eChapters

Estimates of heritability use statistical analyses to help to identify the causes of differences between individuals. Because heritability is concerned with variance, it is necessarily an account of the differences between individuals in a population. Heritability can be univariate–examining a single trait – or multivariate – examining the genetic and environmental associations between multiple traits at once. This allows a test of the genetic overlap between different phenotypes: for instance hair colour and eye colour. Environment and genetics may also interact, and heritability analyses can test for and examine these interactions (GxE models).

Polygenic characters exhibit a wide range of expression but the action of genes may be either additive or non-additive. According to Fisher et al. (1932), Smith (1936) Lush (1945), Panse (1946) and Mather (1949) the genetic advance can be achieved through selection of the heritable variation in only due to additive. So, selection for a particular character based on phenotypic variability without estimating the heritable part of it will not be successful. Heritability estimates along with genetic advance are normally more helpful in predicting the gain under selection than heritability estimates alone (Singh, 1997). Therefore, the heritability enters into every formula connected with breeding methods and many practical decisions are taken considering the heritability value.

Heritability measures the fraction of phenotype variability that can be attributed to genetic variation. This is not the same as saying that this fraction of an individual phenotype is caused by genetics. For example, it is incorrect to say that since the heritability of personality traits is about 0.6, that means that 60% of your personality is inherited from your parents and 40% comes from the environment. In addition, heritability can change without any genetic change occurring, such as when the environment starts contributing to more variation. As a case in point, consider that both genes and environment have the potential to influence intelligence. Heritability could increase if genetic variation increases, causing individuals to show more phenotypic variation, like showing different levels of intelligence. On the other hand, heritability might also increase if the environmental variation decreases, causing individuals to show less phenotypic variation, like showing more similar levels of intelligence. Heritability increases when genetics are contributing more variation or because non-genetic factors are contributing less variation; what matters is the relative contribution. Heritability is specific to a particular population in a particular environment. High heritability of a trait, consequently, does not necessarily mean that the trait is not very susceptible to environmental influences.Heritability can also change as a result of changes in the environment, migration, inbreeding, or the way in which heritability itself is measured in the population under study. The heritability of a trait should not be interpreted as a measure of the extent to which said trait is genetically determined in an individual.
The extent of dependence of phenotype on environment can also be a function of the genes involved. Matters of heritability are complicated because genes may canalize a phenotype, making its expression almost inevitable in all occurring

Any phenotype is the result of interaction of genotype and the environment. Any genotype cannot express itself unless proper environment for its expression is made available. Likewise, environment cannot create any phenotype unless a genotype is there to be acted upon by the environment. However, the effect of genotype and the environment is not fixed, its keeps on changing depending upon the relative role of the genotype. Heritability therefore specifies the proportion of the total phenotypic variability that is due to genetic causes. In other words, heritability is defined as the ratio of genetic variance to the total phenotypic variance. Heritability is the degree to which the characteristics of a plant are repeated and expressed in the progeny. This can be expressed quantitatively as follows:

Heritability (h²) = Genotypic variance/Phenotypic variance

While dealing with polygenic traits and the continuous variation in plant breeding programs, it is important to know as to what extent the phenotype is decided by the genotype and to what extent by the environment. It is well known fact that what we observe i.e. phenotype is the result of genotype, environment and interaction between the genotype and the environment. The total variance is phenotypic variance or the variance of phenotypic values and various components of variance are as shown in Table 6.1.

Introduction

Apart from the general way of flood-flushing practiced at different sites of Indus Civilization, mention may be made of the following practices particularly undertaken in Sind. This is evident in the writings of inscriptions on seals from Mohenjo-Daro which state: ‘Two canals were constructed in the month of Kudam (Aquarius) and Mina (pisces). Another seal records that it took ‘thirteen months to construct a canal’. These canals were cut at low gradient and waters were allowed to merge ultimately into low ground in a direction oblique to the river so as to secure a great fall as possible. This fall varied from a foot to a few inches in a mile. They were up to hundred feet wide and about a dozen feet deep, not enough to draw off from the river except in flood. These were natural streams and probably seasonal. The perennial canals of the Indus system were cut to an extra depth and could receive water even when the main river was low, but their real purpose seems to increase the discharge during inundation.

Irrigation system

Irrigation system was consisting of lifting of water by water-wheel and by means of Shaduf from adjoining water sources. There was also provision of tank irrigation. Rice cultivation shows necessary moisture of soil probably retained by now using contour bunding for locking up monsoon rain-waters by tank-irrigation. Rainfall under vernal equinox or winter solstice has not been given much importance in the context of agriculture. Artificial rain making agents was the twin stars, Asvinis and Dadhici, described as horse headed sign. The exact time of their appearance cannot be ascertained definitely. Their association with cool season can be surmised from their name Dasra implying the same as referred to in the text of Panini. Moreover, their attributes as sender of hima (cold or snowfall) after the scorching heat of summer associates them as belonging to vernal equinox. That they appeared at the time of sun’s movement to another house, is explicitly mentioned in the Rigveda. It is a fact which shows the rising of these stars at the junction of two solstices, summer and winter. The Rigveda in one place described them as associated with winter solstice. They were found to have been associated with three kinds of watery discharges, viz. rain (vristi), dew (madhu) and snow (hima).

