eChapters

Agroforestry is a new name for a set of old practices. The farmers have been practicing agroforestry since ancient times. The general concept of agroforestry is to integrate trees and agriculture so as to create a more diversified landscape, while providing the producers with new environmental and economic benefits. In other words, agroforestry is a method of farming that allows trees and shrubs to grow along with crops and/or livestock, therefore blending agriculture and forestry in the same production system. This relatively young science was brought from the realm of indigenous knowledge into the forefront of agricultural research four decades ago and was promoted widely as a sustainability-enhancing practice that combines the best attributes of both forestry and agriculture.

Multipurpose trees and shrubs are defined as all woody perennials that are purposefully grown to provide more than one significant contribution to the production and/or service functions of a land-use system that they occupy. In agroforestry systems, different species of trees and shrubs can be planted with many types of crops in a variety of patterns. Thus, it is required to know about the methods of propagation and nursery raising, planting and other silvicultural management practices along with the diverse uses of multipurpose trees and shrubs of tropical and subtropical areas before their selection for forestry and agroforestry activities. It is important to select the most suitable tree species since it is not easy to replace them once they have been planted.

MANGIUM (Acacia mangium)

Acacia mangium is a single-stemmed evergreen tree that grows to 25-35 m in height and up to 60 cm in diameter. The bole is usually straight, often fluted near the base, free of branches for up to half its height. Mangium is native to Australia, Indonesia and Papua New Guinea. However, it tolerates varied site conditions and has adaptability to different planting objectives. Mangium shows most vigorous growth on well-drained, fertile soils in high rainfall areas in the humid tropics. It is valued for its rapid growth and has been planted throughout the humid tropics and is a major plantation species in the Asia-Pacific. Provenances from Papua New Guinea consistently show better growth in height and diameter.

A series of efforts have been made to initiate the work on post-harvest grain technology in India. H.M. Lefroy, the 1^st Imperial Entomologist appointed by the British Government in India in 1905 had given a tentative list of storage insects in 1906. This list of storage insects was further supplemented by T.B. Fletcher in 1914. The problems of grain storage were discussed at Pusa, Bihar at the Entomological meetings held during the years 1917, 1919 and 1923.

The Department of Food was established in 1942 by the Government of India. The executive wing of the Food Department was responsible for the purchase, movement, transport and distribution of food grains. Central Food Technology Research Institute (CFTRI) at Mysore was established in 1950 with a mandate to train personnel and evolve technology relating to food processing and preservation. The Central Warehousing Corporation was set up on 2^nd March, 1957 under Agricultural Produce (Warehousing and Development) Act 1956. On 1^st January, 1965 Food Corporation of India was established.

In 1958, the Department of Food started a centre at Hapur known as Grain Storage Research and Training Centre with the main objective to train the personnel of State Government engaged in food procurement, storage and distribution. This centre was upgraded during 1968-1973 with the technical and financial assistance of UNDP and this centre was redesignated as Indian Grain Storage Institute (IGSI). Two field stations at Ludhiana and Bapatla (later shifted to Hyderabad in March 1979) were established in 1968-69. Subsequently, three stations of IGSI at Jabalpur (October, 1980), Udaipur (February, 1981) and Jorhat (May, 1981) were also established. The overall objective was to minimize losses of food grains by development of modernized grain storage practices for the farmers, traders, cooperatives and large storage of food grains in the country and also to evolve the methodology to be adopted by the Save Grain Compaign which has its headquarters in the Department of Food.

Insect infestation occurs in stored grains and grain products to variable extent depending upon the storage conditions in developing countries. The losses of nutritional compounds are proportional to the extent of insect infestation, nature of insect feeding and distribution of nutritional chemicals in different seed components.

1. Sources of Insect Infestation

There are many sources that leads to infestation in storage, viz., left over seed from bins or stores or spilled seeds under the stacks, cleanings, sweepings of storage structure, processing plants, old infested stores, old gunny bags, insect infested transport vehicles, storing insect infested seeds with fresh stock or vice-versa, entry of insects from neighbouring stores and carry over of field infestation

The damage to food grains in the storage may be caused due to insect attack, mould, fungi, bacteria, rodents, heat and moisture. The value of grain for milling purposes and human food is directly correlated with the amount of insect contamination present. The immature stages of rice and granary weevils, lesser grain borer, Angoumois grain moth and occasionally the flat grain beetle, cadelle, rust red flour beetle and saw toothed grain beetle live inside the kernels where they are hidden from view until they emerge.

