Download Advanced Plant Production Level 4 Student`s Book

Advanced
Plant Production
Student’s Book
FET FIRST
Level 4
W Burger
FET FIRST Advanced Plant Production NQF Level 4 Student’s Book
© W Burger 2008
© Illustrations and design Macmillan South Africa (Pty) Ltd 2008
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First published 2008
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South Africa
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Cover design by Deevine Design
Artwork by Alan Kennedy
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eISBN: 9781431020713
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Contents
Topic 1 Plant propagation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Module 1: Natural plant propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Unit 1.1: Asexual plant production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Unit 1.2: Sexual plant production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Unit 1.3: Pollination and fruit setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Module 2: Artificial plant propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Unit 2.1: Plant propagation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Unit 2.2: Techniques of plant propagation by seeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Unit 2.3: Techniques of vegetative plant propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Unit 2.4: Techniques of plant propagation – grafting and budding . . . . . . . . . . . . . . . . . . . . . . . . .45
Unit 2.5: Selecting plant materials and hormones for plant propagation . . . . . . . . . . . . . . . . . . . .52
Module 3: Nursery techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Unit 3.1: Nursery operations and seed propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
Unit 3.2: Container techniques in a nursery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Unit 3.3: Nursery operations and vegetative propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
Topic 2 Flower production
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Module 4: Growing flowers for the market . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Unit 4.1: Flower cultivars for the markets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87
Unit 4.2: Propagation techniques relevant to flower production . . . . . . . . . . . . . . . . . . . . . . . . . . .96
Module 5: Protecting flowering plants from pests and diseases . . . . . . . . . . . . . .104
Unit 5.1: Pests of flowering plants and their control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
Unit 5.2: Diseases of flowering plants and their control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113
Module 6: Managing flower production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
Unit 6.1: Planting of flowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
Unit 6.2: Caring for flower plants in containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128
Unit 6.3: Nursery operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
Portfolio of Evidence Guideline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
A guide to the responsible control of insect,
mite and soil pests and diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144
Colour photographs of some common flowering
plants propagated in nurseries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
Colour illustration of soil testing kit it to determine
the nutrient content and pH of soil water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151
Colour photographs of Nature’s helpers:
Natural predators of plant pests and diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
Colour photographs of organisms that damage plants
and the symptoms of damage and disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
Topic 1
Plant
propagation
1
Module 1
Natural plant
propagation
Overview
In this module you will:
• explain asexual plant propagation methods with examples
• explain sexual plant propagation methods including
pollination and fruit setting.
Introduction
Production of food – vegetables, fruit, cereals and fibre (such as
cotton) – can only happen if the plant is able to reproduce. You must
have noticed that under natural conditions, plants reproduce
themselves. There are two main methods of reproduction or
propagation in nature. These methods are sexual reproduction and
asexual reproduction.
In nature, flowers develop on plants as a result of pollination and
fertilisation. Pollen is carried by wind, water or animals (mainly
insects). The pollen grain is transferred from the male flower to the
female flower. This is sexual
reproduction as it involves a male and
a female. But in nature you will also
find that some plants reproduce
Words &
through root development from
Terms
various parts of the plant, i.e. the
P
ro
p
agation: re
vegetative parts. We call this kind of
producing
making m
or
ore of the
plant reproduction asexual or
same
S
exual rep
vegetative reproduction.
roduction
During domestic plant production
practices, the farmer uses the same
basic principles of plant
propagation that are found in
nature – the farmer will use seeds
for sexual reproduction of plants
or will use vegetative parts of the
plant for asexual production.
: in a plan
sexual rep
t,
rod
pollen is tr uction happens wh
en
ansferred
fr
anthers o
nto the sti om the
gma of a
flower in
a process
called
‘pollinatio
n’
Asexual re
productio
n: in a pla
asexual re
nt,
productio
n takes pla
through th
ce
e non-rep
roductive
vegetative
or
parts of a
plant, e.g
roots, ste
. the
ms and le
aves
Pollinatio
n: to tran
s
fer pollen
from the a
nthers to
the stigm
a flower
a of
Vegetativ
e: the non
-reproduc
parts of a
tive
pla
stems and nt, e.g. the roots,
leaves
2
Module 1
Unit 1.1: Asexual plant
reproduction
1.1.1 Introduction
Asexual reproduction involves reproduction (i.e. the production of
offspring) that does not involve the fertilisation (i.e. there is fusion of
gametes). The most common form of sexual reproduction, and one
that you may be familiar with, is vegetative reproduction. Vegetative
reproduction is reproduction using the vegetative parts of the plant
such as fleshy underground stems (e.g. rhizomes or bulbs),
aboveground stems or leaves. Vegetative reproduction occurs
naturally in many plants. This natural feature has been exploited by
farmers for many hundreds of years. Vegetative reproduction is
commonly called vegetative propagation by gardeners and
horticulturists.
