inbred line & their application

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Definition of Inbred Line
• Inbred lines are homozygous genotypes
produced by repeated selfing with selection
over several generations.
• It is a breeding material that is
homozygous.
• An inbred line consists of individuals with
the same genotype.
• It is developed and maintained by repeated
selfing of selected plants.
Introduction
• Inbred lines are developed from a variable
source population. The source population is
generally an open-pollinated variety (First
cycle inbreds) or it may be synthetic, a single
cross or a double cross (Second, third or
fourth cycle inbreds).
• Inbreds are usually developed through a
suitable system of close inbreeding (6-7
generation of selfing).
• 1 Selfing = 3 full-sib mating = 6 half-sib mating
are achieved same level of inbreeding.

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Inbred Line Development in
Cross Pollinated Crops
• In principle, developing inbred lines from
cross-pollinated species is not different from
developing pure lines in self-pollinated
species.
• The pedigree method of breeding is the
most widely used method to develop inbred
lines & it is referred to as “standard
method” when an open pollinated
population is sampled.
• After each selfing desirable plants are
selected and self pollinated or sib pollinated.
Usually it takes 6-7 generations to attain near
homozygosity.
• The purpose of inbreeding is to fix the
desirable characters in homozygous condition
in order to maintain them without any genetic
change.
• Inbred lines are developed for the production
of Hybrid seeds.
• There are three operations involved in the
production of hybrid varieties-
a) Development of inbred lines
b) Evaluation of inbreds
c) Production of hybrid seed

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Methods
• There are two methods of developing
inbred lines-
a) Selfing of heterozygous populations
(Pedigree method, Bulk method, Single
seed descent method, Back cross method)
b) Doubling of haploids

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Procedure
• 1st year Plants with desirable phenotypes are selected
Plants should be vigorous & disease free &
may be selected on the basis of GCA estimates
Self-pollination
• 2nd year 30-40 plants are space planted
Best plants are selected from best progeny
Self-pollination
• 3rd – 6th yr same as 2nd year but no of generations of
self pollination increases & selection is
primarily among the progenies
• 7th 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
• Various schemes have been suggested to improve the
existing inbreds in respect of-
I. Productivity of inbreds
II. Disease & insect resistance
III. Combining ability of inbreds to increase yielding ability of
hybrids
The following methods are used-
a) Pedigree selection
b) Backcross method
c) Convergent improvement
d) Gamete selection
e) Somatic hybridization
f) Somaclonal variation
g) Genetic engineering
Production of Doubled Haploids
• An individual with the doubled chromosome
number of the haploid.
• The technique of doubled haploids may be
used to produce complete homozygous diploid
lines in just 1 year (versus more than 4 years
in conventional breeding) by doubling the
chromosome complement of haploid cells.
• There are three steps involved in the
production of doubled haploids-
a) Haploid production
b) Haploid identification
c) Genome doubling

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• The production of doubled haploids leads
to homozygosity in a single generation
after recombination of selected parents.
• Selection is more efficient for oligogenic or
polygenic traits in DHs because the genes
are fixed in a homozygous background,
limiting dominance genetic variation and
segregation.
• The DH method prevents losses of
valuable genetic variations better than the
conventional selection method.
Applications of Inbreds in
Crop Improvement
• Inbred lines are genotypes that are
developed to be used as parents in the
production of hybrid cultivars and synthetic
cultivars in the breeding of cross-pollinated
species.
• The success of a crop breeding program
relies on choice of the best parents
possessing complementary and desired
traits.

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 Inbreds are highly desirable in comparison to open-
pollinated varieties or other populations with a
broad genetic base due to following reasons-
i. Inbreds can be maintained indefinitely without a
change in their genotype, while the genetic make-
up of populations like open-pollinated varieties is
likely to be modified by the evolutionary forces.
ii. The hybrids derived from inbreds are
homogeneous or nearly so, year after year, while
those produced from open-pollinated varieties are
likely to be variable & hence their performance
can't be accurately predicted.
iii. The uniformity of inbred-derived hybrids is also
desirable from the viewpoint of uniform quality of
the produce as well as.
iv. From the view point of seed certification.
• The inbred lines are identified by numbers,
letters or combination of both. In India inbred
lines are developed and released through co-
ordinate maize improvement scheme and are
designated as CM (Co-ordinate maize), CS
(Co-ordinate sorghum) etc.
• CM-100-199 - Yellow flint
• CM-200-299 - Yellow Dent
• CM-300-399 - White Flint
• CM-400-499 - White Dent
• CM-500-599 - Yellow
• CM-600-699 - White 2

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• In India, Hybrid varieties were first to exploit
heterosis in maize. The first hybrid varieties in maize
were released in 1961, when four double cross
hybrids, viz., Ganga1, Ganga101, Ranjit & Deccan,
were released for cultivation.
• In sorghum, first hybrid CSH1 was released in 1964.
• In pearlmillet, first hybrid HB1 was released in 1964.
• GCH3 (1968) in castor
• H4 (1970) in cotton
• BSH1 (1980) in sunflower
• ICPH-8 (1991) in pigeonpea
• PGSH51 (1994) in rapeseed
• PRH10 (2001) in rice
• GTH1 (1996) in tobacco were first released hybrid
varieties.