BSPP News 31 Autumn 1997 - Online Edition

The Newsletter of the British Society for Plant Pathology
Number 31, Autumn 1997

People and Places

Scottish Agricultural Science Agency, East Craigs

It has been some time since SASA's activities were last reported in the Newsletter and it may be helpful to members to know something of the backgroundto the Agency and its plant pathology responsibilities.

SASA became an Executive Agency of The Scottish Office on 1 April 1992, having previously been known as Agricultural Scientific Services or, moreusually, by the name of its headquarters - East Craigs, where in the 1920s theBoard of Agriculture for Scotland established its Variety Registration and SeedTesting Station. Seed testing and variety testing, to meet the National Listingrequirements of EU Directives, are still important activities, but to thesehave been added seed certification, plant health including quarantine, pesticide usage surveys, food and wildlife monitoring for pesticides and aspectsof wildlife damage to crops. The station currently employs around 100scientists, approximately onethird of whom are indirectly or directly involvedin crop protection.

SASA's principal functions are to support The Scottish Office Agriculture, Environment and Fisheries Department (SOAEFD) by providing the scientific inputfor work required by EU Directives, UK Regulations and various scheme requirements and to provide SOAEFD with the scientific information and advice it needs to develop and implement policy. This may, perhaps, seem rather dull toour colleagues involved in front-line research, but the reality is quitedifferent and SASA staff enjoy the challenge of turning what can sometimes seemrather dry legislation into practical procedures for Ministers, policy makers,consultants and growers.

Most plant pathologists at SASA work within the Potato and Plant Health Division and, as the name implies, much of the division's work relates to planthealth legislation and seed potato classification (certification). Dr JaneChard leads the Plant Health Section where she and her staff help SOAEFD developpolicies and testing procedures that aim to protect the Scottish seed potatoindustry (worth between £50m and £100m per year) and other agriculture and horticulture enterprises against non-indigenous pathogens. Not surprisingly, in view of the situation in western Europe in recent years, potatobrown rot (Ralstonia solanacearum) and ring rot (Clavibacter michiganensis ssp. sepedonicus) have occupied much of her group's time in the last year or so.Dr John Wood and Karen Breckenridge have conducted surveys of EU and Scottishproduced seed potatoes and have confirmed Scotland's freedom from brown rot andring rot.

Dr Colin Jeffries, Carol Brattey and Carolyn Nisbet operate the UK Potato Quarantine Unit on behalf of all the UK AgriculturalDepartments, with Tina James providing testing for potato spindle tuber viroid.Any non-EU potato material, including material for research purposes, enteringthe UK must undergo comprehensive testing in the Unit before general release.Recent interceptions have included bacterial ring rot, potato spindle tuberviroid and a number of potato viruses, including a previously unknown virus, potato latent virus. Akhtar Ali oversees SOAEFD's licensing arrangementsfor the importation of nonindigenous pathogens for research purposes and alsoprovides, with Susan Irvine, diagnostic support to the Department'sagricultural and horticultural staff in respect of fungal pathogens.

Dr Kevin O'Donnell (currently the BSPP's membership secretary) leads theDiagnostics and Molecular Biology Section at SASA. The section has thedual role of undertaking diagnostic testing in support of SOAEFD's statutoryrequirements and of developing new diagnostic tests. Isla Browning, MaureenDarling and Lynn Young provide a virus testing service in support of theScottish Seed Potato Classification Scheme. Isla and Maureen also test newpotato varieties for susceptibility to potato wart (Synchytrium endobioticum)disease as a requirement of EU legislation.

Robert Burns and Edna George run SASA's Monoclonal Antibody ProductionUnit where antibody lines are developed and produced for use in SASA's testing programmes and are also widely marketed to other testing institutes. Vince Mulholland and Lynn Young are involved in developing nucleic acidbasedassays to a level where they are robust enough for highvolume, routine use. Apriority here is the development of polymerase chain reaction (PCR) based teststo detect tuberborne potato viruses, though assays for a wide range of otherpathogens are also being developed. We also have interests in developingalternative DNA amplification methods - for example, the ligase chainreaction.

Scientific support in relation to invertebrate plant pests is provided by Dr Jon Pickup's Zoology Group. Andrew Harris manages thenematology laboratory which supports SOAEFD's programme of potato cyst nematodetesting, and Paul Shave's entomology laboratory supports the aphid monitoringarrangements for the Seed Potato Classification Scheme and development work onthe epidemiology of aphidborne potato viruses.

