Inbred line

inbred line & their application

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Definition of Inbred Line
•Inbredlinesarehomozygousgenotypes
producedbyrepeatedselfingwithselection
overseveralgenerations.
•Itisabreedingmaterialthatis
homozygous.
•Aninbredlineconsistsofindividualswith
thesamegenotype.
•Itisdevelopedandmaintainedbyrepeated
selfingofselectedplants.
Introduction
•Inbredlinesaredevelopedfromavariable
sourcepopulation.Thesourcepopulationis
generallyanopen-pollinatedvariety(First
cycleinbreds)oritmaybesynthetic,asingle
crossoradoublecross(Second,thirdor
fourthcycleinbreds).
•Inbredsareusuallydevelopedthrougha
suitablesystemofcloseinbreeding(6-7
generationofselfing).
•1Selfing=3full-sibmating=6half-sibmating
areachievedsamelevelofinbreeding.

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Inbred Line Development in
Cross Pollinated Crops
•Inprinciple,developinginbredlinesfrom
cross-pollinatedspeciesisnotdifferentfrom
developingpurelinesinself-pollinated
species.
•Thepedigreemethodofbreedingisthe
mostwidelyusedmethodtodevelopinbred
lines&itisreferredtoas“standard
method”whenanopenpollinated
populationissampled.
•Aftereachselfingdesirableplantsare
selectedandselfpollinatedorsibpollinated.
Usuallyittakes6-7generationstoattainnear
homozygosity.
•Thepurposeofinbreedingistofixthe
desirablecharactersinhomozygouscondition
inordertomaintainthemwithoutanygenetic
change.
•Inbredlinesaredevelopedfortheproduction
ofHybridseeds.
•Therearethreeoperationsinvolvedinthe
productionofhybridvarieties-
a)Developmentofinbredlines
b)Evaluationofinbreds
c)Productionofhybridseed

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Methods
•Therearetwomethodsofdeveloping
inbredlines-
a)Selfingofheterozygouspopulations
(Pedigreemethod,Bulkmethod,Single
seeddescentmethod,Backcrossmethod)
b)Doublingofhaploids

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Procedure
•1
st
year Plants with desirable phenotypes are selected
Plants should be vigorous & disease free &
may be selected on the basis of GCA estimates
Self-pollination
•2
nd
year 30-40 plants are space planted
Best plants are selected from best progeny
Self-pollination
•3
rd
–6
th
yr same as 2
nd
year but no of generations of
self pollination increases & selection is
primarily among the progenies
•7
th
year Individual plant progenies are nearly homo-
zygous& homogeneous, selfing may be
Inbred lines discontinued & maintained by sib-pollination
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Production of Hybrid Seed
Hybrid varieties are commonly developed by
crossing two unrelated, homozygous inbred
lines.
Production of Hybrid seed on commercial
scale requires-
a)Easy emasculation of female parent
b)Effective pollen dispersal from the male
parent to ensure a satisfactory seed set in
female parent.

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Improving the characteristics of
inbred lines
•Variousschemeshavebeensuggestedtoimprovethe
existinginbredsinrespectof-
I.Productivityofinbreds
II.Disease&insectresistance
III.Combiningabilityofinbredstoincreaseyieldingabilityof
hybrids
Thefollowingmethodsareused-
a)Pedigreeselection
b)Backcrossmethod
c)Convergentimprovement
d)Gameteselection
e)Somatichybridization
f)Somaclonalvariation
g)Geneticengineering
Production of Doubled Haploids
•Anindividualwiththedoubledchromosome
numberofthehaploid.
•Thetechniqueofdoubledhaploidsmaybe
usedtoproducecompletehomozygousdiploid
linesinjust1year(versusmorethan4years
inconventionalbreeding)bydoublingthe
chromosomecomplementofhaploidcells.
•Therearethreestepsinvolvedinthe
productionofdoubledhaploids-
a)Haploidproduction
b)Haploididentification
c)Genomedoubling

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•Theproductionofdoubledhaploidsleads
tohomozygosityinasinglegeneration
afterrecombinationofselectedparents.
•Selectionismoreefficientforoligogenicor
polygenictraitsinDHsbecausethegenes
arefixedinahomozygousbackground,
limitingdominancegeneticvariationand
segregation.
•TheDHmethodpreventslossesof
valuablegeneticvariationsbetterthanthe
conventionalselectionmethod.
Applications of Inbredsin
Crop Improvement
•Inbredlinesaregenotypesthatare
developedtobeusedasparentsinthe
productionofhybridcultivarsandsynthetic
cultivarsinthebreedingofcross-pollinated
species.
•Thesuccessofacropbreedingprogram
reliesonchoiceofthebestparents
possessingcomplementaryanddesired
traits.

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Inbredsarehighlydesirableincomparisontoopen-
pollinatedvarietiesorotherpopulationswitha
broadgeneticbaseduetofollowingreasons-
i.Inbredscanbemaintainedindefinitelywithouta
changeintheirgenotype,whilethegeneticmake-
upofpopulationslikeopen-pollinatedvarietiesis
likelytobemodifiedbytheevolutionaryforces.
ii.Thehybridsderivedfrominbredsare
homogeneousornearlyso,yearafteryear,while
thoseproducedfromopen-pollinatedvarietiesare
likelytobevariable&hencetheirperformance
can'tbeaccuratelypredicted.
iii.Theuniformityofinbred-derivedhybridsisalso
desirablefromtheviewpointofuniformqualityof
theproduceaswellas.
iv.Fromtheviewpointofseedcertification.
•Theinbredlinesareidentifiedbynumbers,
lettersorcombinationofboth.InIndiainbred
linesaredevelopedandreleasedthroughco-
ordinatemaizeimprovementschemeandare
designatedasCM(Co-ordinatemaize),CS
(Co-ordinatesorghum)etc.
•CM-100-199-Yellowflint
•CM-200-299-YellowDent
•CM-300-399-WhiteFlint
•CM-400-499-WhiteDent
•CM-500-599-Yellow
•CM-600-699-White2

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•InIndia,Hybridvarietieswerefirsttoexploit
heterosisinmaize.Thefirsthybridvarietiesinmaize
werereleasedin1961,whenfourdoublecross
hybrids,viz.,Ganga1,Ganga101,Ranjit&Deccan,
werereleasedforcultivation.
•Insorghum,firsthybridCSH1wasreleasedin1964.
•Inpearlmillet,firsthybridHB1wasreleasedin1964.
•GCH3(1968)incastor
•H4(1970)incotton
•BSH1(1980)insunflower
•ICPH-8(1991)inpigeonpea
•PGSH51(1994)inrapeseed
•PRH10(2001)inrice
•GTH1(1996)intobaccowerefirstreleasedhybrid
varieties.