The advantage of vegetative propagation is that it is quick and the
offspring resemble the parent because they are genetically identical to
the parent plant. Some examples are:
• Potatoes that propagate by means of tubers or a section of tuber
• Strawberries that propagate by means of runners
• Pear trees in an orchard that have been propagated by stem or bud
cuttings
• Succulent nursery plants that are propagated from sections of a
leaf
• Ferns which can be propagated from rhizome cuttings
• Onion plants that can be propagated by separating out the bulbs
The rest of this unit gives you an overview of the some of the more
common methods of plant propagation used in nurseries. Module 2
and Module 3 will give you more details on these techniques and
more practical information.
1.1.2 Rhizomes
A rhizome is a thickened underground stem that grows more or less
parallel to the soil surface. There are terminal buds at the tip of the
rhizome. The plant increases in length through these terminal buds.
New plants may also be formed from the buds. Roots will develop at
the nodes of the stem (the ‘joints’), as you can see in Fig. 1.1 on the
next page.
Words &
Terms
Terminal:
found at th
e end of
somethin
g such as
a stem
Module 1
3
Pedical which
develops into the
new flower shoot
Leaf
New plant
developing from
a terminal (end)
bud
Rhizome
Old part of
rhizome
Side shoot of
the rhizome
Adventitious roots
Fig. 1.1: A rhizome
A rhizome is a thickened underground stem that grows more or less
parallel to the soil surface. There are terminal buds at the tip of the
rhizome. The rhizome increases in length due to growth from these
terminal buds. New plants may also be formed from these buds.
Roots will develop at the nodes of the rhizome. As the rhizome grows
longer, the new shoots that have grown above the ground form a
dense clump of plants. These plants can be separated by dividing up
the rhizome. Care must be taken when dividing to make sure that
each plant let is still attached to a section of the rhizome with a good
number of roots. Each section of the rhizome must also have two or
more buds to ensure the potential for new growth.
Think about it
If you plant a rhizome with no
buds, it cannot produce shoots
and it will die.
In the workplace
Timing is very important when dividing up rhizomes or bulbs. In most regions it is best to wait for
the plant to finish blooming before digging up the rhizome or bulb. Many rhizomatous plants suffer if
they are not divided up, so dividing them every 3 to 5 years keeps them vital and increases flowering.
Common nursery plants that have rhizomes include: maidenhair ferns elephant’s ear; many lilies and
irises. You will learn more about vegetative propagation using of various plant organs, including
rhizomes, later in this course.
4
Module 1
1.1.3 Bulbs
Fleshy leaves
A bulb is a short underground stem with a number of
fleshy leaves in which food is stored. At the upper end
of the underground stem there is a terminal bud that is
completely enclosed by fleshy leaves. At the bottom end
of the stem there are many short roots. One or more buds
may develop on the stem between the fleshy leaves.
Under favourable conditions, these buds produce a
number of smaller bulbs which in turn may grow out
to form new plants.
Terminal bud
from which
flowers develop
New small bulb
Underground stem
The onion is a very good example of a plant that
propagates vegetatively by forming bulbs.
Adventitious roots
Fig. 1.2: Bulb of the onion
1.1.4 Cuttings (or slips)
Cuttings (or slips) are plant shoots that are cut
off from the mother plant and planted in order
to propagate the parent plant. The cuttings
develop their own roots and leaves.
Medium-thick shoots about 10 mm in diameter
with a medium node length give the best results.
300 – 350 mm
Internode length
Node
Fig. 1.3: A vine slip
All grape cultivars and many perennial shrubs are propagated
by means of slips (or cuttings).
?
1.1.5 Runners
Runners are side shoots with very long internodes. Roots grow where
a shoot touches the ground; a new plant is formed at that point.
To start with, this plant is fed by the mother plant. The new plant
eventually separates from the mother plant when the shoot rots away.