Dr Stuart Carnegie and his colleagues in Potato Section provide scientific advice and information to SOAEFD'spolicy makers in support of the Seed Potato Classification Scheme and Stuartmonitors the commercial production of high grade (virus tested stem cutting)seed. Sandra Goodfellow and Jim Maguire maintain and distribute to high gradeseed growers pathogentested nuclear stock which is the foundation of healthyScottish seed. The section also provides support to SOAEFD through theprovision of training plots and during seed tuber inspection courses.

Stuart Carnegie, Arlene Cameron, Paul Haddon and Jenny Craigie have recently completed a Potato Marketing Boardfunded project which examined, incollaboration with Geoff Hide and colleagues at Rothamsted, the health of seedand ware potatoes during multiplication. Stuart's work on the epidemiology oftuberborne pathogens over many years has shown the importance of good seed store hygiene in reducing the buildup of tuberborne fungal pathogens.

Valerie Cockerell is responsible for seed health testing within the Official Seed Testing Station at SASA. Valerie's work has assumedgreater prominence following the withdrawal of organomercury cereal seedtreatment fungicides in 1992 and, with support from the HomeGrown CerealsAuthority and Zeneca Crop Protection, Valerie, Margaret Jacks and OSTSstaff have recently conducted comprehensive surveys of the health of UKproducedcereal seed and Valerie has collaborated with colleagues in ADAS, NIAB and PSD to develop guidelines for cereal seed treatment usage.

My direct involvement with seed quality and seed treatments has been all but given up as I try to get to grips with the station's potato and plant healthwork, assume the chairmanship of the Standing Committee for Crop Protection inNorthern Britain, in succession to James Gilmour who has recently retired fromSAC, and act as local arrangements co-ordinator for next year's InternationalCongress of Plant Pathology. My SASA colleagues and I, and indeed all Scottishplant pathologists, look forward to welcoming BSPP members to ICPP98 in August.Look out for the Invitation to Register  it will be on your desk soon.

Bill Rennie

Glasgow University

In 1994 the 11 departments of Biology were merged into a single resource unit, the Institute of Biomedical and Life Sciences. The Institute consists of 6research-centred Divisions of cognate areas, largely formed by combiningdepartments but some departments were split with staff being moved intoseparate divisions. The latter was the case for the department of Botany, the biochemical/molecular biologically orientated botanists moving to the Divisionof Biochemistry and Molecular Biology while the `whole organism' orientatedbotanists moved to the Division of Environmental and Evolutionary Biology. Thishas lead to plant pathology in Glasgow being split between two Divisions withDon Clarke's group housed in Environmental and Evolutionary Biology while JoelMilner's group is housed in Biochemistry and Molecular Biology.

Don Clarke's group is housed in the Brian Laboratories (shared withPlant Ecology) located in the old walled garden of the Garscube estate somefive miles from the main campus. We are not a lone part of the University asthe estate also houses the Vet School, the Beatson Institute and several otherresearch institutes and a magnificent sports facility which yours truly is fartoo old to make use of; although I believe there is a bar somewhere in the pavilion. Work continues on parasites, particularly powdery mildews, downy mildews and rusts of Senecio spp., both British and foreign. Theparticular interests at the moment are the two new parasites, the Albugo and the rust Puccinia lagenophorae, to determine thewithin and between species specificities of these parasites. A postgraduatestudent, Abdella Ahkhka, is comparing the reactions of wild and cultivatedbarleys to infection by Erysiphe graminis f.sp. hordei. Overthe last 5 years, in collaboration with a local timber preservation company whoobtained a local enterprise grant and some EEC money to fund the work we havebeen researching pesticide free methods, specifically biological controlmethods, for controlling timber dry rot in buildings.

Joel Milner's interests lie in the field of plant virology. One of hismain areas of research concerns those plant-virus interactions which areinvolved in symptom expression following infection by compatible viruses.Ongoing work in his laboratory includes a project, funded by the BBSRC andcarried out in collaboration with the John Innes Centre, which is aimed atidentifying genes in Arabidopsis that control symptom character andseverity during infections by cauliflower mosaic virus. Research in this areaalso involves collaborations with researchers at CNR, Pisa and in Quebec. Inaddition he has a long standing interest in plant rhabdoviruses, and iscollaborating with researchers in the Department of Electrical Engineering onthe development of novel methods for the purification of viruses.

