ABSTRACT
Epidemiologyisthestudyofthedevelopmentandspreadofdiseaseinoculum andofthefactorsaffectingtheseprocesses,1anddealswiththeeffectsofthe biotic(hostandpathogen)andabioticenvironment.VanderPlank2defined epidemicsasthescienceofdiseaseinpopulationsinvolvingthepersistenceand spreadofinoculumandenvironmentalfactorsaffectingdiseaseincidenceon particularplantpopulations.Epidemiologicalstudiesareimportantindisease forecastinganddiseasecontrol.VanderPlank2appliedmathematicalmodelsto epidemiologicalstudiesofplantdiseases.Plantdiseaseepidemicreferstothe developmentandrapidspreadofadiseaseonaparticularkindofcropcultivated overalargearea.3Epidemicsdevelopwhenasusceptiblecultivarisplantedover alargeareainthepresenceofavirulentpathogencoupledwithafavorable environment.Thedevelopmentanddeclineofepidemicsisabalancebetween inoculumpotentialanddiseasepotential:
DiseaseseverityInoculumpotentialx (inoculumdensity
xcapacity)
Diseasepotential (proneness
xsusceptibility)
Inoculumpotentialisthenumberofinfectivepropagules(inoculumdensity) andtheirpathogeniccapacity.Diseasepotentialishostsusceptibility,whichmay beinfluencedbyanunfavorableenvironment,nutritionalimbalances,and/ora susceptiblegrowthstage.Hostsusceptibilityiscontrolledgenetically,anddevelopmentofanepidemicdependsonthenumberofinfectivepropagules,their pathogeniccapacity,hostsusceptibility,andtheeffectoftheenvironmenton pathogenvirulenceandhostpronenesstodisease.Thesesamefactorsaffectthe epidemiologyofseedbomepathogens.
