Mode of Pollination

and
Method of Reproduction
Reproduction : process by which living organisms give
rise to the offspring of similar kind (species).

Reproduction: process of multiplication of living beings.

Choice of breeding procedure depends:

A. Mode of reproduction and
B. Mode of pollination of a crop species.

Mode of reproduction is of two types: viz.

a. Asexual reproduction and
b. Sexual reproduction.
Mode of reproduction and pollination determine

Genetic constitutions of the species,

The type of breeding schemes and
varieties used,
Ease in controlled pollination,
Feasibility of gene transfer and
creation of genetic variation, and
Stability of varieties after release.
 Comparison of Asexual and Sexual Reproduction

Items/ clue Asexual Sexual Reproduction

Reproduction
1 Fusion of gametes none yes
2 Type of cell division mitosis meiosis
3 Genetic variety usually identical great genetic variety
4 Adaptation to less adapted better adapted
environment
5 Number of parents one two
 Isogamy Heterogamy
Fusion of Fusion of
morphologically similar morphologically
gamets called dissimilar gametes called
conjugation and the fertilization and the
zygote thus formed zygote thus formed
called zygospore. called oospore,
Plant bearing similar Plant bearing dissimilar
gametes are said to be gametes are said to be
isogamous. heterogamous.
 It is common to lower Heterogamy is common
plants such as Mucor, in higher plants
Spirogyra
1. ASEXUAL REPRODUCTION

Multiplication of plants without the fusion of male

and female gametes.

Asexual reproduction can occur either by vegetative

plant parts or by vegetative embryos, which develop
without sexual fusion (apomixis).

Asexual reproduction is of two types: viz.

Vegetative reproduction, and

Apomixis.
Vegetative reproduction:

Multiplication of plants by means of various vegetative plant parts.

Vegetative reproduction is again of two types: viz

(i) Natural vegetative reproduction, and
(ii) Artificial vegetative reproduction.

Natural vegetative reproduction:

Underground stems:
Rhizome : Turmeric (Curcuma domestica), Ginger (Zingiber offlcinale)
Tuber : Potato (Solanum tuberosum)
Corm : Arvi (Colocasia esculenta), Bunda (C. antiquorum)
Bulb : Garlic (Allium sativum), Onion (A. cepa)

Sub aerial stems: runner, sucker, stolon, etc. Ex: mint (Mentha sp), rose,
strawberry, banana, etc.

Bulbils: modified forms of flower. Dioscorea sp.

Modified roots: Sweet potato

Artificial vegetative reproduction:
Multiplication of plants by vegetative parts through artificial
method is known as artificial vegetative reproduction.

Such reproduction occurs by cuttings of stem and roots, and

by layering, grafting and gootee.

Examples:
Stem cuttings: Sugarcane (Saccharum sp.), grapes (Vitis
vinifera), roses, etc.

Root cuttings. Sweet potato (Ipomea), citrus, lemon, etc.

Layering, grafting and gootee are used in fruit and

ornamental crops.
 Species Structures
Tulip, onion, Easter lily bulb
potato, Jerusalem artichoke tuber
Iris, lily-of-the valley rhizome
Gladiolus, Crocus corm
Strawberry, Ajuga runner
Dahlia, sweet potato tuberous root
Stolons are
horizontal
stems that
grow either
above or
below
ground.
Asexual reproduction
Fig. 42.19
 Cutting Propagation
– Produce adventitious roots.
Cells near the wound must dedifferentiate and create a
new meristematic region.
 Cutting

•
 Grafting
•Segments of different plants are
connected and induced to grow
together as one plant.
–Scion - Top section of a graft.
–Rootstock - Bottom section of a
graft.
–Successful grafting depends on
good contact between the
vascular cambium of the scion
and that of the rootstock.
Air Layering
 Layering

•
 Grafted and budded plants…

Species Graft/bud Type

Apples chip, T-bud, cleft
Conifers side veneer
Pecans patch
Roses T-bud (shield)
Grapes modified wedge
 Significance or advantages of vegetative/ clonal
reproduction:

leads to continuity of same genotype with great

precision, because all the progeny of asexually
reproduced plant will have similar genotype and
phenotype.

useful in obtaining large number of genetically

identical individuals of a genotype, irrespective of
the degree of heterozygosity.

Promising individuals occurring at any stage in a

breeding program can be easily picked up and
maintained by asexual reproduction.
Sexual
Reproduction
SEXUAL REPRODUCTION

Multiplication of plants through embryos which have developed

by fusion of male and female gametes is known as sexual
reproduction.

All the seed propagating species belong to this group.

