Download 4. What is the difference between open-pollinated varieties

4.Whatisthedifferencebetweenopen-pollinatedvarietiesandhybrid
varieties?
Thequestionthatisoftenaskedintheorganicsectoris:‘Whatisthedifferencebetweenahybridanda
open-pollinatedvariety,andwhataretheadvantagesanddisadvantages?Andwhatfitsinbestwith
organicfarming?
Whatisa‘open-pollinated’variety?
Aopen-pollinatedvarietyisproducedusingthetraditionalmethodofcrossingandthenselectionof
offspringinseveralgenerations(basepopulation),seeFigure1.
Afterafewyears(usuallyafter5-6generations)ofsystematicselectionthevarietybecomesstableand
thecharacteristicshardlyeversegregateoutagain.Thismeansthatalltheoffspringarevirtuallythe
same,whichiswhytheterm'open-pollinated'isused.Soplantscomefromseedsofopen-pollinated
varietieswithvirtuallythesamecharacteristicsasthevarietypurchased.
Figure1.Diagramofthebreedingofanopen-pollinatedvariety(left)andanF1hybrid
variety(right)(courtesytoM.Haring)
F1hybrid
Open-pollinated
variety
Crossing
X
Basepopulation
Offspringinthe
Inbredparent
Inbred
sub-sequent
parent
lineA
generationsline
line
Selectionfrom
F1hybridseed
thepopulation
OffspringofanF1hybrid
Newselection
(=F2seed)
Whatisa(F1)hybridvariety?
F1hybridmeansliterally‘firstoffspringafteracrossing’.InthecaseofF1hybridsthebreedingprocessis
dividedintotwophases:inbreedingandcombinationsofcrossings.Sotheprocessismorecomplicated
andrequiresmoreinterventionbybreedersthaninthecaseofanopen-pollinatedvariety.
Thefirststepistodevelopparentlines.Theseparentslines(themotherandthefather)shouldeachbeas
uniformaspossible;andtheparentlinesforacrossingshouldalsobeverydifferent.Uniformparentlines
areproducedbyinbreeding.Inthecaseofself-pollinators(tomatoes,peppers)thisisfairlysimple:selfpollinatorsarenaturalinbreeders.Butinthecaseofcross-pollinators(suchaschicoryandcabbage)all
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sortsoftechniquesareneededtocarryout(manual)inbreeding.Thesecondstepistotestwhich
combinationofinbredlineswillproduceagoodF1hybridoncrossing.
Onceyouhavevariousinbredparentlines,youcanquicklymakenewcombinations(varieties).Thishas
beenoneofthemotivationsforbreederstomovefrom‘open-pollinated’varietiesto‘hybrid’varieties.
Afterall,thebreedingofanewvarietycantaketenyears.Sobreedershavealwayslookedforfasterways
ofbreeding.Hybridisationhasbeenanimportantstepinthis.
Advantagesofopen-pollinatedvarieties
Thefirstadvantageofopen-pollinatedvarietiesisthatthereisalwayssomeformofgeneticvariation
betweentheplantsinthefieldandsodiseasesspreadlessfastthaninthecaseofgeneticallyidentical
plantsofahybridvariety.
Anotheradvantageisthatgrowerscanpropagatethesevarietiesthemselves,i.e.theycanrepeatedly
obtainseedandsowitagain,seeFigure2.Theseedproductioncyclecanthereforebecontinued
indefinitely,fromgenerationtogeneration.Asthereisalwaysalittleundetectedvariationinanopenpollinatedvariety,youhavetoapplysomeselectioninthisseedproductioninordernottoobtaintoo
muchnon-desirablevariation.Avarietycanotherwise‘degenerate’anddeviatetoomuchfromthe
characteristicsdesiredoriginally. Figure2.Anorganicgrowerinacabbagefieldherselfselectingcabbagesfromanopen-pollinated
variety(left)andobtainingseedsfromthem(right)
Disadvantageofopen-pollinatedvarieties
Thefarmsavedseedofopen-pollinatedvarietiesobtainedbygrowersisadisadvantageforbreeders.
