How to Breed Carrots for Organic · PDF fileHow to Breed Carrots for Organic Agriculture ... Mating systems for seed production ... are covered in Principles and Practices of Organic

How to Breed Carrots for Organic Agriculture www.seedalliance.org�

How to Breed Carrotsfor Organic Agriculture

Organic Seed AllianceAdvancing the ethical development and stewardship of the genetic resources of agricultural seedPO Box 772, Port Townsend, WA 98368

This publication was made possible through a grant from Organic Farming Research Foundation and Seed Matters

How to Breed Carrots for Organic Agriculture www.seedalliance.org2

Section I: Introduction...................................................................................................................................................3 Section II: Introduction to Breeding........................................................................................................................3Section III: Breeding Goals...........................................................................................................................................3Section IV: Germplasm..................................................................................................................................................4

Section V: Reproductive Biology.................................................................................................................................4

Section VI: Plant Breeding............................................................................................................................................5 Matingsystemsforseedproduction................................................................................................................................5 Generatingbreedingpopulations.....................................................................................................................................5 Makingthecross-pollination................................................................................................................................7 Controlledpollination.............................................................................................................................................7 Straincross...................................................................................................................................................................7 Massselection.............................................................................................................................................................8 Familyselection.........................................................................................................................................................8 Breedingtimeline.....................................................................................................................................................................8 Breedingsummary................................................................................................................................................................11Glossary............................................................................................................................................................................13

References and Resources.........................................................................................................................................15

Table of Contents


Carrotshavelongbeenanimportantfreshmarketcroparoundtheworld.Thebreadthofregionalpreferenceshasensuredthatawidevarietyoftypesandvarietiesexistacrossculturesthatusethisnutritionallyimportantvegetableasanev-erydaystapleoftheirdiet.Worldwide,therearedozensofdifferentmarkettypesofcarrots,eachwithhundredsofuniquevarietiesthathavebeenimportanttosomesegmentofthemarketoverthelastcentury.WhenEuropeancarrotswereimport-edtoNorthAmerica,theyweregrownprimar-ilyasafall-harvestedvegetable,storedthroughwinterandusedforcooking.Ascarrotsgainedpopularityasafreshmarketcropforallseasonsinearly20thcenturyAmerica,therewasaneedforbunchingcarrotssoldwiththeirtopsintact.Thisneeddemandedthinner,sleekrootedcarrotswithoutlargeshouldersthatpushtherootsapartatoddangleswhenbunched.Aneweraofinno-vationinplantbreedingdeliverednewtypesofcarrotsthatrepresentcombinationsofthediffer-enttypesfromaroundtheworld.Thisinnovationhasbeenheightenedinthelast20yearswiththereintroductionofolder,uniquelycoloredcarrotsintothemarketplace.

Acenturyago,carrotseedproductionandbreed-ingwasthedomainofseriouscarrotgrowersandthesmallregionalseedcompaniesthatwerethenorminNorthAmericaandinmanyplacesaroundtheworld.Bythemid-20thcentury,bothseedproductionandbreedingbecamemorespecialized,andmostcommercialfarmersinNorthAmericanolongerconsideredproducingtheirowncarrotseed.Thecommercialopen-pollinated(OP)car-rotvarietiesbredandmaintainedfromthe1920suntilwellintothe1970sweresuccessfulinsupply-ingthevariousneedsofboththefreshmarketandprocessedvegetabletrade.TheseedcompaniesgrowingthebeststrainsofthesevarietieswerequitecompetentatmaintainingaselectionofeachOPvarietywithahighdegreeofuniformity,whileavoidingthepitfallsofinbreedingbyselectingtoonarrowly.Withtheadventandsubsequentcom-mercialdominanceofhybridcarrotsbeginninginthe1970s,fewerseedprofessionalshadtheskills

toselectandmaintainhigh-qualityOPvarieties.

Thegoalofthismanualistoexplainsimplemeth-odsfordevelopinganOPcarrotvariety.WhilecarrotbreedingprogramsatlargeseedcompanieshavelargelyabandonedOPs,thereareanumberofreasonswhyOPsarebestsuitedtoservefarmerbreedersaswellasindependentseedcompaniesthataddressregionalneeds.BybreedinganOPvarietythatretainsadequategeneticvariabilitywhileselectingforuniformityforalloftheimpor-tantmarkettraits,itispossibletoproduceavari-etythatcansubsequentlybeselectedforthevariedclimatesandculturalneedsofdifferentregions.

Werecommendthatfarmerbreedersfirstdevelopbreedinggoals.InOrganicSeedAlliance’s(OSA)Introduction to On-Farm Organic Plant Breeding,weoutlinethegeneticconceptsofbreedingandprovidefarmerbreedersatemplateforbreedingcrops.Thesearethebasicstepsforbreedingcropsonyourfarm:

1.Developyourbreedinggoals

2.Identifyparentalmaterial,includingconductingtrialstofindthebestparents

3.Makecrosses

4.Selectandrecombineyourselectedbreedingmaterial

Thefirststepofanybreedingprojectistodevelopbreedinggoals.Belowisalistofthemostimpor-tanttraitsforcommercialcarrots,includingthefoliartraitsthatareparticularlyimportantfororganicgrowers.ThesetraitswillbediscussedfurtherintheSelectionsection.

Germination/strengthofemergenceSeedlingvigor

••

I. Introduction

*Definitionsfortechnicalwordsthatareitalicizedandboldedcanbefoundintheglossary

II. Introduction to Breeding

III. Breeding Goals


CanopydevelopmentandweedcompetitivenessMaturityslotTopattachmentDiseaseresistanceColorintensityCorecolorRootshapeRoottipfillFlavorSweetnessHarshnessStorability

Germplasmisacollectionofgeneticresourcesinaspecies,andistherawmaterialthataplantbreederusestodevelopnewvarieties.Breedersof-tenusethetermgermplasmtorefertosub-groupsoftheentiregermplasmthatexistsforacrop.Forinstance,carrotbreedersrefertothe“purplecar-rotgermplasm”orthe“Alternariablightresistantgermplasm”asawaytospecifythecrop’sbreedingmaterialusedintheirwork.Whileabreederwillprobablyneverusemorethanafractionofthismaterialforbreedingpurposes,youshouldlearnasmuchaspossibleaboutavailablematerialthatincludestraitsthathelpyoumeetyourdesiredbreedingobjectives.However,nooneiseverfullyawareofallthegermplasmthatmaybeusefulforanyparticularbreedingproject,whichiswhylearningaboutthecropthatyouareinterestedinbreedingisalifelongpursuit.

