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How to Breed Carrots for Organic Agriculture

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Four new resources from Organic Seed Alliance (OSA), developed and produced with funding from OFRF and Clif Bar Family Foundation’s Seed Matters initiative, provide a wealth of information for farmers who want to learn the art and craft of plant breeding. The comprehensive manuals walk farmers through the methods of breeding new crop varieties on the farm. - See more at: http://ofrf.org/blogs/new-tools-organic-farmers-teach-diy-plant-breeding#sthash.clHAu7FF.dpuf
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  • 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

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org3

    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.InOrganicSeedAlliances(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

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

    CanopydevelopmentandweedcompetitivenessMaturityslotTopattachmentDiseaseresistanceColorintensityCorecolorRootshapeRoottipfillFlavorSweetnessHarshnessStorability

    Germplasmisacollectionofgeneticresourcesinaspecies,andistherawmaterialthataplantbreederusestodevelopnewvarieties.Breedersof-tenusethetermgermplasmtorefertosub-groupsoftheentiregermplasmthatexistsforacrop.Forinstance,carrotbreedersrefertothepurplecar-rotgermplasmortheAlternariablightresistantgermplasmasawaytospecifythecropsbreedingmaterialusedintheirwork.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

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

    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

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org6

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

    Whengoodbreedingmaterialhasbeenidenti-fied,mostbreederswillmakeanumberofcrosses,incorporatingseveraldifferentcombinationsofthebestmaterialavailable.Initialcross-pollinationsareoftenmadeinagreenhousebetweensingleplantsinsmallmuslinorperforatedplasticpollina-tionpillowtubesthatcovertheflowersofthetwoplants.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.

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org7

    mostfarmersarenotwillingtomanageanumberofcrosses.Inmostfarmer-ledbreedingprojects,thegoalisusuallytocreateafinishedvarietybyperformingonlyoneortwocrossesbetweentwowell-chosenparents.

    Inordertocapturemoreofthegeneticvariationfromtheinitialcrossbetweenanytwoparents,werecommendatechniqueusedbyforagebreed-ersknownasastrain cross.Astraincrossisthecrossingoftwosmallpopulationsofthechosenparentvarieties.Tousethistechnique,selectanumberofcarrotrootsfromeachofthetwoparen-talpopulations.Theadvantageoffarmerbreedersusingastraincrossisthatbyusinganumberofse-lectedindividualsfromeachofthetwoparentsyouarecapturingagreaternumberofpossiblegeneticcombinationsfromtheoverallgeneticbreadthofbothparents.Straincrossescanbedoneinasmall,meshpollinationcageorinanopenfieldifisolatedfromotherfloweringcarrotsorferalQueenAnnesLace(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

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org8

    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 selectionincarrotscanbedonefollowingthebasicprinciplesoutlinedinOSAsIntroduction 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.RefertoOSAsIntroduction 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 timelineThefollowingtimelineisbasedonOSAsapproachtobreedingcross-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

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org9

    whenperformingon-farmbreedingwithabien-nialcrop.Ifgoodparentalmaterialisidentifiedinatrial,itcanbeusedasasourceforrootsofthese-lectedparentsandallowedtoflowerandintermateinthesecondyear.Inordertopotentiallyusetrialrootsattheoutsetofabreedingproject,producealargeenoughpopulationofeachaccessioninthetrialtoselectandharvestatleast60to80rootsfromtouseasparents.Whileonly20to30rootsareneededtoperformastraincrossinthesecondyear,itisimportanttostoreatleasttwiceasmanyrootsasyoupredictwillbeneeded,sinceaper-centageofstoredrootswillrotorbeginsproutingexcessivesecondaryroots.Selectedrootsshouldbehealthyandundamagedwithminimaltolittlesproutingwhenexaminedthefollowingspring.Rootsthathaventsprouted,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,isolatedfieldatleastonemilefromotherfloweringcarrotsorQueenAnnesLace.Alternatively,planttheserootsinameshisolationtentwithintroducedpollinatinginsects.Theplantsarethenallowedtofreelyintermate(openlypol-linate).Plantsshouldbeevaluatedregularlyastheycometofullflowerforanyabnormalitiesintheirgrowthorreproductivetraits.Carrotplantswillof-tenproduceasmallpercentageoffloweringplantswithobviousdeleterioustraits,suchasleavesoriginatinginumbelsorumbelsborneonjointedflowerstalks,andtheseneedtobeeliminated.

    Mass selection:Atthispoint,ifyouprefertoonlypracticemassselection,harvestseedattheendoftheseasonfromallhealthyplantswithoutobviousflawsasabalancedbulk.Thismeansthatarough-lyequalquantityofseedisharvestedfromeachplantinthepopulationandiscleanedandmixedtogetherintoonebulkedpopulation.

    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.org0

    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.HarvestandselectthecropforbothrootandfoliarcharacteristicsusingthegriddedselectiontechniquedescribedinOSAs 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%oftheless-than-idealroots.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,mayhaveamarkedeffectonthecropsabilitytocompetewithweedsinor-ganicsystems.

    Thematurityismeasuredinthenumberofdaysfromplantinguntiltheroothasfilledoutitsfullshape,includingfillingoutthetipoftheroot(tipfill)andachievingitsfullmarketablesizeandweight.

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

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

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

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

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

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

    Root shaperequiresselectingforthegeneraltaperoftheroot,whichisbasedonthediameterattheshoulderrelativetothediameteratthetiporbot-tomoftheroot.Selectingforastrongbluntingorfillingoftheroottiphelpstoenforceashifttoalesspronouncedroottaper.

    Root tip fill isoftenusedasanindicationthatacarrothasreachedamarketablesize.Selectingforearlybluntingiscommoninalmostallmoderncarrotvarietiestogivegrowersmoreflexibilitywithharvestdates.

    Root smoothnessismostassociatedwiththeprominenceanddepthofthelateralsecondaryrootscars,whicharepresentalongtheentirelengthoncarrots.Whentheserootscarsareprominent,it

    makestherootappeartoberibbedandroughasopposedtosmoothandsleek.

    Flavorincarrotsisquitecomplex,withalargenumberofvolatileflavorcompounds,mostlyterpenoids,givingcarrotstheircharacteristicflavor.Whenterpenoidsareinafavorablebal-ance,therootshaveapleasantcarrotyflavor.Ifterpenoidsaretooprominent,thecarrotcantasteharsh,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.

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org3

    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.

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

    Hybrid vigor:theincreaseinvigorofhybridsovertheirparentaltypes,alsoknownasheterosis.

    Ideotype:torthepurposesofthistext,animag-inedcropvarietyrepresentingtheidealtobereachedthroughabreedingproject.

    Inbred:avarietyproducedbysuccessiveinbreed-ingoveranumberofgenerations.Alsocalledaninbredline.

    Inbreeding depression:thedecreaseinavarietysfitnessduetoinbreeding.

    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.

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

    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.

  • How to Breed Carrots for Organic Agriculture www.seedalliance.org6

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

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