ABSTRACT
The story of agriculture is mainly the story of weed interference. Weeds are considered one of the mainproblemsinagricultureandareresponsibleforlargeyieldlossesinvariouscropseveryyear (Lampkin,1990;Bhuler,1996;Anaya,1999).Theireffectontheagriculturalproductioncanbe quantiabletoalossofone-thirdofthetotalproduction,duetocompetitivefactors(Oerkeetal., 1994).Plantsundergocontinuousexposuretovariousbioticandabioticstressesintheirnaturalenvironment. Stress is often dened as any factor that decreases plant growth and reproduction below thepotentialofthegenotype(Osmondetal.,1987).However,bioticstressremainsabroadlydened andpoorlyunderstoodformofplantstress,partlybecauseitsapplicationisdifculttocontrol,and partlybecauseitsphysiologicalconsequencesareoftenhighlyvariable(Ayres,1992).Tosurvive undersuchconditions,plantshaveevolvedcomplexmechanismstoperceiveexternalsignals,allowing optimal response to environmental conditions (Fujita et al., 2006). For example, plants compete witheachotherforlight,water,andnutrientelements;therefore,thepotentialinherentabilityto directlyinhibitcompetitorsistheirstrategytosurvive.Competitiontakesplaceinoptimalhabitats; therefore,plantsorevengroupsofplantshavetomovetolessfavorableandsparselypopulated habitats.Movementwillonlybesuccessfulifnutritioncanbeobtainedelsewhere.Whilethevast majority of plants and weeds are autotrophic where nutrition is guaranteed by the formation of leavesandroots,thereareheterotrophicplants,suchasparasiticones,wherenutritionisguaranteed bytheirhost.Parasiticweedsareseriouspestsinagriculturaleldsandposeatremendousthreat toworldagriculture,mainlybecausetheyareatpresentalmostuncontrollable.Parasiticplantshave losttheirautotrophicwayoflifeduringtheirdevelopmentprocess.Thesystemismadeupofthe coexistence of two different organisms, which supports one of them (parasite) on the expense of the other(host).Thehostthroughleavescansynthesizeorganicsubstanceandphotosynthesize(chlorophyll+solarenergy),whilethroughroots,itcansynthesizeinorganicsubstanceandtheuptakeof waterandminerals.Ontheotherhand,theparasiteobtainscarbohydratesfromanotherorganism. Hence,theyaredirectlyorindirectlydependentonautotrophicplantsforcarbohydrates,nitrogen,
28.1 Introduction .......................................................................................................................... 735 28.2Types of Parasitic Plants ....................................................................................................... 736
28.2.1Important Parasitic Weed Species ............................................................................ 737 28.2.1.1Orobanchaceae ........................................................................................... 737 28.2.1.2Scrophulariaceae ........................................................................................ 738 28.2.1.3 Cuscutaceae ............................................................................................... 738
28.3Metabolic Pathway ................................................................................................................ 739 28.4Damage ................................................................................................................................. 741 28.5Conclusion ............................................................................................................................ 742 References ...................................................................................................................................... 744
water, etc. Usually, the host differs from the total number of different species that can be parasitized,andiscalled“hostrange,”whileitbecomes“hostpreference”whenitdevelopsintothemost desirablehostforoptimalgrowth.Parasitesacquiredcropsastheirfoodresource,enablingthem tosurviveinlargenumbersevenonnutrient-poorsites,sinceparasitismallowsplantstoaccessa richhydroponicnutrientsource.Evolutionisopportunisticandparasitesarethegreatestopportunists. Parasitic weeds are serious pests in agricultural elds; they are a taxonomically diverse group ofangiospermsthatrelypartiallyorcompletelyonhostplantsforcarbon,nutrients,andwater. Root-parasitizingweedsareofeconomicimportancebecausetheyreducecropyieldandquality. Theparasitesremovewater,minerals,andphotosynthatesfromthecrop,reducingthehost’sability togrowanddevelop.Cropsthatareparasitizedusuallygrowmoreslowly,and,dependingonthe severity of infestation and the parasite, biomass production is lowered or the host is almost killed. Fordecadesitwasassumedthatimprovedbreedingandagronomycouldovercometheparasites, andlittleeffortwasinvestedinunderstandingthenatureofparasitism.Becauseofthelackofcontrolmethodsatthetimeofattachment,themainmeansofcontrollingparasiticweedshadfocused onthevaryinglevelsofhosttoleranceandonreducingthesoilseedbank,preventingseedsetand inhibiting spread from infested to noninfested areas (Boari and Vurro, 2004; Vurro et al., 2009).