Grain from casual inspection appears to be in good condition but may contain enough internal infestation which render it unfit for human food or unfit for purchase for future sale as milling stock. In general, millers have found that wheat with more than 0.5 per cent of infested kernels is unfit for milling. The need for a rapid and accurate method of estimating insect contamination in grain offered for sale has become more and more important to both grain dealers and millers.

Methods for Estimation of Damage

In order to assess the damage caused to food grains due to any one or combination of various factors; physical, chemical and micro-analytical methods are employed according to the necessity and information required. Various methods have been employed by field workers as well as by laboratory technicians in estimating damaged grains in food grains with particular reference to detection of insect infestation which alone cause maximum damage. These methods have been described below.

A number of insects infest seeds in storage. These insects infest seeds to fulfill their feed and shelter requirements, which result into qualitative as well as quantitative loss of seeds. Indian climate is very favourable for their multiplication and growth throughout the year. Storage pests move along with commercial products from one area to another and even to different countries in the world. Some adult insects are strong fliers and may spread from one to another place of storage or from source of infestation. Generally, all insects infesting seeds in storage belongs to insect order Coleoptera and Lepidoptera (Table 4.1). Some minor species belong to Pscoptera. These pests cause losses to man by destroying large quantities of grain, corn, legumes (beans, lentils and peas), milled cereal products, flour, bran, macaroni and other paste products, dried fruits, dried vegetables, cheese, nuts, candy and other food materials. They contaminate and thus eliminate for human consumption, far more food than they eat and either cause direct loss or transmit diseases to man and his domestic animals. These insects can be categorized as major or minor pests according to the loss of seeds caused by them. Similarly, on the basis of their feeding behavior, they can be grouped as follows:

There are several species in this cosmopolitan family that are of importance chiefly as pests of stored foods, flour, grain, seeds and bulbs, feeding on these products or the fungi that develop on them. These mites are mostly very minute, almost colourless, with the body bearing a few long setae, and with the legs terminating in one claw and usually a sucker. When very abundant the mites and their cast skins form a buff-colored dust and give rise to a characteristic odour. The living mites move slowly away from a source of light. An interesting characteristic of these mites is a nymphal resting stage (hypopus) during which they take no food but attach themselves to other mites, insects and humans by means of suckers and are thereby transported to other suitable places for development, where they drop off, moult, feed, and develop into adult stage. The hypopus may be resistant to fumigants. However, the cheese mites, Tyrophagus casei do not have a hypopial stage. Prolonged storage of products subject to infestation without cleaning of pantries and shelves where such materials are placed. These mites can subsist on organic debris in cracks, crevices and corners and are readily spread to other areas.

It is interesting to note that only 25 of about 1200 species of birds found in India have been reported to inflict damage to crops, vegetables and fruits. The exact ecological causes for population increase of individual species have yet to be studied. It would appear that, in general, the granivorous birds became abundant with the increase in area under grain crops and the subsequent storage of grain in godowns and bulk storage. The details of important bird pests are given below:

Economic Importance of Rodent Pests

• They consume and damage foods in the fields and in stores. In addition, they spoil it in store by urine and droppings reducing the sale values.
• Due to their gnawing and burrowing habit they destroy many articles (packing, clothes and furniture) and structures (floors, buildings, bridges, etc). By gnawing the electrical cables they can cause fires.
• They are responsible for transmitting diseases dangerous to human and domestic animals.

Among many pests of agricultural crops and stored grain products, rodents are the major pests which do the great damage. Rodents including rats, mice and squirrels are gnawing animals having chisel like teeth. They have highly developed sense of smell, taste and hearing. They are omnivorous and feed on grains, vegetables, fruits, meat and other products in the houses or in the fields. Rats daily consume food equal to about 10 per cent of their body weight and the figure may go up to 30 per cent in case of mice. Rats are among the most destructive pests of paddy in the field causing about 5-10 percent damage. It is estimated that these animals destroy 30 per cent of the total world’s cereal production. In India, 10 million tonnes of food grains are lost every year. It is often said that if rodent ravages could be controlled, a huge amount of food grains can be saved.