Strawberries are a good example of a plant that propagates by means
of runners.
Mother plant
Shoot (runner)
New plant
Soil surface
Adventitious roots
??
Did you know?
Slips or cuttings must be cut
from mother plants that show
good growth and high
productivity.
Words &
Terms
Node: the
place on a
plant stem
from whic
h leaves o
r branche
grow
s
Node leng
th:
between tw the distance
o nodes
Internode
: the secti
on of the
stem betw
een two n
odes
Cultivar:
a variety o
f a plant
Perennial:
plants tha
t live for
more than
two years
Fig. 1.4: Strawberries as examples of propagation by means of runners
Module 1
5
1.1.6 Tubers
Soil surface
A tuber is a short, thickened underground stem in which
starch is stored. On the surface of the tuber there are
small, inactive or ‘sleeping’ buds from which roots and
then stems develop.
Main stem
Side stem
New tuber
The potato is a well-known example of a plant that
propagates by means of tubers.
Adventitious
roots
Old tuber
shrinking away
Fig. 1.5: Tubers of a potato plant
Assessment activity 1
Investigating methods of reproduction
Do an investigation in a garden or vegetable farm, either at your home or at the college. Make a list
of all the different kinds of plants in the garden. Identify the method of reproduction by means of
which each plant is propagated – asexual or sexual reproduction. In the case of plants which
reproduce asexually, identify the kind of vegetative reproductive organ that is involved.
Put your findings into a table as follows:
Kind of plant
Method of reproduction
Sexual
Asexual
(kind of vegetative reproductive
organ involved)
1.
2.
3.
Assessment activity 2
Drawing asexual reproductive organs
Draw and label the different types of organs that you found in the previous activity that were
involved in vegetative reproduction.
6
Module 1
Assess yourself
Assess your performance in the following activities:
Activity
1
2
3
4
5
Investigating methods of reproduction
Drawing asexual reproductive organs
1 = not achieved, 2 = not yet competent, 3 = competent, 4 = highly competent, 5 = outstanding
Unit Summary
The unit deals with the different ways in which plants reproduce vegetatively or asexually.
Unit 1.2: Sexual plant reproduction
1.2.1 Introduction
Sexual reproduction involves the coming together of the male and
female gametes to produce off spring that contain genetic material
from both gametes. Gametes are the male and female sex cells that are
involved in sexual reproduction. A gamete can be a sperm cell or an
egg cell as in mammals, or a male nucleus (inside the pollen tube) and
an egg cell in the ovule as in flowering plants. A gamete is produced
by meiosis, which is a special kind of cell division that produces cells
with half the number of genes (called n) found in the cells that make
up the rest of the plant or animal body. When the sex cells fuse
during fertilisation they form a zygote with the correct number of
genes for that species (called 2n). The zygote develops into an adult
plant or animal
Sexual reproduction in flowering plants involves the following
important steps:
• The production of gametes: The male gamete is enclosed in the
pollen produced at the end of the stamens in the pollen sacs; and
the female gamete is enclosed in the ovule produced in the ovary
of the flower.
• Pollination: This occurs when a ripe pollen grain reaches a ripe
stigma.
• Fertilisation: This occurs when the pollen tube that grows down
the style enters the ovule and the nuclei of the male and female
gametes fuse. Section 1.2.5 on page 12 shows you how this takes
place.
Module 1
7
• Fruit and seed development: The fertilised ovule develops into the
seed and the ovary develops into the fruit.
• Seed dispersal: Seed are dispersed (carried away from the parent
plant) by wind, water and animals. The advantage of dispersal is
that the new seedlings do not grow too close to the parent plants
and therefore do not compete for resources such as soil, water, soil
nutrients and sunlight.
• Seed germination: When a seed is dispersed and lands in an area
that is favourable for growth, the seed will germinate and a new
seedling will grow. If this seedling grows to adulthood and takes
part in sexual reproduction again, then we can say the sexual
reproductive cycle has been completed.
1.2.2 Pollination
Pollination is the process whereby a ripe pollen grain reaches a ripe
stigma of the same flower or of another flower on the same plant or
on another plant of the same species. Two main types of pollination
strategies are found in plants:
• Self-pollination
• Cross-pollination
Self-pollination
Self pollination occurs when the pollen grain from one flower reaches
the ripe stigma of the same flower or of another flower on the same
plant. If the pollen comes from another plant, and if the two plants
arise from the same pure-bred population, then we can also call this
process self-fertilisation. This kind of self-fertilisation occurs in cereals
(except rye and corn) and garden peas.
