PROPAGATION OF CROPS (CONTINUED) Lesson note

PROPOSED LESSON NOTE FOR THE SECOND WEEK ENDING 23^th SEPTEMBER, 2022

2022/2023 ACADEMIC SESSION

SUBJECT: AGRIC SCIENCE

CLASS: GRADE 8

NUMBER OF STUDENTS: 21

AVERAGE AGE: 12+ YEARS

PERIOD(S): 2^nd AND 5^th PERIOD ON MONDAY AND FRIDAY RESPECTIVELY

GENDER: MIXED

DURATION: 40 MINUTES

DATE: 19/09/2022

TOPIC: PROPAGATION OF CROPS (CONTINUED)

SPECIFIC OBJECTIVES: By the end of the lesson the students should be able to;

i. explain asexual propagation;

ii. state the advantages and disadvantages of asexual propagation.

ENTRY BEHAVIOUR: Students are familiar with propagation of crop by seed.

INSTRUCTIONAL METHODS/TECHNIC: Questions, simulation, visual.

INSTRUCTIONAL MATERIALS: Textbook, lesson note, laptop, projector, marker, whiteboard, Pictures showing grated mango, cassava stem.

INTRODUCTION: Questions posed to the students include

Question 1: How do you plant cassava?

Expected Answer: You cut the cassava stem, dig the soil and put the stem and cover it with soil

STEP I: CROP PROPAGATION BY VEGETATIVE ORGANS (ASEXUAL)

You may not know that cassava is propagated by part of its stem. When cassava is ready for harvest, its tubers which are below the ground, are dug out. The tuber may be used for making different food items such as fufu, gari. lt an can also be used for making starch or paste (gum). The leaves on the cassava stems are removed and the stems are cut into pieces of about 20-30cm and up to 1 metre in length. The short stems which are known as 'stem cuttings' are stuck into the ground at the beginning of a new planting season to propagate cassava. Each stem cutting has at least four to six buds. The longer stem cuttings of up to 1 metre in length give a bigger yield of cassava tubers. When we use part of a plant other than its seed to get (produce) more types of the same plant, this is called "Vegetative Propagation". Methods of asexual propagation include budding, grafting, cutting, layering.

Question 2: Can you name three other crop plants that can be propagated in this way?

Expected Answers: water leaf, sugar cane, mango

Asexual propagation involves reproduction from the vegetative parts of plants since these parts can grow again i.e. regenerate. For instance, stem cuttings have the ability to form adventitious roots, while root cuttings can grow a new shoot system. Leaves can in fact grow new roots and shoots. A stem and a root or two stems can be grafted (joined) together to produce a new plant. Farmers, gardeners and horticulturists all make use of vegetative propagation to produce new plants from virtually any vegetative part. Crops can therefore be increased in number by planting parts of the different vegetative organs such as stems, roots or leaves.

We have known already that the method is called Vegetative Propagation or Asexual Reproduction. Cassava, for example, is propagated from stem cuttings. Man has learnt through experience to multiply his plants vegetatively by using many methods or techniques. Some of these practices are both an art and a science. The art of vegetative plant propagation can only be learnt from an experienced propagator or through practice. Onion and garlic is propagated from bulb, pineapple is propagated from sucker, ginger is propagated from corm,

Question 3: What do you think are the likely advantages of asexual propagation?

STEP II: ADVANTAGES OF ASEXUAL PROPAGATION

(i) Vegetative propagation has the advantage of producing new crops which look exactly like the original parent plant. If, for instance, you propagate mango trees from a mango plant which is tall and has very many big, succulent, sweet, non-fibrous fruits, all the new mango trees will also be tall and carry very many big, succulent, sweet, non-fibrous fruits.

(ii) Crops that are vegetatively propagated normally have uniform yields, similar crop quality and come into bearing (i.e. fruiting) early and at the same time.

(iii) You can get many new plants from one plant, and very quickly too. Plants which look differently from all others, but which are special or are considered of valuable material can be easily and quickly multiplied by using this method.

(iv) Vegetatively propagated crops mature faster and yield higher than those raised from seeds. For instance, vegetatively propagated cocoa starts to bear fruits in eighteen months to two years, whereas those produced from seeds take four to five years to bear fruits. Plants that are growing under adverse soil and weather conditions when they are vegetatively propagated perform better than their counterparts that were raised from seeds.

(vi) It is also the use of vegetative propagation that can assure retention of resistance to diseases and pests of the original plant.

DISADVANTAGES OF ASEXUAL PROPAGATION

i. The new plants may not grow uniformly if some of them are planted on poor soil.

ii. Some of the cuttings could readily spread the much-feared (dreaded) disease of cassava mosaic virus if the parent plant was infected by the disease. This shows that the disease that was existing in the parent stock i.e. cassava stem cuttings in this case, shows up (is manifested) in the new offspring plants. It is therefore very important that only matured, healthy, disease-free and vigorous parent plants are used for vegetative propagation.

iii. Vegetative propagation is generally more expensive than the use of seeds, because the planting materials e.g. stem cuttings are usually bulky, they are not easy to transfer or carry from place to place and moreover, they are not easily stored and they require a lot of space for their storage.

SUMMARY/CONCLUSSION:

i. Asexual propagation involves reproduction from the vegetative parts of plants since these parts can grow again i.e. regenerate.

ii. There advantages as well as disadvantages of asexual propagation.

EVALUATION: Oral questions

1. What is asexual propagation? Name two asexual methods by which crops could be propagated.

2. List the advantages and disadvantages of asexual propagation.

ASSIGNMENT:

1. What are the advantages of vegetative propagation?

2. What are the disadvantages of vegetative propagation?

3. What characters do plant breeders select in an effort to improve the type of crops that they grow?

4. How can you prevent the spread of diseases in vegetative propagation?