Of the 84 species of order Rodentia in India, 50 belong to family Muridae. The important ones belong to two sub-families, viz., Murinae and Gerbillinae. Murinae has 18 species of genus Rattus, 2 of Bandicota, 7 of Mus, 2 of Apodemus and a few each under eight other genera. The sub-family Gerbillinae has 2 species of Gerbillus, one each of Tatera and Meriones. Family Sciuridae has 10 species of flying squirrels and 13 species of tree squirrels in India.

As the name indicates, micro-organisms are very minute, cellular, living organisms which cannot be seen with the naked eyes (however, large colonies of fungi can be seen). Micro-organisms affecting stored grain can be divided into the following groups in order of their significance:

1. Fungi
2. Actinomycetes
3. Yeast
4. Bacteria
5. Protozoa (not found in sound food grains)

Fungi, bacteria and actinomycetes are grouped under the Thallophyta of the plant kingdom. The most important factors for their normal development are: (i) Nature of Food, (ii) Moisture, (iii) Oxygen and (iv) Temperature.

In the past several insect pests had entered India and are causing economically perceptible damage to native crops. The Government of India, in line with the International Standards on Phytosanitary Measures (ISPM), notified ‘Plant Quarantine Order, 2003’ to reduce the risk of introduction of exotic insect pests in India. The storage insect pests of quarantine concern for India have been listed in Table 9.1.

Since commencement of the settlement of world, the search for food had been uppermost, thereby, practising the conservation of food is a basic need for ensuring its ample supply to human being. The problem of food storage is growing fast day by day with the increase in the population. The existing shortage of protein and caloric requirements will not only be solved by growing more food and resorting to family planning measures but also by saving the produce from deterioration and wastage, and its efficient allocation to meet the growing requirement of population. In countries with varied climatic conditions, it is a steady struggle of man with insects, mites, rodents and microbes in getting the food stuff.

Need and Objectives of Storage

Since times immemorial, man adopted a particular system of storage and certain produce storage standards. Some of the storage methods are still in use in several regions, in the capacity varying from one kg to several hundred quintals, like hollowed gourds, skin bags, mud bins, excavated stones, woven baskets, underground pits etc., particularly in the tropics. The problems of storage in developing countries are more acute than that in well developed countries and a considerable disparity seems to be there in food availability. All need a food supply that should be nutritious, clean; free from insects, rodents, birds, other animal filth and harmful chemical residues. There are two types of needs, one immediately after harvest and the other in off season. There is no need of storing the produce for immediate requirement but for the latter case, the need to conserve produce properly is inevitable. Further, the need for storage has always arisen for one reason to distribute commodity in deficit production areas and the other based on improved quality standards. In all the way, therefore; growers, processors, transporters and warehouse owner must assist to comply with these requirements.

A series of efforts have been made to initiate the work on post harvest grain technology in India. The history of post harvest grain technology in India goes back as early as 1888 when COATS published several papers from Calcutta related to biology of stored grain pests. The first professional was appointed in the year 1905, known as Imperial Entomologist, Harold Maxwell Lefroy adorned with this post. Lefroy (1906) for the first time gave a tentative list of storage insects, which was further supplemented by Fletcher (1914). The problems of grain storage were discussed at the entomological meetings held at Pusa, Bihar in the years 1917, 1919 and 1923. The first step towards establishing an Institute in India was in the year 1950 when Central Food Technology Research Institute (CFTRI) was established at Mysore (Karnataka) with a mandate to train personnel and evolve technology related to food processing and preservation. The Central Warehousing Corporation was set up on 2^nd March 1957 under the Agricultural Produce (Warehousing and Development) Act 1956. The Food Corporation of India was established on 1^st January 1965.

In India, the farmers in traditional bulk and bag storage for food, feed and seed stored about 65-70 per cent of the total food grains and seed purposes till next harvest. Rest 30-35 per cent are procured and stored by food grain organizations, like Food Corporation of India (FCI), Central Warehousing Corporation (CWC), State Warehousing Corporations (SWCs), cooperatives, rural godowns and other state government agencies. In 1958, the Department of Food established a centre at Hapur known as Grain Storage Research and Training Centre (GSRTC) with the main objective to train the personnel of state government engaged in food procurement, storage and distribution. This centre was upgraded during 1968-1973 with the technical and financial assistance of UNDP and GSRTC and redesigned as Indian Grain Storage Institute (IGSI). The field stations at Ludhiana and Bapatla (later shifted to Hyderabad in March, 1979) were established in 1968-69. Subsequently, three stations were also established at Jabalpur (1980), Udaipur (1981) and Jorhat (1981).