The flowers of some self-pollinating plants remain buried in the
ground to prevent cross-pollination, e.g. the flowers of groundnuts.
Others remain closed until fertilisation has occurred. In other selfpollinated plants that open, the stigma and the anthers usually ripen
at the same time to increase the chances of self-pollination.
The advantage of self-pollination is that the plant is not dependent on
a pollinator. Also, the offspring will resemble their parents, which
have successful characteristics. The disadvantage of self-pollination is
that the offspring are genetically very similar to the parent plant. This
reduces the amount of variation found in that population of plants.
Less variation means that the population of plants will not be able to
respond to dramatic environmental change. For example, if all the
plants in the population are only able to grow within a small
temperature range, then temperatures higher or lower than that range
may destroy the entire population. However, if the population shows
greater variation (e.g. a greater range of temperatures under which
they can grow), some plants in that population may survive if the
weather becomes extreme either way.
8
Module 1
Words &
Terms
Cross-po
llination:
tran
pollen fro
m the anth sferring
er of a
flower on
one plant
to the
stigma of
a flower o
n another
plant
Self-pollin
ation: tra
ns
pollen fro
m the anth ferring
er to the
stigma of
the same
flower or
another fl
ower on th
e same
plant
Cross-pollination
Cross-pollination takes place when a ripe pollen grain from one
flower reaches a ripe stigma of another flower of another plant of the
same species. Cross-pollination increases the genetic variation of a
population of plants of the same species because the offspring inherit
characteristics from both parent’s that combine in a way that is unique
to every offspring.
Many plants display both self- and cross-pollination. As a result the
chances of survival and successful pollination are increased.
1.2.3 Agents of cross-pollination
An agent of pollination is any natural force that aids pollination by
carrying the pollen from one flower to another. These natural agents
can be abiotic (non-living) such as wind and water or biotic (living)
such as insects and other animals. Plants have become adapted over
millions of years to the various pollinating agents in the environment.
Wind pollination
Many plants are pollinated by the wind. Most commonly these are the
plants of the grass family, such as the large number of wild grass
species and the well known cereal crops wheat and maize. Wind
pollinated plants have the following characteristics:
• They produce large amount of non-sticky and light pollen that can
be blown from flower to flower or from population to population.
• The usually lack large and/or colourful petals and sepals.
• The usually lack insect-attracting smells.
• The flowers are small and densely packed.
• They have large exposed and sticky stigmas for receiving the
wind-blown pollen.
• They have long well exposed anthers for releasing pollen into the
passing wind.
Many wind-pollinated plants also self-pollinate if the wind fails. Selfpollination can be seen a ‘back-up mechanism’ which will take place
if, for example, the windy season is erratic. Wind is a far more
unreliable pollinating agent than, for example, insects – which is
probably how this ‘back-up’ mechanism evolved.
Water pollination
Water pollination is not as common in flowering plants as wind and
insect pollination. Some wetland grasses and reeds as well as water
weeds and water lilies release their pollen into the water where it is
carried to receptive flower.
Module 1
9
Insect pollination
A large number of flowering plants are pollinated by insects. In fact,
flowering plants and insects have a long evolutionary history
together. During the Late Cambium period, many millions of years
ago, an explosion in the diversity of one lead to an explosion in the
diversity of the other. Insect-pollinated flowers have the following
characteristics:
• They attract insects in some way e.g. shape, colour and/or smell
• The relationship between a flowering plants and its insect
pollinator is often very specific, e.g. some species of orchard
resemble the mate of a certain species of wasp. When the wasp
tries to mate with the orchard, pollen sticks to the body of the
wasp and is transferred to another flower when the wasp pays the
other flower a visit. Pollination will only take place if this specific
species of orchard and wasp are present in the same place and at
the correct time of the year.
Among the insects that pollinate flowers are: butterflies, bees, beetles,
flies, wasps and ants. These pollinators, especially the bees, are very
important in the fruit and flower industry because without
pollination, seed will not set and fruit will not form.
Animal pollination
Birds and mammals such as bats and rodents pollinate plants as well.
