Bananasareoneoftheworld’smostimportantfoodcrops.Theyarealsooneofthemostvaluableexports.Bananasdonotgrowfromseeds.Instead，theygrowfromexistingplants.Bananasarethreatenedbydiseasebecausealltheplantsonafarmarecopiesofeachother.Theyallsharethesamegeneticweaknesses.Forexample，theCavendishbananaismostpopularinNorthAmericanandEuropeanmarkets.However，somekindsoffungusorganismseasilyinfecttheCavendish.BlackSigatokadiseaseaffectstheleavesofCavendishbananaplants.Thediseaseiscontrolledonlargefarmsbyputtingchemicalsontheplant’sleaves.Farmersputantifungalchemicalsontheircropsuptoonceaweek.
Anotherfungaldiseaseismoreserious.Panamadiseaseattackstherootsofthebananaplant.Thereisnochemicaltreatmentforthisdisease.Infectedplantsmustbedestroyed.PanamadiseasehasaffectedcropsinSoutheastAsia，AustraliaandSouthAfrica.ThereisconcernthatitmayspreadtobananasgrownintheAmericas.ThiscouldthreatenanimportantexportproductforCentralandSouthAmerica.
TheInternationalNetworkfortheImprovementofBananaandPlantainsupportsresearchonbananas.ThegrouphasheadquartersinFranceandotherofficesinthemajorbananagrowingareasoftheworld.Thegroupsaysthatmoreresearchmustbedonetodevelopimprovedkindsofbananas.Thegroupsaysthatfungaldiseasesmainlyaffectonlyonekindofbanana.Infact，therearefivehundreddifferentkindsofbananas.FoodandAgricultureOrganizationoftheUnitedNationshassaidthattheCavendishbananarepresentsonly10%ofworldproduction.
TheUNagencysaysfarmersshouldgrowdifferentkindsofbananas.Thisprotectsagainstdiseasesthataffectonlyonekind.ExpertswarnthatdiseasemaycausetheCavendishbananatodisappear.Thishappenedearliertoanotherpopularbananabecauseofitsgeneticweaknessagainstdisease.
60．Whatdoesthispassagemainlytellus?
A．Bananasaretheworld’smostimportantfoodcrops.
B．Therisktoapopularbananashowstheneedtogrowotherkinds.
C．Therearefivehundreddifferentkindsofbananas.
D．Howtogrowbananasindifferentcountries.
61．Bananasarethreatenedbydiseasebecause_