Introduction

The increase in agricultural production, particularly food grain is one of the major problems of national planners to achieve the target in the food production. Our farmers have been utilized more and more the modern methods of agriculture including the use of chemicals for protection of crop and stored products against the pests. A successful farmer knows that what pests to expect on his crops and stored products, when and under what conditions their attack will be possible. But due to insufficient knowledge of chemicals and their application, our farmers use them without care and injudicious manner, therefore, these chemicals not only give poor kill of insects but also cause the hazards to man and domestic animals. Success in pest control operations depends on many factors such as correct identification of pest, proper timing of insecticidal application, right choice of chemicals and their formulations, doses and method of application.

Fumigants are still widely used for the control of insects and other pest organisms. Because of their unique characteristics and the great adaptability of fumigation technique, fumigants can often provide effective and economical control where other forms of pest control are not feasible. The development of light weight plastic sheets to enclose spaces or materials requiring fumigation has extended its use and made control procedures easier and much more adaptable. Among the fumigants, aluminum phosphide, ethylene dibromide (EDB), Ethylene dibromide- carbon tetrachloride (EDCT) etc. are most common in tropical and sub-tropical while methyl bromide is prevalent in temperate regions. Modern technology and research have also brought to notice certain problems with fumigants that are previously unknown. Among these, adverse effects on seed quality are most important. Thus, fumigants used in seed stores should not affect the viability of the seeds, should not be persistent, non-corrosive and highly diffusible.

All due precautions have to be exercised in handling pesticides because many of these leave toxic residues on treated food materials and plants which accumulate in higher concentrations in animals which consume these.

General Precautions

Read the precautions given by the manufacturer of the pesticides carefully. Store the pesticides under lock and key; prevent access of children to these; empty containers must be disposed off safely.

Blood and skin contaminations must be avoided.

The godown for fumigation must be made airtight by closing the doors, windows, ventilators, crevices etc.

In case of fumigation, the operator must use a suitable gas mask. It is a face-piece connected to a canister containing an absorbent material for the vapours of the fumigants by means of a flexible non-kinking breathing tube and provided with valves so that all air inhaled by the user passes through the canister and the exhausted air passes directly to the outside atmosphere through a non-return valve. The absorbent canister carries instructions indicating the number of hours for which it is effective in an atmosphere charged with the fumigant.

After the required exposure period, aerate the godown thoroughly. First open the entrance door, keep it open for 6-7 hours, then only enter and open other doors or windows.

Insecticide resistance to both fumigants and contact insecticides is an increasing problem in controlling stored grain and grain product insects throughout the world (Table 14.1). Hence, persons engaged in food commodity storage and preservation world over are concerned about the resistance of stored product insects to contact insecticides and fumigants. It is, therefore, necessary to work out strategies to delay or minimize the probability of resistance evolution. Resistance to pesticides is the ability of a strain of insects to tolerate doses of toxicants which would prove lethal to a normal population of insects of the same species. Resistance results when occasional resistant individuals arise in a population and survive the pesticidal treatment. These survivors then reproduce and confer the resistance to their offspring in succeeding generations. Resistance is the ability of a population (of insects) to survive a dose (of insecticide) that would normally kill 100 per cent of a susceptible population. Insecticide resistance is a dynamic phenomenon dependent on biochemical, physiological, genetic and ecological factors.

The chances of development of insecticide resistance in stored grain insect pest are more because of their life style, i.e., to remain confined in limited area. This results in more common inbreeding of the homozygous resistant strain resulting into homozygous resistant progeny. At the same time their management, once detected, can be easily achieved with the application of sufficiently acceptable sufficiently higher dose of the most appropriate insecticide to eliminate all the resistant survivors

The insect pest of stored grains can be conveniently divided into two groups, i.e., coleopterous and lepidopterous, therefore, the subject on these two groups has been pooled accordingly.

The produced food grains have to be stored either for short or long duration for utilization in the coming times for food, feed and seed. In storage, these undergo 9.33 per cent losses due to various agencies such as rodents, insects and mites, microorganism and moisture in India, whereas, in other developing countries, the losses are as high as 30 to 50 per cent. Therefore, with an urge to produce more, there is still urgent need to protect the produce in the storage to meet the challenge. As a result of improved storage technology, the losses in Government Warehouses could be reduced to minimum but at farmers’ level, where 60-70 per cent of the produce is retained, the losses are still too high.