Bird pollination is fairly common while bat and rodent pollination is
found mostly in tropical or subtropical forested areas.
The two large groups of birds that pollinate flowers are the sunbirds
of Africa and Asia and the humming birds of the Americas. Both
groups have long beaks that allow them to reach inside the corolla
tube of the flower. Hummingbirds are well known for their ability to
hover in front of a flower while taking in nectar. Sunbirds however, sit
on the flower stalk and collect the nectar.
Bird-pollinated flowers have the following characteristics:
• They often have a red, orange or yellow petals, sepals or stamens
which are attractive to birds.
• They often have a corolla tube formed by the fusion or partial
fusion of the petals of the flower.
• They are usually not scented as most birds do not have a welldeveloped sense of smell.
• They produce a larger amount of nectar than the insect pollinated
flowers as birds use more energy and require more nectar.
1.2.4 Wind- and insect-pollinated flowers
Most of the plants you will encounter in horticulture and agriculture
will be wind- or insect-pollinated. The flowers of plants that are
adapted to wind pollination often have no colour or strong smell.
An example is the wheat plant.
10
Module 1
?
??
Did you know?
There is a mutualistic
relationship (or relationship of
mutual benefit) between
flowering plants and bees. The
bees pollinate the flowers, while
the flowers produce nectar –
which the bees need to produce
honey. The flowers also produce
pollen, which the bees use to
produce wax in the beehive.
With this method of reproduction, there is no need for the flower to
have scent or colour as it does not need to attract insect pollinators.
This is different from the flowers that are pollinated by birds and
insects. Butterflies, bees, beetles, and so on are attracted to the shapes,
smell and bright colours of the flowers. When a bird or an insect visits
a flower for nectar, it acts as an agent of cross-pollination. The pollen
grains stick to it and brush off when it visits another flower.
Table 1.1: The most important differences between insectand wind-pollinated plants
Insect-pollinated flowers
• Well-developed and colourful petals/sepals
and /or strong attracting smells.
• Flowers often have elaborate shapes that attract
the insect or make it easy for the insect to land
and enter. Sometimes these shapes exclude
certain insects, only allowing certain species in.
• Stamens and anthers are positioned where the
insect will have maximum chance of coming into
contact with them.
• Pollen is sticky and heavier than windtransported pollen.
Wind-pollinated flowers
• Colour and smell not required for pollination.
As a result these have not developed or have been
lost during the evolutionary history of the plant.
• Small clustered flowers.
• Long stamens and anthers that protrude into the
wind, and often feathery stigmas to maximise the
chances of receiving pollen.
• Very light non-sticky pollen produced in large
quantities since the chances of successful
pollination are smaller than if the pollen was
carried on an insect.
Fig. 1.6: A wind-pollinated flower (wheat) and an insect-pollinated flower.
Can you recognise the differences listed in the table above?
Module 1
11
1.2.5 Example of sexual reproduction in a
typical flower
A pollen grain from the anther of a flower is transferred to the stigma
of another flower (called the receptive flower) of the same kind of
plant. As soon as the pollen grain lands on the stigma, it begins
germinating. The pollen grain grows down the style in the form of
a long pollen tube. The contents of the pollen grain move downwards
in the tube. The pollen grain has two nuclei: the vegetative nucleus
which determines the growth of the tube; and the generative nucleus.
The generative nucleus subdivides to form two male gametes (germ
cells that fuse together during reproduction).
Male
reproductive
organ
Words &
Terms
Receptive
: one that
receives
Gametes:
germ cell
s th
together d
uring repro at fuse
duction
Stigma
Anther
filament
Style
Female
reproductive
organ
Ovary
Ovules that
develop into
seeds
Petals
Sepals
Pedicel
Fig. 1.7: Generalised diagram of a flower adapted to insect-pollination
Stigma
Pollen grain
Pollen tube
Ovary
Pistil
Style
Male gametes
Vegetative nucleus
Pollen tube
Integument
Male gametes
Ovum (egg cell) develops into
the embryo after fertilisation
Endosperm cell develops into
starch for the growing embryo
Ovule
Germ sac
Fig. 1.8: Process of fertilisation
12
Remains of
pollen wall
Module 1
Vegetative
nucleus
Fig. 1.9: Germinating pollen grain
Fertilisation
The pollen tube grows through the opening of the ovum into the germ
sac. The vegetative nucleus now disappears. The tip of the pollen tube
splits open and releases two male gametes into the germ sac.