The new plants arise from the embryos which have developed
from the fusion of male and female gametes

Sexual reproduction plays an important role in creating and

maintaining vast genetic variability in crop plants, which is
essential for crop improvement.

In such species, genetic variability can be created by: (1)

crossing over, (2) hybridization, and (3) polyploidy.
 Isogamy Heterogamy
Fusion of Fusion of
morphologically similar morphologically
gamets called dissimilar gametes called
conjugation and the fertilization and the
zygote thus formed zygote thus formed
called zygospore. called oospore,
Plant bearing similar Plant bearing dissimilar
gametes are said to be gametes are said to be
isogamous. heterogamous.
 It is common to lower Heterogamy is common
plants such as Mucor, in higher plants
Spirogyra
Summary of vegetative propagation in angiosperms
Name of Origin of organ Region of Example
perennating food
organ storage
1. Bulb short, vertical fleshy scale onion
stem leaves

2. Corm short, vertical swollen gladiolus

stem stem base
3. Rhizome horizontal stem entire ginger
length of
stem
4. Tuber side branch of tip of stem potato
stem side branch
Angiosperm Life Cycle
Plant reproductive modes
• Comparison of reproductive modes of plants:
– Angiosperm life cycle

How are new organisms produced?

 Significance of sexual reproduction

Sexual reproduction plays an important role in creating and

maintaining vast genetic variability in crop plants, which is
essential for crop improvement

Sexual reproduction offers opportunities to combine desirable

genes together from different sources.

Crossing over takes place only during meiosis and leads to new
gene combinations.

Crossing over does not take place in asexually reproducing

species.

In asexually propagating species variability is created only

through somatic mutations.
Apomixis: development of seed without sexual fusion
(fertilization).

In apomixes, embryo develops without fertilization. Thus

apomixis is an asexual means of reproduction. Apomixis
is found in many crop species.

Apomixis: genetically controlled reproductive process by

which embryos and seeds develop in the ovule without
female meiosis and egg cell fertilization. Apomixis
produces seed progeny that are exact replicas of the
mother plant (Ramalu et al, 1998).

Apomixis: natural process that allows clonal production

through seed, resulting in offspring that are genetically
identical to the mother plant.

Apomixis allows the immediate fixation of any genotype

including F1 hybrid (Trends in Pl Science, 1998).
Types of Apomixis
A. Obligate apomixis:
Reproduction in some species occurs only by
apomixis. This apomixis is termed as obligate
apomixis.

B. Facultative apomixis:
But in some species sexual reproduction also occurs
in addition to apomixis. Such apomixis is known as
facultative apomixis
Parthenogenesis:
Parthenogenesis refers to development of embryo from the egg
cell without fertilization: When the embryo develops from a
haploid egg cell, it is known as haploid parthenogenesis
(Example: Solanum nigra.).
Sometimes, embryosac develops without reduction division
which gives rise to diploid embryos. Such parthenogenesis is
known as diploid parthenogenesis. (Example: Taraxacum)

Apogamy: The origin of embryo from either synergids or

antipodal cells of the embroyosac is called apogamy. . It is of
two types: viz. (1) haploid apogamy and (2) diploid apogamy
(Ex: Allium, Iris,).
Apospory:

In apospory, first diploid cell of ovule lying outside the

embryosac develops into another embryosac without reduction.
The embryo then develops directly from the diploid egg cell
without fertilization.

Apospory is of two types: viz. (1) generative apospory

(archesporium cell- Parthenium) and (2) somatic apospory
(nucellus or integument-. Malus, Crepis, Poa ).

Adventive embryony:

The development of embryo directly from the diploid cells of

ovule lying outside the embryosac belonging to either nucellus
or integuments is referred to as adventive embryony.
There is no production of another embryosac like apospory. Ex:
Citrus and Mango.
Fig 6. Longitudinal Section of a Mature Ovule (anatropous type)
Fig. 1. Comparison of sexual and asexual reproduction. Reduced life cycle
stages (n) are in white, unreduced stages (2n) are in black.
Figure 1. Main developmental
pathways of natural apomixis in
flowering plants (adapted from
Hörandl, 2018).
Meiotic developmental pathways
(c,e) and biparental seed
development (d,e) (green
gametophytes, embryo, and
endosperm tissues); apomictic
developmental pathways (a,b,d) and
maternal seed development (a–c,e)
(yellow gametophytes and
endosperm tissue, red egg-cell and
embryo tissue); blue seed embryo is
derived from a fertilized unreduced
egg-cell. MMC, megaspore mother
cell; MC, megaspore; NC, nucellus
cell; BIII hybrid, offspring produced
by fertilization of unreduced egg
cells. Size of nuclei corresponds to
relative ploidy level.
 Terms Brief description/definition
A. Asexual Reproduction Multiplication of plants without fusion of male and female
gametes
1. Vegetative Reproduction Multiplication by vegetative plant parts
a. Natural Multiplication by Rhizome, tuber, corm, bulb, runner suckers
and stolon
b. Artificial Multiplication by stem and root cuttings, rafting, layering and
budding