The management of insects in stored products is in transition from a dependence on regular applications of chemical insecticides to the use of integrated pest management (IPM). IPM involves understanding interactions between stored product environment and insects associated with stored products, and replacing all or most of the chemical applications with cost effective non chemical alternatives. The increased emphasis in adopting IPM strategies for stored product insects is primarily due to consumers’ demand for food free from pesticide residues. The transition from a heavy reliance on chemicals to little or no chemical input and increased use of non chemical approaches requires a thorough understanding of stored product insects, their identification, monitoring, biology, ecology and response to chemical and non chemical management options. The current scenario of stored grain protection in India depends totally and judicious use of IPM strategies. For safe storage of food grains, both the preventive and curative measures are required:

Objectives

• To study working principles of simple microscope
• Study different parts of simple microscope

Introduction

This is the first ever microscope. It was founded by Leeuwenhoek in 17^th century. He combined a convex lens with a specimen holder, for seeing the magnified images of small objects. It looks like a magnifying glass because it has the capacity to magnify between 200 and 300 times. A simple microscope is a small focal lens used to view the magnified images of small objects. It is just like a hand lens and glass with relatively lower magnification power.

Objectives

• To study working principles of compound microscope
• Study different parts of compound microscope

Introduction

A compound microscope is an optical instrument consisting of two short focal-length convex lenses that are used to observe the highly magnified images of small objects by naked eyes. The compound microscope is capable of magnifying up to 1000 the image of a small object by complex system of lens arrangement. The working distance varies from 0.14 to 4 mm. Compound microscopes generally require the sample to be seen to be sufficiently thin, or translucent, to allow the light to pass. Such microscopes provide high magnification, but the view is two-dimensional.

Objectives

• Differentiate between fixatives and stains.
• Describe methods of staining.
• List the commonly used fixatives and stains and their composition.
• Describe the uses of above mentioned solutions and stains.

Introduction

Every time a part of an organism is removed, the action of bacteria will soon disintegrate, dry or putrefy it. They must be kept as close to normal as possible or in other words preserved and fixed in order to study these. Chemicals are required in many practical of Biology. Some of these chemicals preserve and specifically colour certain cell parts while others are used as solutions. You will learn about certain fixatives (preservatives) and stains in this chapter.

Objectives

• Better understand the process and different stages of mitosis.
• Prepare your own specimens of onion root in which you can visualize all of the stages of mitosis.

Principle

The genetic information of plants, animals and other eukaryotic organisms resides in several (or many) individual DNA molecules, or chromosomes. For example, each human cell possesses 46 chromosomes, while each cell of an onion possesses 8 chromosomes. All cells must replicate their DNA when dividing.

DNA replication in eukaryotes is followed by the process called mitosis which assures that each daughter cell receives one copy of each of the replicated chromosomes. During the process of mitosis, the chromosomes pass through several stages known as prophase, metaphase, anaphase and telophase. The actual division of the cytoplasm is called cytokinesis and occurs during telophase. During each of the preceding stages, particular events occur that contribute to the orderly distribution of the replicated chromosomes prior to cytokinesis.

An onion root tip is a rapidly growing part of the onion and thus many cells will be in different stages of mitosis. The onion root tips can be prepared and squashed in a way that allows them to be flattened on a microscopic slide, so that the chromosomes of individual cells can be observed easily. The super coiled chromosomes during different stages of mitosis present in the onion root tip cells can be visualized by treating with DNA specific stains, like Feulgen stain and Acetocarmine stain.

Objectives

• Better understand the process and different stages of meiosis.
• Prepare your own specimens of onion root in which you can visualize all of the stages of meiosis.

Principle

Meiosis is a type of cell division in which the number of chromosomes is halved (from diploid to haploid) in the daughter cells, i.e., the gametes. It occurs in cell that produce gametes in sexually reproducing organisms. The division is completed in two phases, meiosis I and meiosis II. Meiosis I is a reductional division in which the chromosomes of homologous pairs separate from each other. Meiosis II maintain same number of chromosomes, hence, is called as equational division. Stages of meiosis can be observed in a cytological preparation of the pollen mother cells of the anthers of f lower buds.