Inthemodernworldwheremostofthenewercar-rotvarietiesareF1hybrids,plantbreedersshouldbeonthelookoutforgoodOPmaterial.ThereareafewcommonOPvarietiesstillcommerciallyavailableinNorthAmerica,andanumberofoldervarietiescanberequestedthroughtheGermplasmResourcesInformationNetwork(GRIN)oftheU.S.DepartmentofAgricultureorinheirloomseedcollections.Unfortunately,carrotshavealimitedgermplasmpoolcomparedtoothercommonvege-tablecropspecies,asbiennialrootcropsarehardertoreproducethanmostannualseedcrops.Also,ifOPcarrotvarietiesarenotmaintainedthroughdili-gentselectionwhenseedisincreased,theirpheno-typicconstitutionusuallydegeneratesrapidly.

••••••••••••

Agoodbreedermustbeopentofindingcommer-cialOPvarietiesfromaroundtheworldthatarestillbeingactivelymaintained.Thisisoftenthemostvaluablebreedingmaterial,asitcanmostrapidlybedevelopedintonewvarieties.SomebreedershavealsousedF1hybridsforparentalmaterialintheirbreedingwork.Thedetailsofhybridcarrotbreedingarebeyondthescopeofthismanual,butnotethatF1hybridcarrotseedisproducedusingnaturallyoccurringcytoplasmic male sterility (CMS)inthefemaleparent.Seedcol-lectedfromF1progenyorsubsequentgenerationswillhavecytoplasmwiththesesterilityfactorsthatcouldresultinfuturesterilityproblems.There-fore,itmaybebesttostartabreedingprojectwithOPmaterial.Thatsaid,iftheprogenyfromanF1hybridvarietyexhibitsgoodfertilityintheF2andF3generations,theprogenyofthisexistingF1hy-bridlikelyhadplentyofnuclear restorer genestoadequatelyrestorethesterilityoftheCMS,andthematerialmaybeusedindevelopinganOPvariety.

Whileplantbreedingdiscussionsoftenbeginwithwhichparentsarebesttocross-pollinateforcre-atingabreedingpopulation,allbreedersshouldrememberthatthebreedingprocesssometimesbeginswithanalreadyexistingpopulationofthecrop.Inthissituation,breedersfindanexistingOPpopulationthathasadequategeneticvariationforthedesiredtraits,whichallowsthemtobypassthestepsofchoosingparentsandmakingacross.Therearealsocaseswhereabreederdiscoversadiversepopulationthathasoccurredduetoanun-intendedcrossinthefieldandrealizesthatitholdspromiseasabreedingpopulation.Thepointisthatgermplasmiswhereveryoufindit,andallgoodfarmersandplantbreederslearntorecognizegoodgermplasmforspecificbreedingneedsovertimeastheygainexperiencewiththecrop.

Carrotsareabiennialcross-pollinatedspeciesthatrelyoninsectpollination.Manyspeciesofpollinat-inginsectsareattractedtocarrotflowers,includingwasps,Syrphidflies(alsoknownashoverflies),wildbees,anddomesticbees.Flowersareborneonaseriesofcompoundumbels,startingwithasinglecentralinflorescence,knownastheprimaryor

IV. Germplasm

V. Reproductive Biology


kingumbel,followedbyafewsecondaryumbels,andthenmanymoretertiaryumbels.Inmostcli-mates,thebestseedisharvestedfromtheprimaryandsecondaryumbels,astheywillhavethelongestperiodoftimetofullymaturetheirseed.Themul-tiple-floweredumbeletsoneachcompoundumbelusuallyhaveatleastadozensmallperfectflowerswithfivestamens,fivepistils,andfivesepals.Theovaryofeachblossomhastwolocules,eachpro-ducingasingleseedwhensuccessfulfertilizationhasoccurred.Whilecarrotsarefullyself-fertile,amajorityoftheseedproducedisduetocross-pol-linationbetweenplantsinthepopulation.Muchofthiscross-pollinationisduetothefactthatcarrotsareprotandrous:theanthers onanyparticularflowershedpollenbeforethestigmaofthatsameflowerisreceptivetofertilization.Thisdecreasesthechancesofself-pollination,asinsectswillflyfromumbeltoumbelinanattempttofindmatureflowers.Protandryisanevolutionarymechanismtoenforceamajorityofcross-pollinationincar-rots,asthisspeciesismoresusceptibletopotentialinbreeding depressionfromexcessiveself-pollina-tionsthanmostagriculturalcrops.

Producingcarrotseedonthefarmisusuallydoneacrosstwoseasons,whichisnaturalforthecropwhengrowinginitsnativehabitat.Carrotrootsforplantbreedingpurposesareproducedduringonegrowingseason,andaredugupandevaluatedforrootcharacteristicsattheendofthefirstsea-son.Thesecarrotsshouldbeplantedlaterintheyear.Thatwaytherootsgrowtomarketablesizeaslateaspossibleattheendofthefirstseason,minimizingwinterstoragetime.Overwinteringcanalsobedoneinsitu,orinthefield,inmilderclimates,buttherootsmustbevernalizedinei-thercase.Aswithallbiennialcrops,carrotsneedtobevernalizedinordertoflower.Vernalizationisaprocesswherethebiennialplant(inthiscasethecarrotroot)isexposedtoatleast8to10cu-mulativeweeksoftemperaturesatapproximately50F(10C)orbelowbetweentheirfirstseasonofvegetativegrowthandtheirsecondseasonofre-productivegrowth.Thisisaccomplishedeitherbyallowingtherootstooverwinterinthegroundinregionswithmildwintersorbystoringtherootsatidealstorageconditions--35F(2C)and95%humidity--throughwintermonths.Thestepsforpreparingandstoringtherootsinacoldroom

arecoveredinPrinciples and Practices of Organic Carrot Seed Production in the Pacific Northwest,availableatwww.seedalliance.org.