2. Apomixis Development of embryo without sexual fusion

Parthenogenesis Development of embryo from egg cell without fertilization
Apogamy Development of embryo either from synergids or antipodal cells
Apospory Origin of embryo from diploid egg cell of another embryosac
developed from diploid 'tissues.
Adventive Embryony Origin of embryosac directly from diploid cells belonging to
either nucellus or integument.

B. Sexual Reproduction Multiplication of plants by fertilized embryos.

Autogamy Development of seed by self pollination.
Allogamy Development of seed by cross pollination
Causes of parthenogenesis:

inability of the pollen tube to discharge the contents

inside the embryosac.
insufficient attraction between male and female
gametes
early degeneration of the sperm
very long style
schlerenchymatous style
short pollen tube
slow rate of pollen tube growth
stimulation of pollination in the absence of pollen tube
incompatibility.
Arificial induction of Parthenogenesis:

by the stimulation of widely related pollen or

foreign pollen

by low temperature,

by pollinating with X-ray irradiated pollens

by treatment with certain chemicals like belviton,

Auxin, GA3. All these help in inducing
parthenogenetic development of egg cell.
Mode of Pollination
Self and Cross
Pollination
Autogamy: Self Pollination: Inbreeding

Development of seed by self pollination is known as

autogamy.

Autogamy is the closest form of inbreeding.

Autogamy leads to homozygosity.

Autogamous species develop homozygous balance

and do not exhibit significant inbreeding depression.
Allogamy: Cross Pollination: Outbreeding

Development of seed by cross pollination is called

allogamy.

This is the common form of outbreeding.

Allogamy leads to heterozygosity.

Allogamous species develop heterozygous balance

and exhibit significant inbreeding depression on
selfing.
Mechanisms promoting autogamy (Causes of self pollination):

Bisexuality.
Presence of male and female organs in the same flower is known
as bisexuality. All the self pollinated plants have hermaphrodite
flowers.

Homogamy.
Maturation of anthers and stigma of a flower at the same time is
called homogamy. As a rule, homogamy is essential for self
pollination.

Cleistogamy.
When pollination and fertilization occur in unopened flower
bud, it is known as cleistogamy. wheat, barley, oats and several
other grass species. Flower never open.
Chasmogamy:
Flower do open but self pollination occurs just before
anthesis, is known as chasmogamy. Ex: wheat, barley,
rice and oats.

Position of Anthers:
In some species, stigmas are surrounded by anthers in
such a way that self pollination is ensured.
Ex: tomato and brinjal.

In some legumes, the stamens and stigma are enclosed

by the petals. Ex: greengram, blackgram, soybean,
chickpea and pea.

Geitinogamy: Special term for maize

Mechanisms promoting allogamy (Causes of cross pollination):

Dicliny. It refers to unisexual flowers.

Monoecy:
When male and female flowers are separate but present in the
same plants, it is known as monoecy.
In some crops, the male and female flowers are present in the
same inflorescence such as in mango, castor and banana.
In some cases, they are on separate inflorescence as in maize.
Other examples are cucurbits, grapes, strawberry, cassava,
rubber etc

Dioecy:
When staminate and pistillate flowers are present on different
plants, it is called dioecy. Ex: papaya, date palm, pointed gourd,
teasle gourd, spinach, hemp, asparagus, etc
 Table 5.3 Terminologies for Sex Expression in Plant

Type of Plants Expression of Sex

Hermaphrodite Perfect flower (bisexual; a flower with androecium and gynoecium)
Monoecious Separate male and female flowers on the same plant (not
synonymous with imperfect and should never be applied to
individual flower)
Dioecious Separate male and female flowers on different plants
Andromonoecious Perfect and male flowers on the same plant
Gynomonoecious Perfect and female flowers on the same plant
Trimonoecious Perfect, female, male flowers on the same plant (polygamous)
Androdioecious Perfect and male flowers on different plants
Gynodioecious Perfect and female flowers on different plants
Source: From Westergaard, M., Adv. Genet., 9, 217–281, 1958. With permission.
Dichogamy: Maturation of anthers and stigma of the
same flower at different times.