Don Clarke

Plant Pathology in Northern Ireland

Disease control in short rotation coppice willow

Short Rotation Coppice (SRC) grown willow is being developed as a viable energy crop. There has been considerable commercial interest in growing willowwith several large areas being planted recently. However the major limitingfactor to sustaining viable yields has been the susceptibility of many of the Salix clones used, to rust caused by Melampsora epitea var.epitea. Control of the disease is difficult, with the use of fungicidesnot being an option.

In Northern Ireland we have had considerable success in reducing the impact of rust on the crop by growing mixed clonal stands of willow. Clones have been chosen from a clonal selection programme on the basis of their yield andresistance to rust and some have been included in a large trial whichincorporates mixtures of up to 20 different clones. Clonal mixtures reducedisease impact by delaying the onset of disease, slowing down its build up andlowering final levels at the end of the season. However, based on preliminarydata, it would appear that the number of clones within a mixture has littleeffect, with disease reduction in the 5 way mixture being as good as in thelarger mixtures of 10, 15 or 20 clones.

Nevertheless, when very susceptible clones are included, they do not survive, although through compensation from neighbouring, less susceptible clones means that there is almost no effect on yield. In 1996 /97 some clones,most notably Salix burjatica Germany, which had been grown in N.Ireland for several years with only low levels of rust became very sensitive tothe disease and in a number of trials were wiped out.

In Northern Ireland, where the rust disease pressure is high, we areconfident that the use of carefully selected clonal mixtures provides a way inwhich high yields can be obtained and the long term sustainabiity ofplantations achieved.

Enterprise in plant pathology teaching

Plant pathology graduates, in common with others, need the ability to communicate effectively with colleagues, employers, customers etc. Therefore,within the plant pathology element of theagriculture, food science and science courses at the Queen's University ofBelfast (QUB) we have put an emphasis on developing oral and written skills,inter-personal and group skills, curriculum vitae preparation and interviewtechniques etc. Students are given instruction and the opportunity to developthese skills, within the context of the plant pathology being taught.

During the past two years there has been a British Council funded collaboration with the University of Agricultural Sciences and Veterinary Medicine (UASVM), Bucharest, Romania, as part of a Romanian Academic Links Programme. The purpose of this programme has been to introduce enterprise intothe curriculum of the UASVM. There have been two visits by the Romanianco-ordinator, Dr Agatha Popescu, to Belfast.

In May 1997 three members of staff from QUB spent two weeks in Bucharest where we introduced, both a group of staff and a group of students to theconcepts of enterprise and the importance of transferable skills for allgraduates. Staff were involved in discussions on how best to provide thenecessary skills to graduates and how this may affect their teaching. Thestudent group, comprising approximately 20 students drawn from all facultiesand years, were enthusiastic in their involvement, especially in some of thegroup skills exercises. They were particularly pleased to be given theopportunity to express their aspirations and opinions in a relaxed andnon-threatening atmosphere.

Dr Popescu has made a World Bank application to extend the incorporation ofenterprise into courses throughout the UASVM in Bucharest and to other Universities in Romania.

Alistair McCracken
DANI & Queen's University, Belfast


Bill Clark and Rosie Bryson are currently working on the effects ofstrobilurin analogue fungicides on wheat physiology, and in-field sensing ofwinter wheat crop canopies, with particular reference to the interactions ofnitrogen and disease on green leaf area, canopy duration and radiationinterception. Tim O'Neill is leading a MAFF Horticulture LINK Project incollaboration with HRI Efford, SAC Auchincruive, SRI, the University of Readingand Campbell Scientific Ltd on the "Integrated control of botrytis inprotected container-grown ornamentals". The project commenced in April andis funded by HDC and industrial partners in addition to MAFF. Irene Koomenpresented a paper on "Biological control of post-harvest diseases on fruit".at the 1997 Silsoe Postharvest Convention held on the 25 March.

In a recent HDC-funded project investigating the control of downy mildew inbrassica seedlings, John Davies discovered that the mixture of Aliette® and Courgel AG614, a non ionic polysaccharide, had a synergistic effect, resultingin improved disease control and crop growth. The benefits have prompted HDC andRhône Poulenc to file a patent for this mixture.