Mating systems for seed productionTherearebasicallytwowaysthatcarrotvarietiesareproduced,eitherasopen-pollinatedvarietiesorasF1hybrids.Producingopen-pollinatedvariet-iesisrelativelyeasytodoifthegroweris(1)inaclimatesuitedtothereproductivephaseofcarrots,and(2)willingtoputinthetimetolearnthein-tricaciesofworkingwithabiennialseedcropandlearnthedisciplineofselectingforasetoftraitsinanOPwithoutoverlynarrowingthegeneticbaseofthepopulation.Producinghybridcarrotvarieties,ontheotherhand,requiresmaintainingaseriesofparentalinbredlines.Theseincludebothsterileandfertilemalelinesforeachfemaleparent,aswellasafertilemaleparentallineforeachhybrid.Toproducehybridseed,youmustfirstproduceseedofeachoftheparentlinesinseparateisolatedfieldsatleastayearbeforehybridproduction.Then,whenthehybridseedcropisproduced,thehybridseedisharvestedonlyfromthefemalepar-ent,asallofthemaleparentrowsaredestroyed.Thisprocessismuchmorecostlyandtime-con-sumingthanproducingOPseed,andisusuallyoutsideofwhatmostfarmerbreedersarewillingtodoinboththebreedingandtheproductionofacarrotvariety.

Generating breeding populationsAswithallbreedingprojects,youshouldchoosetherightparentstocrosstocreateaneffectivepopulationwiththepotentialofgeneratingprog-enywiththecombinationoftraitsyouareseeking.Thisrequiressomecareintheselectionofparentvarietiesorothergermplasmtofindorcreateausefulbreedingpopulation.Mostimportantly,thisprocessbeginswiththebreederhavingagoodworkingknowledgeofthetraitsinpotentialbreed-ingstocks.Identifyingthesetraitsrequiresgrow-ingfieldtrialsofexistingcarrotmaterialunderconditionsthataresimilartothoseusedbygrow-ers.Trialsneedtostartbeforethefirstcrossesaremadetoallowyoutoevaluateexistingmaterialforthetraitsyouhaveidentifiedasimportant(see

VI. Plant Breeding


Selection).Tolearnmoreaboutconductingvarietytrials,refertoOSA’sOn-farm Variety Trials: A Guide for Organic Vegetable, Herb, and Flower Producers,atwww.seedalliance.org.

Whengoodbreedingmaterialhasbeenidenti-fied,mostbreederswillmakeanumberofcrosses,incorporatingseveraldifferentcombinationsofthebestmaterialavailable.Initialcross-pollinationsareoftenmadeinagreenhousebetweensingleplantsinsmallmuslinorperforatedplasticpollina-tion“pillowtubes”thatcovertheflowersofthetwoplants.Insectpollinatorsmustbeintroducedintothesepollinationbags.Theseinsectsaretypicallyhousefliesorbluebottlefliesthatcanbepurchasedinthelarvalstage.Somesmall-scalebreedingprojectsusefeatherdustersintheeventthatfind-ingaflysourceisproblematic.Thedownsideofthissingle-plantbysingle-plantcrossingmethodisthatyouwillgetalimitedsampleofthegenesfromeachoftheparentalpopulations.Thisisbecausenooneplantinacross-pollinatedcropspeciesvarietycontainsallofthegeneticvariationpresentinthatvariety.Thismaynotbeaproblemincommercialhybridbreedingprogramswheremanycrossesaremadewiththeexpectationthatonlyafewwillresultinfinishedvarietiesorinbreds.However,

*IsolationtentscanbepurchasedfromRedwoodEmpireAwningatwww.redwoodempireawning.com.

Carrot crossing in outdoor pillow tubes: Initial single crosses can be made outdoors with homemade muslin fabric and small round metal frames that surround carrot flowers. Note the small black plastic tube with a cork on top where you can add fly larvae weekly that will hatch in the pillow tubes. Only seed produced inside of the pillow tubes is used for breeding.

Carrot pollination by flies: The common house fly and blue bottle fly are often reared and used by carrot breed-ers as they are effective pollinators.

House flies in carrot pillow tubes: For an isolated carrot pollination it is recommended that you use a high density of flies. Pillow tubes here are made from a perfo-rated plastic mesh used by cheese makers.


mostfarmersarenotwillingtomanageanumberofcrosses.Inmostfarmer-ledbreedingprojects,thegoalisusuallytocreateafinishedvarietybyperformingonlyoneortwocrossesbetweentwowell-chosenparents.

Inordertocapturemoreofthegeneticvariationfromtheinitialcrossbetweenanytwoparents,werecommendatechniqueusedbyforagebreed-ersknownasa“strain cross.”Astraincrossisthecrossingoftwosmallpopulationsofthechosenparentvarieties.Tousethistechnique,selectanumberofcarrotrootsfromeachofthetwoparen-talpopulations.Theadvantageoffarmerbreedersusingastraincrossisthatbyusinganumberofse-lectedindividualsfromeachofthetwoparentsyouarecapturingagreaternumberofpossiblegeneticcombinationsfromtheoverallgeneticbreadthofbothparents.Straincrossescanbedoneinasmall,meshpollinationcageorinanopenfieldifisolatedfromotherfloweringcarrotsorferalQueenAnne’sLace(Daucus carota),whichwillreadilycrosswithcultivatedcarrots.*Theadvantageofmakingastraincrossinanopenfieldisthatinmostloca-tionstherewillbeamplewildpollinators,nativewaspsandbees,toensureadequatepollination.

Making the cross-pollinationMakecertainthatcarrotrootshavebeenvernal-izedsothattheyflower.RefertotheReproductive Biologysectionaboveforinstructiononhowtovernalizecarrotroots.

Whenmakingacarrotcross,eitherbetweentwoplantsinapollinationpillowtubeorwithtwopar-entpopulationsinastraincross,labelthedifferentparentrootswithapedigreestake.Thatway,thecrossedseedthatresultscanbeharvestedsepa-ratelyfromthedifferentparents.

