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4. Whatisthedifferencebetweenopen-pollinatedvarietiesandhybridvarieties?

Thequestionthatisoftenaskedintheorganicsectoris:‘Whatisthedifferencebetweenahybridandaopen-pollinatedvariety,andwhataretheadvantagesanddisadvantages?Andwhatfitsinbestwithorganicfarming?

Whatisa‘open-pollinated’variety?Aopen-pollinatedvarietyisproducedusingthetraditionalmethodofcrossingandthenselectionofoffspringinseveralgenerations(basepopulation),seeFigure1.

Afterafewyears(usuallyafter5-6generations)ofsystematicselectionthevarietybecomesstableandthecharacteristicshardlyeversegregateoutagain.Thismeansthatalltheoffspringarevirtuallythesame,whichiswhytheterm'open-pollinated'isused.Soplantscomefromseedsofopen-pollinatedvarietieswithvirtuallythesamecharacteristicsasthevarietypurchased.

Whatisa(F1)hybridvariety?F1hybridmeansliterally‘firstoffspringafteracrossing’.InthecaseofF1hybridsthebreedingprocessisdividedintotwophases:inbreedingandcombinationsofcrossings.Sotheprocessismorecomplicatedandrequiresmoreinterventionbybreedersthaninthecaseofanopen-pollinatedvariety.Thefirststepistodevelopparentlines.Theseparentslines(themotherandthefather)shouldeachbeasuniformaspossible;andtheparentlinesforacrossingshouldalsobeverydifferent.Uniformparentlinesareproducedbyinbreeding.Inthecaseofself-pollinators(tomatoes,peppers)thisisfairlysimple:self-pollinatorsarenaturalinbreeders.Butinthecaseofcross-pollinators(suchaschicoryandcabbage)all

Figure1.Diagramofthebreedingofanopen-pollinatedvariety(left)andanF1hybridvariety(right)(courtesytoM.Haring)

F1hybrid

InbredparentlineA

Inbredparentline

OffspringofanF1hybrid(=F2seed)

F1hybridseed

X

Crossing

Open-pollinatedvariety

Basepopulation Offspringinthesub-sequentgenerationsline

Newselection

Selectionfromthepopulation

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sortsoftechniquesareneededtocarryout(manual)inbreeding.ThesecondstepistotestwhichcombinationofinbredlineswillproduceagoodF1hybridoncrossing.Onceyouhavevariousinbredparentlines,youcanquicklymakenewcombinations(varieties).Thishasbeenoneofthemotivationsforbreederstomovefrom‘open-pollinated’varietiesto‘hybrid’varieties.Afterall,thebreedingofanewvarietycantaketenyears.Sobreedershavealwayslookedforfasterwaysofbreeding.Hybridisationhasbeenanimportantstepinthis.

Advantagesofopen-pollinatedvarietiesThefirstadvantageofopen-pollinatedvarietiesisthatthereisalwayssomeformofgeneticvariationbetweentheplantsinthefieldandsodiseasesspreadlessfastthaninthecaseofgeneticallyidenticalplantsofahybridvariety.

Anotheradvantageisthatgrowerscanpropagatethesevarietiesthemselves,i.e.theycanrepeatedlyobtainseedandsowitagain,seeFigure2.Theseedproductioncyclecanthereforebecontinuedindefinitely,fromgenerationtogeneration.Asthereisalwaysalittleundetectedvariationinanopen-pollinatedvariety,youhavetoapplysomeselectioninthisseedproductioninordernottoobtaintoomuchnon-desirablevariation.Avarietycanotherwise‘degenerate’anddeviatetoomuchfromthecharacteristicsdesiredoriginally.

