This document discusses heterosis, or hybrid vigor, which is the increased size, yield, and other favorable traits exhibited by the offspring of two genetically distinct parent plants. The exact genetic mechanisms are unknown, but it is believed to result from the expression of favorable traits from both parents in their hybrid offspring. Breeders have been developing crops based on heterosis for decades by artificially crossing parental lines to produce superior hybrid seeds. Many important crops like maize, wheat, rice, and cotton have been improved through heterosis breeding. The economic benefits come from using these hybrid seeds along with other advanced agricultural practices.
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Heterosis and its exploitation in plant breeding
1. Sijo.A
B.sc. Botany & Biotechnology
Mar ivanios College
HETEROSIS AND ITS
EXPLOITATION IN PLANT
BREEDING
2. Introduction
Over the past several decades, breeders have
been improving many crops on the basis of the
first generation (F1) hybrids.
This method involves the annual production of
progenies by artificial crossing in large cultivated
areas.
3. Heterosis and its manifestation
Heterosis or hybrid vigour is the superiority of the
F1 hybrids over parents in one or more
characters.
The exact genetic mechanism behind heterosis is
not definitely known.
Still it is generally held that a tendancy for the
expressions of the features of both the parents in
the hybrids is the basis of heterosis.
4. Manifestations
(i) Increased size, vigour vitality and yield
(ii) Better quality of the yield
(iii) Greater adaptability to diverse environmental
conditions.
(iv) High resistance and tolerance against pests,
pathogens and climatic conditions.
(v) High reproductive potential
(vi) Early maturation, flowering and fruit setting
Apart from these,heterosis
involves other changes at molecular, metabolic,
cellular and organismal also. Some of such
changes are following.
5. Manifestation at
Molecular level
1. Increased rate of DNA duplication
2. Gentic transcription
3. Genetic translation
4. Enzyme activity
• Metabolic level
• Increased and effective co-ordination and
regulation of metabolic processes and
morphogenetic events.
6. Manifestation at
Cellular level
Increased rate of cell proliferation
Organism level
High rate of cellular growth and differentiation,
increased synthesis, accumulation and utilization
of substances.
7. Practical utilisation
In some agricultural crops, heterosis is much
prominent and so it is extensively used for the
production of superior varieties.
Many ornamentals, fruit plants, vegetables,
cereals, etc. have been produced in this way.
Examples are maize, bajra, johar, wheat, barley,
rice, cotton etc.
The best economic advantage of heterosis is
attained by using heterotic hybrid seeds in
combination with advancced farming practices,
mainly irrigation, application of fertilizers etc.
8. In india, a lot of work has been done on
heterosis breeding in a number o
economically important crops such as
sugarbeet, brinjal, lady’s finger etc
In 1989, ICAR launched a hybrid project
entitled “Promotion of Research and
Development Efforts on Hybrids in Selected
Crops” to promote hybrid research.
9. The hybrid undergo self pollination and
increases their homozygous condition.
As a result recessive allele is increased and
vigour is reduced. This is called Inbreeding
depression.
After several generations of inbreeding, a
stage may be reached beyond which no
further inbreeding depression occurs. This
stage is called inbreeding minimum.
10. Mainly there are four levels of inbreeding
depression.
(i) High inbreeding depression level
In this case inbreeding depression is so high that
only very few inbred lines survive after 3 or 4
generations of inbreeding.
(ii) Low inbreeding depression
Here the effect of inbreeding depression is very
low and some of the inbred lines have normal
vigour and yield.
(iii) Zero inbreeding depression
Self pollinates(inbred) progeny does not exhibit any
effect of inbreeding depression, but shows some
degree of heterosis.