazole applications, where between 2.1% and 9.5% of leaf area 2 was affected, depending on timing, compared to 18.4% in control plots. On leaf 3 two applications of potassium chloride or epoxyconazole proved most effective, reducing the severity of S. tritici from 28.6% in control plots to 22% for potassium chloride and 9.7% for epoxyconazole treated plots. This may be because leaf 3 was more severely infected. Therefore foliar applied potassium chloride can suppress S. tritici, although to a lesser degree than epoxiconazole.

In vitro experiments were undertaken to investigate whether the potassium or the chloride ion was the most active against S. tritici mycelial growth and spore germination. Potassium chloride, sodium chloride and potassium nitrate were used. All three salts significantly reduced mycelial growth and spore germination. Both potassium chloride and sodium chloride caused an almost linear reduction in mycelial growth up to 2 M concentration. potassium nitrate caused an greater reduction of mycelial growth up to 1 M concentration compared with the chloride salts. Concentrations of potassium nitrate greater than 1 M did not cause a further reduction in growth. Spore germination was significantly reduced from 98% to approximately 2% by all three salts at concentrations of 1.5 M and 2.0 M. Since all three salts were effective, it cannot be only the potassium ion or only the sodium ion which is responsible for reducing mycelial growth and spore germination. It is possible that this reduction is caused by adverse osmotic conditions.

Survival of Phytophthora infestans sporangia exposed to solar radiation
E. S. G. Mizubuti & W. E. Fry
Dept. of Plant Pathology, 334 Pl. Sci. Bldg., Cornell University, 14853 Ithaca, NY, USA

Sporangia of Phytophthora infestans of the US-1 and US-8 clonal lineages were collected from lesions and exposed to direct solar radiation (SR) and viability assessed by germination. Exposures during a three-hour period from 800 to 1100, from 1100 to 1400 or from 1400 to 1700 on sunny days (SR> 600 W/m2) resulted in practically complete inhibition of germination after each exposure period regardless of the time of the day. Sporangia were then exposed on sunny or cloudy days (< 400 W/m2) from 1100 to 1400 with samples taken at hourly intervals. In sunny days after one hour of exposure sporangia had low germination levels. On overcast (SR < 300 W/m2) days survival after three hours was only slightly reduced. On cloudy days the average ED95 of solar radiation was 7.7 MJ/m2 and the effective time (ET95) necessary to inactivate 95% of the sporangia was 7.9h. On sunny days, one hour exposure periods from 1100 to noon with samples taken at every 15 min confirmed the previous results of reduced viability after one hour. Overall, on sunny days the average ED95 was 2.8 MJ/m2 and ET95 was 1.1h. The ET95 of non-exposed sporangia was on average 16.8h. These results suggest a differential effect of SR on cloudy days compared to sunny days. Apparently sporangia of both clonal lineages were similarly sensitive to solar radiation.

A Multiplex PCR method for the simultaneous detection of Tomato Yellow Leaf Curl and Tomato Mottle geminiviruses
Jane Morris
Central Science Laboratory, Sand Hutton, York YO 4 1LZ

A rapid, sensitive Multiplex PCR (MPCR) test suitable for the diagnosis of L. esculentum infected with Tomato yellow leaf curl virus (TYLCV)/Indian tomato leaf curl virus (ITmLCV) and Tomato mottle virus (TMoV) was developed. All virus isolates tested were successfully amplified using degenerate primers designed by Deng et al; 1994. MPCR generated a 377 base pair TMoV specific DNA fragment and a 540bp TYLCV/ITmLCV fragment. MPCR DNA products were visualised using ethidium bromide staining following agarose gel electrophoresis. The viral origin of the MPCR products was confirmed by cloning and sequencing. Additionally, sequence data was generated for an unsequenced isolate of TYLCV originating from Turkey. This isolate was found to be almost identical to the published sequence for an Israeli isolate of TYLCV (Navot et al.; 1991), but shared less than 25% homology with the published sequence for a Sicilian isolate of TYLCV (Crespi et al.; 1995).MPCR was found to have several advantages over the currently used Indirect ELISA assay. The MPCR test allowed TMoV DNA to be distinguished from that of TYLCV/ITmLCV isolates, and could be carried out more rapidly than the ELISA assay with results achievable within a working day. A comparison of the sensitivity of detection of MPCR with Indirect ELISA indicated that the MPCR assay was more sensitive.

