Crop Improvement refers to the ways of developing and breeding of crop varieties which are better than the existing varieties in a number of characters
Aims of Crop improvement
The breeders involves in improving our crops usually have certain aims in mind when doing their work. These aims include:
- To increase Yield: the varieties of crops so-developed by breeders are capable of giving very high yield or quantity of crop per unit of the land.
- To improve the quality of produce: the quality of farm produce enhances its usefulness and value. Plant breeders can improve on the taste, colour, size, nutritive value and fiber content of crops.
- To adapt to climatic condition : plant breeders develop varieties of crops that are able to withstand extreme condition of cold ,drought, and wind by adjusting the growth cycle of the variety better to suit the available growing season
- To increase resistance to diseases: they could also develop varieties of crops which are not only resistant to diseases but produce high yield in the presence of diseases.
- To meet the power of growers : improvements in farming methods may particular characteristics desirable to growers in their plants
- To obtain uniformity of plants: one of the aims is to breed crops which can grow and mature uniformly to facilitate mechanism or ease of harvesting.
- To breed crops with early maturity: also to produce crops which will mature early.
- To improve harvesting qualities: breeders try to produce crops that can be harvested with ease and without damaging to the seeds/fruits.
- To improve the nutritional value of the produce: also to develop crops that have nutritional value like high protein, mineral vitamins, etc. which are useful to man.
- To meet the needs of consumers (processors or industrialists): the demand by food processors as well as other consumers creates pressure for new quality of plants.
MENDELIAN LAWS OF INHERITANCE
To understand the mendelian laws the following terms need to be understood
- Character or Traits: these are the inherited attributes which the plant breeders select. E.g. seed colour , seed size , plant height , disease resistance etc.
- Chromosomes: these are the rods or thread shaped bodies found in the nucleus of a cell. The chromosomes houses or contains the genes .
- Gene: these are hereditary units or units of inheritance.
- Gamete: this is a mature sex cell which takes part in sexual reproduction. There are two types of male gamete or spermatozoa (in animals) and pollen grains (in plants) and female gamete or egg or ovum (in animals) and ovules (in plants). Gamete is usually Haploid
- Zygote: is a single cell formed as a result of union of a male gamete with a female gamete.
- Allelomorphs : these are pairs of genes on the position of a chromosome (i.e. locus) that control contrasting characters.
- Phenotype : these are the physical and physiologically expressed traits of an individuals e.g. height
- Genotype: this is a term used to describe those traits or sum total of the genes inherited from both parent.
- Dominant Character: this is the character shown in an individual without any significant influence of the contrasting characters present in the same individual on the dominant character.
- Recessive character: this is unexpressed character in the presence of a dominant character in an individual.
- Homozygous: a plant is said to be homozygous if the two members of a pair of genes controlling a given pair of contrasting characters are identical.
- Backcross : is a cross between an offspring and one of the parents
- Heterogeneous : a plant is said to be heterogeneous if the two members of a pair of genes controlling a given pair of contrasting characters are different e.g. (Tt) for tallness
- Hybrid: this is the offspring got from crossbreeding two pure varieties of any species.
- Filia generation: the offspring of parents make up the filia generation.
Mendel’s laws of inheritance are in two forms
- Mendel’s 1st law of segregation of genes : this 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
- Mendel’s 2nd law of independent assortment of genes : states that each character behaves as a separate unit and is inherited independently of any other character
Process of crop improvement
The process of crop improvement includes
- Breeding or Hybridization
This involves the importation of introduction or some varieties of crop with desirable characteristics into area where they have not existed before.
Advantages of introduction
- It helps to introduce new varieties of crops to a new area
- It may enhance greater productivity
- It may perform better if there is better climatic condition in the new location
- It may also perform better if there is better soil condition in the new area
- Absence of pests and diseases
- It helps to upgrade the quality of the local varieties of crops
Disadvantages of introduction
- There is the possibility of introducing new crop diseases
- The new crop may not be able to adapt to climatic condition of the new location
- It also introduce new pests to the new environment
- The introduced crop may not be able to adapt to soil conditions of the condition
This involves the artificial picking of crops with desirable characteristic which are most favoured by the environment.
Method of selection includes:
- Mass selection : crops are selected or rejected on the basis of their own performance or merits
- Pure line selection : only one crop plant with good character
- Pedigree selection : crops are selected on the basis of the performance of their ancestors.
- Progeny selection: crop plants are selected on the basis of the performance of their offspring of progeny.
Advantages of selection
- It ensures that only the best naturally available crop is grown
- Crops with desired qualities are selected
- Seeds from best stands are multiplied for distribution
- Crops with undesirable characters are detected and rejected.
- It reduces the spread of diseases and pests
Disadvantages of selection
- Selection is tedious and time consuming
- It is very expensive in terms of time and money.
- It requires expertise which may not be available.
- It brings about the elimination of some desirable traits f the parent stock.
Breeding or hybridization
Hybridization is a method by which an offspring is produced through the crossing of two different plant varieties of the same species.
Types of breeding
- In-breeding: this is pollination and fertilization of closely related crop plants in order to retain certain desirable characteristics. This can lead to pure breed or pure line.
- Cross breeding: this is the pollination and fertilization of unrelated crop plants belonging to different breeds. This results in the production of an offspring which is superior to the average performance of the parents. This is called Hybrid vigour “heterosis”.
Advantages of breeding
- It can produce a superior offspring resulting in hybrid vigour or heterosis ( cross breeding )
- Progeny grows more rapidly (cross breeding).
- Production of pure-line (in breeding).
- Offspring can withstand variations of environment (cross breeding).
Disadvantages of breeding
- It could lead to “inbreeding depression”. Which is the depression of loss in vigour and performance of offspring (in breeding ).
- There is a drop in production or yield of crops in terms of quantity and quality (in breeding)
- It may lead to poor or low resistance to disease attack (in-breeding).
Methods of improving Crop Productivity
Productivity of crops can be achieved through a combination of methods which includes :
- Crop improvement methods: crops ca n be improves through introduction, selection and hybridization.
- Proper timing of planting: crops should be grown at the right time to avoid high temperature, inadequate rainfall or abundance of pests and diseases during growth.
- Adoption of better cultivation methods: such as crop rotation which adds nutrients to the soil, prevent erosion, pests and diseases outbreak and helps to increase yield.
- Use of manures and fertilizers: the use of manure like farm yard, compost and green manure in combination with the use of fertilizers helps to add nutrients to soil and promotes good growth of crops.
- Control of pests of crops: the control of pests of crops which cause reduction in yield and growth can help in the improvement of crops.
- Control of diseases of crops
- Use of resistance varieties: some varieties of crops are capable of resisting disease’s attack and can mature early; thereby by increasing the yield of crops.
- Use of good crop varieties: there are some varieties of crops which naturally will grow well in different environmental conditions.
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