Skip to content

Methods of Crop Improvement and Production of Hybrid Seed

Crop improvement will always be an important aspect of agricultural industry because crop products are essential to the existence of man. In the past, new land was always cleared and plowed out by the peasant farmer for increased food production.

This means of expansion of arable land is seldom possible today. The increased world grain yields were achieved by growing more productive varieties and hybrids, greater fertilizer use and other improvement practices.

The breeding of more productive types is the only stable method of increasing crop yields. Improved cultivars of many crops are rapidly replacing inferior local varieties in most countries of the world.

The maintenance, production and appropriate distribution of seed stock of improved types have resulted in striking increases in crop yields in many countries.

Some of the outstanding accomplishment of crop breeding is the development of disease-resistant varieties of wheat, rice, maize, sugarcane, potatoes sorghum and alfalfa.

This article treats those aspects of crop improvement such as methods of crop breeding and production of hybrid seeds as well as examined the Mendelian laws of inheritance.

Mendel’s Work in Genetics

Gregor Mendel (1822-1884) carried out the first quantitative studies on inheritance. He published the results of his work in1867. These laid down the basic laws of genetics.

Mendel’s conclusions about inheritance were based on his hybridisation experiments in which he considered either one pair of contrasting characters or two pairs of contrasting characters involving cross between plants with these characters.

The cross involving only one pair of contrasting character is called monohybridisation and the related experiment is called monohybrid experiment or monohybrid cross. Likewise, the cross involving two pairs of contrasting characters is called dihybridisation and the related experiment is referred to as dihybrid experiment or cross experiment.

Mendelian Laws

From the results of his experiments, Mendel came to certain conclusions which are referred to as the principles of Mendelian Inheritance or Mendel’s Laws of Heredity. Mendel’s two important laws are: The Law of Segregation (of genes), and The Law of Independent Assortment (genes).

a. Law of Segregation

This is Mendel’s first law of heredity. It states that:

The hereditary characters of an organism are determined by genes (called ‘factors’ by Mendel) which are discrete unchanging units (do not blend) of inheritance;

A gene for a character may have alternative forms (alleles) which express the character in different ways;

In a diploid organism, each character is controlled by two copies of each gene which may be identical alleles (homozygous) or different alleles (heterozygous);

If a diploid organism has two different alleles (heterozygous) for a character, one allele may be dominant, dictating the expression of the character to the complete exclusion of other (the recessive allele);

In a diploid organism that is heterozygous for a character, the two alternative alleles separate (segregate) from each other during meiosis (called ‘factor’ reducing process by Mendel), each going randomly to a different gamete.

b. Law of Independent Assortment

This is Mendel’s second law. It states that during gamete formation, the way one pair of alleles for a given character distributes itself in the gametes does not affect the way other allelic pairs (for other characters) distribute themselves. This, however, only applies to allelic pairs on different homologous chromosomes.

Read Also : Samoyed: Description, Health, Origin and Care Guide

As a result, this law may now be restated in the following way: alleles on different chromosomes assort independently during meiosis (gamete formation).

Or this law states that each pair of contrasting characteristics (genes) behaves or segregates independently of those of any other pair. One gene apparently has no influence on another for a different characteristic.

Law of Paired Units

There are unit carriers of heredity which occur in pairs. One each pairs came from the mother while the other came from the father. The unit carriers were called by Mendel determiners or factors but they are now known as genes.

Law of Dominance

When two hereditary units of a pair are unlike, the one which functions and produces its character or effect is called dominant while the other which remains undeveloped or unexpressed is called recessive.

Crop Improvement

Crop improvement has been in progress since primitive man first exercised a choice in selecting seed from wild plants for growing under cultivation. The greatest advances were made before the dawn of civilisation.

Crop Improvement

Material progress was also made thereafter. However, not until the last century, when some knowledge of genetics was acquired, did crop breeding become a science with the outcome of breeding methods reasonably predictable.

Remarkable increases in yield followed the breeding and distribution of semi dwarf, photoperiod- insensitive cultivars of rice and wheat that are resistant to lodging under heavy nitrogen fertilization.

Crop breeding is concerned mainly with more abundant, stable and economical crop production, but is also deeply motivated by social and humane wants. Farmers now have smooth-awned cereals that do not irritate the eyes, mouth, or skin of the farm workers or livestock.

Consumers now have some food products that are higher in protein or certain essential amino acids. They also have sweeter and tenderer sweet corn as well as lighter bread made from stronger wheat.

Crops that are easier for man to harvest and feed crops that are more palatable or less toxic to livestock have been developed. Improved cultivars have helped to alleviate crop failures and their accompanying human and livestock starvation.

Objectives of Crop Improvement

Crop breeders are yet to create a perfect crop variety. Each variety has several weaknesses or defects that curtail maximum yield and quality. The objectives or crop breeding is therefore, to correct these deficiencies while developing new cultivars with higher yield capabilities.

First generation hybrids with increased vigour, growth, and reproduction have markedly increased the yields of several crops. Improvements of the following characteristics are considered the objectives of crop breeding:

To produce crops that are resistant to common diseases and pest;

To produce crops that are resistant to adverse weather condition such as drought, cold, heat and salt;

To produce crops that have adaptation to variable photoperiods;

To produce crops with adaptation to heavy grazing or frequent cuttings;

Crops with enhanced market quality e.g. higher content of fiber, of protein, sugar, starch, or other extractives; better processing quality for textiles, foods, beverages, and drugs, and better colour;

Seed quality e.g. higher or lower seed-setting tendency, greater longevity, high viability, larger size and non-shattering;

Growth habit e.g. more erect or prostrate stems, more or less tillering or branching, more uniform flowering and maturity, more uniform height, longer life, and better ratio of tops to roots;

Harvesting quality e.g. stronger, shorter, or taller stalks, erect stalks and heads, non-shattering qualities, easier processing and freedom from irritating awns and fuzz;

Productive capacity e.g. greater vigour, higher fertility and faster recovery after cutting;

Feeding quality of fodder e.g. palatability, leafiness, hull percentage, nutritive value and texture.

Read Also : How to Make Homemade Banana Fruit Juice in Under 5 Minutes

Share this:

Leave a Reply

Your email address will not be published. Required fields are marked *


0
YOUR CART
  • No products in the cart.