Crop improvement is defined as the science that deals with the development of new crop varieties with superior quality and quantity.
AIMS OF CROP IMPROVEMENT
- To increase yield
- To improve the quality of produce
- To adapt to climatic conditions
- To increase resistance to diseases
- To increase resistance to pests
- To meet the needs of growers
- To produce crops with uniform agronomic characteristics
- To breed crops with early maturity
- To improve nutrient value of the produce
- To meet the needs of consumers
- What is crop improvement?
- State five aims of crop improvement
DEFINITION OF SOME GENETIC TERMS
- Genes: These are hereditary unit or basic unit of inheritance
- Chromosomes: They are rod or thread like bodies found in the nucleus of a cell
- Character or Trait: These are the inheritance attributes or features possessed by an organism e.g. seed colour
- Gamete: It is a mature sex cell
- Zygote: is a single cell formed as a result of the union of a male gamate with a female gamate
- Allelomorphs (allele): These are pairs of genes on the position of a chromosome that control a character
- Phenotype: is the sum total of all observable features of an organism i.e. physical, physiological and behavioural traits e.g. height, weight and skin colour
- Genotype: is the sum total of the genes inherited from parent.
- Dominant character: This is a trait or character that is expressed in an offspring when two individuals with contrasting character or traits are crossed
- Recessive character: This is the character or trait which does not produce the effect in the presence of dominant character.
- Homozygous: An individual is said to be homozygous if it has two similar genes for the same character, i.e. the pair of gene controlling a given pair of contrasting characteristics are identical e.g TT for height T for Tall or tt for height t for short
- Heterozygous: An individual is said to be heterozygous if the two members of a pair of genes controlling a pair of contrasting characters are different. e.g Tt for height T for Tall and t for short
- Filial generation: The offspring of parents make up the filial generation. The first, second and third filial generations are represented by F1, F2 and F3 respectively.
- Hybrid: These are offsprings from a cross between parents that are genetically different but of the same species.
- Hybridization: This is the crossing of plants with contrasting characters. There are two major types of hybridization, this includes monohybridization and Dihybridization.
Dihybridization involves the crossing of plants with two pairs of contrasting characters.
Monohybridization involves the crossing of two pure traits.
- Mutation: is a change in the genetic make-up of an organism resulting in a new characteristic that is inheritable.
- Define; A. Gene B. Chromosome C. Trait
- Explain; A. Mutation B. Hybridization C. Genotype
- The first law of Mendel is also called the law of segregation of genes states that; genes are responsible for the development of the individual and that they are independently transmitted from one generation to another without undergoing any alteration. This is clearly seen in monohybrid crossing.
- The second law of Mendel which is also called the law of independent assortment of genes state that each character behaves as a separate unit and is inherited independently of any other character. This is clearly seen in the dihybrid crossing.
PROCESS OF CROP IMPROVEMENT
These includes; introduction, selection and breeding of hybridization.
- INTRODUCTION: This involves the importation or introduction of some varieties of crops with desirable characteristics into areas where they have not existed before.
- It helps in bringing a new variety to a new areas
- It may enhance greater productivity
- It may perform better if there is a better climate condition
- The past of the crop of the crops is usually absent in the new area
- There is possibility of introducing a new diseases
- The crop may not be able to adapt to climatic condition of the new environment
- It may introduce now pests to the new environment
- It may not be able to adapt to the soil condition of the area
- SELECTION: This involves the picking of crops with desirable characteristics which are most favored by the environment. Selection could be natural or artificial.
Natural selection involves the ability of a crop to survive wide range of environmental conditions and still remain standing.
Artificial selection involves use of man’s intelligence to retain crops with desired traits on the farm.
Methods of Artificial Selection
- Mass Selection: Crops with desirable characteristics are selected among others.
- Pure line Selection: Only one crop plant with good characteristics is selected
- Pedigree Selection: Crop plants are selected based on the performance of their ancestors
- Progeny Selection: Crop plants are selected based on the performance of their offsprings
ADVANTAGES OF SELECTION
- It ensures that only the best naturally available crop is grown
- Crops with desired qualities are selected
- Seeds from the best stands are multiplied for distribution
- It reduces the spread of diseases and pests
DISADVANTAGES OF SELECTION
- Selection is tedious and time consuming
- It is very expensive in term of time and money
- It requires expertise
- It causes elimination of some desirable traits of the parent stick
- BREEDING OR HYBRIDIZATION: is a method by which an offspring is produced through the crossing of two different plant varieties of the same spices
TYPES OF BREEDING
- Inbreeding: This is the pollination and fertilization of closely related crop plants. This can lead to pure breed or pure line
- Pure line: It is obtained when a plant is being self-fertilized or crossed continuously with a closely related species for many generations so that the desirable qualities it possess does not change from one generation to another.
- Cross Breeding: This is the pollination and fertilization of unrelated crop plants belonging to different breeds. This results in production of hybrids
ADVANTAGES OF BREEDING
- It can produce a superior offspring resulting in hybrid vigor or heterosis
- Progeny grow more rapidly in cross breeding
- Offsprings can withstand the variation of environment
DISADVANTAGES OF BREEDING
- Inbreeding leads to depressing or loss in vigor and performance of offspring.
- There is drop in production of the crops in quantity and quality in inbreeding
- It may leads to poor or low resistance to disease attacks in inbreeding
METHODS OF IMPROVING CROP PRODUCTIVITY
- By crop improvement (Introduction, selection and breeding)
- Planting at the proper time
- Adoption of better cultivation methods
- Use of manures and fertilizers
- Control of pests of crops
- Control of diseases of crops
- Use of Resistant varieties
- Use of good crop varieties
- State the Mendelian laws
- What is crop improvement
- List three aims of crop improvement
- State two advantages of breeding
- State two methods of improving crop productivity
- Essential Agricultural Science for senior Secondary School by O.A. Iwena Chapter 39 pages 366-376
- Answer the following questions from WAEC PAQ 2005 theory question 6, 2008 theory question 6, 2009 theory question 5 and 2011 theory question 6
- The unit of inheritance is ______ A. chromosomes B. eggs C. genes D. gamates
- __ are thread like bodies found in the nucleus of a cell A. chromosomes B. eggs C. genes
- The fusion of male and female gamate result in ____ A. embryo B. genes C. gamates
- An individual with pair of identical genes for the same character is called ____ individual. A. homozygous B. heterozygous C. gamates D. zygote
- The character which express itself in the presence of the other is said to be ____
- dominant B. recessive C. sexual D. asexual
- a. What is crop improvement?
- State two aims of crop improvement
- a. State the Mendelian laws
- State two methods of improving crop productivity
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