One of the male gametes combines with the ovum or egg cell to form
a zygote (a fertilised ovum). The other male gamete combines with
the endosperm cell to form the endosperm of the fruit.
Double fertilisation
This fertilisation of both of the male gametes in the pollen tube – one
with the egg cell and the other with the endosperm cell is called
double fertilisation
The development of the embryo
Words &
Terms
Zygote: a
fertilised
ovum
Endosperm
: the tissu
e inside th
seed of a
flowering
e
plant that
surrounds
and feeds
the embry
Cotyledon
o
s: the firs
t leaves
Hypocoty
l: th
plant betw e part of an embry
o
ee
and the ra n the cotyledons
dicle
Integume
nts: outer
protective
layer or c
overing
Micropyle
: a small
hole in th
seed coat
e
After fertilisation, endosperm develops from the fertilised endosperm
nucleus. This endosperm fills the entire germ sac, except for a small
space occupied by the embryo itself. Endosperm forms the tissue in
the cotyledons of the embryo. This tissue provides food for the
germinating embryo.
In the meantime, the zygote develops into an embryo. The embryo
develops to form a hypocotyl with a growth tip at the top, called the
plumule. In the case of dicotyledonous plants, the hypocotyl also
develops two cotyledons and a root tip (germ root).
The development of the seed
As a result of these changes, the germ sac enlarges and eventually
takes up all the space inside the ovule. The ovule now also starts to
enlarge. The integuments often harden and dry out to form the seed
covering (testa). A seed is therefore no more than a developed and
ripened ovule. The micropyle remains open, because this is where
water will later enter the seed during germination.
The development of the fruit
After the seed has developed, the stamens, petals and style of the
flower all fall off the plant. The ovary remains because it encloses and
protects the developing seed. When the ovule starts enlarging, the
ovary also enlarges and changes. The fruit now develops out of the
ovary. you will learn more about fruit setting in Unit 1.3.
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13
Learning activity 1
Comparing sexual reproduction in plants and animals
Study the table below. The first column gives a step-by-step description of the reproduction process
of plants. The second column contains keywords. Use these keywords to describe the same series of
steps as in the reproduction in animals. Compare each step for animals with the same step for
plants. Use the keywords in brackets to help you. The first answer has been filled in for you.
Process of reproduction in plants
Process of reproduction in animals
Transfer of pollen from anther (of one flower) to
stigma (of another flower).
Mating of male and female animals and the release of
semen into the vagina
The transfer of pollen is called pollination. It can take (Cross-fertilisation; male and female animals)
place between flowers of different plants (crosspollination) or between flowers of the same plant or
flower (self-pollination).
The agents of cross-pollination are bees, birds and
(Attraction between male and female)
other animals. The shapes, smells and bright colours
of the flower attract them.
When a pollen grain lands on a stigma, it germinates (Movement of sperm)
and grows down the style in the form of a pollen tube.
A pollen tube grows through the cervix of the ovum
into the germ sac.
(Sperm penetrates ovum)
One of the male gametes combines with the ovum
(egg cell) to form a zygote.
(Sperm cell fuses with ovum)
After fertilisation, the zygote develops into an embryo. (Ovum phase; embryonic phase)
The germ sac enlarges and takes up all the space
inside the ovule. As a result, the ovule enlarges.
(Foetal phase)
The ovule develops into a seed.
(Parturition)
Learning activity 2
Comparing insect-pollinated and wind-pollinated flowers
Compare a flower adapted to cross-pollination with one adapted to wind-pollination. Use the key
words in brackets to help you.
Insect-pollinated flower
Wind-pollinated flower
(sepals)
(petal crown)
(pollen production)
stigma (gluma)
(gluma)
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Module 1
Assess yourself
Assess your performance in the following activities:
Activity
1
2
3
4
5
Comparing sexual reproduction in plants and animals
Comparing insect-pollinated and wind-pollinated flowers
1 = not achieved, 2 = not yet competent, 3 = competent, 4 = highly competent, 5 = outstanding
Unit Summary
The unit deals with the different ways in which plants reproduce sexually.