Controlled pollinationForasimplecrossbetweentwocarrotplantsfromdifferentvarieties,plantthetwoparentalrootsinseparatepotsinthegreenhouseorinthesoil(ifmakingthecrossinasmallpollinationtentorpillowtubeoutdoors).Astheplantssendoutflowerstalksandformflowers,coverthemwithacloth,plasticpollinationbag,ortent.Theseenclo-suresneedtobesecuredbeforethefirstflowersopenandarereceptivetopollination.Pollinat-

inginsectsmustnowbeintroduced.Housefliesandbluebottlefliesaremostcommonlyusedforthispurpose.Thelarvaeoftheseflyspeciesmustbeintroducedweeklyattheonsetofflowering,approximatelyahalf-teaspoonperpollinationbagortube.Theyusuallysurviveforoneweekinthesecages.Theseflieswillseekpollenandnec-tarandpollinatewiththeirmovementacrosstheflowers.Byaddingacottonballsoakedinsugarwatereverytwodays,thelifespanofthefliescanbeextendedbyseveraldays.Thismethodisusedextensivelybycommercialcarrotbreederswhomaymakehundredsofcrossesperyear.Pollina-tionenclosuresprovidetheadvantageofallowingyoutomakeanumberofcrossesinonelocationwithoutthethreatofcross-pollination.

Strain crossMostfarmerbreedersareunlikelytomakemorethanoneortwocrossesafteridentifyinggoodmaterialanddecidingonaspecificsetofbreed-inggoalsforadesiredphenotype.Thestraincrossmethodisoftenusedforasingle,isolatedcross.Inastraincrossofarootcroplikecarrots,selectatleast20to30ofthebestrootsfromeachofthetwoparentsandplantthemintwoseparaterows,sidebyside,withtheintentofharvesting,clean-ing,andbaggingtheseedasseparatelotsinthefirstyear.TheseedinlotAcontainsseedoftwodifferentconstitutions,withbothAxBandpureA(fromcrossesbetweenAplantsandsomeAplantself-pollinations).Likewise,theseedinlotBcon-tainsbothBxAandpureB.Inplantbreeding,youdenotethepedigreeofthecrossbyputtingthema-ternalparentfirstandthepaternalparentsecond,henceAxBdenotesAasthematernalseedparentandBasthepaternalpollenparent.

Inthesecondyear,seedfromthetwolotswillbeplantedintoseparatebeds,preferablyintworeplications(twobedsofeach).Thelotsarekeptseparate,astherecanbeaphenotypicdifferencebetweentherootsofthereciprocalhybridcrosses:AxBandBxA.Whilethereisnoeasygeneticexplanationforthis,inrarecasestherecanbeadiscernabledifferencebetweenthereciprocalhy-brids.Whenharvestingrootsattheendofthefirstseason,evaluatethetwopopulationsforgeneralperformanceandrootshape.Ifitisobviouswhichpopulationissuperiorinperformance,makethis


onepopulationthebreedingpopulationanddis-cardtheothers.Otherwise,thehybridrootsfrombothcanbeselectedandcombined.Uponfurtherevaluation,thedifferencebetweenthehybridroots(AxBandBxA)andthepureroots(AxAandBxB)willbecomeobvious.Therootsthathaveresultedfromcross-pollinationareoftendifferentinseveralways,especiallyifthephenotypicdiffer-enceofthetwoparentsispronounced.Ingeneral,thehybridrootswilloftendemonstrateamarkedincreaseinvigorwithincreasedrootand/ortopsize.Thehybridsmayalsoexhibitamarkeddif-ferenceinshapeorcolor,aswellasanobvioushybridshapethatisintermediatebetweenthetwoparents.Incontrasttohybridrootsresultingfromcrossesbetweenthetwoparents,purerootsresult-ingfromself-orsiblingpollinationswillbepheno-typicallysimilartotheoriginalparentalmaterial.Theobvioushybridrootsshouldbeselectedandsavedforthenextphaseofthebreedingprogram.

Mass selectionOnceyouhavecreatedabreedingpopulationthroughcontrolledpollinationortheuseofastraincross,thenextstepistobeginselection.Mass selectionincarrotscanbedonefollowingthebasicprinciplesoutlinedinOSA’sIntroduction to On-Farm Organic Plant Breeding.Selectionbeginsbyproducingthecropunderuniformfieldcondi-tionsandwiththeuseofgriddedselectiontoselectevenlyacrossthebreedingpopulation.Fortunately,inbiennialrootcrops,itispossibletogrowtherootstofullvegetablematurityandthenselectthedesiredphenotypebeforereplantingfortherepro-ductivephaseofthelifecycle.Onlythedesired,se-lectedplantswillcross-pollinatetocontributetheirgenestothenextbreedingcycle.Youcanalsoselectplantsastheyre-growfoliageandformflowersintheirsecondseason.Abnormalitiesintheforma-tionanddevelopmentofumbelsandflowerstruc-turesaremorecommonthanmanycarrotgrowersrealize.Theseabnormalitiesshouldbeeliminatedwhenobvious,preferablybeforetheonsetofpol-lination.Selectingbeforepollinationincreasestheefficiencyofmassselection.Selectingforhealthy,reproductivefeaturesandbountifulseedproduc-tionisanimportantandoftenforgottenpartofthebreedingprocess.Whenpracticingmassselectionincarrots,maintainaslargeofapopulationaspos-sible,savingseedfromatleast100to120healthy

plantsineachbreedingcycle.

Family selectionFamily selectioncanbeusedtomakerapidgainsinbreedingcross-pollinatedspecies,andcarrotsarenoexception.RefertoOSA’sIntroduction to On-Farm Organic Plant Breedingforthebasicconceptsoffamilyselectionincross-pollinatedcrops.Thebreedingmethoddescribedhereforcarrotsishalf-sibling(half-sib)familyselection.Anothermethodistousepollinationbagstomakeaseriesofself-pollinationsonindividualplantswithflies,whichwouldmakeself-pollinated,orS1,families.

Ahalf-sibfamilyisproducedbysavingseedfromasinglecarrotplantthathasbeenopenlypollinatedbyotherplantsofaselectedpopulation.Theseedfromthissingleplantallsharethesamemother,whilethepaternalinheritancemaycomeviapollenfromanyoftheotherplantsinthepopulation.Bysystematicallyselectinghalf-sibfamiliesforseveralgenerations,youcanretainfavorabletraitswhileavoidingsevereinbreeding.