Objectives

• Find out the number and types of gametes and gametic recombination in monohybrid, dihybrid and trihybrid crosses.

Principle

Gametes are reproductive cells that join together to form a new cell called a zygote during sexual reproduction. Pollen in seed-bearing plants, is the gametophyte producing male gamete. Female gametes (ovules) are included in the ovary of plant. At maturity a sexually reproducing individuals forms the gametes. Homozygote generate only one form of gamete. Homozygous referring to a diploid cell or organism possessing two identical alleles of a specific gene (e.g. AA or aa). Heterozygote generate different types of gametes. Heterozygous referring to a diploid cell or organism possessing two different alleles of a specific gene (e.g. Aa).

Objectives

• Better understand the monohybrid cross.
• Calculation of monohybrid phenotypic, genotypic and testcross ratios.

Principle

Monohybrid cross deals with the study of inheritance of one pair of contrasting characters. The alleles of contrasting character selected in the monohybrid cross will show exact dominance and recessive relationship. It is also defined as a cross is made between two true-breeding parents differing for a single trait, producing an F₁ generation. These plants are intercrossed to produce an F₂ generation. Monohybrid crosses study led to the Mendel’s law of segregation. Monohybrid cross was first produced in pea by Mendel to explain the “law of segregation”. When parents with distinct phenotypes are crossed, in F₁ generation, only one type of plants appears phenotypically. However, segregation can be observed in F₂ progeny and the population can be divided into two phenotypes classes. After counting the individuals. It is observed that 75% of them express the dominant phenotype and 25% of them express recessive phenotype.

Objectives

• Better understand the dihybrid cross.
• Calculation of dihybrid phenotypic, genotypic and testcross ratios.

Principle

A cross is made between two true-breeding parents differing in two pairs of genes, producing an F₁ generation. These plants are inter-crossed to produce an F₂ generation. Mendel second law i.e., Law of independent assortment can be explained by studying the inheritance of two characters at a time, simultaneously. When two phenotypically distinct parents differing with respect to two characters governed by two pair of genes are crossed together. Each pair of genes assorts independently into all possible combination forming four kinds of progeny, two of these are parental type and two are recombinant types.

Objectives

• Better understand the law of independent assortment.

History

The law was proposed by Gregor Johann Mendel with the other laws together called as ‘Mendelian laws of inheritance’, in 1866. He used pea plant as a model organism, and studied 7 characters.

Principle

The Law of Independent Assortment, also known as “Inheritance Law”, states that alleles of different genes assort independently of one another during gamete formation. Independent assortment for two genes can be explained by assuming that the two genes are located in two different chromosomes. The two alleles of a gene will be located in the two homologues of the concerned chromosome. Independent separation of these two pairs of chromosomes at anaphase I of meiosis will lead to the independent segregation of the genes located in them. Thus any allele of one gene is equally likely to combine with any allele of the other gene and pass into the same gamete. Independent segregation of two genes produces four different types of gametes in equal proportion. A random union among these gametes gives rise to sixteen possible zygotes. These zygotes yield a 9:3:3:1 phenotypic ratio, which is known as the typical dihybrid ratio. When two pairs of independent alleles enter into F₁ combination, both of them have their independent dominant effect. These alleles segregate when gametes are formed but the assortment occurs independently at random and quite freely.

Objectives

• Chi-square test for goodness of fit of genetic ratios.

Introduction

Karl Pearson developed the chi square test of statistical significance which is commonly used in Mendelian and population genetics. Chi square (χ²) test is a test of statistical significance which is used to test the significance difference between observed and expected frequencies or ratios. The purpose of χ² test is to decide if a set of observed data is according to an expected ratio or if it agrees well with an expected or theoretical distribution.

The chi square test of independence allow us to evaluate whether the segregation of alleles at one locus is independent of the segregation of alleles at another locus. To distinguish between inheritance patterns that obey Mendel’s laws versus those that do not, a conventional strategy is to make crosses and then quantitatively analyze the offspring’s. Based on the observed outcome, an experimenter may make a tentative hypothesis. For example, it may seem that the data are obeying Mendel’s laws. Hypothesis testing provides an objective, statistical method to evaluate whether the observed data really agree with the hypothesis.