Figure2.Anorganicgrowerinacabbagefieldherselfselectingcabbagesfromanopen-pollinatedvariety(left)andobtainingseedsfromthem(right)

Disadvantageofopen-pollinatedvarietiesThefarmsavedseedofopen-pollinatedvarietiesobtainedbygrowersisadisadvantageforbreeders.Theymissoutonincometofundtheirbreedingofnewvarieties.Iftheorganicsectorwantstoencouragethebreedingofnewopen-pollinatedvarieties,thecostsofbreedingneedtobeinvesteddifferently.ReadaboutthisinSection10.

AdvantagesofanF1hybridvarietyThefirstadvantageofhybridseedsforgrowersisthehighdegreeofuniformity:alltheplantsare,forexample,readyforharvestingatthesametimeandarethereforesuitableforaone-off,mechanicalharvest.Theylookalikeandtheyprovideauniformsorting.Asecondadvantageisthatinsomecasesthereisadditionalgrowthvigour(‘heterosis’),asaresultofwhichtheplantgrowsmorevigorousorproducesahigheryield.

Open-pollinatedras

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DisadvantagesofanF1hybridvarietyThedisadvantageforgrowersisthefactthattheirownfarm-savedseeddoesnotproduceusableseed.HybridvarietiescaninprincipleproduceseedbutintheF2thecharacteristicssegregateoutagainandavariationisproducedthatisnotwantedbythemarket.Inthiswayseedcompaniesprotectthemselvesagainstfarmsavingseeds.Thismakesgrowersdependentontheseedcompanies,whohavetoconstantlycrosstheinbredparentlinestobeabletobringnewF1seedontothemarket.PartlyforthisreasonF1seedismoreexpensivethanofanopen-pollinatedvariety.Butforsomegrowerstheadvantagescompensateforthedisadvantages.Inorganicfarminghybridvarietiesarepermittedandareusedincertaincrops.

Whyisinbreedingnecessaryinthecaseofahybridvariety?Inbreedingofparentlinesmeansthatdesiredvarietycharacteristicsare‘fixed’faster,asaresultofwhichtheparentlineseachbecomeveryhomogenous.Thentwodistinctiveparentlinesarecrossed,whichproducestheso-calledF1hybridseed.TheplantsfromF1seedoffspringhavethecharacteristicsofthetwoparentlinescombinedandalltheplantsareidenticalandthusproduceauniformfield.Inthecaseofanopen-pollinatedvarietymoredeviationsarepossible.

Arehybridvarietiespermittedinorganicfarming?Aslongastheseedisproducedunderorganicgrowingconditions,hybridvarietiesarepermittedinorganicfarming.Thereareseveralhybridvarietieswhoseparentlineshavebeentooweakenedbyinbreedingandthatcanproducegoodseedonlywiththeuseofpesticides;thesevarietiesarethereforenotdesirableintheorganicsector.

Figure3.Breedingforahybridvarietyforcabbage:manuallyinbreedingandcrossing(Photo:J.Myers,OregonStateUniversity)

Bio-dynamicfarmingandhybridvarietiesBio-dynamic(BD)farmingisaspecificwayoffarmingwithinorganicagriculturalmovementthathasitsownvisionandhasadditionalrulesinadditiontothoseoforganicfarming.Forbio-dynamicfarmingthedevelopmentofanopen-pollinatedvarietyisthemostnaturalwayofbreeding.Noartificesareused,suchasinbreedinginthecaseofplanttypesthatarenaturallycross-pollinators.FromaspecificBDpointofviewthepropagationofone'sownseedfitsinwiththedevelopmentofone's‘own’farmindividuality.Afterall,byrepeatedlyproducingseedgrowerscanadaptavarietytosuittheirownbusiness.Theydothisbyconstantlyselectingcertainplanttypesintheoffspringoftheseedthatfitinbestwiththefarmandthelocalconditions.Thefactthatanopen-pollinatedvarietyisconstantlyabletoproduceavitalsubsequentgenerationisinkeepingwiththeBDvision.HybridvarietiesthereforefitinlesswellwiththeBDfarmingperspective.