Breeding timelineThefollowingtimelineisbasedonOSA’sapproachtobreedingcross-pollinatedcropsusingpopula-tionimprovementviatwoapproaches:family selectionandmass selection.Thefamilyselectionmethodisanalternativetothepedigreebreedingusedinmostmoderncarrotbreedingprograms.Sincecarrotsareabiennialcrop,eachbreedingcycleinthistimelinetakestwogrowingseasonstocomplete.Abreedingcycleisasinglegenerationinthereproductivelifecycle.

Year 1Root year – Cycle 1:Determineyourbreedingobjec-tivesandevaluatepotentialparentsorbreedingpopulations.Yourpreliminaryinvestigationintowhichcarrotvarietiesarebestsuitedaspotentialparentstomeetyourbreedinggoals,aswellaswhichvarietiesareadaptedtoyourenvironmentandproductionneeds,istimewell-spent,especiallywhenconductingameaningfultrial.Thisprelimi-narystepisveryimportant,especiallyifyoucanidentifyanexistingpopulationwithdesiredchar-acteristicstoselectfromortwoparentsthatarephenotypicallysimilarbuthavedifferentdesirabletraits.Eitherofthesecaseswillusuallysavetime


whenperformingon-farmbreedingwithabien-nialcrop.Ifgoodparentalmaterialisidentifiedinatrial,itcanbeusedasasourceforrootsofthese-lectedparentsandallowedtoflowerandintermateinthesecondyear.Inordertopotentiallyusetrialrootsattheoutsetofabreedingproject,producealargeenoughpopulationofeachaccessioninthetrialtoselectandharvestatleast60to80rootsfromtouseasparents.Whileonly20to30rootsareneededtoperformastraincrossinthesecondyear,itisimportanttostoreatleasttwiceasmanyrootsasyoupredictwillbeneeded,sinceaper-centageofstoredrootswillrotorbeginsproutingexcessivesecondaryroots.Selectedrootsshouldbehealthyandundamagedwithminimaltolittlesproutingwhenexaminedthefollowingspring.Rootsthathaven’tsprouted,andthatappearingoodcondition(freeofdamage,injury,ordisease),canbegoodbreedingstockwhendevelopingcarrotvarietiestomarketafterlong-termstorage.

Year 2Flower year – Cycle 1:Inthissecondseasonofthefirstbreedingcycle,youwillplantatleast20to30parentalrootsofeachvarietyafterafinalselectionfortheirstorability.FollowthestepsformakingastraincrossdescribedintheMaking the cross-pollinationsection.Atseedmaturity,harvestseedfromthetworowsseparatelyintotwoseparatebagsmarkedappropriately:AxBorBxA.

Year 3Root year – Cycle 2: Seedharvestedfromthetwoseparateparentalrowsinyear2shouldbesownintoseparaterowsandgrowntovegetablematu-rityforevaluation.Evaluateboththefoliarcharac-teristicsandtherootsofbothrowsatfullmaturity.Ifthereciprocalhybridsaresimilarinallcharac-teristics,combinethemintoasinglepopulation.Iftherearediscernabledifferencesbetweenthetwopopulations,choosethesuperiorpopulationforselectionanddiscardtheother.Eachoftheserowswillproducetwobasictypesofroots:thosethatareobvioushybridsbetweenthetwoparents,andthosethatarerecognizableastheparentaltype(seeStrain crosssectionabove).Selectasmanyhealthyhybridroots(atleast100ifpossible)forstorageandreplantinginyear4.

Year 4Flower year – Cycle 2:Afterstorage,selectatleast40to60ofthehealthiestrootsinspring.Planttheserootsassoonasspringconditionsstabilizeandthereisnothreatofhardfrosts.Planttheserootsinanopen,isolatedfieldatleastonemilefromotherfloweringcarrotsorQueenAnne’sLace.Alternatively,planttheserootsinameshisolationtentwithintroducedpollinatinginsects.Theplantsarethenallowedtofreelyintermate(openlypol-linate).Plantsshouldbeevaluatedregularlyastheycometofullflowerforanyabnormalitiesintheirgrowthorreproductivetraits.Carrotplantswillof-tenproduceasmallpercentageoffloweringplantswithobviousdeleterioustraits,suchasleavesoriginatinginumbelsorumbelsborneonjointedflowerstalks,andtheseneedtobeeliminated.

Mass selection:Atthispoint,ifyouprefertoonlypracticemassselection,harvestseedattheendoftheseasonfromallhealthyplantswithoutobviousflawsasa“balancedbulk.”Thismeansthatarough-lyequalquantityofseedisharvestedfromeachplantinthepopulationandiscleanedandmixedtogetherintoone“bulked”population.

Family selection:Attheendoftheseason,harvestseedfromallremaininghealthyplantswithoutobviousflaws,andthencleanandbagseparately.Eachoftheresultingseedpacketswillcontainseed

Strain cross hybrid progeny: Pictured here are six hybrid roots from a strain cross, flanked by the two parents of the cross. The six hybrid roots in the middle exhibit a phenotype that is intermediate between the parents. The hybrid roots also demonstrated notable vigor in their foliar growth in the field. Interestingly, the hybrid roots are obviously later in their root maturity as a vegetable crop.

How to Breed Carrots for Organic Agriculture www.seedalliance.org�0

thatarelargelytheresultofsiblingmatingandeachisconsideredahalf-sibling(half-sib)fam-ily.Therewillalsobeapercentageofseedineachhalf-sibfamilypacketthatistheresultofself-polli-nationofthatplant.Theseseedpacketsarenum-beredsequentially.

Year 5Root year – Cycle 3: seespecificsformassselectionandfamilyselectionasfollows.

Mass selection:Plantseedofthebulkedpopula-tionintouniformfieldconditions,payingattentiontosoiltype,fertility,andirrigation.Plantalargeenoughplottoproduceatleast1,000to1,200car-rots.Inmassselectionofarootcroplikecarrots,alargepopulationofatleast1,000rootsprovidesforgoodselectionopportunities.Growthecroptothestageofvegetablematuritythatfitsthemarketyouareaddressinginyourbreeding.HarvestandselectthecropforbothrootandfoliarcharacteristicsusingthegriddedselectiontechniquedescribedinOSA’s Introduction to On-Farm Organic Plant Breed-ing.Storeatleast200to300well-selectedroots.