Centre for Research in Agronomy

ADAS and the University of Nottingham have set up a joint Centre forResearch in Agronomy, bringing together research projects funded by growers,the Home-Grown Cereals Authority and MAFF. The formation of the Centre wasannounced by David Shannon, MAFF's Chief Scientist, at the opening of newresearch facilities at ADAS Boxworth, Cambridge. The purpose of the Centre,with Professor Keith Scott as its Head, is to develop and promote a fundamentalapproach to the improvement of crops and on-farm decision making.

The research base, which will encompass work being undertaken at the University and ADAS's five arable research centres, will be used to sustain agriculture through the educational, training and consultancy activities ofboth organisations. Pathologists involved in projects within the Centre includeNeil Paveley, Rosie Bryson, Steve Parker, David Jones and Fen Beed.

John Davies
ADAS Terrington

Central Science Laboratory

Back in April this year, CSL's Plant Disease Diagnosis Team hosted the inaugural meeting of the `UK Phytodiagnosis Discussion Group'. The group wasformed following informal discussions held at the European Federation of Plant Pathologists meeting in Bonn and the BSPP meeting in Canterbury to considerproblems faced by plant pathologists involved in routine diagnosis. The firstmeeting focussed on diagnosis of Phytophthora spp. and was attended by diagnosticians from anumber of different organisations within the UK and also representatives fromthe Dutch Plant Protection Service.

The two-day meeting provided an ideal forum to demonstrate current and new methods for the diagnosis for Phytophthora, as well as allowing discussion on new Phytophthora diseases. The meeting was consideredsuccessful enough for the group to want to reconvene next year and David Roseof the Forestry Commission, Alice Holt, kindly offered to host the nextmeeting. Any enquiries concerning the group and the next meeting can be sent toeither David Rose or Charles Lane (

Further afield, CSL has been continuing to expand its interests in areas of overseas work. On the R&D side, David Stead (Plant & Environmental Bacteriology Team) has, in collaboration with fellow bacteriologists in theNetherlands, Belgium and France, won an EU contract to provide technicalassistance for the control of potato brown rot in Egypt. The project, incollaboration with the Egyptian Ministry of Agriculture, will provide laboratoryfacilities and training to allow the testing of potatoes for export and also toprovide the epidemiological information that is required to help control thedisease.

CSL has also been developing new areas of work in overseas consultancy. Amajor event was the revision of the International Plant Protection Convention(IPPC), for which Alan Pemberton (Plant Health Consultancy Team) gave technicalsupport to the UK and EU delegations at the FAO Technical Consultation, Rome.CSL Plant Health Group pathologists and entomologists continue to play an active part in the Phytosanitary Regulations Working Party and many Panels of the European and Mediterranean Plant Protection Organization.

CSL has also been closely involved with the International Standards onPhytosanitary Measures being developed by the FAO IPPC Secretariat. David Ebbels (Plant Health Consultancy Team) has undertaken several plant health consultancy missions for FAO (in Cyprus) and the EU PHARE programme (inSlovenia and Slovakia) aimed at assisting eastern European countries toharmonise their plant health services with the legislation and practices of theEU. In addition, Claire Sansford (Plant Health Consultancy Team) has visitedthe BBA (Federal Biological Research Centre for Agriculture and Forestry) inBraunschweig and Kleinmachnow, Germany, in order to discuss relationshipsbetween the Federal Ministry of Agriculture, the BBA, and the Plant ProtectionServices of the Lander. The visit allowed discussion of Claire's main area ofinterest, Pest Risk Assessment and Analysis. There may be some futurecollaborative work between the UK and Germany in support of our work at thePlant Health Standing Committee of the EU.

Rick Mumford

David Ebbels retires from CSL

After his school days in Australia, David's enthusiasm for plant pathologywas first fired when, in Ceylon (now Sri Lanka) as a junior tea planter, in thequiet of the evenings he read E C Large's gripping account of the "Advanceof the Fungi". He read botany at Reading and investigated soil sterilantsfor the control of root pathogens (especially those of wheat) for his Ph.D. atRothamsted Experimental Station, Harpenden, before taking up the post of cottonpathologist and head of section at the Cotton Research Station, Ukiriguru,Tanzania. His major research project in Africa was on Fusarium wilt of cotton but David's immense interest resulted in wide-ranging publications from the Tanzanian plant disease check list to the Myxomycetes of East Africa.