The underlying principles behind a statistical approach is to evaluate the goodness of fit between the observed data and the data that are predicted from a hypothesis. This is sometimes called a null hypothesis because it assumes there is no real difference between the observed and expected values. A high deviation would be found between the observed and expected values. If this occurs, the hypothesis is rejected. Hopefully, the experimenter can subsequently propose an alternative hypothesis that has a better fit with the data.

The null hypothesis is a particular claim concerning how the data is distributed. More will be said about the construction of the null hypothesis later. The null and alternative hypotheses for each chi square test can be stated as

Objectives

• Detection of linkage using Chi-square test for goodness of fit.

Introduction

The tendency of two or more genes to stay together during inheritance is known as linkage and it is the consequence of the concerned genes being located in the same chromosome. Linked genes do not show independent segregation, as a result the ratios obtained in F₂ and test cross generation are significantly different from the expected ratios of 9:3:3:1 and 1:1:1:1, respectively.

Detection of linkage χ² using test

In genetic experiments, when the material under study is segregating simultaneously for two characters, it may be of interest to know whether the two characters are inherited independently or they are linked. The χ² test can be used for this purpose. χ² test is used in detecting linkage in back crosses and inter crosses.

First the χ² is computed based on the theoretical segregating ratios. If χ² is not significant it may be concluded that the loci segregate independently. If χ² is significant we may suspect linkage between the loci. The χ² is then partitioned into components assignable to different factors.

Objectives

• Study of gene mapping.

Introduction

All the genes that are linked together form a linkage group. Genes of a linkage group may be presented on a single straight line in the same order in which they are normally present on the concerned chromosome. The number of different linkage groups in a species is, as a rule, equals to its gametic chromosome number (n). The distance between two neighbouring genes is proportional to the frequency of recombination (%) between them depicted on a line drawing. Such a line drawing depicting the linked genes the recombination frequencies between them is known as Linkage map, Genetic map or Chromosome map. Linkage maps provide information on the genes that are linked together and the frequencies of recombination that may be expected between them. The frequency of recombination between two linked genes cannot exceed 50% which is the frequency in case of independent segregation.

Objectives

• Better understand the phenomenon of multiple alleles.

Introduction

The word allele is a general term to denote the alternative forms of a gene or contrasting gene pair that denote the alternative form of a gene is called allele. These alleles were previously considered by Bateson as hypothetical partner in Mendelian segregation. Mendel and his followers used the term ‘allele’ or ‘alleleomorph’ to denote the alternative form of the normal gene. It means the genes for tall and dwarf characters of pea plant are alleles. The former is normal or wild allele and the later is mutant allele. A gene can mutate several times producing several alternative expressions. When three or more alleles are found for any particular gene, these are called ‘multiple alleles’. These occupy the same locus in homologous chromosomes.

Multiple alleles are defined as genes that are members of the same gene pair and are located on the same locus. All of them control the same character but each of the allele affects that character somewhat differently than the others. In any diploid organism, a particular gene pair is represented by two alleles of the series, one allele on each of the two chromosomes of a homologous pair. This is because an organism has just two chromosomes of each type. These form a homologous pair. However, in the individuals of a population or species, many alternative forms of the same gene may be present. The grouping of all the possible alleles of a gene pair is defined as a system of multiple alleles and their mode of inheritance is called multiple allelism. The multiple allele system can be represented as A1, A2, A3, A4 etc.

Objectives

• Better understand the various types of gene interaction.

Introduction

Gene interaction is the phenomenon of two or more genes that affect each other’s expression in different ways in the development of a single character of an organism. It is the modification of normal phenotypic expression of gene due to interaction between alleles or non-alleles. In such situation, two or more than two genes may interact to give rise to a particular phenotype

Objectives

• Better understand the phenomenon of probability.

Introduction

The concept of probability is basis to many principles of classical genetics (segregation, independent assortment etc.) The principals of population genetics are based on the considerations of laws of probability. Probability is the likelihood of occurrence of an event.

Trial

A trial refers to an opportunity provided for an event to occur, e.g. tossing of a coin once constitute one trial as it provides an opportunity for head or tail to occur. A new borne can be either a boy or a girl.

Definition

Based on various standard sources, plant breeding has been defined in various ways. A few important and standard definitions are:

The art and science of changing plants genetically.

Plant breeding is the genetic adjustment of plants to the service of man.

Improvement of crop plants as the result of process of evolution directed by man for his own ends. The basic principles of plant breeding are thus the principles of evolution. Directed evolution as imposed in plant breeding differs from natural evolution chiefly in a greatly reduced time-scale, and in a more precise control over the factors which govern hybridization and selection.