Family selection:Planttheseedofthese40to60familiesintoshortrows(6to9ft/2to3m)inthefashionofareplicatedtrial,withatleasttworan-domizedreplicationspreferred.Theseprogenyrowscanbeevaluatedforalloftheimportantfoliartraits,fromseedlingvigor,canopydevelopment,andfoliardiseaseresistancethroughoutthesea-son.Atrootharvest,evaluateallroottraits.Themostpromisingfamilieswillexhibitsuperiortraitsinamajorityoftheroots(atleast60to65%)foranumberofthebreedinggoals.Thisisoftenonlyafractionofthehalf-sibfamiliesthatareoriginallyproducedinthepreviousyear.Inourexperience,thiswillbeabout20to25%ofthefamilies,or4to5familiesforevery20familiesproduced.Thebestrootsfromthesesuperiorfamiliesarethenselectedaftereliminatingatleast25to35%ofthe“less-than-ideal”roots.Selectedrootsfromthesuperiorfamiliesarethenstoredinindividualfamilybagsforcontinuedselectionandbreedinginyear6.

Year 6 Flower year – Cycle 3: seespecificsformassselec-tionandfamilyselectionasfollows.

Mass selection:Evaluatetherootsfortheirstorabil-ityandselectthebest150to200rootsforreplant-inginisolation.Selectrootsthathavesomecom-binationofthetraitsofinterest,butknowthatyouwillprobablynotfindalargepercentageofrootsthathaveallornearlyallofthetraitsyouaretryingtoisolateinyourdesiredideotype.Plantsshouldalsobeevaluatedforanyfoliarorfloweringabnor-malities.Eliminatetheseplantsbeforepollinationoccurs.Harvestseedatseedmaturityasabalancedbulkasyoudidinyear4.

Family selection:Thestoredrootsfromthesupe-riorselectedfamiliesinyear5areplantedinanopenfieldinindividualfamilyrows.Asbefore,dur-ingflowering,eliminateanyindividualsfromthesefamiliesthatexhibitaberrantreproductivegrowth.Ifafamilyhasalargepercentageofplantswithaberrantfoliarorreproductivegrowth,eliminatetheentirefamilyrow.Allowallhealthyfamiliestoopenlypollinateusingnativeorintroducedpollina-tors.Attheendoftheseason,harvest,cleanseedfromeachofthesefamiliesseparately.

Year 7Root year – Cycle 4:Atthispointyouwillessentiallyrepeattheprocedurefollowedinyears5and6forbothmassselectionandfamilyselection.

Mass selection: Plantthebulkedpopulationagainasyoudidinyear5withatleast1,000rootsforselection.Thecropproducedthisyearshouldhaveahigherpercentageofrootsthatexhibitcharacter-isticsyouaretryingtocombinethroughselection.Selectandstoreatleast200oftheserootsasyoudidinyear5.

Family selection:Repeattheprocedureofyear5byevaluatingtheselectedsuperiorfamiliesfromthepreviouscyclebasedonfoliarandrootcharacteris-tics.Apredictableoutcomeatthispointinhalf-sibfamilyselectionistofindonly1or2familiesfromtheapproximately4or5selectedfamiliesthatareworthyofcontinuedbreeding.Thisisespeciallytrueifthephenotypesoftheparentsaresimilarasdiscussedbelow.Asthefamiliesarenarroweratthispoint,youcanincreasetheselectionpressureyouapplytotherootsoftheselectedfamilies.Iffamilyselectionrevealsthatonefamilyisclearlysuperior,selectingfromthispointforwardwill

How to Breed Carrots for Organic Agriculture www.seedalliance.org��

bethesameasisusedinmassselection.Ifselect-ingdowntoonefamily,retainatleast100to150rootsbeforeproceeding.Iftwoormorefamiliesareworthyofselection,proceedasinyear5bystoringrootsoftheselectedfamiliesseparately.Fortwoormorefamilies,storeatleast80to100rootsforfloweringinthenextyear.

Year 8 Flower year – Cycle 4:Repeattheprocedureforseedproductionoftheselectedrootsasinyear6forbothmassselectionandfamilyselection.Ifyouhaveselecteddowntoasinglehalf-sibfamilyusingfamilyselectioninthiscycle,harvestseedasabal-ancedbulkandproceedtothenextcycle.Practicemassselectionwiththisfamily.

Year 9 and 10 (and beyond)Ifpracticingmassselection,continueasintheprevioustwo-yearcyclesuntilyouhaveachievedadegreeofuniformityinthepopulationthatmeetsyourneeds.Infamilyselectionyouwillhaveeas-ilynarrowedyourchoicetoasinglehalf-sibfam-ilybynow,ifnotbefore.Witheithermethod,youmaynowhaveausefulOPpopulationthatservesasauniquecarrotvariety.Besuretomaintainthepopulationbygrowingatleast100to200rootseachcycleandselectingatleast100to150rootsforseedproductionforsubsequentgenerations.Vigilantselectionpressureisneededtomaintainahigh-qualityOPvariety.

Breeding summaryThenumberofbreedingcyclesdependson1)howsimilarthetwoparentsare,and2)thedegreeofuniformityyouneedforyourproductionand/ormarketdemands.Inthefirstinstance,themoresimilartheparentalphenotypes,thefasteryoumaybeabletoattainuniformityinrelativelyfewbreed-ingcycles.Conversely,themoredissimilartheparentalphenotypesare,themorebreedingcyclesyoumayneedtoattainadistinct,uniformpheno-type.Thesetwo-yearcyclesmustberepeateduntilthedesiredphenotypeisattained.

Plantbreedersofopen-pollinatedvarietiesareal-waysfacedwiththechallengeofhowuniformava-rietymustbetomeetthestandardsofthemarket.TheplantbreederandeducatorR.W.Allardstatesthat,“truenesstotypeinanopen-pollinatedpopu-

lationisastatisticalfeatureofthepopulationasawhole;itisnotacharacteristicofindividualplants”(Allard,1999).Inotherwords,breedersmustmakeavaluejudgmentonthenumberofcyclesneededtoattainthedegreeofuniformityrequiredfortheirmarketorproductionsystem.Atthepointwherethepopulationproducedthroughthisprocesshassufficientuniformityforthemostimportantpro-ductionandmarkettraits,withsomedegreeofin-herentvariationforinsignificanttraits,thevarietymaybeacceptableforrelease.Thebetteryouknowyourpotentialmarket,thebetteryourchancesofknowingwhenthebreedingpopulationisaccept-ableinthemarketplace.