Protogyny :When pistil matures before anthers, it is

called protogyny such as in pearl millet.
Protandry: When anthers mature before pistil, it is
known as protandry. Ex: maize, sugarbeet, potato and
several other species.

Heterostyly:
When styles and filaments in a flower are of different
length, it is called heterostyly. It promotes cross
pollination. Ex: Linseed
• Herkogamy:
Hindrance to self-pollination due to some physical barriers such
as presence of hyline membrance around the anther is known as
herkogamy. Such membrane does not allow the dehiscence of
pollen and prevents self-pollination: Ex: Alfalfa.

• Self incompatibility:
The inability of fertile pollens to fertilize the same flower is
referred to as self incompatibility.
It prevents self pollination and promotes cross pollination. Ex:
Brassica, Radish, Nicotiana, and many grass species. It is of two
types sporophytic and gametophytic .

• Male sterility:
In some species, the pollen grains are non functional. Such condi-
tion is known as male sterility. It prevents self-pollination and
promotes cross pollination. Three types: viz, genetic, cytoplasmic
and cytoplasmic genetic. It is a useful tool in hybrid seed
SIGNIFICANCE OF POLLINATION

The mode of pollination plays an important role in plant

breeding. It has impact on five important aspects :

Gene action

Genetic constitution

Adaptability

Genetic purity and

Transfer of genes.
Determination of mode of reproduction of a crop species:

Critical examination of flower

 Mechanism like dioecy, monoecy, protandry, protogyny =
Cross pollination
 Mechanism like bisexuality, homogamy, cleistogamy = self
pollination.
Seed set under isolation
 If seed set, then the plant is to be said as self pollinated
 If do not seed set, then the plant is said to be cross pollinated

Seed set under isolation with bagging or caging

 Seed set is only indicative of self pollinated crop
 No seed set is the indicative of cross pollinated crop

Selfing and inbreeding effect on the vigour of the plant

 Loss of vigour due to inbreeding is common in cross
pollination
Crop Groups based on pollination:
 Self pollinated crop: less than 5% cross
pollination
 Often self pollinated crop: more than 5% cross
pollination
 Cross pollinated crop: less than 5% self
pollination
 Often cross pollinated crop: more than 5% self
pollination
Unisexial flower: Monoecism
 Classification of crops based on mode of
pollination and mode of reproduction
Autogamous species Allogamous species Often allogamous species
Rice, wheat, barley, oat, Corn , pearlmillet, rye, Sorghum, cotton,
cheakpea, pea cowpea, alfalfa, raddish, cabbage pigeonpea, tobacco, rai,
soybean, blackgram, ,sunflower, sugerbeet, tobacco, triticale etc..
common bean, mothbean, castor, red clover, white
linseed, lentil, sesamum, clover, safflower, spinch,
khesri, sunnhemp, chilles. onion, garlic, turnip,
Tomatoes, brinjal, okra, squash, muskmelon, water
peanut, potato etc.. melon, cucumber,
pumpkin, kenaf, oilpalm,
carrot, coconut, papaya ,
sugercane, coffee, cocoa,
tea,apple, pears, peaches,
cherries, grapes, almond,
strawberries, pineapple,
banana, irish, cassava, taro,
rubber, sweet potato etc..
Floral Biology of
crop plants
Breeding methods applicable to crop species depends on
 mode/methods of reproduction and
 floral biology of the species

Floral biology of crop plants

 A flower usually consists of sepals, petals, stamens and/ or pistil
 A flower containing both stamens and pistil is called a perfect or
hermaphrodite or complete flower
 If it contains stamens but not pistil is known as staminate flower, while a
pistillate flower contains pistil but not stamens is called incomplete flower.

Floral biology
 Floral biology is the study of the science of flower which includes opening of
the flower (antheisis), dehiscence of anthers, pollen viability and stigma
receptivity (Kallo, 1988).
 Floral biology is the study of flower life which mainly includes taxonomy,
physiology and embryology

In taxonomy
Number and relative position of the floral parts exposed including nectarines and
flower colors
In physiology
 Time of flower bud emergence
 No. of flower stalk/plant and no. of flower/inflorescence
 Time of anthesis and its duration
 Time of anther dehiscence and duration of pollen viability
 Time of stigma receptivity and its duration
 Time of availability of nectare
 Withering time of floral parts
 Causes of self or cross pollination

In embryology
 Time required for pollen germination and pollen tube growth down to the
ovary
 Time required for fertilization and no. of ovule fertilized
 Embryo endosperm relationship

Parameters of floral biology are influenced by environmental factors like

temperature, light, humidity and genetic factors as well. Deviation in different
parameters also occurred at different locations