This document discusses principles of plant breeding, specifically asexual reproduction and vegetative reproduction. It describes various natural and artificial methods of vegetative reproduction including underground stems, bulbs, runners and cuttings. It also discusses apomixis, an asexual reproduction process where embryos form without fertilization. Obligate and facultative apomixis are described. The role of asexual reproduction in plant breeding is to rapidly produce pure lines and maintain superior genotypes. Clonal selection is the process used to select superior clones from mixed populations of asexually reproducing crops like sugarcane and potato.

2. Presented by: Hitesh V. Jasani
Ph.D. (Plant Molecular Biology and Biotechnology),
Principles of Plant Breeding

3. Asexual reproduction
 Multiplication of plants without the fusion of male
and female gametes is known asexual reproduction.
 Asexual reproduction can occur either
 By vegetative plant parts or
 By vegetative embryos which develop without sexual
fusion.
 Asexual reproduction is of two types,
1. Vegetative reproduction.
2. Apomixis.

4. Vegetative Reproduction
 Vegetative reproduction refers to multiplication of
plants by means of various vegetative plant parts.
 Vegetative reproduction is again of two types :
1. Natural vegetative reproduction.
2. Artificial vegetative reproduction.

5. Natural vegetative reproduction
• In nature, multiplication of certain plants occurs by
underground stems, subaerial stems, root and bulbils.
 Underground stems:
The underground modifications of stem generally
serve as strong organs and contain many buds. These
buds develop into shoots and produce plant after
rooting.
 Rhizome : Turmeric, Ginger
 Tuber
: Potato
 Corm
: Arvi, Bunda
 Bulb
: Garlic, Onion

6. Rhizome : Turmeric (Curcuma domestica), Ginger(Zingiber officinale)
Bulb : Garlic (Allium sativum), Onion (A. cepa)

7. Corm :Bunda (Colocasia antiquorum), Arvi (Colocasia esculenta)
Tuber : Potato (Solanum tuberosum)

8.  Sub-aerial Stems:
These modifications include
runner, stolon, sucker etc..
Sub-aerial stems are used for
the propagation of mint
(Mentha sp.), date palm,
strawberry, banana etc..
Sucker of Banana
Runner of Mint
Stolon of Strawberry

9.  Bulbils:
o
o
o
Bulbils are modified forms
of flowers that develop into
plants
directly
without
formation of seeds.
These are vegetative bodies
as their development does
not involve fertilization and
seed formation.
They develop into plants
when fall on the ground.
Bulbils are found in garlic,
lily etc..
Bulbils of garlic
Bulbils in tiger lily

10.  Leaves:
o This is not very common and It
is seen in plants such as
Bryophyllum.
o It has fleshy leaves and
adventitious buds are present at
the margins of the leaves.
o These buds fall off and grow
into new plants.

11. Artificial vegetative reproduction
 Multiplication of plants by vegetative parts through
artificial method is known as artificial vegetative
reproduction.
• Stem cuttings: Sugarcane (Saccharum sp.), Grapes
(Vitis vinifera), Roses, etc.
• Root cutting: Sweet potato, Citrus, Lemon, etc.
• Layering, grafting are used in fruit and ornamental
crops.

12. Cutting:
Layering:

13. Grafting:

14. Significance
Vegetative reproduction has several advantages.
 It leads to continuity of same genotype with great
precision, because all the progeny have similar
genotype and phenotype.
 Useful in obtain large number of genetically identical
individuals.
 Promising genotype can be maintained.
 It makes use of desirable bud mutations. Mutants can
be directly released as varieties.

15. Apomixis
• Apomixis: Development of seed or embryo without
fertilization (sexual fusion).
• Obligate Apomixis: A plant which reproduces only
by asexual reproduction.
• Facultative Apomixis: A plant which has the
potential to reproduce either sexually or asexually.
Both process may occur simultaneously or one may
be predominant.

16.  Parthenogenesis: Development of embryo from egg
cell without fertilization.
Haploid : Embryo develops from haploid egg cell.
Example - Nicotiana, Maize etc..
o Diploid : Embryo develops from diploid egg cell.
Example - many grasses like Taraxacum etc..
o
 Apogamy: Development of embryo either from
synergids or antipodal cells.
Haploid : Embryo develops from haploid synergids or
antipodal cells.
o Diploid : Embryo develops from diploid synergids or
antipodal cells. Example – Allium etc..
o

17.  Apospory: First diploid cell of ovule laying
outside the embryosac develops into another
embryosac without reduction.
Then develops directly from the diploid egg cell
without fertilization.
Examples- Parthenium, Crepis etc..
 Adventive Embryony: Embryos develop directly
from vegetative cells of the ovule, such as nucellus.
Adventive embryony occurs in Mango, Citrus etc..

18. The Ideal Apomictic System
1. All the progeny of plants should be apomictic so that
progeny have the same genotype as the maternal parent.
2. The apomictic genotype should preferably be fully male
fertile and self-incompatible, and reproduce via
pseudogamy.
3. In case of diplospory, chromosomes should not pair or
recombine during first meiotic division. which may give
rise to variation among the progeny.
4. Apomixis should be dominant over sexual reproduction.
Usually, apomixis is governed by two or more genes.
5. Expression of apomixis should be little affected by the
environment.

