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REVIEWARTICLESomaclonalvariationsandtheirapplicationsinhorticulturalcropsimprovementHareKrishna1MahdiAlizadeh2DhurendraSingh1UdayvirSingh1NiteshChauhan1MalihehEftekhari2RadhaKishanSadh1Received:26August2015/Accepted:20October2015/Publishedonline:13February2016TheAuthor(s)2016.
ThisarticleispublishedwithopenaccessatSpringerlink.
comAbstractTheadvancementsmadeintissueculturetechniqueshasmadeitpossibletoregeneratevarioushorticulturalspeciesinvitroasmicropropagationprotocolsforcommercialscalemultiplicationareavailableforawiderangeofcrops.
Clonalpropagationandpreservationofelitegenotypes,selectedfortheirsuperiorcharacteris-tics,requirehighdegreeofgeneticuniformityamongsttheregeneratedplants.
However,planttissueculturemaygenerategeneticvariability,i.
e.
,somaclonalvariationsasaresultofgenemutationorchangesinepigeneticmarks.
Theoccurrenceofsubtlesomaclonalvariationisadraw-backforbothinvitrocloningaswellasgermplasmpreservation.
Therefore,itisofimmensesignicancetoassurethegeneticuniformityofinvitroraisedplantsatanearlystage.
Severalstrategieshavebeenfollowedtoascertainthegeneticdelityoftheinvitroraisedprogeniescomprisingmorpho-physiological,biochemical,cytologi-calandDNA-basedmolecularmarkersapproaches.
Somaclonalvariationcanposeaseriousprobleminanymicropropagationprogram,whereitishighlydesirabletoproducetrue-to-typeplantmaterial.
Ontheotherhand,somaclonalvariationhasprovidedanewandalternativetooltothebreedersforobtaininggeneticvariabilityrela-tivelyrapidlyandwithoutsophisticatedtechnologyinhorticulturalcrops,whichareeitherdifculttobreedorhavenarrowgeneticbase.
Inthepresentpaper,sourcesofvariationsinducedduringtissueculturecycleandstrategiestoascertainandconrmgeneticdelityinavarietyofinvitroraisedplantletsandpotentialapplicationofvariantsinhorticulturalcropimprovementarereviewed.
KeywordsMicropropagationSomaclonesOxidativestressEpigneticvariationMolecularmarkersCropimprovementIntroductionPlanttissueculturetechniquesprofferasubstitutemethodofvegetativepropagationofhorticulturalcrops(Krishnaetal.
2005;Alizadehetal.
2010).
Clonalpropagationthroughtissueculture(popularlyknownasmicropropaga-tion)canberealizedrelativelyrapidlywithinasmallspace(Krishnaetal.
2008;Eftekharietal.
2012).
Theuniformityofindividualplantswithinaclonepopulationisamajoradvantageofclonalcultivarsincommercialproduction(KrishnaandSingh2013).
However,geneticvariationsdooccurinundifferentiatedcells,isolatedprotoplasts,calli,tissuesandmorphologicaltraitsofinvitroraisedplants(Bairuetal.
2011;Curraisetal.
2013).
In1981,LarkinandScowkraftcoinedageneralterm''somaclonalvariation''forplantvariantsderivedfromanyformofcellortissuecultures.
Atpresent,micropropagatedplants,invariouscrops,suchasstrawberry,papaya,banana,grapes,pineapple,citrus,tomato,cucumber,watermelon,rhododendron,orchids,etc.
,arepreferredoverplantspropagatedthroughconventionalmeans.
However,eversincetherstformalreportofmorphologicalvariantsinsugarcaneplantspro-ducedinvitroin1971(HeinzeandMee1971),severalinstancesofsomaclonalvariationshavebeenreportedin&HareKrishnakishun@rediffmail.
com1ICAR-CentralInstituteforAridHorticulture,Beechwal,Bikaner,Rajasthan334006,India2DepartmentofHorticulture,FacultyofAgriculture,GorganUniversityofAgriculturalSciencesandNaturalResources(GUASNR),Golestan,Gorgan,Iran1233Biotech(2016)6:54DOI10.
1007/s13205-016-0389-7differenthorticulturalcrops.
Thenotableexamplecouldbebananainwhichoccurrenceofoff-typesfromtissuecul-turedplantletsrangedfrom6to38%inCavendishculti-vars(Sahijrametal.
2003);however,itcouldbeashighas90%(Smith1988).
Fromthepointofcommercialmicropropagation,variationofanykind,inparticular,geneticvariationsmaybeconsideredobstructiveandworthless;since,suchvariationsmayleadtolossofgeneticdelity.
However,plantcellandtissueculturesrenderincreasedgeneticvariabilitycomparativelyfasterandwithoutapplyingasophisticatedtechnology.
Thistech-nologyholdsamplescopeincropimprovementofhorti-culturalcrops,whicharelargelypropagatedvegetatively,partly,duetoreasonslikelongerjuvenilephaseasinperennialfruitcrops,occasionalinbreedingdepression,selfandcrossincompatibility,narrowgeneticbaseespeciallyinornamentals,etc.
Further,somaclonalvariationsrequirelessspaceandtimeforscreeningofdesirabletraitsinvitrounlikecrossseedlingsofperennialcrops,whichrequireagreatdealoflandareaandtime.
Somaclonesmayitselfhavenumerousapplicationsinplantbreedingandgeneticimprovementsandrecoveryofsuchnovelvariantscanbeenhancedbyapplyingsuitableinvitroselectionpressure(Jain2001;Lestari2006).
SourcesofvariationsdetectedinplanttissuecultureTissuecultureisanefcientmethodofclonalpropagation;however,theresultingregenerantsoftenhasanumberofsomaclonalvariations(LarkinandScowcroft1981).
Thesesomaclonalvariationsaremainlycausedbynewlygener-atedmutationsarisingfromtissuecultureprocess(Satoetal.
2011b).
Thetriggersofmutationsintissueculturehadbeenattributedtonumerousstressfactors,includingwounding,exposuretosterilantsduringsterilization,tissuebeingincomplete(protoplastsasanextremeexample),imbalancesofmediacomponentssuchashighconcentra-tionofplantgrowthregulators(auxinandcytokinins),sugarfromthenutrientmediumasareplacementofpho-tosynthesisintheleaves,lightingconditions,thedisturbedrelationshipbetweenhighhumidityandtranspiration(Joyceetal.
2003;Satoetal.
2011b;SmuldersanddeKlerk2011).
Muchofthevariabilityexpressedinmicropropagatedplantsmaybetheresultof,orrelatedto,oxidativestressdamageinicteduponplanttissuesduringinvitroculture(CassellsandCurry2001;Tanurdzicetal.
2008;NivasandDSouza2014).
Oxidativestressresultsinelevatedlevelsofpro-oxidantsorreactiveoxygenspecies(ROS)suchassuperoxide,hydrogenperoxide,hydroxyl,peroxylandalkoxylradicals.
TheseROSmayinvolveinalteredhyper-andhypo-methylationofDNA(Wacksman1997);changesinchromosomenumberfrompolyploidytoaneuploidy,chromosomestrandbreakage,chromosomerearrange-ments,andDNAbasedeletionsandsubstitutions(CzeneandHarms-Ringdahl1995),whichinturnmayleadtomutationsinplantcellsinvitro(Fig.
1).
SomaclonalvariationshowsasimilarspectrumofgeneticvariationtoinducedmutationasbothofthemresultinqualitativelyanalogousgamutofDNAchanges(Cassellsetal.
1998).
Differentfactorsaffectthefrequencyofdevelopmentofsomaclonesunderinvitroconditions.
Explant/explantsourceDifferencesinboththefrequencyandnatureofsomaclonalvariationmayoccurwhenregenerationisachievedfromdifferenttissuesources(Sahijrametal.
2003).
Highlydifferentiatedtissuessuchasroots,leaves,andstemsgenerallyproducemorevariationsthanexplantswithpre-existingmeristems,suchasaxillarybudsandshoottips(Duncan1997).
Ingeneral,theolderand/orthemorespecializedthetissueisusedforregeneration,thegreaterthechancesthatvariationwillberecoveredintheregen-eratedplants(Table1)asundersuchconditions,adventi-tiousshootregeneration(shootorganogenesis)takesplacefromatypicalpointsoforigindirectlyorindirectlythroughacallusstage(e.
g.
,fromleaves,petioles,shootinternodes,rootsegments,anthers,hypocotyls,cotyledons,etc.
;Pijutetal.
2012).
Somaclonalvariationcanalsoarisefromsomaticmutationsalreadypresentinthedonorplant,i.
e.
,presenceofchimerainexplants(Karp1994).
ModeofregenerationBothcultureinitiationandsubsequentsubcultureexposeexplantstooxidativestress(Krishnaetal.
2008),whichmayresultinmutations(CassellsandCurry2001).
Itseemsevidentthat'extreme'proceduressuchasprotoplastcul-tureandalsocallusformationimposestress(SmuldersanddeKlerk2011).
Magnitudeofthisstressdependsonthetissueculturetechnique.
Therefore,theproductionofplantsviaaxillarybranchingdoesnotnormallyresultintheproductionofvariants,whileculturesthatgothroughacallusphasearetheonesthattheoreticallypromoteahighermutationrate(Zayovaetal.
2010).
Investigationsindicatemorechromosomevariabilityinthecallusphasethaninadventitiousshoots(Saravananetal.
2011),indicatingalossofcompetenceinthemoreseriouslydisturbedgenomes.
Thiscouldbeexplainedbythedifferentgradeofdisturbancewithwhichthecellsareconfronted.
Intherstcase,cellsfollowapatternofdivisionwhichisthenormaloneinthedevelopingplant.
Ontheotherhand,callusformationimpliesa54Page2of183Biotech(2016)6:54123dedifferentiationphasefollowedbyuncontrolledcelldivisions(Vazquez2001).
Sometypesoftissueculturemimic,insomeaspects,otherstressfulsituationsas,forexample,protoplastpreparationinwhichcellwalldegra-dationresemblestheinfectiveprocessofsomepathogens.
Therefore,thetypeandmagnitudeofthestressimposedonculturedcellsvariesaccordingtothetechniqueused.
Incontrasttopopularbeliefthatthegrowthofunorganizedcallusisnecessaryforinductionofgeneticvariation,variabilitycouldbenoticedinplantsregeneratedfromexplantsadventitiously(Farahanietal.
2011;BhojwaniandDantu2013).
Sometimesforregenerationunderinvitroconditions,somaticembryogenesisisthepreferredpathwayforgen-eratingpropagules.
Ithasbeensuggestedthatregenerationviaembryogenesishasbetterchanceofobtaininggeneti-callyuniformplantsthanthroughorganogenicdifferenti-ation(Vazquez2001).
Thisisso,becauseDNAintheinitialstagesofdevelopmentinsomaticembryogenesiscontainslowerlevelsofmethylationthaninthelaterstages(Sahijrametal.
2003).
Variationininvitroculturesraisedthroughsomaticembryogenesishasbeenreportedinsev-eralhorticulturalcropslikehazelnut(Diaz-Salaetal.
1995),Citrusparadisi(Haoetal.
2004),oilpalm(Jaligotetal.
2004),rose(Xuetal.
2004),potato(Sharmaetal.
2007),grapevine(Schellenbaumetal.
2008),coffee(Menendez-Yuffaetal.
2010),olive(Levaetal.
2012),tamarillo(Curraisetal.
2013)andbrinjal(NaseerandMahmood2014).
EffectoflengthofcultureperiodandnumberofsubculturecyclesThelongeracultureismaintainedinvitro,thegreaterthesomaclonalvariationis(Kuznetsovaetal.
2006;Gaoetal.
2010;Farahanietal.
2011;Jevremovicetal.
2012;Sunetal.
2013).
VariantkaryotypesarefoundtoamasswithincreasingageofcallusandasaresultthechancesofFig.
1Mechanismofsomaclonalvariationinmicropropagatedplantsasaresultofoxidativeburstuponinvitroculture3Biotech(2016)6:54Page3of1854123Table1OccurrenceofsomaclonalvariationsasaffectedbythechoiceofexplantsS.
no.
CropspeciesExplants/explantssourcePresenceorabsenceofsomaclonalvariations(/-)References1Africanviolet(Saintpauliasp.
)LeafsegmentsMatsudaetal.
(2014)2Almond(Prunusdulcis)Axillarybranching-Martinsetal.
(2004)3Chimeric'Maricongo'bananaVegetativeandoralaxistipKrikorianetal.
(1993)Cavendishgroupofbananas(Musasp.
)ChimericshoottipIsraelietal.
(1995)Bananacv.
MartamanShoottip-Rayetal.
(2006)4Brinjal(Solanummelongena)Hypocotyl-MallayaandRavishankar(2013)Callusinductiononleaves,nodesandintermodalexplantsNaseerandMahmood(2014)5Chrysanthemum(Dendranthemagrandiora)CallusfromleavesandinternodesMilerandZalewska(2014)6Europeanviolet(ViolauliginosaBesser)LeafandpetiolefragmentsSlazaketal.
(2015)7Gerbera(GerberajamesoniiBolus)Capitulum-Bhatiaetal.
(2009,2011)8GloxiniaLeafexplantsHuandXu(2010)9HedychiumcoronariumKoen.
Axillarybudexplants-Paridaetal.
(2013)10Hop(HumuluslupulusL.
)Meristemtissue-Patzak(2003)11KaempferiagalangaBudsofrhizomes-Mohantyetal.
(2011)12Kiwifruit(Actinidiadeliciosa(Chev.
)LiangandFerguson)cv.
'Tomuri'LeafbladesandpetiolesPradoetal.
(2007)13Oilpalm(ElaeisguineensisJacq.
)MaturezygoticembryosRivaletal.
(2013)ImmaturezygoticembryoSanputawongandTe-chato(2011)ImmatureleavesLuciaetal.
(2011)14Papaya(CaricapapayaL.
)AxillaryshoottipsunderwentcryopreservationKaityetal.
(2009)15Patchouli(Pogostemonpatchouli)CallusinductiononinternodalandleafexplantsRavindraetal.
(2012)16Potato(Solanumtuberosum)CallusculturesofstemexplantThiemeandGriess(2005)CallusinductionviafreshsproutsMuniretal.
(2011)17Sweetcherry(Prunusavium)ShootapicalportionsPiagnaniandChiozzotto(2010)18RootstockMr.
S2/5,selectedfromahalf-sibprogenyfromPrunuscerasiferaErhrLeafMuleoetal.
(2006)19SwertiachirayitaAxillarymultiplication-JoshiandDhawan(2007)20Turmeric(CurcumalongaL.
)Latentaxillarybudsofrhizome-Nayaketal.
(2010)Axillarybudsofunsproutedrhizome-Pandaetal.
(2007)CallusculturesestablishedfromrhizomesegmentsKaretal.
(2014)21Vitisspp.
Nodalsegment-Alizadehetal.
(2008)54Page4of183Biotech(2016)6:54123variantplantsproducedduringsuccessivesubculturealsoincreases,ingeneral(Zayovaetal.
2010).
Furthermore,therapidmultiplicationofatissue,duringmicropropagation,mayaffectitsgeneticstability.
Khanetal.
(2011)reportedthataftertheeighthsubculture,thenumberofsomaclonalvariantsincreasedwithasimultaneousdecreaseinthemultiplicationrateofpropagulesinbanana.
Similarly,Clarindoetal.
(2012)suggestedalimitoflessthan4monthsstorageofcoffeecellaggregatesuspensionsfortrue-to-typemasspropagationasploidyinstabilitywasnoticedinlong-terminvitroculture.
SimilarlywhenFarahanietal.
(2011)raisedolivecultivars,underinvitroconditions,throughinternodecuttings,signicantdiffer-encewasobservedinmorphologicalcharactersamongtheregeneratedplantsafterseventhsubculture,whichwaslaterconrmedbyRAPDanalysis.
However,C-valueanalysisshowedthatnosignicantchangehasoccurredduringsubculturinginbotholivegenotypes.
Thisindicatesthatthegeneticchangesaccompaniedbysomaclonalvariationcouldbeduetothechangesinthenucleotidecontentofthegenome,probably,owingtomutations(insertions/dele-tions)andnotduetoquantitativechanges.
Notonlythenumberofsubculturebuttheirdurationalsocontributestoenhancingtherateofsomaclonalvari-ations,especiallycellsuspensionandcalluscultures(Bairuetal.
2006;Sunetal.
2013).
Studieshaveshownthatsomaclonalvariationismoreapparentinplantsregeneratedfromlong-termcultures(EtienneandBertrand2003).
Rivaletal.
(2013)noticedthatinvitroproliferationinducesDNAhypermethylationinatime-dependentfashionandchangesinDNAmethylationisinvolvedinmodulatingtheexpressionofembryogeniccapacityofoilpalmduringtissueculture.
CultureenvironmentExternalfactorslikegrowthregulators,temperature,light,osmolarityandagitationrateoftheculturemediumareknowntoinuencethecellcycleinvivoinplants,con-siderably,whichindicatesthatinadequatecontrolofcellcycleinvitroisoneofthecausesofsomaclonalvariation(Karp1994;NwauzomaandJaja2013).
Normalcellcyclecontrols,whichpreventcelldivisionbeforethecompletionofDNAreplication,arepresumedtobedisruptedbytissueculture,resultinginchromosomalbreakage(Phillipsetal.
1994).
Chromosomebreakageanditsconsequences(dele-tions,duplications,inversions,andtranslocations)causeaberrationsinvitro(Duncan1997).
Plantgrowthregulatorscanaffecttherateofsomaclonalvariationbothdirectlyandindirectlybyincreasingthemultiplicationrateandinduc-ingadventitiousshoots(Gaoetal.
2010).
AccordingtoD'Amato(1985),itcannotbeexcludedthatsomeplantgrowthregulators(PGRs)atcertainconcentrationsorincombinationwithothergrowthregulatorsand/orparticularconstituentsofaculturemedium,mayactasmutagens.
Severalgrowthregulators,suchas2,4-dichlorophenoxyaceticacid(2,4-D),naphthaleneaceticacid(NAA)andBAP(6-benzylaminopurine),syntheticphenylureaderiva-tives(4-CPPU,PBUand2,3-MDPU)havebeenmostfre-quentlyconsideredtoberesponsibleforgeneticvariability(Siragusaetal.
2007;Sunetal.
2013;SalesandButardo2014).
Prolongedcultivationinmediumcontaining2,4-DinuenceshigherDNAploidylevelsincalluscells(daSilvaandCarvalho2014).
Intheirexperimentwithbanana,SalesandButardo(2014)observedthatadditionofsyn-theticauxin2,4-Dinculturemediumledtohighlevelofmethylationevents,particularly,cytosinemethylationeitherattheinternalorexternalcytosineend,whichlargelyresultedinvariationsintissueculturedplants.
AlterationingenomicDNAmethylationrateisbeingattributedforthedevelopmentof'mantled'somaclonalvariantinoilpalm(Eeuwensetal.
2002;Jaligotetal.
2011).
Similarly,Arn-hold-Schmitt(1993)observedthatindole-3-aceticacid(IAA)andinositolinthegrowthmediuminducedDNArearrangementsandmethylationchangesincarrot(Daucuscarota)calluscultures.
Matsudaetal.
(2014)observedthatpercentageofsomaclonalvariationsdramaticallyincreasedwhenPGRs(0.
5ppmBAand0.
1ppmNAA)wereaddedtothemediuminoculatedwithleaf/leafsegmentsexplantsofAfricanviolet.
Kinetinhasbeenshowntocauseextensivehypomethy-lationofDNAinproliferatingculturesofcarrotrootexplantswithin2weeks(Arnhold-Schmitt1993),andaux-ins,includingNAA,havetheoppositeeffectandcausehypermethylation(LoSchiavoetal.
1989).
Moreover,thereisevidencethatdifferentialexpressioninchromatinremodelinggenesandhistonemethylationgeneshappensduringtissueculture,whichleadstodisruptioninthemethylationpathwayinanon-specicmannerandhypo/hypermethylationpatternsofDNAinducedintissueculture.
Thiscanbestabilizedandtransmittedtoplantsregeneratedfromthesecultures(Shearmanetal.
2013).
Notonlytheconcentration,butalsotheratioofdifferentgrowthregula-torsaffectstheoccurrenceofvariationsinvitro.
Eeuwensetal.
(2002)observedthat,ingeneral,arelativelyhighauxin/cytokininratioresultedinthelowestincidenceofvariant'mantled'oweringinoilpalm,whileusingmediasupplementedwithrelativelyhighcytokinins/auxinratioresultedinahighincidenceofmantledowering.
TheroleofcytokininwasfurtherconrmedbyOoietal.
(2013),whonoticedthatthemantledinorescencesofoilpalmcontainedhigherlevelsofcytokininslikeisopentenyladenine9-glu-cosideandlowerlevelsoftrans-zeatin9-glucoside,dihy-drozeatinriboside,anddihydrozeatinriboside50-monophosphatecomparedwithnormalinorescences.
3Biotech(2016)6:54Page5of1854123GenotypeandploidyThough,theinvitromorphogenesisseemstobehighlydependentonplantgrowthregulatorsandmediausedforculture,itisagaingenotypespecic(Alizadehetal.
2010;Eftekharietal.
2012).
Amongfactorsaffectingsomaclonalvariation,plantgenotypeisprobablythemostimportantdeterminantofvariation(Shenetal.
2007;Ticanetal.
2008;NwauzomaandJaja2013).
Earlier,Eeuwensetal.
(2002)characterizedoilpalmclonesaslow/moderateriskandhighriskwithregardto'mantle'owering(whereinantherprimordiainbothmaleandfemaleowersturnintoeshysupplementarycarpels),onthebasisofterminalinorescencedatageneratedunderinvitroconditions.
Clonesclassiedashighriskattheoutsetgaveasigni-cantlyhigherincidenceofmantledoweringintheeldthanlow/mediumriskclones,conrmingthatdataonter-minalinorescencesproducedinvitroallowseffectivescreeningofmaterialwithregardtotheriskofmantledowering.
Itislikelythatthisresultfromacombinationofdifferencesingenotypeanddifferencesinepigeneticallyinheritedchangesareinducedduringthepre-embryogenicstagesofthecultureprocess,i.
e.
,callusinitiationandmaintenance.
IdenticationofvariationintissuecultureBothgeneticandepigeneticalterationsareassociatedwithinvitropropagation,whichmayhavephenotypicconse-quences,andarecollectivelycalledsomaclonalvariation(LarkinandScowcroft1981;Guoetal.
2007).
Asaresult,somaclonalvariationischaracterizedbytheintricacyofthechanges,whichareexhibitedatvariouslevels,includingphenotypic,cytological,biochemicalandgenetic/epige-netic(Kaeppleretal.
2000).
Therefore,thestrategyforthedetectionofsomaclonesshouldbebasedonsuchmanifestations.
Awidevarietyoftoolsareavailableforthedetectionandcharacterizationofsomaclonalvariantswhichareprimarilybasedonthedifferencesinmorphologicaltraits(Perezetal.
2009,2011;Nhutetal.
2013),cytogeneticalanalysisforthedeterminationofnumericalandstructuralvariationinthechromosomes(Clarindoetal.
2012;Curraisetal.
2013;Abreuetal.
2014),biochemical(Vujovicetal.
2010;Karetal.
2014),molecularDNAmarkers(KrishnaandSingh2007;PathakandDhawan2012;Hossainetal.
2013;Bello-Belloetal.
2014)ortheircombinations(Horacˇeketal.
2013;Deyetal.
2015;Stanisˇicetal.
2015).
Thebesttestforassessingsomaclonalvariationistofruitouttheplantsandconductanextensivehorticulturalevaluation,whichisunfortunatelyalong-termendeavorwithwoodyfruitcrops,particularly(Grosseretal.
1996).
Everytoolhasitsownadvantagesandlimitationsinassessmentofthevariations(Table2),whichgoverntheiruseforrestrictedorlarge-scaleapplication.
Thechoiceoftechniqueforanygivenapplicationdependsuponthematerialusedandthenatureofthequestionbeingaddressed(Karp2000).
MolecularbasisofsomaclonalvariationHowasingleplantgenotypecanresultinavarietyofphenotypicoutcomesunderthesameinvitroculturecon-ditionsisstillfarfrombeingcompletelyunderstood.
Severalbasesforsomaclonalvariationhavebeenproposed,whichincludechangesinchromosomenumber(Mujibetal.
2007;Levaetal.
2012),pointmutations(D'Amato1985;Ngezahayoetal.
2007),somaticcrossingoverandsisterchromatidexchange(Duncan1997;Bairuetal.
2011),chromosomebreakageandrearrangement(CzeneandHarms-Ringdahl1995;Alvarezetal.
2010),somaticgenerearrangement,DNAamplication(Karp1995;Tiwarietal.
2013),changesinorganelleDNA(CassellsandCurry2001;Bartoszewskietal.
2007),DNAmethy-lation(Guoetal.
2007;Linaceroetal.
2011),epigeneticvariation(Kaeppleretal.
2000;Guoetal.
2006;SmuldersanddeKlerk2011),histonemodicationsandRNAinterference(MiguelandMarum2011),segregationofpre-existingchimeraltissue(BrarandJain1998;Vazquez2001;Ravindraetal.
2012;NwauzomaandJaja2013)andinsertionorexcisionoftransposableelements(Gupta1998;Satoetal.
2011b).
Inparticular,transposableelementsareoneofthecausesofgeneticrearrangementsininvitroculture(Hirochikaetal.
1996;Satoetal.
2011a).
Tissuecultureisreportedtoactivatesilenttransposableelements,resultinginsomaclonalvariations.
Insertionsoftransposableelementsandretrotransposonscanfunctionasinsertionalmutagensofplantgenomes,whereaswide-spreadactivationmayresultinawidegamutofchromo-somalrearrangements(Tanurdzicetal.
2008).
Inturn,theserearrangementscanleadtomisregulationofgenes,aneuploidyandnewtransposoninsertions(SmuldersanddeKlerk2011).
However,manyaspectsofthemechanisms,whichresultinsomaclonalvariations,remainundened.
Itistherefore,inevitabletoexplorethegenome-widechangethroughsequencingofwhole-genomeoftheconcernedcrop.
Next-generationsequencingtechnologyhasenabledthewhole-genomesequencingofindividualplants(Miyaoetal.
2012).
Anewgenerationofsequencingtechnologies,from54Page6of183Biotech(2016)6:54123Illumina/Solexa,ABI/SOLiD,454/Roche,andHelicos,hasprovidedunprecedentedopportunitiesforhigh-throughputfunctionalgenomicresearch(MorozovaandMarra2008;Metzker2010).
Somaclonalvariationsvis-a`-viscropimprovementGeneticvariationisanessentialcomponentofanyconven-tionalcropbreedingprogram.
Thetypicalcropimprovementcycletakes10–15yearstocompleteandincludesgermplasmmanipulations,genotypeselectionandstabilization,varietytesting,varietyincrease,proprietaryprotectionandcropproductionstages.
Planttissuecultureisanenablingtech-nologyfromwhichmanynoveltoolshavebeendevelopedtoassistplantbreeders(Karp1992;Mathur2013).
Tissuecul-ture-inducedsomaclonalvariationisakintovariationsinducedwithchemicalandphysicalmutagens(Jain2001)andoffersanopportunitytouncovernaturalvariabilityfortheirpotentialexploitationincropimprovement.
Likeanyothertechnology,invitroinducedsomaclonalvariationhasitsownmeritsanddemerits,likethetwosidesofthesamecoin.
AdvantagesTheadvantagescomprise:(1)itischeaperthanothermethodsofgeneticmanipulationanddoesnotrequire'containment'procedures.
(2)Tissueculturesystemsareavailableformoreplantspeciesthancanbemanipulatedbysomatichybridizationandtransformationatthepresenttime.
(3)Itisnotnecessarytohaveidentiedthegeneticbasisofthetrait,orindeed,inthecaseoftransformation,tohaveisolatedandclonedit.
(4)Novelvariantshavebeenreportedamongsomaclones,andevidencesindicatethatboththefrequencyanddistributionofgeneticrecombina-tioneventscanbealteredbypassagethoughtissueculture.
Thisimpliesthatvariationmaybegeneratedfromdifferentlocationsofthegenomethanthose,whichareaccessibletoconventionalandmutationbreeding(Karp1992).
(5)ThereTable2StrengthsandweaknessesofdifferentmarkersystemsfortheassessmentofclonaldelityAdvantagesDisadvantagesMorphologicaltraitsVisualdifferentiationSensitivetoontogenicchangesandotherenvironmentalfactorsDoesnotrequireanylaboratoryfacilityLimitedinnumbersSuitableforpreliminarydetectionTime-consumingCytologicalmarkers(ow-cytometry)Samplepreparationandanalysisisconvenientandrapidincaseofinow-cytometryCytosoliccompoundsmayinterferewithquantitativeDNAstaininginow-cytometryRapidandefcientmethodforroutinelarge-scalestudiesofploidylevelAbsenceofasetofinternationallyagreedDNAreferencestandardsincaseofinow-cytometryUnfailingdetectionofeventhesmallestmodicationsinchromosomenumberTime-consumingchromosomecountingIsozymemarkersCodominantexpressionSensitivetoontogenicchangesandotherenvironmentalfactorsEaseofperformanceLimitedinnumbersNotallofthesereagentsystemsworkefcientlywithallplantspeciesTissue-specicexpressionDNAmarkersCodominantexpressionAnysourceDNAcanbeusedfortheanalysisPhenotypicallyneutralNotsensitivetoontogenicchangesandotherenvironmentalfactorsCapabilitytodetectculture-inducedvariationbothattheDNAsequenceandmethylationpatternlevelsRAPDmarkersaredominantanddonotpermitthescoringofheterozygousindividuals.
Besides,theyexclusivelyidentifysequencechangesPossiblenon-homologyofsimilarsizedfragmentsasISSRisamultilocustechniqueDisadvantagesofAFLPsincludetheneedforpuried,highmolecularweightDNA,thedominanceofallelesandthepossiblenon-homologyofcomigratingfragmentsbelongingtodifferentlociInvolvementofhighdevelopmentcostsinSSRmarkersifadequateprimersequencesforthecropspeciesofinterestareunavailable.
Further,mutationsintheprimerannealingsitesmayresultintheoccurrenceofnullalleles(noamplicationoftheintendedPCRproduct),whichmayleadtoerrorsinscoring3Biotech(2016)6:54Page7of1854123isnopossibilityofobtainingchimericexpressionifsomaclonesareraisedthroughcellculture(Evans1989).
Somaclonalvariationhasbeenmostsuccessfulincropswithlimitedgeneticsystems(e.
g.
,apomicts,vegetativereproducers)and/ornarrowgeneticbases.
Inornamentalplants,forinstance,theexploitationofinvitro-generatedvariabilityhasbecomepartoftheroutinebreedingpracticeofmanycommercialenterprises.
DisadvantagesOneoftheseriouslimitationsofsomaclonalvariationwhichmakesitcomparativelydifculttouseisthat,despitetheidenticationoffactorsaffectingthevariationresponseofagivenplantspecies,itisstillnotpossibletopredicttheoutcomeofasomaclonalprogram(Karp1992)asitisrandomandlacksreproducibility.
Further,asalargenumberofgeneticchangesarebasedonpointmutationsorchromosomerearrangements,mostR1segregate.
Thereforeforquantitativetraitssuchasyield,itisvirtuallyimpos-sibletoselectindividualswithimprovementsintheR1generation.
Thoughtechniquesforselectionofsomaclonesresistanttovariousbioticandabioticstresseshadbeenworkedoutinmanyhorticulturalcrops,unfortunately,noinvitroselectionmethodsexistforcomplicatedtraitssuchasyield,solublesolids,sweetness,textureorshelflife(Evans1989).
Somaclonalvariationcanbecomeapartofplantbreedingprovidedtheyareheritableandgeneticallystable.
Onlyalimitednumbersofpromisingvarietiessofarhadbeenreleasedusingsomaclonalvariations.
Thisisperhapsduetothelackofinteractionbetweenplantbreedersandtissueculturescientists,andnon-predictabilityofsoma-clones(Jain2001).
Further,thoughthenewvarietieshavebeenproducedbysomaclonalvariation,inalargenumberofcasesimprovedvariantshavenotbeenselecteddueto(1)thevariationswereallnegative;(2)positivechangeswerealsoalteredinnegativeways;(3)thechangeswerenotnovel,or(4)thechangeswerenotstableafterselngorcrossing(Karp1992).
RecoveryofsomaclonalvariantsTherecoveryofvariantscanbeimprovedbypromotingthefactorswhichareresponsibleforthedevelopmentofsomaclonalvariationssuchasprotoplastculture(Kotharietal.
2010)andemployingcallusandcellsuspensioncultureforseveralcyclesandregenerationoflargenumberofplantsfromlong-termcultures(BarakatandEl-Sammak2011).
Indirectorganogenesisisanimportantmeansofretrievinggeneticvariationthroughsomacloneswithusefultraitsofagronomicorindustrialuse.
Besides,plantgenotypeisamajorfactor,whichdeterminesthetypeandfrequencyofsomaclonalvariation.
Forinstances,Solana-ceousplantslikepotato(Sharmaetal.
2007)andtomato(Bhatiaetal.
2005)produceagamutofsomaclonalvari-ationthanmanyothercommercialhorticulturalcrops.
However,tobeofpracticalvalue,thefrequencyofsomaclonalvariationshouldbesufcientenoughtoselectdesirabletraits,andtheselectedlinesshouldperformwellundermultipleenvironments(Duncan1997).
Theef-ciencyofrecoveringvariantsinvitrocanfurtherbeenhancedbyapplyingselectionpressurethroughscreeningofdesirabletraits,e.
g.
,invitroselectionfortoleranceagainstabioticandbioticstresses(BarakatandEl-Sammak2011).
Thisattainsmoresignicanceinviewofthefactthattheselectionofdesirabletraitstakesseveralyearsandmanygenerationsundereldconditions.
Invitroselectioncanshortenconsiderablythetimefortheselectionofdesirabletraitsunderinvitroselectionpressurewithmin-imalenvironmentalinteraction,andcancomplementeldselection(Jain2001).
Therecoveryofsomaclonescanbeincreasedbycombiningmicropropagationwithinducedmutagenesisinvitro(AfrasiabandIqbal2010).
Kuksovaetal.
(1997)notedthatsomaclonalvariationandmutagenscanbecombinedtoincreasethefrequencyofinducedmutation.
Likewise,irradiationfollowedbyadventitiousbudregenerationhasbeenreportedtohaveallowedtherecoveryofmutantswithusefulagronomictraitsinGypsophilapaniculataL.
(BarakatandEl-Sammak2011).
YangandSchmidt(1994)treatedinvitroleavesofthecherryrootstock'209/1'(Prunuscerasus9P.
canescens)withX-rayswithLD50closeto20Gy.
Amongplantsregeneratedfromleaveswith20Gy,onewasphenotyp-icallydifferent,andwassubsequentlyisolatedandcloned.
Thissomaclonewasextremelydwarfedandwasstableinbothgreenhouseandeldtests.
Employingmorethanonemutagenresultsinfurtherimprovementinrecoveryofsomaclonesinvitro.
Murtietal.
(2013)exposedthestrawberry'DNKW001'tothedosesof0,30,80,130,180,230,280,300and325GyandsimilardosesofgammaraysEMS7lMtreatments.
TheirresultsshowedthatGammarayirradiationEMSwasmoreeffectivetogeneratemoretypeandmagnitudeofvariants.
PurwatiandSudarsono(2007)regeneratedfourvariantlinesinabacabananafrom(1)embryogeniccalli;(2)ethylmethylsulphonate(EMS)-treatedembryogeniccalli;(3)EMS-treatedembryogeniccalli,followedbyinvitroselectiononFoc(Fusariumoxysporumf.
sp.
cubense)cultureltrate(EMSCFline)and(4)EMS-treatedembryogeniccalli,followedbyinvitroselectiononfusaricacid.
TheFocresistanceabacavariantsweresuccessfullyidentiedfromfourtestedabacavariantlines,althoughwithdifferentfrequencies.
However,more54Page8of183Biotech(2016)6:54123Table3InvitroselectionofdesirabletraitsanddevelopmentofsomecommerciallyexploitedvarietiesthroughsomaclonalvariationindifferenthorticulturalcropsS.
no.
HorticulturalcropCharacteristicofsomacloneReferences1AglaonemaCultivar'MoonlightBay'and'DiamondBay'from'SilverBay,'and'EmeraldBay,'from'GoldenBay'Hennyetal.
(1992,2003)2Apple(Malus9domesticaBorkh.
)ResistancetoErwiniaamylovoraChevreauetal.
(1998)3ApplerootstocksM26andMM106(MaluspumilaMill.
)ResistancetoPhytophthoracactorumRosatietal.
(1990)4ApplerootstockMalling7Resistancetowhiterootrot(Dematophoranecatrix)Modgiletal.
(2012)5Anthuriumsp.
'OrangeHot'derivedfrom'RedHot'cloneHennyandChen(2011)6Banana(MusaacuminataL.
)Semi-dwarfandresistanttoFusariumwiltTC1-229Tangetal.
(2000)Largerbunchsizevar.
TC2-425;ResistanttoFusariumoxysporumf.
sp.
cubense(Foc)race4;bunch40%heavierthancv.
FormosanaHwang(2002)Fusariumwilt-resistantsomaclonalvariantsofbananacv.
RasthaliGhagetal.
(2014)Var.
CIEN-BTA-03,resistanttoyellowSigatokaGimenezetal.
(2001)10somaclones;GCTCV215-1releasedforcommercialplantingHwangandKo(1992,2004)Var.
CUDBT-B1,reducedheightandearlyoweringMartinetal.
(2006)Var.
Tai-ChiaoNo.
5,superiorhorticulturaltraitsandresistancetoFusariumwiltLeeetal.
(2011)7Begonia(Begonia9elatior)Plantmorphology,numberofowersperplant,andowersizeJain(1997)8Brinjal(SolanummelongenaL.
)Stress-tolerantsomacloneselectionFerdausietal.
(2009)9BlackberryThornlessvar.
'LincolnLogan'Halletal.
(1986)10Capsicum(CapsicumannuumL.
)Yellowfruitedvar.
BellsweetMorrisonetal.
(1989)11CalthearoseopictaDevelopedcommoncultivarslikeAngela,Cora,Dottie,EclipseandSaturnChaoetal.
(2005)12Carrot(DaucuscarotaL.
)Resistancetoleafspot(Alternariadauci)Dugdaleetal.
(2000)ResistanttodroughtRabieietal.
(2011)13Carnation(DianthuscaryoplyllusL.
)ResistanttoFusariumoxysporumf.
sp.
dianthiEsmaieletal.
(2012)14Celery(ApiumgraveolensL.
)Fusariumresistantvar.
UC-TCHeath-PagliusoandRappaport(1990)Multiple-resistant(insectresistanceagainstSpodopteraexiguaanddiseaseresistanceagainstFusariumyellow)somaclonesK-26,K-108andK-128Diawaraetal.
(1996)15CelosiaargenteaL.
ResistancetonematodeOpabodeandAdebooye(2005)16CereusperuvianusShootswithdifferentareolescharacteristicsResendeetal.
(2010)17Chilipepper(CapsicumannuumL.
)EarlyoweringandincreaseofyieldcomponentsHossainetal.
(2003)18Chrysanthemum(Dendranthemagrandiora)Variationinleaf,owershapeandpetalsizeAhloowalia(1992)DaisytypechrysanthemumJevremovicetal.
(2012)AttractivevariantswithchangedinorescencecolorsMilerandZalewska(2014)19Citrusspp.
ResistanttoPhomatracheiphilaDengetal.
(1995)SalinitytoleranceBen-HayyimandGoffer(1989)20CupheaviscosissimaJacq.
Signicantlysuperiorovertheparentsformeanplantheight,leafarea,seedyield,percentcaprylicacidandlauricacidcontentsBen-SalahandRoath(1994)3Biotech(2016)6:54Page9of1854123Table3continuedS.
no.
HorticulturalcropCharacteristicofsomacloneReferences21CymbopogonwinterianusJowittAromaticgrassvar.
CIMAP/Bio-13with50–60%increasedoilyieldMathuretal.
(1988)IncreasedtotaloilyieldandqualitywithhighgeraniolcontentNayaketal.
(2003)CymbopogonmartiniiIncreasedoilcontentPatnaiketal.
(1999)22Dieffenbachiasp.
Novelanddistinctfoliarvariegationwithtaller,largercanopyandlongerleavesthan'Camouage'parentalplantsShenetal.
(2007)23Garlic(AlliumsativumL.
)ConsistentlyhigherbulbyieldthantheparentalcloneVidaletal.
(1993)Resistanceagainstthepathogenicfungi'Sclerotiumcepivorum'Zhangetal.
(2012)24Geraniumspp.
VigourousandattractiveowerSkirvinandJanick(1976)Isomenthone-richsomaclonalmutantGuptaetal.
(2001)Cv.
'CIMPawan,asomacloneoftheBourbontypevarietyBipuli,withmoreherbageandessentialoilyieldthanBipuliSaxenaetal.
(2008)25Gerbera(GerberajamesoniiBolus)NovelcultivarsMinervaandKumar(2013)26Ginger(ZingiberofcinaleRosc.
)Toleranttowiltpathogen(Fusariumoxysporumf.
sp.
zingiberiTrujillo)Bhardwajetal.
(2012)27Grapevine(VitisviniferaL.
)ResistanttoBotrytiscinereaandPlasmoparaviticolaKuksovaetal.
(1997)28Haemerocallisspp.
Dwarf,shortowers,malesterilevar.
YellowTinkerbellGriesbach(1989)29Hedychium(ornamentalginger)Ramata,dwarfandvariegatedcultivarSakhanokhoetal.
(2012)30Javacitronella(Cymbopogonwinterianus)SomaclonalvariantvarietyCIMAP/Bio-13,whichyields37%moreoiland39%morecitronellonthanthecontrolvariantMathur(2010)31Kiwifruit(Actinidiadeliciosa)5somaclones,derivedfromcv.
Tamuri,toleranttoNaClCabonietal.
(2003)32Mango(MangiferaindicaL.
)ResistanttoColletotrichumgleosporiensisLitzetal.
(1991)33Mint(Menthaarvensis)IncreasedherbandoilyieldKukrejaetal.
(1991;2000)34Myrobolan(PrunuscerasiferaErhr)Waterlogging-tolerantclonevariant(S.
4)ofmyrobolanrootstcockMr.
S2/5forpeachcv.
SunCrestIaconaetal.
(2013)35Olive(Oliveeuropea)Busholivesomaclone(BOS),columnarolivesomaclone(COS)Levaetal.
(2012)36Patchouli(Pogostemonpatchouli)HigherherbyieldandessentialoilcontentRavindraetal.
(2012)37Pea(PisumsativumL.
)ResistancetoFusariumsolaniHoracˇeketal.
(2013)38Peach(PrunuspersicaL.
)SomaclonesS156andS122resistanttoleafspot,moderatelyresistanttocankerincvs.
SunhighandRedhavenHammerschlagandOgnjanov(1990)Resistanttoroot-knotnematode(MeloidogyneincognitaKofoidandWhite)Hashmietal.
(1995)SomacloneS122-1wasfoundresistanttobacterialcanker(Pseudomonassyringaepv.
syringae)Hammerschlag(2000)39Pear(Pyrussp.
)ResistanttoErwiniaamylovoraViseur(1990)Pearrootstock(PyruscommunisL.
)'OldHome9Farmingdale(OHF333)'TolerancetothereblightNachevaetal.
(2014)40PhilodendronCultivars'BabyHope'from'Hope'Devanandetal.
(2004)41PicrorhizakurroaHigherglycosidecontentsincludingkutkosideandpicrosideIinsomaclone14-PderivedthroughAgrobacteriumrhizogenesmediatedtransformedhairyrootculturesofP.
kurroaMondaletal.
(2013)54Page10of183Biotech(2016)6:54123FocresistanceabacaplantswereidentiedfromEMSCFlinethantheothers.
Earlier,Bidabadietal.
(2012)suggestedthatthesubjectingofshoottipsculturesofbananatoEMS(200mM)treatmentscouldprovideanalternativestrategyforinducingvariants.
Recently,Iuli-anaandCerasela(2014)suggestedirradiationofinvitroraisedplantswithultravioletradiations(UV-C)forinductionofsomaclonesinpotato.
Table3continuedS.
no.
HorticulturalcropCharacteristicofsomacloneReferences42Pineapple(AnanascomosusL.
,Merr.
)SpinelessvariantJayaetal.
(2002)Cvs.
P3R5andDwarf,variationinfruitcolor,growthhabit,fruitsizeandlengthofplantgenerationcyclePerezetal.
(2009,2012)43Potato(SolanumtuberosumL.
)Non-browningvar.
WhiteBaronAriharaetal.
(1995)SomaclonesforheattoleranceDasetal.
(2000)SomaclonesIBP-10,IBP-27andIBP-30,derivedfromcultivarDesiree,showedhigherresistancetoAlternariasolaniandStreptomycesscabieiVeitia-Rodriguezetal.
(2002)Improvedsize,shape,appearance,starchcontentandstarchyieldThiemeandGriess(2005)Superiorprocessingattributesthancv.
'RussetBurbank'Nassaretal.
(2011)High-yieldinggenotypeSVP-53HoqueandMorshad(2014)Increasedphytonutrientandantioxidantcomponentsovercv.
'RussetBurbank'Nassaretal.
(2014)44QuinceA(Cydoniaoblonga)HighsoilpHDolcet-Sanjuanetal.
(1992),Marinoetal.
(2000)45SteviarebaudianaHighglycosidecontents(steviol,stevioside,andrebaudioside)Khanetal.
(2014)46Strawberry(Fragariasp.
)ResistanttoFusariumoxysporumf.
sp.
fragariaeToyodaetal.
(1991)ResistanttoAlternariaalternateTakahashietal.
(1993)ResistanttoPhytophthoracactorumBattistiniandRosati(1991)ImprovedhorticulturaltraitsBiswasetal.
(2009)ResistanttoVerticilliumdahliaeKlebZebrowska(2010)'Serenity',apalerskin-colored,lateseason,resistanttopowderymildewandVerticilliumwiltsomaclonalvariantoftheshort-daycv.
'Florence'Whitehouseetal.
(2014)47Sweetpotato(IpomeabatatasL.
Lam.
)ToleranttosalinityAnwaretal.
(2010)48Sweetorange(Citrussinensis(L.
)Osb.
)SomacloneofOLL(OrieLeeLate)sweetorange;latematuring;suitableforfreshmarketorprocessing,exceptionaljuicequalityandavorGrosseretal.
(2015)49St.
Augustinegrass[Stenotaphrumsecundatum(Walt.
)Kuntze]Freeze-tolerantsomaclonalvariantSVC3Lietal.
(2010)50SyngoniumpodophyllumSchott22cultivars,derivedfromoriginal'WhiteButtery'clone,withdistinctandstablefoliagecharacteristicsHennyandChen(2011)51Tomato(LycopersiconesculentumL.
)Highsolidcontentsvar.
DNAP9Evans(1989)52Tulip(Tulipasp.
)''Bs6'',selectedfromamongthemicropropagatedplantsofthecultivar'BlueParrot'withred-violetcoloredlongerowerandstemPodwyszynskaetal.
(2010)53Torenia(Toreniafournieri)FlowercolorsomaclonalvariantsNhutetal.
(2013)54Turmeric(CurcumalongaL.
)HighessentialoilyieldingsomaclonesKaretal.
(2014)TurmericsomacloneresistanttoFusariumoxysporumf.
sp.
ZingiberiKuanaretal.
(2014)55Indianginseng(Withaniasomnifera(L.
)Dunal)Withanolide(12-deoxywithastramonolide)-richsomaclonalvariantRanaetal.
(2012)3Biotech(2016)6:54Page11of1854123ApplicationofsomaclonalvariationsItiswellacceptedthatsomaclonalvariationsarisingoutofuniquetissuecultureenvironmentareveryoftennoticedphenomenoninclonallypropagatedplants,whichcanadvantageouslybeutilizedasasourceofnewvariationinhorticulturalcrops(Karp1995).
However,suitabletoolsfordetection,evaluation,identicationandimprovementofresistantclonesshouldbedesignedinordertorealizethebenetsofsuchvariations(Sahijrametal.
2003).
Cropimprovementthroughsomaclonalvariationenablesbreed-erstoobtainplantstoleranttothebioticorabioticstress,suchasdrought,highsalinity,highorlowsoilpHanddiseasetolerance(Yusnitaetal.
2005).
Anumberofcul-tivarshavebeendevelopedthroughsomaclonalvariationindifferenthorticulturalcropsforarangeofusefultraits,whicharepresentedinTable3.
ConclusionsSeveralstrategieshavebeenfollowedtoascertainthegeneticdelityoftheinvitroproducedprogeniesinviewofthefactthatthecommercialviabilityofmicropropaga-tiontechnologyisreliantuponmaintenanceofgeneticdelityintheregeneratedplants.
Therefore,athoroughassessmentofmicropropagatedplantsbecomesverycriti-cal,especially,forperennialcropssuchasfruitspecies,whichhavealongpre-bearinggrowthperiod.
Theef-ciencyandsensitivityofnewmoleculartoolshasenabledustodetectsomaclonalvariationatanearlystage.
Thesetoolshavebecomeveryusefulfortherapiddetectionandaccurateidenticationofvariants.
Nevertheless,themor-phologicalandcytologicalassaysshouldcontinuetoremainastheprimaryandessentialassayforthesustainedsuccessofdelitytestsassociatedwithproductionofclo-nalplants.
Though,ononehand,tissueculture-inducedvariationsposeamajorthreattothegenomicintegrityofregeneratedplants,theyprovidetoolsforimprovementtoplantbreeders,particularlyforcropswithanarrowgeneticbase,i.
e.
,selfpollinatedandvegetativelypropagated.
Irrespectiveofourgoaleitherforproductionoftrue-to-thetypeplantingmaterialorcreationofvariability,amulti-disciplinaryapproach(involvingconcernedsciencesofhorticulture,geneticsandplantbreeding,physiology,cytologyandmolecularbiology)withallourpreviousknowledgeandexperienceshouldbefollowedtoachievethedesideratum.
AcknowledgmentsAuthorsaregratefultotheDr.
S.
K.
Singh,PrincipalScientist,DivisionofFruitsandHorticulturalTechnology,IndianAgriculturalResearchInstitute,NewDelhi12,India,forhisvaluableadviceduringthepreparationofthemanuscript.
CompliancewithethicalstandardsConictofinterestTheauthorsdeclarethattheyhavenopotentialconictofinterestregardingsubmissionandpublicationofthismanuscript.
OpenAccessThisarticleisdistributedunderthetermsoftheCreativeCommonsAttribution4.
0InternationalLicense(http://creativecommons.
org/licenses/by/4.
0/),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedyougiveappropriatecredittotheoriginalauthor(s)andthesource,providealinktotheCreativeCommonslicense,andindicateifchangesweremade.
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