Seedling vigorcanberatedasthesizeoftheseed-lings,eitherbyratingtheheightaloneorbyratingboththeheightandwidthtogetheratasetnumberofdaysaftertheplantingdate.Werateseedlingvigorat15and30daysinordertoevaluateinthefirsthalfoftheseason.Theseratingsreflectthedaystogerminationandthespecificsoftheplant-ingdepthandotherenvironmentalchallenges.

Canopy development canbemeasuredbytrackingtherateofgrowthofbothheightandwidthofthecanopyanditsrelationshipwithweedcompeti-tiveness.Therateofdevelopment,andsizeoftheoverallcarrotleafcanopyfromearlyintheseasonuntilfinalharvest,mayhaveamarkedeffectonthecrop’sabilitytocompetewithweedsinor-ganicsystems.

Thematurityismeasuredinthenumberofdaysfromplantinguntiltheroothasfilledoutitsfullshape,includingfillingoutthetipoftheroot(tipfill)andachievingitsfullmarketablesizeandweight.

Top attachmentisasubjectivemeasurementbasedonhowwellthepetiolesareattachedtothecrownoftheroot.Thisisanimportanttraitwhenevaluat-ingprospectivefreshmarketbunchingtypes,andisimportantforanumberofdifferentmechani-calharvestersusedforcarrots.Thetraitisoftengaugedundertherealworldchallengesofbunch-ingorharvestingthecrop.

Disease resistance,includingAlternarialeafblight,Alternariacrownrot,AsterYellows,Bacterialblight,Cavityspot(Pythiumsp.),Cercosperaleaf


blight,andRoot-knotnematodes(Meloidogynespp.).Thesearepathogenspeciesforwhichselec-tionforresistanceunderfieldconditionshasbeendemonstratedtobeeffective.

Color(orange,yellow,purple,andredtypes)isbasedoninheritedmajorgenesthatcontrolpig-menttypesincarrots.Thewhiterootcolor,whichisduetotheabsenceofpigment,issimplyinher-itedanddominanttothepigmentedtypes,henceeasilyeliminatedinthegenerationafteranerrantcrosswithQueenAnne’sLaceoccurs.Allofthepig-mentedtypeshaveothergeneticfactorsthatcangreatlyenhancetheintensityofthecolor.Enhanc-ingcolorisachievedthroughrepeatedselectionandinter-matingofhighcolormaterialasintensityofcolorisaquantitative trait.

Core coloristhecolorofthexylemtissueoftheroot.Oldercarrotvarietiesoftenhavecoresthathaveadifferentcolorthanthepredominantphloemcoloroftheroot.Thexylemcanalsoexhibitlesspigmentationthanthephloemwhentheyareofthesamerootcolor.Palerxylem(core)colorcansometimesbepredictedwiththeobser-vationofpale-coloredstorageroottips(tails),butanaccurateassessmentofxylemcolorcanonlybedonewellbycuttingthetipoftherootofftoviewinteriorcolor.Thispracticedoesnotinterferewithseedproduction,sincealltheplantreproduc-tiveorgansarederivedfromgrowingpointsinthecrownofthecarrot.

Root shaperequiresselectingforthegeneraltaperoftheroot,whichisbasedonthediameterattheshoulderrelativetothediameteratthetiporbot-tomoftheroot.Selectingforastrong“blunting”orfillingoftheroottiphelpstoenforceashifttoalesspronouncedroottaper.

Root tip fill isoftenusedasanindicationthatacarrothasreachedamarketablesize.Selectingfor“earlyblunting”iscommoninalmostallmoderncarrotvarietiestogivegrowersmoreflexibilitywithharvestdates.

Root smoothnessismostassociatedwiththeprominenceanddepthofthelateralsecondaryrootscars,whicharepresentalongtheentirelengthoncarrots.Whentheserootscarsareprominent,it

makestherootappeartoberibbedandroughasopposedtosmoothandsleek.

Flavorincarrotsisquitecomplex,withalargenumberofvolatileflavorcompounds,mostlyterpenoids,givingcarrotstheircharacteristicflavor.Whenterpenoidsareinafavorablebal-ance,therootshaveapleasant“carroty”flavor.Ifterpenoidsaretooprominent,thecarrotcantaste“harsh,”sometimesdescribedassoapy,piney,oroverlyfloral.Flavorisratedasasubjectivetraitwithtrainedtastersandshouldbeconsideredseparatelyfromsweetness.Therecanbelargedif-ferencesbetweentastersintheirabilitytoper-ceivetheharshflavorsincarrots.

Sweetnessisaprominentpartofcarrotflavorandisusuallyevaluatedbybreedersasaseparatecompo-nentofoverallflavorduringtasteevaluations.

Succulence or textureisanimportantcomponentofcarroteatingquality.Consumersprefercarrotsthataresucculent,tender,andjuicyratherthanoverlyhard,tough,orsoft.Onenegativeproductionattributethatcanaccompanysucculentcarrotsisagreatertendencyforrootstobreakorcrack.Whilebreedingcarrotsformoresweetnessorlessharsh-nesshasnotbeenfoundtohaveanyaccompanyingnegativeproductionattributes,breedingformore

Blunting of carrot roots: These ‘Rumba’ carrot roots exhibit different degrees of “blunting” or root tip fill, which is the rounding of the root tips that occurs in some variet-ies as the crop matures. Note that the third root from the right has the most well filled tip of these roots.


succulencecanintroduceproductionchallenges.Storability of rootsisdonebybringingcarrotsoutofstorageatregularintervalsduringtheoff-seasontoevaluatetherootsfortheirfirmnessandabilitytoresistrotandnotsproutlateralrootsorshoots.Rootscanalsobeevaluatedforflavorandsweet-nessatthesesameintervals.

GlossaryAnther:male,pollen-bearingstructuresoftheflower.