19. Development of Apomictic Lines
Apomictic lines can be developed by the following
three different approaches:
1. Gene Transfer from wild species:
Genes controlling apomixis can be transferred into a
crop species from a related wild species, e.g., from
Tripsacum dactyloides into maize, from Pennisetum
orientate into pearlmillet.
2. Induced Mutations:
This approach aims at developing apomictic forms in
normally sexually reproducing species by utilising
induced or even spontaneous mutations.

20. These efforts have focused primarily on sorghum,
where two mutant lines showing facultative apospory
have been isolated.
3. Isolation of Apomictic Recombinants from
Interspecific Crosses:
Sometimes apomictic recombinants can be recovered
from segregating generations of crosses between two
sexually reproducing species. For example, seed
formation has been reported in the intergeneric hybrids
between T. aestivum and Avena sativa, H. vulgare and
T. aestivitm etc…

21. Role in plant breeding
 Rapid production of pure lines
Apomixis is an effective means for rapid production
of pureline.
 Maintenance of superior genotypes
Apomixis is useful in maintaining the characteristics
of mother plant from generation to generation.
 Conservation of heterosis
In some cases, hybrid vigour may be conserved for
many generation by using recurrent apomixis.

22. Advantages of Apomixis
 Obligate apomixis permits fixation of heterosis in the
hybrids. Therefore, farmers can resow the seeds
produced by apomictic hybrids generation after
generation.
 The new hybrid variety could be multiplied from few
hybrid seeds in the same manner as purelines. This
greatly simplifies hybrid seed production.
 Even such parents that flower at different times may be
crossed in a greenhouse to obtain few hybrid seeds,
which can be used to establish the new hybrid variety.
 The nucleus seed of hybrid varieties can be
conveniently maintained as hybrid varieties.

23. Problems in Utilization of Apomixis
• Apomixis is a very complicated phenomenon.
• Estimation of the level of facultative apomixis, is
tedious and time consuming.
• In case of facultative apomicts, the proportion of sexual
progeny is affected by environmental factors like daylength and temperature.
• In the absence of morphological markers linked with
apomictic development, maintenance of apomictic
stock becomes difficult.
• The genetic basis of apomixis is not clear in most
cases.

24. Clonal Selection
Clone : Progeny of a single plant obtained by asexual
reproduction.
Clonal Selection : A procedure of selection superior
clones from the mixed population of asexually
propagated crops such as sugarcane, potato etc..

25. Main feature of clones
1. Homologous constitution
The progeny of clone is genetically identical and have
same genetic constitution. Thus clones are homologous.
No genetic variation within a clone.
2. Heterozygosity
Asexually propagated crops are heterozygous so clone
is also heterozygous. Progeny looks similar
phenotypically but is heterozygous.
3. Wider adaptation
Clones are more adaptable to environmental variation
due to high level of heterozygosity than pure line.

26. 4. Vigorous growth
Clones have hybrid vigour which is conserved due to
sexual reproduction. Most of the varieties of
sugarcane and potato are hybrids
5. Source of variation
There are three sources of variation in a clone. Viz.
bud mutations, mechanical mixture, and occasional
sexual reproduction.
6. Segregation in F1
When hybridization is done between different clones,
segregation occurs in F1 generation. Each F1 plant is
potentially a new variety, therefore, selection is
practised in F1.

27. Procedure of Clonal selection
First Year
Mixture of clones
Few to several hundred to thousand superior
plants selected.

28. Second Year
Clones from selected Plants
i. Clones from the selected plants grown separately
ii. Inferior clones are rejected

29. Third Year
Preliminary yield trial
i. Preliminary yield trial with standard checks.
ii. Selection for quality, disease resistance, etc..
Disease nurseries may be planted
iii. Few outstanding clones selected

30. Fourth Sixth Year
Multilocation yield trials
i. Mutilocation yield trials with standard checks
ii. Best clone Identified for release as a new variety

31. Seventh Year
Seed multiplication
i. The best clone is released as a new variety
ii. Seed multiplication for distribution begins

32. Merits





Variety evolved by this method retains all the
characters of the parental clones for several years.
Varieties are highly uniform like pure lines. They are
highly stable because there is no risk of deterioration
due to segregation and recombination.
Effective method for genetic improvement of
asexually propagated crops.
Useful in isolation the best genotype from a mixed
population of asexually propagated crops.
The selection scheme is useful for maintaining the
purity of clone.

33. Demerits
This selection method utilizes the variability already
present in the population, and it has not been devised
to generate variability.
Genetic makeup cannot be improved by this method
without hybridization.
Varieties developed by clonal selection are highly
prone to new of a disease.

34. Achievements
 In India, this method successfully used for
developing new varieties in potato, sugarcane,
banana, citrus and grapes.
 Kufri Red and Kufri safed in potato.
 Ko 11, ko 22 and Neelam in mango.
 Co 541, CoS 510 etc.. In sugarcane.
 Pride monthan and High gate in banana.

35. References
• Essentials of Plant Breeding By Phundan Singh.
3rd Ed. pp: 52-55, 128-131.
• Plant Breeding By B. D. Singh. 6th Ed.
pp: 48-50, 371-373.
• Plant Breeding By B. D. Singh. 9th Ed.
pp: 55-57, 377-382.
• leavingbio.net/vegetativepropagation.htm
• Vegetative Propagation | Tutorvista.com
• Wikipedia, the free encyclopedia
• Breeding methods of clonally propagated crops By
Maria Andrade et al., July 2009