Unit 1.3: Pollination and fruit
setting
1.3.1 Introduction
From Unit 1.2 you have seen that there is an important moment in
crop production. This is the moment when a ripe pollen grain from
the anther of a flower lands on the receptive stigma of that flower or
on the flower of another plant of the same species. From what we
have said here, you can work out a few of the conditions necessary
for a flower to be successfully pollinated:
• the pollen grain must be ripe
• the stigma must be receptive
• the ripe pollen grain must come into contact with a ripe stigma on
the same flower or between flowers of the same species.
This important moment is brought about by agents that transfer the
pollen from an anther to a stamen which, as you know, is called
pollination. The different methods of pollination – self-pollination and
cross-pollination – need different agents of pollination.
?
??
Did you know?
The crop farmer has no
control over some of the
agents of pollination. However,
there are agents that the
farmer can control to increase
pollination.
Wind, water and animals are the main agents of cross-pollination.
The wind
Grain plants are adapted in the following ways to wind pollination:
• They produce a large quantity of pollen.
• The pollen is light and dry so that the wind can blow it around
easily.
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15
•
•
Some pollen grains have air sacs that enable them to float through
the air (for example, the pollen of the pine flower).
The female flowers are usually very simple and bare so that pollen
can easily enter the flower to pollinate the stigma.
Water
In the case of water plants, the female flowers are carried on the water
surface and the male flowers are formed below the water. When the
male flowers are ripe, they are released and float to the water surface.
They drift up against the female flower, the pollen makes contact with
the stigma and pollination takes place.
Animals
Insects are the most important agents of cross-pollination in the
animal kingdom. Plants that are usually pollinated by insects and
birds are adapted to attract them. Examples of this adaptation are
brightly coloured petals, smells and nectar.
Assessment activity 1
Research on adaptations in pollination agents
The following five animal agents of pollination are adapted to transfer pollen grains from one
flower to the stigma of another flower. Look for information in books, wildlife magazines or on the
Internet and list the ways in which they are adapted. You can also make some direct observations
and come up with your own conclusions.
Bees: ___________________________________________________________________________________
________________________________________________________________________________________
Birds: __________________________________________________________________________________
________________________________________________________________________________________
Butterflies: _____________________________________________________________________________
________________________________________________________________________________________
Moths: _________________________________________________________________________________
________________________________________________________________________________________
Ladybirds: ______________________________________________________________________________
________________________________________________________________________________________
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Module 1
1.3.2 Fruit setting
Words &
Terms
Fruit setting can only take place after the two sex gametes have
combined. Anything that prevents this combination during pollination
will cause fruit setting to fail.
Fruit sett
ing: to pro
duce fruit
seeds afte
s or
rp
these fruit ollination, and for
s and see
ds to deve
lop
Partheno
carpy: the
process th
occurs wh
at
en fruit se
tting take
place with
s
out fertilis
ation
In certain types of fruit, pollination takes place but it may not lead to
fertilisation. The pollen, however, contains a hormone that causes
fruit setting to take place. When fruit is produced without the ovules
being fertilised, we call it parthenocarpy.
Different types of fruit are classified according to the way in which
they develop. There are simple, compound, multiple and accessory
fruits. We will look at each in turn.
Simple fruits
Simple fruits develop directly from the ovary. Examples of this type
of fruit are the dry, fleshy and stone fruits.
Dry fruits
?
??
Did you know?
Parthenocarpy occurs when
fruit setting takes place
without fertilisation. The type
of fruit that develops from this
process has no pips. Examples
of these are the Washington
navel orange, bananas and
eggplant. In modern farming –
many hormones are used –
such as giberellic acid, to
produce seedless fruit that has
a commercial value. Sultana
grapes are an example of
parthenocarpy. Treatment with
giberellic acid lets the grape
berries enlarge to the size
most people like. Thus there is
a good demand for these
grapes.
With these fruits, the ovary wall hardens to form a woody or leathery
skin. The seed itself is the part of the fruit that we can eat. Nuts are a
well-known example of dry simple fruits (see Fig. 1.10).
Fruit stalk
Nut
Remains of style
Pericarp
Fig. 1.10: Dry, simple fruits (nuts)
Fleshy fruits
The ovary wall (or part of it)
becomes fleshy when the seed
ripens. With berry fruit, such
as grapes, the whole wall
becomes fleshy (see Fig. 1.11).
a
Grapes (Vitas)
b
Longitudinal section
Fruit stalk
Seed
Placenta
Pericarp or fruit wall
Fig. 1.11: Berry fruits, e.g. grapes
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