Protecting Brassica plants from Plasmodiophora brassicae
Lisa Page & Geoff R. Dixon
The Department of Horticulture, SAC / University of Strathclyde, SAC-Auchincruive, Ayr, KA6 5HW, UK

Brassica seedlings raised in peat compost modules appear to be more susceptible to Plasmodiophora brassicae (clubroot) than those grown in other media. Peat is a sterile medium hence it may fail to elicit host protective mechanisms, thereby increasing vulnerability to symptom development. Hypotheses regarding root camouflage (Gilberts et al., 1993) suggest rhizosphere communities differ between various growing media, some exposing the host to increased disease risk. While soil-borne pathogens such as Pythium spp. and Colletotrichum spp. were controlled by organic composts added to the root zone (Zhang et al., 1996).

The aim of the current project is to understand mechanisms which lead to the suppression of P. brassicae in organic media. This may lead to improved knowledge of the manner by which the root environment elicits host resistance mechanisms. Work has commenced by surveying the interaction of several growing media as substrates in which clubroot is either repressed or enhanced. Preliminary results support the view that peat based composts induce greater disease development.

Use will be made of a range of crude organic extracts and other compounds such as salicylic acid which are well demonstrated to enhance specific acquired resistance.

Gilbert, Handelsman & Parke (1994). Phytopathology, 84: 222-225.
Zhang, Dick & Hoitink (1996). Phytopathology, 86:1066-1070.

CIH1, A biotrophy-related gene expressed specifically at the intracellular interface formed between Colletotrichum lindemuthianum and French bean
Sarah Perfect1, Jon Green1 & Richard O'Connell2
1 University of Birmingham, UK., 2IACR-Long Ashton, UK

Colletotrichum is a large genus of plant pathogenic fungi causing anthracnose on a wide range of crops. C. lindemuthianum is a hemibiotrophic species which causes anthracnose of bean, Phaseolus vulgaris. During the initial biotrophic stage of infection, the fungus differentiates infection vesicles and primary hyphae within host epidermal cells. These specialised intracellular hyphae invaginate the host plasma membrane, from which they are separated by a matrix layer. Monoclonal antibodies (MAbs) raised to isolated infection structures have been used to identify proteins present at the fungal-plant interface.

One of these MAbs, designated UB25, recognises a protein epitope in a 40kDa N-linked glycoprotein specific to intracellular hyphae. Indirect immunofluorescence and EM-immunogold labelling show that the glycoprotein is present in the infection peg, and the fungal walls and matrix surrounding the intracellular hyphae. However, it is not present in secondary necrotrophic hyphae, which suggests that it is specific to biotrophic infection structures. The glycoprotein may therefore be involved in the establishment and maintenance of biotrophy.

A cDNA library has been constructed from total RNA isolated from infected bean hypocotyl epidermis. The MAb UB25 has been used to immunoscreen the library and positive clones have been isolated and sequenced. Southern analysis indicates that the CIH1 glycoprotein recognised by UB25 is fungally encoded and is present in several Colletotrichum species. Analysis of the deduced amino acid sequence of CIH1 revealed the presence of two distinct domains, one of which is proline-rich and contains short repetitive motifs with tyrosine-lysine pairs. Tyrosine residues have been implicated in the oxidative cross-linking of proteins such as extensins. Cross-linking studies of CIH1 indicate that this glycoprotein has the potential to be oxidatively cross-linked by peroxidase in the presence of hydrogen peroxide. The functional significance of this will be discussed.

