Advanced Plant Production

Transcription

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2 Advanced Plant Production Student s Book FET FIRST Level 4 W Burger

3 FET FIRST Advanced Plant Production NQF Level 4 Student s Book W Burger 2008 Illustrations and design Macmillan South Africa (Pty) Ltd 2008 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, photocopying, recording, or otherwise, without the prior written permission of the copyright holder or in accordance with the provisions of the Copyright Act, 1978 (as amended). Any person who does any unauthorised act in relation to this publication may be liable for criminal prosecution and civil claims for damages. First published Published by Macmillan South Africa (Pty) Ltd Private Bag X Northlands Gauteng South Africa Text design by Resolution Cover design by Deevine Design Artwork by Alan Kennedy Typesetting by Resolution The publishers have made every effort to trace the copyright holders. If they have inadvertently overlooked any, they will be pleased to make the necessary arrangements at the first opportunity. eisbn: WIP: 2095M000 It is illegal to photocopy any page of this book without written permission from the publishers. The publisher would like to thank the following for permission to use photographs in this book: The Gardener Magazine, Johan Gerber, pages ; Kim Smith, page 73

4 Contents Topic 1 Plant propagation Module 1: Natural plant propagation Unit 1.1: Asexual plant production Unit 1.2: Sexual plant production Unit 1.3: Pollination and fruit setting Module 2: Artificial plant propagation Unit 2.1: Plant propagation methods Unit 2.2: Techniques of plant propagation by seeds Unit 2.3: Techniques of vegetative plant propagation Unit 2.4: Techniques of plant propagation grafting and budding Unit 2.5: Selecting plant materials and hormones for plant propagation Module 3: Nursery techniques Unit 3.1: Nursery operations and seed propagation Unit 3.2: Container techniques in a nursery Unit 3.3: Nursery operations and vegetative propagation Topic 2 Flower production Module 4: Growing flowers for the market Unit 4.1: Flower cultivars for the markets Unit 4.2: Propagation techniques relevant to flower production Module 5: Protecting flowering plants from pests and diseases Unit 5.1: Pests of flowering plants and their control Unit 5.2: Diseases of flowering plants and their control Module 6: Managing flower production Unit 6.1: Planting of flowers Unit 6.2: Caring for flower plants in containers Unit 6.3: Nursery operations Portfolio of Evidence Guideline Index A guide to the responsible control of insect, mite and soil pests and diseases Colour photographs of some common flowering plants propagated in nurseries

5 Colour illustration of soil testing kit it to determine the nutrient content and ph of soil water Colour photographs of Nature s helpers: Natural predators of plant pests and diseases Colour photographs of organisms that damage plants and the symptoms of damage and disease

6 Topic 1 Plant propagation 1

7 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 through root development from various parts of the plant, i.e. the vegetative parts. We call this kind of plant reproduction asexual or vegetative reproduction. 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. Words & Terms Propagation: reproducing or making more of the same Sexual reproduction: in a plant, sexual reproduction happens when pollen is transferred from the anthers onto the stigma of a flower in a process called pollination Asexual reproduction: in a plant, asexual reproduction takes place through the non-reproductive or vegetative parts of a plant, e.g. the roots, stems and leaves Pollination: to transfer pollen from the anthers to the stigma of a flower Vegetative: the non-reproductive parts of a plant, e.g. the roots, stems and leaves 2 Module 1

8 Unit 1.1: Asexual plant reproduction 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 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 the end of something such as a stem Module 1 3

9 Pedical which develops into the new flower shoot Leaf New plant developing from a terminal (end) bud Side shoot of the rhizome Rhizome Old part of 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

10 1.1.3 Bulbs 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. The onion is a very good example of a plant that propagates vegetatively by forming bulbs 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. All grape cultivars and many perennial shrubs are propagated by means of slips (or cuttings) 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. Fig. 1.2: Bulb of the onion mm Internode length Fig. 1.3: A vine slip Fleshy leaves Terminal bud from which flowers develop New small bulb Underground stem Adventitious roots Node?? Did you know? Slips or cuttings must be cut from mother plants that show good growth and high productivity. Mother plant Shoot (runner) New plant Soil surface Words & Terms Node: the place on a plant stem from which leaves or branches grow Node length: the distance between two nodes Internode: the section of the stem between two nodes Adventitious roots Cultivar: a variety of a plant Perennial: plants that live for more than two years Fig. 1.4: Strawberries as examples of propagation by means of runners Module 1 5

11 1.1.6 Tubers 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. The potato is a well-known example of a plant that propagates by means of tubers. Assessment activity 1 Fig. 1.5: Tubers of a potato plant Soil surface Main stem Side stem New tuber Adventitious roots Old tuber shrinking away 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) 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

12 Assess yourself Assess your performance in the following activities: Activity 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 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 on page 12 shows you how this takes place. Module 1 7

13 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 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. Words & Terms Cross-pollination: transferring pollen from the anther of a flower on one plant to the stigma of a flower on another plant Self-pollination: transferring pollen from the anther to the stigma of the same flower or another flower on the same plant 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

14 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 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

15 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 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.?? 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. 10 Module 1

16 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

17 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). Words & Terms Receptive: one that receives Gametes: germ cells that fuse together during reproduction Male reproductive organ Anther filament Petals Stigma Style Ovary Ovules that develop into seeds Sepals Female reproductive organ Pedicel Fig. 1.7: Generalised diagram of a flower adapted to insect-pollination Pistil Ovary Style Stigma Pollen grain Pollen tube Male gametes Vegetative nucleus Integument Ovum (egg cell) develops into the embryo after fertilisation Endosperm cell develops into starch for the growing embryo Ovule Germ sac Remains of pollen wall Pollen tube Male gametes Vegetative nucleus Fig. 1.9: Germinating pollen grain Fig. 1.8: Process of fertilisation 12 Module 1

18 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 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. Words & Terms Zygote: a fertilised ovum Endosperm: the tissue inside the seed of a flowering plant that surrounds and feeds the embryo Cotyledons: the first leaves Hypocotyl: the part of an embryo plant between the cotyledons and the radicle Integuments: outer protective layer or covering Micropyle: a small hole in the seed coat 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. Module 1 13

19 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 Transfer of pollen from anther (of one flower) to stigma (of another flower). The transfer of pollen is called pollination. It can take 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 other animals. The shapes, smells and bright colours of the flower attract them. When a pollen grain lands on a stigma, it germinates 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. One of the male gametes combines with the ovum (egg cell) to form a zygote. Process of reproduction in animals Mating of male and female animals and the release of semen into the vagina (Cross-fertilisation; male and female animals) (Attraction between male and female) (Movement of sperm) (Sperm penetrates ovum) (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 (Foetal phase) inside the ovule. As a result, the ovule enlarges. 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 (sepals) (petal crown) (pollen production) stigma (gluma) Wind-pollinated flower (gluma) 14 Module 1

20 Assess yourself Assess your performance in the following activities: Activity 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 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. Module 1 15

21 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: 16 Module 1

22 1.3.2 Fruit setting 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. 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. Words & Terms Fruit setting: to produce fruits or seeds after pollination, and for these fruits and seeds to develop Parthenocarpy: the process that occurs when fruit setting takes place without fertilisation 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 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). Fig. 1.10: Dry, simple fruits (nuts) Fruit stalk Nut Remains of style Pericarp?? 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. 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 Module 1 17