Heterosis may be defined as the superiority of an F1 hybrid over both its parents in terms of yield, size, quality or some other characters. Inbreeding depression – loss of vigour due to continuos selfing is known as inbreeding depression

1. Synthetic and Composite Variety
Amit Kumar
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2. Heterosis
• Heterosis may be defined as the superiority of an
F1 hybrid over both its parents in terms of yield,
size, quality or some other characters.
Inbreeding depression – loss of vigour due to
continuos selfing is known as inbreeding depression
γ × γ =γ
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3. 2. However
magnitude is less
in self pollinated
crop compare to
cross pollinated
3. And chief drawback
in the use of hybrid in
self pollinated crop is
the difficulty in
production of large
quantity of hybrid
seed
1. Heterosis
reported in
both self and
cross
pollinated
vegetable crop
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4. • Self pollination- homozygous in nature- less
variation- low allelic variation- low yield variety-
scope of hybrid development
• Genetic variability ?????
• Creation of genetic variability- objective of
hybridisation
• The mating or crossing of two plants or lines of
dissimilar genotype is known as hybridisation
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5. • Single cross- I1x I2, Double cross- (I1xI2)x (I3xI4)
• Three way cross- (I1xI2)xI3
• Top cross- when an inbred is crossed with an open pollinated
variety (Inbred- variety cross)
• Test cross- when a cross is made to assess combining ability, it
is known as test cross and the progeny derived from this is
called test cross progeny
• Varietal cross- when two open pollinated varieties are mated it
is usually known as varietal cross or POPULATION CROSS
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6. • Variety means a genotype under the cultivation practices or
can say genotype which is notified by different agency like
state and central certification agency
• Hybrid varieties are the first generation F1 from crosses
between two pure-lines, inbred lines, open pollinated
varieties, clones and other populations that are genetically
dissimilar.
• An inbred is a nearly homozygous line obtained through
continuous inbreeding accompanied by the selection , in a
cross pollinated species. Maintained by self pollination
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7. Random mating population
Cross pollinated crops are highly heterozygous
due to the free inter-mating among their
individuals. They are called random mating
population
γ γ γ γ γ γ
γ γ γ γ γ γ
γ γ γ γ γ γ γ
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8. • Synthetic variety
• first suggested by Hayes and Garber in 1922
• Synthetic varieties are open pollinated populations
developed through random mating of selected genotypes
(Lonnquist, 1961).
• A synthetic variety is produced by crossing in all
combination a number of lines that combine well with
each other, and is maintained by open pollination in
isolation
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9. • Hence it is a mixture of several single cross
hybrids of F1
• Line used for synthetic development is- inbred
lines, clones, OPV, tested for GCA.
• Such variety exploit portion of heterosis.
• Lines that have high GCA are selected as
parents of synthetic variety
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10. • Merit of Synthetic
• where pollination control is difficult, this may
utlised some heterosis
• May used this seed in next season
• Perform better than the hybrid in some
environment, because of wider genetic base
• Cost is low relatively hybrid
Demerit-
• Not possible in self pollinated species
• Produce lower yield than hybrid, because it utilise
only gca
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11. Thanks
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