Theymissoutonincometofundtheirbreedingofnewvarieties.Iftheorganicsectorwantstoencourage
thebreedingofnewopen-pollinatedvarieties,thecostsofbreedingneedtobeinvesteddifferently.Read
aboutthisinSection10.
AdvantagesofanF1hybridvariety
Thefirstadvantageofhybridseedsforgrowersisthehighdegreeofuniformity:alltheplantsare,for
example,readyforharvestingatthesametimeandarethereforesuitableforaone-off,mechanical
harvest.Theylookalikeandtheyprovideauniformsorting.Asecondadvantageisthatinsomecases
thereisadditionalgrowthvigour(‘heterosis’),asaresultofwhichtheplantgrowsmorevigorousor
producesahigheryield.
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DisadvantagesofanF1hybridvariety
Thedisadvantageforgrowersisthefactthattheirownfarm-savedseeddoesnotproduceusableseed.
HybridvarietiescaninprincipleproduceseedbutintheF2thecharacteristicssegregateoutagainanda
variationisproducedthatisnotwantedbythemarket.Inthiswayseedcompaniesprotectthemselves
againstfarmsavingseeds.Thismakesgrowersdependentontheseedcompanies,whohavetoconstantly
crosstheinbredparentlinestobeabletobringnewF1seedontothemarket.PartlyforthisreasonF1
seedismoreexpensivethanofanopen-pollinatedvariety.Butforsomegrowerstheadvantages
compensateforthedisadvantages.Inorganicfarminghybridvarietiesarepermittedandareusedin
certaincrops.
Whyisinbreedingnecessaryinthecaseofahybridvariety?
Inbreedingofparentlinesmeansthatdesiredvarietycharacteristicsare‘fixed’faster,asaresultofwhich
theparentlineseachbecomeveryhomogenous.Thentwodistinctiveparentlinesarecrossed,which
producestheso-calledF1hybridseed.TheplantsfromF1seedoffspringhavethecharacteristicsofthe
twoparentlinescombinedandalltheplantsareidenticalandthusproduceauniformfield.Inthecaseof
anopen-pollinatedvarietymoredeviationsarepossible.
Arehybridvarietiespermittedinorganicfarming?
Aslongastheseedisproducedunderorganic
growingconditions,hybridvarietiesarepermittedin
organicfarming.Thereareseveralhybridvarieties
whoseparentlineshavebeentooweakenedby
inbreedingandthatcanproducegoodseedonly
withtheuseofpesticides;thesevarietiesare
thereforenotdesirableintheorganicsector.
Figure3.Breedingforahybridvarietyforcabbage:
manuallyinbreedingandcrossing(Photo:J.Myers,
OregonStateUniversity)
Bio-dynamicfarmingandhybridvarieties
Bio-dynamic(BD)farmingisaspecificwayoffarmingwithinorganicagriculturalmovementthathasits
ownvisionandhasadditionalrulesinadditiontothoseoforganicfarming.Forbio-dynamicfarmingthe
developmentofanopen-pollinatedvarietyisthemostnaturalwayofbreeding.Noartificesareused,
suchasinbreedinginthecaseofplanttypesthatarenaturallycross-pollinators.FromaspecificBDpoint
ofviewthepropagationofone'sownseedfitsinwiththedevelopmentofone's‘own’farmindividuality.
Afterall,byrepeatedlyproducingseedgrowerscanadaptavarietytosuittheirownbusiness.Theydo
thisbyconstantlyselectingcertainplanttypesintheoffspringoftheseedthatfitinbestwiththefarm
andthelocalconditions.Thefactthatanopen-pollinatedvarietyisconstantlyabletoproduceavital
subsequentgenerationisinkeepingwiththeBDvision.Hybridvarietiesthereforefitinlesswellwiththe
BDfarmingperspective.
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