AGRICULTURAL SCIENCE
MEANING OF CROP PEST
A pest can be described as any organism capable of causing damage to crop plant. Types of Crop Pest Important pests of crop plants are grouped into the following classes: insects birds; rodents; monkeys; man; nematodes. Insect pests can be classified into various groups based on their mode of feeding. These groups of insect pests include: biting and chewing insects; piercing and sucking insects; boring insects. Biting and Chewing Insects: These insect pests possess strong mandible and maxillae (mouthparts) which enable them to bite and chew plant parts. Examples are: termites, grasshoppers, leaf worms, army worms, mantids, locusts and beetles. Piercing and Sucking Insects: These insect pests…
MEANING AND CAUSES OF DISEASES OF CROPS
A plant disease may be defined as a departure or deviation of the plant from the normal state of health, presenting marked symptoms or outward visible signs. In other words, disease is an unfavourable condition caused either by the pathogens present within a living organism or by nutritional deficiency. It usually results in physiological and anatomical abnormalities expressed in characteristic symptoms. The harmful effects of a disease to the plant or to any of its parts and products generally result in the reduction of the economic value of the plant. Causes of Diseases The primary causes of disease can be classified into two groups – pathogens and physiological factors.…
PROCESSES OF CROP IMPROVEMENT
The processes of crop improvement include: Introduction. Selection. Breeding or Hybridization. a) Introduction: This involves the importation of introduction or some varieties of crops with desirable characteristics into areas where they have not existed before. In other words, it involves the movement of crop from its origin or supposed centre of evolution to another region or area where it can adapt. Crops with desired qualities are identified in their centres of origin and then procured. Such crops are then introduced into the breeder’s country for testing and multiplication. Such imported crops are usually quarantined by the nation’s plant quarantine service before introduction into the country importing it. Introduction is…
MENDEL’S WORK IN GENETICS
Gregor Mendel (1822-1884) was a monk in an Augustinian monastery in Brunn, Austria. He is often regarded as the father of genetics because his work formed the foundation for scientific study of heredity and variation. Mendel’s Experiments Gregor Mendel carried out several experiments on how hereditary characters are transmitted from generation to generation. He worked with garden pea (Pisum sativum). His major aim was to find out the pattern of inheritance of different characteristics on the pea plant. Methods used by Gregor Mendel in his experiment Gregor Mendel used two major methods in conducting his experiments. These methods were grouped into monohybrid inheritance and dihybrid inheritance. Reasons…
DEFINITION OF SOME GENETIC TERMS
In order to understand the Mendelian Laws and its usefulness in plant breeding, it is important to know some technical words which we shall come across in crop improvement. Genes: Genes are hereditary units or basic units of inheritance. They are located in chromosomes and are responsible for the transmission of characters from parents to offspring. Chromosomes: Chromosomes are rod or thread-like bodies found in the nucleus of a cell. The chromosomes house or contain the genes. Characters or traits: These are the inheritable attributes or features possessed by an organism, e.g. seed colour, seed size, plant height, etc in plants. Gamete: Gamete is a matured sex cell which takes…