After six years he returned to Harpenden with his young family, joining thePlant Pathology Department of the MAFF Plant Pathology Laboratory (now part ofthe Central Science Laboratory). Recruited to lead the crop certification workhe quickly became responsible for technical guidance relating to all aspects ofMAFF statutory control of crop diseases. Well respected by UK growers and PlantHealth Inspectors alike, he has travelled widely in Europe being anauthoritative member of EU and EPPO working groups on crop certificationspecialising in particular on potatoes, top fruit and soft fruit.

David Ebbels, who retired recently from the
Central Science Laboratory. 

He has also managed with great delicacy the difficulttask of balancing scientific excellence with the practical realitiesto be faced by Government in the control of such serious quarantinediseases as hop Verticillium wilt, beet rhizomania and, most recently, potato brown rot. On all of thesesubjects he has published extensively but perhaps he will be bestremembered for his editorial work, such as on the 1993 BCPCMonograph No. 55 "Plant Health and the Single Market".David has never lost his love of travel and in the last year or sohas been involved with FAO and EU plant health training andconsultancy programmes in Cyprus, Slovenia and now Slovakia. Thiswork he intends continue alongside other pathology orientated taskssuch as the UK Check List of Plant Diseases. In recognition of his23 years outstanding and continuing contribution to the work of CSL,David has been made the first Honorary Fellow of CSL. We wish Davidand Shirley a long, happy and fulfilling retirement.

Alan Pemberton

Harper Adams Agricultural College

Plant pathology is a component of several full-time courses taught at HarperAdams. The HND and B.Sc. courses in Agriculture, and the B.Sc. in RuralEnvironmental Protection, each contain Crop Protection modules. At postgraduatelevel Crop Protection is available as both a Diploma and M.Sc. course andrecently a new M.Sc. in Crop Biotechnology has been introduced to cover theincreasing application of biotechnology to crop protection problems.

In addition the College is the major provider of short courses leading to the BASIS Certificate in Crop Protection. BASIS is an independent registrationscheme, recognised under the Control of Pesticides Regulations, which certifiesthe professional competence of consultants, advisors and representativesworking in the crop protection industry. Between December 1996 and September1997 ten BASIS courses have been run at Harper Adams attended by more than 100participants.

Research activities within the College have expanded significantlyin recent years and in July Dr Patrick Fair was appointed as the first Directorof Research. Two research groups are investigating topics relating to plantpathology. Dr Pat Haydock heads a group of nematologists working on theactivity and persistence of nematicides used to control potato cyst nematodes.Molecular diagnostics are being used in the Fusarium group tostudy stem base diseases of cereals. This work is coordinated by Dr SimonEdwards.

In June, Dr Peter Jenkinson and Dr John Clement visited the Cambridgeshiresite of Cereals 97. They presented results from a three year project, funded byHGCA, which has examined Fusarium ear-blight on winter wheat. InAugust, Dr Pat Haydock visited Moscow to present papers at a conferenceorganised by the Russian Society of Nematologists. During the summer, AdrianWarner was funded by a BSPP bursary to work on an evaluation of two forecastingsystems for Late Blight of potato. Forecasts of blight periods generated by theAdcon AgroExpert (Ullrich-Schrodter model) and the Hardi Metpole (NEGFRY model)systems were compared. The study, which was conducted for the British PotatoCouncil, was directed by Dr Peter Jenkinson.

John Clement

Horticulture Research International

Virus and phytoplasma diseases

Recent visiting workers to HRI Wellesbourne are Dr Przennyslaw Lehmann ofthe Institute of Plant Genetics, Poznan, Poland, working with Dr John Walsh andDr Carol Jenner on evaluating transgenic Brassica napus lines containing the coat protein gene of turnip mosaic virus and Dr VesselaMavrodieva from the Plant Protection Institute at Kostinbrod, Bulgaria workingwith Drs Dez Barbara and Nicola Spence on cucumber mosaic virus.

Rebecca Young started an 8 week Sainsbury Summer Studentship in June. Shewill be working on a joint project between Richard Napier and Dez Barbara using peptide phage displaylibraries.