The rapid detection of Colletotrichum gloeosporioides in yam tubers by ELISA
Jeff C. Peters1, L. Kenyon2, M. James3 & A. Jarma1
Department of Agriculture, The University of Reading, Earley Gate, Reading, Reading, RG6 6AT
2 Naturl Resources Institute, Central Avenue, Chatham Maritime, Kent, ME4 4TB.
3 Ministry of Agriculture, Graeme hall, Barbados

Colletotrichum gloeosporioides causes, the often-devastating disease, anthracnose, on yam (Dioscorea spp.) vines. However, the pathogen can also infect tubers, causing disfigurement of the periderm and necrotic lesions in the underlying cortex (Green & Simons, 1994). As yams are almost entirely propagated by seed tubers (setts), planting material infected with C. gloeosporioides is thought to be an important source of new infections (Adebanjo & Onesirosan, 1986). Therefore, a rapid and reliable method for detecting C. gloeosporioides in yam setts would help prevent anthracnose epidemics by identifying farmer's seed supplies which have high levels of infection. In the study presented here, yam tubers, which were inoculated with C. gloeosporioides, developed characteristic discoloration of the meristem and cortex. The pathogen could be re-isolated from infected tissue; however, this can take up to 72 hours. An ELISA test, modified from Hughes (in press), was developed to detect C. gloeosporioides directly from tuber tissue in less than 4 hours. this diagnostic tests was primarily successful in diagnosing superficial infections by detecting C. gloeosporioides in the outer periderm layer. However, the ELISA also detected the pathogen in the deeper meristematic layer in, what is thought to be, naturally infected tubers.

Adebanjo, A. & Onesirosan, P.J. (1986). Surface bore infection of Dioscorea alata tubers by Colletotrichum gloeosporioides. Journal of Plant Protection in the Tropics 3: 135-137.
Green, K.R. & Simons, S.A. (1994). 'Dead skin' on yams (Dioscorea alata) caused by Colletotrichum gloeosporioides. Plant Pathology 43: 1062-1065.
Hughes, K.J.D., Lane, C.R. & Cook, R.T.A. (In Press). Development of a rapid method for the detection and identification of Colletotrichum acutatum. In: Diagnosis and Identification of Plant Pathogens; Proceedings of the European Foundation for Plant Pathology, 4th International Symposium 1996, Bonn, Germany.

Experiences with blight forecasting
Moray C. Taylor1, N.V. Hardwick1, N.J. Bradshaw2 & A.M. Hall3
Central Science Laboratory, Sand Hutton, York YO4 1LZ
2 ADAS Cardiff, St. Agnes Road, Cardiff
3 University of Hertfordshire, College Lane, Hatfield

The Smith period is the major late blight forecasting scheme available to UK growers and provides recommendations, based on specific weather conditions, on when to begin a protective fungicide spray programme. Warnings of impending blight attack are issued by ADAS, using weather data from a selected set of the Meteorological Office's synoptic network of weather stations. The stations are widely separated and often located many miles from the major potato growing areas which means that one station has to cover a large geographical area. Within such an area the conditions experienced in many potato fields may be quite different from those at the meteorological station leading either to false alarms or, more seriously, a failure to warn sufficiently ahead of an outbreak to allow sprays to be applied.

Since the 1960's new, more complex, forecasting systems have been published which aim to give more accurate forecasts provided their weather data requirements can be met. The last few years have also seen the proliferation of in-crop weather stations which give an indication of the conditions on very local scale. These provide an excellent opportunity to test forecasting systems fully and gain an indication of their usefulness to individual growers.

Using frequently recorded in-crop weather data from each of five widely dispersed locations during 1996-1997, the Blitecast, NEGFRY, Sparks, Ullrich & Schrdter and Smith Period forecasting systems were evaluated with respect to time of first blight warning, the first occurrence of blight and the number of sprays recommended. No single system proved effective at all sites in all years. The schemes varied widely in their ability to predict blight infection particularly in the drier year of 1996. Furthermore the number of applications recommended could be doubled or halved depending which scheme was used despite being challenged with the same meteorological data.

Of all the systems evaluated only the Smith Period was consistently successful in triggering spray applications prior to blight appearing in the crop. It is concluded that the Smith Period is still effective forecasting scheme, despite being prone to initiate sprays well ahead (especially in dry years) of the blight outbreak, as it is the least likely to fail.

Using disease survey data to develop schemes for predictinG epidemics of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape in England and Wales
Judith A.Turner1, S. Welham2, B.D.L. Fitt2, P. Gladders3 & K. Sutherland4
Central Science Laboratory, Sand Hutton, York, YO4 1LZ
2 IACR-Rothamsted, Harpenden, Hertfordshire, AL5 2JQ
3 ADAS Boxworth, Cambridge, CB3 8NN
4 Scottish Agricultural College, 581 King Street, Aberdeen, AB24 5UA

Data on incidence and severity of light leaf spot (Pyrenopeziza brassicae) of winter oilseed rape has been collected as part of the MAFF Winter Oilseed Rape Pest and Disease Survey since 1987. Light leaf spot is a serious disease of oilseed rape in the UK but the disease incidence and severity differ between regions and between seasons. During the last ten years the incidence of light leaf spot at pod ripening has varied between 5% and 46% plants affected with highest levels occurring in 1987, 1988 and 1994. Based on these data, annual yield losses, after fungicide application to control the disease, were estimated to range between 13M and 49M. Fungicide inputs to control diseases of oilseed rape have increased substantially since 1992 with costs exceeding 8M in 1996 when disease risk was relatively low. The extent of the losses during epidemics and the high costs of inputs clearly indicate the need for a forecasting scheme for this disease, not only to reduce yield losses but to reduce fungicide inputs in years with low disease risk. Analyses of the survey data indicated a strong link between the incidence of plants affected with light leaf spot on the pods and the subsequent incidence of plants with leaf infection at stem extension in the following spring. Disease levels in surveyed crops were greatly influenced by the timing of sprays to control light leaf spot. Sprays applied during mid-November proved most effective. The data were further analysed to identify additional seasonal and crop risk factors involved in outbreaks of light leaf spot. Analyses identified agronomic factors such as sowing date, cultivar and geographical location as important crop risk factors. These risk factors have been integrated into a predictive model to forecast epidemics of light leaf spot which can be used at a time when spray decisions need to be made. Meteorological factors have been recently included to improve accuracy of the model. Regional predictions made during 1996 for the 1997 growing season indicated that accurate forecasts were possible.

Dispersal of the mycoparasite Coniothyrium minitans by soil mesofauna
Roger H. Williams1*, John M. Whipps1 & Roderic C. Cooke2
Horticulture Research International, Wellesbourne, Warwick, U.K.
2 University of Sheffield, Sheffield, U.K.
* Present address: IACR-Rothamsted, Harpenden, Hertfordshire, U.K.

Coniothyrium minitans, a mycoparasite with proven biocontrol activity against Sclerotinia sclerotiorum in the field and glasshouse, was found to spread from sites of application during glasshouse biocontrol trials. Whilst details regarding the mechanisms of dispersal are unclear, Coniothyrium minitans was recovered from collembolans collected during these trials and it was observed that numerous mites and insects were frequently associated with decaying plant material in the glasshouse. This led to speculation that soil mesofauna may be involved in transmission of the mycoparasite. Consequently, the mite, Acarus siro, and the collembolan, Folsomia candida, were used to investigate the role of soil mesofauna in the dispersal of Coniothyrium minitans. Both arthropods transmitted the mycoparasite from colonised wheat grains to uninfected sclerotia of Sclerotinia sclerotiorum in sterile and non-sterile soil adjusted to a range of water potentials (-0.25 to -3.6 MPa). Germinable conidia of Coniothyrium minitans were present in the faeces of both Acarus siro and Folsomia candida whereas only the mite carried detectable inoculum externally. When single faecal pellets produced by Acarus siro that had been feeding on Coniothyrium minitans were applied to sclerotia placed in sterile sand or non-sterile soil, 12 and 8% respectively of the sclerotia became infected with the mycoparasite. These results suggest that soil mesofauna may be important in dissemination of Coniothyrium minitans.