Genetically Modified Herbicide-Tolerant Crops and Sugar Beet—Environmental and Health Concerns - Sweeteners: Nutritional Aspects, Applications, and Production Technology - page 384

12.5 GeNetICaLLY MODIFIeD herBICIDe-reSIStaNt SUGar Beet
Sugarbeet( Beta vulgaris )isacommoncropinEurope,whereithasbeencultivatedforsugar
production since the late eighteenth century. It is a biennial plant. The large, succulent roots of
sugarbeetusedforfoodandfeedproductionareharvestedattheendoftheirstyearofgrowth.
Iflefttogrow,sugarbeetswilllowerandproduceseedsduringthesecondyear.Sugarbeetsare
onlyallowedtolowerforseedproduction,whichmainlytakesplaceinFranceandnorthernItaly.
WildrelativesofsugarbeetoriginatedinAsiaMinor.Sugarbeet'swildrelative,seabeet( B.
vulgaris ssp. maritime ), is an annual in southern Europe and a biennial or perennial in northern
latitudes(e.g.,ScandinaviaandIreland).
Inthecaseofsugarbeets,outcrossingandhybridizationarelimitedduetotheirharvestingbefore
lowering.Onlybolters—sugarbeetsthatlowerduringtheirstgrowingseason—canhybridizewith
eachotherorwithwildrelativeswhenpresent.However,sugarbeetsarecrosscompatiblewithotherspe-
ciesinthegenus Beta suchas B. vulgaris ssp. maritima , B. marcocarpa ,and B. atriplicifolia .Thereisno
evidencethat B. vulgaris canintercrosswithothergeneraintheChenopodiaceaefamily.
Beetspredominantlyreproducebyseed,althoughplantscansometimesgrowbackfrompor-
tions of roots left in the ield after harvest. Volunteer sugar beets are rarely observed growing
amongothercrops,inditches,oronroadsides.Ifvolunteersugarbeetsweretooccurinsubsequent
crops,theycouldbecontrolledbyagriculturalpractices(e.g.,herbicidesortillageduringseedbed
preparation). Most seeds left in the upper 5 cm of soil will germinate. Seeds that are ploughed
deepermayremaindormantuntilconditionsfavorgermination.Beetseedscanremaindormantfor
over10years.Problemswithvolunteerbeetssometimesoccurwhenplantedonthesameieldfor
severalconsecutiveyears.Emergingannualweedbeetfromtheseedbankcanonlybecontrolled
bymechanicalmeansandonlytoacertaindegree.Remainingvolunteerscanreproduceandcould
potentiallycrosswithbolting.Sugarbeetissensitivetofrostandispoorlycompetitiveinnaturalor
agriculturalhabitats.Beetseedsaredispersedonlyovershortdistances.Pollengrainsaredispersed
mainlybywind,butinsectscanplayasmallrole.Beetpollen,however,isquitesensitiveandis
viablefornomorethan24hunderieldconditions.Ingeneral,sugarbeetdoesnotsurviveinthe
environment.Onlyhybridswithwildbeetscanwithstandnaturalcompetitionandlowwintertem-
peratures( www.gmo-compass.org ) Dewaretal.(2000).
Assugarbeetissensitivetoweedcompetition,arelativelycomplexweedcontrolprogramusingive
activeingredientshasbeenusedtocontrolweeds(Buckmannetal.2000),togetherwithmechanical
weedingin50%ofthecrop.Popularpostemergentherbicidalsprayactiveingredientsincludephen-
medipham,metamitron,ethofumesate,desmedipham,trilusulfuronmethyl,lenacil,andchloridazon.
GMHTsugarbeet(RRsugarbeet)hasbeengeneticallymodiiedtobetoleranttotheherbicide
glyphosate, a broad-spectrum, nonselective herbicide that kills plants by binding to an enzyme
(EPSPS),whichpreventstheproductionofessentialaminoacidsintheplants.Thus,weedcontrol
within the GM crop can be achieved by applying glyphosate in place of the suite of herbicides
referredtoabove.RRsugarbeet,ingeneral,wouldbringmajoragronomicandeconomicbeneits
tofarmers(May2003;Liuetal.2008;Lissonetal.2000;May2001).
In the context of the ongoing debate concerning the possible environmental and human health
impactsofgrowingGMcrops,Bennettetal.(2004)reportedtheresultsofalifecycleassessmentcom-
paringtheenvironmentalandhumanhealthimpactsofconventionalsugarbeet-growingregimesin
theU.K.andGermanywiththosethatmightbeexpectedifGMHT(toglyphosate)sugarbeetiscom-
mercialized.Theresultspresentedforanumberofenvironmentalandhumanhealthimpactcategories
suggestthatgrowingtheGMHTcropwouldbelessharmfultotheenvironmentandhumanhealth
thangrowingtheconventionalcrop,largelyduetoloweremissionsfromherbicidemanufacture,trans-
port,andieldoperations.Emissionscontributingtonegativeenvironmentalimpacts,suchasglobal
warming,ozonedepletion,ecotoxicityofwater,andacidiicationandnutriicationofsoilandwater,
weremuchlowerfortheherbicide-tolerantcropthanfortheconventionalcrop.Emissionscontributing