Crop improvement cont'd

Agricultural Science S.S.S 3 First Term

WEEK 2

Crop improvement cont'd

Performance Objectives

Student should be able to:

1. State the process of crop improvement.

2. Discuss the process of crop improvement.

Content

Process of crop improvement

Three general approaches are available to plant breeders to improve their crops. These are:

1. Introduction: This is the introduction of crops from their centres of origin to new places where they can be successfully grown. This was how most of the crops that are now so important in Nigeria agriculture were brought originally from other countries. In this process, any crops being introduced into a country is quarantined to ascertain if it is disease-free. Introduction of new varieties of crops is achieved either by travellers from other countries or by importing these crops for the purpose of improving the existing local crops.

Advantages of introduction

1. It supplements already available stock in an area or country.

2. Improved stock with desirable characteristics can be acquired.

3. It leads to the development of new and superior crop varieties.

4. It helps to determine how well the crops can adapt to the soil and climatic conditions in the country.

5. Selected varieties are used for cross breeding local ones in order to produce high yielding, disease-resistant and adaptable varieties.

Disadvantages of introduction

1. Plant disease and pest alien to the country may be introduced into the country.

2. It may lead to a gradual loss of indigenous varieties.

3. The cost of introduction of new varieties is usually high.

4. It requires skill manpower to be successful.

5. New crops may find it difficult to adapt to the climatic and soil conditions of the new environment.

2. Selection: This is the process of choosing specific individuals or a group of plant from a mixed population. In other words, it is the process of picking out individuals or groups of plants having specific or desirable characteristics. This method of crop improvement has been practised for centuries and is still used by farmers on their farms, usually achieved through proper observation of growing crops with desirable qualities, selection acts only on plant characteristics that a be inherited by offspring. There are three major types of selection depending on what the objectives are.

 

I. Bulk selection: Here the crop is harvested and replanted year after year. The selection is done naturally. Thus, those that are not able to survive are choked off, leaving better performing survivors. This method is cheap but lacks direction. It has often been observed that survival qualities may not really with economic qualities. Excessive seediness is an example of a survival quality which is often not needed in tomatoes, citrus and other vegetables and fruits.

II. Mass selection: In this method, many plants showing desirable characteristics are selected for seed. These seeds are then planted out for subsequent selection. Selection starts with the parents and is based in records of their behaviour in the field and the performance of their offspring under the prevailing ecological conditions.

 

Advantages of mass selection

1. Only species of crops with desirable characteristics are allowed to grow.

2. It results in the retention of high quality and high-performance varieties.

3. It results in the selection of vigorous species that are adapted to the environment.

4. It results in the selection of disease-resistant crops.

Disadvantages of mass selection

1. It reduces the population of varieties of crops available in an area.

2. The performance of the lla ts selected may be due to environment rather than genetic influence.

3. The cost of selection is usually high.

4. If selection is not properly done, it may lead to the rejection of crops with desirable characteristics.

III. Pure line or individual selection: This is an improvement on mass selection. In this method, selection is made of an individual stand of a crop showing in a field. Stand selected are those with desirable qualities and are saved for future planting. The variety developed by this method is uniform.

Disadvantages of pure line selection

1. Crops can easily lose uniformity and purity of cross-pollinated by another variety.

2. It requires skilled manpower.

3. It is tedious and time-consuming.

4. It is not suitable for crops wjichgske several years to produce seeds or fruits.

3. Crossbreeding or hybridization: This is the crossing of two plants which differ in one or more characteristics. The aim is to combine in one plant some desirable qualities of two plants.

Plants which have good characteristics are chosen for breeding e.g varieties which have short growing season can be crossed with varieties with a good yield. Crossbreeding often bring about a new vigour or heterosis. It takes a long time to produce a new hybrid. 10years is considered average for animals. It is however longer than that for perennial crops.

Crossbreeding entails pollination; it is generally carried out by research stations rather than the farmers themselves. Crops can be cross-bred for nearly all characteristics like yield, quality, adaptability, disease and insect resistance.

Advantages of cross-breeding

1. It brings about an increase in yield.

2. With careful manipulation, desirable characteristics can be introduced into a plant.

3. With this method, several disease resistance varieties of crops have been evolved.

4. It brings about a new vigour.

5. It increases the commercial value of crops.

Disadvantages of cross-breeding

1. It has low resistance to disease attack.

2. It is tedious and takes a long time to produce a single cross.

3. It cannot be used to improve crops which do not produce flowers and not propagated by seeds or fruits.