The science and art of manipulating the heredity of plants for a specific purpose.

Plant breeding is a deliberate effort by human to nudge nature, with respect to the heredity of plants, to an advantage. The changes made in plants are permanent and heritable and the professionals who carry out this task are called plant breeders. This effort at adjusting the status quo is instigated by a desire of humans to improve certain aspects of plants to perform new roles or enhance existing ones. As a result, the term “plant breeding” is often used synonymously with “plant improvement” in recent years. Normally the term plant breeding connotes the involvement of sexual process in effecting a desired change; however, it is also true that modern plant breeding also includes the manipulation of asexually reproducing plants (plants that do not reproduce through the sexual process). Breeding is therefore about manipulating plant attributes, structure, and composition, to make them more useful to humans.

Gepts and Hanock (2006) have defined plant breeding as an applied, multidisciplinary science. It is the application of genetic principles and practices associated with the development of cultivars more suited to the needs of human than the ability to survive in the wild; it uses knowledge from agronomy, botany, genetics, physiology, pathology, entomology, biochemistry and statistics. Of particular importance is the ability to transfer, in addition to major genes, large suites of genes conditioning quantitative traits such as productivity and other traits of interest to humans. The ultimate outcome of plant breeding is mainly improved cultivars. Therefore, plant breeding is primarily an organismal science even though it is eminently suited to translate information at molecular level (DNA sequences, protein products) into economically important phenotypes. The traditional definition of plant breeding includes only those scientists who develop new cultivars and improved germplasm, however, many feel this definition should be expanded to include scientists who contribute to crop improvement through breeding research.

Self-Incompatibility

This is lack of self-fruitfulness and is a condition where the pollen from a flower is not receptive on the stigma of the same flower resulting into no seed setting. This happens despite the fact that pollen and ovule development both are normal and viable. This is caused by genetically controlled physiological hindrance to self-fertilization. This occurs widely among diverse families of flowering plants including the Leguminosae, Onagraceae, Rosaceae, Scrophulariaceae, Solanaceae, Compositae, Cruciferae, Papaveraceae and the Gramineae (now called as Poaceae). The incompatibility reaction is genetically governed by a single locus designated as S with multiple alleles whose number can go more than 100 in some species such as Trifolium pretense. East has estimated that this occurs in more than 3000 plant species distributed over 20 families. Lewis classified incompatibility systems into two main groups, namely, heteromorphic and homomorphic and homomorphic system has further been divided into gametophytic and sporophytic types as illustrated below:

Plant genetic resources (PGR) are the genetic material of plants which are of value for present and future generations of humankind. Often used as a synonym to plant germplasm, it can be defined as a seed, a plant or plant part including cell cultures, genes and DNA sequences that are held in a repository or collected from wild as the case may be and that are useful in crop breeding, research or conservation because of genetic attributes. The term is used to describe a collection of genetic resources for an organism or genetic material which forms the physical basis of inherited qualities. In brief, germplasm is the sum total of the hereditary materials in a species. Germplasm is the foundation and lifeblood of plant breeding without which plant breeding activities cannot be conducted. Germplasm is the genetic material that can be used to perpetuate a species or a population. The base germplasm can be improved for better performance of the crop. In the initial stage of a breeding programme, breeder evaluates the available germplasm lines and makes a selection from them for further test and final release to the farmers. Later on, the germplasm serves as a source of the parental lines which are used to initiate another phase of the breeding programme. Besides, using the base germplasm, breeders generate new variability using a variety of breeding methods such as crossing parental lines and developing new lines, induced mutations and more recently gene transfer. This new variability is again subjected to appropriate selection methods leading to identification and further evaluation of new and promising genotypes for release as cultivars. Generally, germplasm includes following types:

Heterosis or hybrid vigour is the condition where an F1 hybrid falls outside the range of the parents with respect to some character or characters. It is also defined as a manifestation of heterozygosity, expressed as increased vigour, size, fruitfulness and resistance to diseases, insects or climate extremes. It has been observed in nearly every crop including both self and cross-pollinated crops. It is converse of inbreeding depression. However, even the species that show little or no inbreeding depression, often benefit from crossing and resultant hybrids. Therefore, heterosis has been more emphasized than the inbreeding depression. It is defined in two basic ways: