1994-Biodiversity in arbuscular mycorrhizal fungi

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Mycol.Res.

98(7):705-715(1994)PrintedinGreatBntain

REVIEW

Biodiversityinarbuscularmycorrhizalfungi

M.GIOVANNETTPANDV.GIANINAZZI-PEARSOW705

llstitutodiMicrobiologiaAgraria,CentrodiStudioperlaMicrobiologiadelSuolo,ViadelBorghetto80,

56124Pisa,Italy

2LaboratoiredePhytoparasitologie,INRA/CNRS,StationdeGinitiqueetd'AmiliorationdePlantes,INRA,BV1540,21034DijonCedex,France

Knowledgeandconservationofdiversityinsymbioticarbuscularmycorrhizalfungiisofcrucialimportancefortheirefficientusein

environmentalconservationandsustainableplantproductionsystems.Therecalcitranceofthesemicroorganismstopureculture,and

theabsenceofinformationaboutplasmogamy,karyogamyormeiosis,meansthatinformationaboutthegeneticalbasesofany

variationsintheirpopulationbiology,ecologicalspecificityorsymbioticactivityisgenerallylacking.Amultidisciplinaryapproachis

necessarytoidentifysignificantdifferencesbetweenpopulations,species

orisolates.Anoverviewispresentedofsomeofthe

morphological,biologicalandmolecularaspects

ofarbuscularmycorrhizalfungithatmaycontributetodefiningandunderstanding

biodiversityinthisgroupofsymbioticmicroorganisms.

Table

1.SomesourcesofbiodiversityinarbuscularmycorrhizalfungiBiodiversity,atermtodescribevariabilitybetweenorganisms

orpopulationsoforganisms,hasdifferentfacetsdependingon

thelevelofdiversityconsidered(species,population,eco-

system)ortheorganismsconcerned(Barbault,

1992).

Biodiversitycanbeexploitedinmanywaysatscientificlevels,

themostwellknownandthemostancientnodoubtbeingin

taxonomyandsystematics,andmorerecentlyforstudiesof

populationbiology,ofevolutionandconservationof

ecosystems,orforselectionofmaterialsforbiotechnology.

Theroleoffungiinthefunctioningandbiodiversityof

terrestrialecosystemshasreceivedlittleattention(Hawks-

worth,

1991).Amongstthoseinteractingwithlandflora,

arbuscularmycorrhizalfungi(Glomales,Zygomycotina)rep-

resentanimportantcomponentbytheirubiquityinthesoil

microbialbiomassandtheirdirectinvolvementinessential

processesattheplant-soilinterface(Harley

&:Smith,

1983;

McGee,Smith

&:Smith,

1989).Mycorrhizalassociationsare

potentialfactorsdeterminingdiversityinecosystems:they

canprobablymodifythestructureandfunctioningofaplant

community,inacomplexandunpredictableway(Grime

efal.,

Morphological

characters

Spores

Wallultrastructure

andcytochemistry

Infectionpatterns

4SBiological

characters

Ontogenyofspores

Sporegermination

Symbioticefficiency

Biogeography

Edaphicrequirements

EnvironmentaltoleranceMolecular

characters

Protein/polypeptides

profiles

Isozymepolymorphism

DNAanalysis1987;Read,

1990).Anyshift

inthemycorrhizalfungal

populationcouldhaveconsequencesforthecompositionof

plantcommunities(survivorship,competition,floristicdi-

versity),causingchangesinthebiologyofnaturalecosystems

(Miller

&Allen,

1992;Molina,Massicotte

&Trappe,

1992).

Ontheotherhand,thecompositionoftheplantcommunity

mayaffectthatofthefungalcommunity:anyfactor(e.g.

host-symbiontcombinations)causingdifferentialreproduc-

tionandsurvivalofarbuscularmycorrhizalfungi(e.g.

sporulationrates)willoperateasaselectiveforceonthe

compositionofthesoilpopulation(Giovannetti

efal.,1988;

Sanders

&Fitter,

1992).Furthermore,differentabioticfactors

(C0

2,pollutants)mayprovokemodificationsinnativeplant

communities,consequentlymodifyingthemycorrhizalstatus

oftheecosystems,andhumanactivities(chemicalinputs,crop

rotation,soilmanagement)mayhaveconsequencesforthe

dynamicsanddiversityofthefungalcommunity.Therefore,

knowledgeofthedifferentfactorsinfluencingthepopulation

biologyofarbuscularmycorrhizalfungiisessentialinany

attempttousetheminenvironmentalconservation(Allen,

1991),biotechnology(Mulongoy

efal.,1992),orinsustainable

agriculture(Bethlenfalvay

&:Linderman,

1992).

Uptonow,some

130specieshavebeendescribedinthe

Glornales,butnotallareactuallyknowntobemycorrhizal

(Walker,

1992;Walker

&:Trappe,

1993).Althoughthesefungi

shownospecificvariationsintheirrangeofhostplants,a

largevariabilitycanbefoundintheirpopulationbiology,

ecologicalspecificityandsymbioticactivity.Aputative

zygosporicstagehasbeenreportedforthelifecycleofone

fungus(GigasporadecipiensHall

&L.K.Abbott)(Tommerup

&

Sivasithamparam,

1990),butthereisnoinformationcon-

cerningtheplasmogamy,karyogamyormeiosisofthese

fungi.This,withthefactthattheyareunculturableorganisms,

MYC98