This was another lively and interesting meeting of the Club, which wasattended by 32 people. It began with a paper by Gareth Hughes (EdinburghUniversity) on sampling strategies for citrus tristeza virus and itstransmission by two aphid species. Using data from Spain, Florida, Costa Ricaand the Dominican Republic, two sampling strategies were compared, samplingindividual trees (6.7% of total) and bulked (4) samples from 25% of trees.
Neil McRoberts from SAC Auchincruive then presented a paper on models ofdisease progress incorporating spatial variability. The idea of consideringepidemics at less than the field level (precision farming) was presented,together with various ideas for modifying existing models to take into accountspatial variability (adding a new spatial heterogeneity parameter; combininglogistic equations with over dispersed probability distributions and byconsidering disease at two adjacent levels in a spatial hierarchy, e.g. plantsand plots).
Janice McNaughton (SAC Edinburgh) presented her work on expression ofpathogenicity in parasexual progency of the eyespot fungus. The majority ofparasexual progency were not pathogenic, indicating that recombination haddisrupted pathogenicity, but novel phenotypes (R-only) and "parasitic",colonisation only forms were obtained. Mary Noble then gave an account ofAleurodiscusamorphus and its representation in drawings by Beatrix Potter.
The afternoon began with S Miller from Scottish Crop Research Institute(SCRI) talking about the potential to control potato diseases with elicitors.David Trudgill (SCRI) gave a paper on the paradox of root knot nematodes (Meloidogynespp) which reproduce by mitotic parthenogenesis; biotrophic pathogens withlittle variation but enormous host ranges. They were likened at times during thetalk to "stealth bombers" and "low flying marvelous Meloidogyne",perhaps a biased reporter here?
Jim Deacon and G Saxena (Edinburgh University) gave a paper on encystmentand germination of zoospores of Catenaria anguillulae on nematodes.Results were presented on the effect of mood swing and heart beat drugs onzoospores and other organisms (primarily spiders!) and the rationale formotility and docking in microorganisms was discussed. Stephan Helfer (RoyalBotanic Garden, Edinburgh) spoke about rust fungi on the Rosaceae, and made aplea for rust specimens, especially of non-commercial plants e.g. Potentillaand Alchemilla.
Posters were given by Vince Mulholland (Scottish Agricultural ScienceAgency) on the use of PCR to discriminate potato cyst nematode at the specieslevel, J Pickup (SASA) on predicting leafroll virus in Scottish seed potatoesand Miriam Zziwa (SAC Edinburgh) on sensitivity of powdery mildew isolates tomorpholine fungicides.
Finally, the group remembered Roger Wastie, who had devoted much time toorganising SMPPC meetings and who died in January.
Scottish Agricultural Science Agency
Autumn 1996 meeting
The autumn meeting of the club was held at the Kerr Building (GlasgowUniversity), home of the Division of Environmental and Evolutionary Biology.After morning coffee amidst the marvellous menagerie (mostly stuffed orskeletal, fortunately) the 35 of us were welcomed by Professor FelicityHuntingford, head of the division.
The BSPP kindly offered travel funds to invite Professor Mike Jeger from theDepartment of Ecological Phytopathology, Wageningen Agricultural University. Hespoke about the modelling of soilborne biocontrol organisms using a radicalenergy-based approach, a method more commonly used in animal studies. Growth ofSporidesmium sclerotivorum hyphae was modelled with differentconcentrations of Sclerotinia sclerotia as a source of energy.
Another lively presentation by Neil McRoberts (SAC, Auchincruive)investigated the eyespot and sharp eyespot sampling procedure used by SAC acrossScotland at spatial scales from region through to the pairs of quadrats in afield. A plot of the relationship between the proportion of quadrats infectedand proportion of plants infected in that field fitted a beta binomialdistribution. Such a relationship is useful in yield loss/disease incidencestudies by increasing the reliability of disease incidence estimates from asmall number of field samples.
The ever enthusiastic Roy Watling (Royal Botanical Gardens, Edinburgh) tookus on a fantastic tour of the ectomycorhizal species found in Malaysianrainforest. Very few comprehensive surveys have been undertaken and it wasparticularly interesting to note that the distribution of orders found in thesetropical forests was similar to that of temperate forests of Britain. There weremany common species but in one survey 79% of samples were classed as new speciesshowing how little we know of these fungi.
Modesty prevents me from enthusing about the next talk by David Cooke (SCRI,Dundee). I spoke of our recent molecular analysis of the inter-relationshipswithin the peronosporales on the basis of internal transcribed spacer (ITS)regions of rDNA. In an examination of the Peronospora species found onraspberry and rose, it was seen that levels of sequence similarity suggestP.rubi and P. sparsa are, in fact, con-specific. Interestingly, theperonosporales species examined so far have also proved to be very similar insequence to many Phytophthora species.
We kicked the afternoon off with potato pathology. Rob Clayton (SAC,Aberdeen) discussed his work on seed potao storage, the sampling strategies andhow to minimise storage losses due to bacterial and fungal attack. This wasaptly followed by a presentation by Beth Hyman (SCRI, Dundee) on the pioneeringwork on protocols for PCR-based Erwinia detection on potato tubers.
Don Clarke (Division of Environmental and Evolutionary Biology, Universityof Glasgow), on home territory, discussed the complex interactions between host(Senecio) and pathogen (Albugo) in natural systems.
Miriam Zziwa (SAC, Edinburgh) spoke to us about her work on the morpholineinsensitivity of wheat and barley powdery mildew. She is investigating theeffects of fungicide dose reduction on build-up of insensitivity in mildewpopulations.
The control of bracken is a great problem in the UK and the presentation ofDoreen Main (Strathclyde University) on formulations and efficacy of thepotential mycoherbicide Ascochyta pteridis was met with interest. Somevirology to finish with as E Cecchin (Glasgow University) presented the use ofArabidopsis as a quasi-host for the examination of host-pathogeninteractions in the tracking down of virulence factors in Cauliflower MosaicVirus.
The BSPP are gratefully acknowledged for their continued support forvisiting speakers and, of course, we thank our new SMPPC organiser Fiona Burnett(SAC Edinburgh) for getting together such an interesting programme and the localhost (Don Clarke) in Glasgow for his hospitality.
Scottish Crop Research Institute
Two meetings were held during the Michaelmas Term. On 15 November, PeterGladders of ADAS Boxworth presented a 20 year review entitled "Controllingwinter oilseed rape diseases - we can do better". A consistent approach tomonitoring diseases in commercial crops since 1976 was now paying dividends.Seasonal variation in eastern England was largely attributable to variation inautumn rainfall in the case of canker (Leptosphaeria maculans) but tovariation in the carry-over of inoculum in the case of light leaf spot (Pyrenopezizabrassicae).
Recent MAFF and HGCA-funded experiments with a "wave" design hadidentified critical periods for disease control and clearly indicated that itwas possible to achieve complete disease control. A further breakthrough in 1995with fungicide timing experiments showed that canker could only be effectivelycontrolled when sprays were used as protectants.
The theory now needs to be translated into farm practice as it is clear thatfungicides are not being used effectively. Many treatments are being applied toolate and disease incidence remains high. The development of forecasting systemsand better understanding of fungicide properties now means we can do better.
"Rhododendron powdery mildew - Epidemiology and identification studies"was presented by Avice Hall of the University of Hertfordshireon 29 November. Members were treated to an insight into the mysterious world ofthe rhododendron enthusiast. This disease probably became established asrecently as 1977 in the UK.
Following disease progress through a range of symptoms and over severalyears on a perennial host produced many challenges not faced by cereal mildewpathologists. Active development takes place from May to September and appearsto be limited by a relatively high temperature requirement. It was some timebefore members realised that the name of the pathogen had not been used - Microsphaerasp. seems to be the safest option at present.