Biennial:thetypeofplantthatnormallyproducesonlyvegetativegrowththefirstgrowingseason,overwinters,andthenproducesaseedcropafterwhichtheplantdies.Theplantrequirestwogrow-ingseasonstocompleteitslifecycle.

Cytoplasm: thecontentsofacellbetweenthenucleusandthecellwall.Inreproduction,thecytoplasmicconstituentsfromthefemalepar-entbecomepartofthecytoplasmoftheoffspring.Theremaybeatransferoftraitsdeterminedbyorganellescontainedinthecytoplasmnotassoci-atedwithchromosomeswithinthenucleus.

Cytoplasmic male sterility (CMS): Sterilityofthemalereproductiveorgansthatisunderextra-nucleargeneticcontrol,usuallygeneticmaterialinmitochondriaorchloroplastorganelles.Thissteril-ityisinheritedmaternally.Itoccursnaturallyinmanyspeciesandhasbeenidentifiedinwellover100cropspecies,includingcarrots.

Family:agroupofgeneticallyrelatedplants.Oftenthenatureoftherelationshipisspecified.Asexamples,seehalf-sib families, full-sib families,andS1 families.

Family selection:selectingindividualplantsorfam-iliesbasedontheoverallperformanceofafamily.

Feral:adomesticatedspeciesthathasrevertedtoawildoruntamedstate.

Full-sib family:afamilystructurewhereplantsinafamilysharethesamemotherandthesamefather.

Genotype:thegeneticcompositionoftheplant.

Germplasm: theentirecollectionofgeneticmate-rialforanygivencropspecies.

Half-sib family:afamilystructurewheretheplantsinafamilysharethesamemother.

Hybrid:theproductofacrossbetweengeneticallydistinctparents.


Hybrid vigor:theincreaseinvigorofhybridsovertheirparentaltypes,alsoknownasheterosis.

Ideotype:torthepurposesofthistext,animag-inedcropvarietyrepresentingtheidealtobereachedthroughabreedingproject.

Inbred:avarietyproducedbysuccessiveinbreed-ingoveranumberofgenerations.Alsocalledaninbredline.

Inbreeding depression:thedecreaseinavariety’sfitnessduetoinbreeding.

Inflorescence:thearrangementofplantflowers,suchasumbel,raceme,spike,tassel,andpanicle.

Male sterility:aninheritedfactorusefulinhybridseedproduction.Itpreventsviablepollenfrombeingproduced.

Mass selection:aformofselectionwhereindi-vidualplantsareselectedbasedontheirindi-vidualperformance.

Nuclear restorer genes:thesearenucleargenesthatcanrestorefertilityinplantswithcytoplas-micmalesterility(CMS).ThesegenesareusuallydominantintheirexpressionandwhenpresentwillrestoremalefertilitytoplantswithCMS.ThesegenesareoftenabundantinwildpopulationsofplantswithnaturallyoccurringCMS.

Open-pollinated:seedproducedasaresultofnaturalpollinationasopposedtohybridseedpro-ducedasaresultofacontrolledpollination.AlsocalledanOP.

Phenotype: theobservable,outwardappearanceofacrop.

Phloem:thevasculartissueinplantsthattrans-portssugarsandothermetabolitesfromthephoto-synthetictissuetotherestoftheplant.Incarrots,thephloemconstitutesthetissuesurroundingthecentralcoreoftheedibleroot.

Polygenic trait:relatingtoorcontrolledbymul-tiplegenes.

Protandry: thereproductivestateofaflower-ingplantwherethemalereproductiveorgansorantherscometomaturitybeforethefemaleflow-eringparts.

Reciprocal cross:twomirroredcrossesmadebetweenasinglesetofparentswhereeachparentservesasboththefemaleandthemale.

Quantitative trait:synonymouswithpolygenictrait(seepolygenic).

S1 family:afamilystructurewheretheplantsinthefamilyallresultedfromthesameself-pollination.

Stigma:theupperpartofthepistilthatreceivesthepollen.

Strain:atermusedbybreedersthatisessentiallytheequivalentofavariety,althoughstrainisalsousedtodescribeaspecificvariantofavarietythatisslightlydifferentfromtheoriginalvarietyinitsphenotypeoradaptation.

Strain cross:atermusedbybreederstospecifyacrossbetweentwodifferentvarietiesorstrainsofacropwheremultipleindividualsofbothstrainsareusedtocreatethebreedingpopulation.

Variety:agroupofplantsofaparticularspeciesthatsharesasetofcharacteristicsortraitsthatdif-ferentiatesitfromothervarietiesofthesamecrop.Thesecharacteristicsmustbedistinctandrela-tivelyuniformacrossalloftheplantsofthevariety.Varietyisasynonymforcultivar.

Vernalization:theexposuretocertainconditionsofcoldtemperatureandphotoperiodtoseedandyoungplants,whichpromotesfloralinductionwithoutdevelopmentoftheplant.

Xylem:thevasculartissueinplantsthattransportswateranddissolvednutrientsfromtheroottoallpartsoftheplant.Incarrots,thexylemconstitutesthecentralcoreoftheedibleroot.


References and ResourcesAllard,R.W.1999.Breedinghybridvarietiesofoutcrossingplants,pgs.198-199.Principles of Plant Breeding,2ndEd.JohnWileyandSons.NewYork.

Colley,M.R.andJ.R.Myers.2007.On-farm Variety Trials: A Guide for Organic Vegetable, Herb, and Flower Producers.OrganicSeedAlliance,PortTownsend,WA.

Navazio,J.P.,M.R.Colley,andJ.Reiten.2010.Princi-ples and Practices of Organic Carrot Seed Production in the Pacific Northwest.OrganicSeedAlliance,PortTownsend,WA.

Zystro,J.andJ.P.Navazio.2014.Introduction to On-farm Organic Plant Breeding.OrganicSeedAlliance.PortTownsend,WA.


AuthorsCompleted 20��John Navazio, Organic Seed AlliancePictures courtesy of John Navazio (OSA) and Laurie McKenzie (OSA) unless otherwise noted

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How to Breed Carrots for Organic · PDF fileHow to Breed Carrots for Organic Agriculture ... Mating systems for seed production ... are covered in Principles and Practices of Organic