Congratulations to Dr Michael Clark who has recently received the first Posnette Award at the 17th International Symposium on Virus and ViruslikeDiseases of Temperate Fruit Crops, Bethesda, Maryland, USA. The award has beengiven in recognition of Michael's outstanding international contribution to theunderstanding and diagnosis of viruslike diseases of temperate fruit crops. Drs Tony Adams, Susan Crossley and David Davies also attended the meeting.Other travellers this year were Dr Nicola Spence and Eve Shaw who attended ameeting of the CEC Alstroemeria Virus Project in Bologna in May.

Fungal diseases

Mr John Carder has taken over the bulb pathology work formerly carried outby Dr Christine Linfield who left HRI in January and a Botrytis Workshop took place at HRI Wellesbourne in March organised by Dr David Harris from HRI East Malling.

Dr John Whipps and Roger Williams attended the EU Biotechnology SectorMeeting in Lund, Sweden in April and presented a paper entitled "Assessing solid-substrate inocula of Coniothyrium minitans for control of Sclerotiniasclerotiorum in glasshouse lettuce". Dr Alison Stewart from Lincoln University, New Zealand visited Dr John Whipps for six weeks in May to continuetheir collaboration on Coniothyrium minitans and biocontrol ofsclerotial pathogens and Dr Roy Kennedy attended the International Conferenceon Cashew and Coconut Production in Dar es Salaam in February.

Tony Roberts and Ezra Shabi (a visiting worker from the Volcani Institute in Israel) presented some of their work on variation in sensitivity of theapple scab fungus (Venturia inaequalis) to fungicides at a meeting ofthe Israeli Phytopathological Society in February. Tony then spent time withEzra visiting apple growing regions in Israel and collecting fungal culturesfor further studies. Ezra will continue to work with us until July and has beenpartially funded by APRC. In May, Professor Ian Crute visited Portugal for the final project team meeting of an EU funded project on parasite resistance in horticultural brassicas.

Bacterial diseases

Joana Vincente joined HRI for 1 year as part of her PhD study on Xanthomonas on Brassicas. She will be working partly in the Plant Pathology and Microbiology Department with Dr Nigel Lyons and Dr John Taylor and partly in thePlant Genetics and Biotechnology Department with Dr Graham King.

General pathology

Dr David Parry took up his position as the new Head of Entomology and PlantPathology at East Malling in April. Dr Alun Morgan, Dr John Whipps, GillTurnbull, Liz Poole and John Thomas attended the Molecular Microbial EcologyConference, at Liverpool in April. Gill Turnbull presented a paper entitled "Whyare Pseudomonads Motile? A Case Study of Soil-Plant Microbe Interactions".

The Pathology Department at Stockbridge House has secured funding for anHDC project on cucumbers to evaluate fungicides for the control of powdery mildew and other foliar and stem diseases. Dr Martin McPherson launched the Stockbridge House Plant Clinic.This new clinic aims to diagnose crop problems and provide guidance on remedialaction for growers and consultants in horticulture. In addition, a series ofidentification cards on pests and diseases of bedding plants prepared by DrsMartin McPherson, Rob Jacobson and Michael De Courcy-Williams was launched atthe at the HRA/OAC Ornamentals Conference at Wellesbourne in February.

John Taylor and Dawn Teverson visited Tanzania in connection with NRI's African Bean Programme setting up a new ODA funded project on in situ conservation of bean mixtures. Dawn visited women farmers fromwhom she collected mixtures in 1991 to discuss changes in mixture compositionand reasons for varietal selection. She will be back in Tanzania in April toplant multi-site field trials.

Rob Jacobson and Martin McPherson participated in the hydroponics conference organised by ISHS in Windsor, Ontario, Canada in May. Rob chaired asession on Crop Protection and presented a paper on `Pest Control in ProtectedCrops'. Martin presented an invited lecture entitled `Is there a SustainableSolution for Root Disease Control in Closed Systems?'. They both took part inan Open Forum in which growers asked the panel questions on pest and diseasecontrol.

A new Horticulture LINK Botrytis Project will investigate integratedchemical and environmental control of Botrytis in protected ornamentals. This involves scientific partnershipbetween HRI (Dr Tim Pettitt), ADAS, SAC, Silsoe and Reading University.

Nicola Spence