4. What is the difference between open-pollinated ...€¦ · obtain seed and sow it again, see...
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7 4. What is the difference between open-pollinated varieties and hybrid varieties? The question that is often asked in the organic sector is: ‘What is the difference between a hybrid and a open-pollinated variety, and what are the advantages and disadvantages? And what fits in best with organic farming? What is a ‘open-pollinated’ variety? A open-pollinated variety is produced using the traditional method of crossing and then selection of offspring in several generations (base population), see Figure 1. After a few years (usually after 5 - 6 generations) of systematic selection the variety becomes stable and the characteristics hardly ever segregate out again. This means that all the offspring are virtually the same, which is why the term 'open-pollinated' is used. So plants come from seeds of open-pollinated varieties with virtually the same characteristics as the variety purchased. What is a (F1 ) hybrid variety? F1 hybrid means literally ‘first offspring after a crossing’. In the case of F1 hybrids the breeding process is divided into two phases: inbreeding and combinations of crossings. So the process is more complicated and requires more intervention by breeders than in the case of an open-pollinated variety. The first step is to develop parent lines. These parents lines (the mother and the father) should each be as uniform as possible; and the parent lines for a crossing should also be very different. Uniform parent lines are produced by inbreeding. In the case of self-pollinators (tomatoes, peppers) this is fairly simple: self- pollinators are natural inbreeders. But in the case of cross-pollinators (such as chicory and cabbage) all Figure 1. Diagram of the breeding of an open-pollinated variety (left) and an F1 hybrid variety (right) (courtesy to M. Haring) F1 hybrid Inbred parent line A Inbred parent line Offspring of an F1 hybrid (= F2 seed) F1 hybrid seed X Crossing Open-pollinated variety Base population Offspring in the sub-sequent generations line New selection Selection from the population
Transcript of 4. What is the difference between open-pollinated ...€¦ · obtain seed and sow it again, see...
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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)
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Open-pollinatedvariety
Basepopulation Offspringinthesub-sequentgenerationsline
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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.