A hernia is the protrusion of an organ through a defect in the wall of the abdominal cavity in which it lies.

Classification
1. On the Basis of Anatomical Site
    Abdominal (umbilical and ventral)
    Diaphragmatic

Preamble

In India, agriculture plays an important role as it accounts for about 18% of the GDP and supports nearly 58% of the total working population for employment. Food grain production increased significantly from a low level of 50 million Tons during 1950-51 to a record of 230.7 million Tons in 2007-08. The demand for food is growing rapidly due to increasing population and rising income levels, hence we need to produce about 320 million Tons of foodgrains by the year 2025. It implies more pressure on our exhisting land, soil and water resources which are already in short supply, degraded, fragile and this similar situation is being faced by mainly developing countries today. Plant parasitic nematodes are of great economic significance. Since most of them live in the soil hence represent one of the most difficult pest problems in terms of identification, demonstration and management.

1. Introduction
Hydrogenation plays a vital role in the transformation of organic compounds, making it essential for synthesizing fine chemicals and pharmaceuticals. This process is widely utilized in both laboratories and for industrial applications (Andersson et al., 2008). Typically, two approaches are used for hydrogenation: traditional one involves direct hydrogenation using pressurized hydrogen gas, and the other relies on transfer hydrogenation (TH), which involves addition of hydrogen into a molecule from a non-H2 sources (Johnstone et al., 1985). The use of high-pressure hydrogen gas, however, demands significant investment in infrastructure, making it less economically feasible for developing a sustainable hydrogenation industry. In contrast, TH has gained increasing attention due to its sustainability, particularly when employing hydrogen donors derived from biomass, such as alcohols and organic acids, which are abundant, cost-effective, and easy to handle instead of using non-renewable H2 gas for reduction of CO2 (Becattini et al., 2021) (Figure 1).
2. Historical Background and Classification
The hydrogen transfer process has a rich history spanning over a century. In 1903, Knoevenagel first demonstrated that palladium black effectively promoted the disproportionation of dimethyl 1,4-dihydroterephthalate into dimethyl terephthalate and cis-hexahydroterephthalate, in which hydrogen transfer was occurred between identical molecules (identical donor and acceptor) (Knoevenagel et al., 1905). This pioneering work established the foundation for hydrogen transfer reactions. Braude and Linstead later categorized these reactions into three distinct types (Braude et al., 1954):

The effect of inbreeding and outbreeding was found in ancient time in animals and human beings since civilization. Hence, the phenomenon “Heterosis” was conceived since pre-Mendelian era. But in plants this phenomenon was recognized only 200 years ago. Koelreuter (1766) first published his scientific investigation on hybridization. Knight (1799) first recorded increased vigour following crossing. Mendel (1865) also observed increased vigour in pea hybrids. Charles Darwin (1876) suggested that cross-fertilization was beneficial whereas self-fertilization was injurious. However, the scientific concept of heterosis phenomenon was established in post-Mendellian era by the monumental work by East (1908) and Shull (1908).
General concepts of Heterosis
• Heterosis is the widely occurring genetically governed biological phenomenon involving both plants and animals.
• It frequently occurs in plants and is found mostly in cross-pollinated plant species than in self-pollinated plants.
• It is built in evolutionary mechanism favouring better survival of heterozygotes in nature.

I. FILL UPS

1. _____ is the increased function of any biological quality in a hybrid offspring.
2. Heterosis is otherwise known as _____.
3. _____ is the reduced fitness in a given population as a result of breeding of related individuals.
4. In _____ heterosis type, naturally occurring mutants are sheltered.
5. The progeny posses superiority over parents in vegetative growth, but reduction in yield is known as _____.
   1. Average heterosis is mathematically expressed as _____.

1. HETEROSIS

1.1. Definition

Heterosis or hybrid vigor or outbreeding enhancement, is the increased function of any biological quality in a hybrid offspring. It is the occurrence of a genetically superior offspring from mixing the genes of its parents.

1.2. Inbreeding depression

Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. In general, the higher the genetic variation within a breeding population, the less likely it is to suffer from inbreeding depression.

13.1 Introduction

F₁ plants produced by crossing two parents with contrasting characters are called hybrids. Hybrids generally exhibit increased vigour and fitness over the parents. This phenomenon is called hybrid vigour or heterosis. Thus, heterosis is the phenomenon in which the hybrid of two genetically dissimilar parents shows increased vigour at least over the mid-parental value. Heterosis is just the reverse of inbreeding depression, which results after selfing the plants of the cross-pollinated crops. Kolreuter (1761-66) was the first to report hybrid vigour in the hybrids of tobacco, Datura, etc. Most of the early plant hybridizers including Mendel (1865) had noticed this phenomenon. Shull (1914) coined the term heterosis from two Greek words, hetero (different) and osis (condition), to replace his own earlier word ‘stimulus of heterozygosis’. In current usage, heterosis and hybrid vigour are used as synonyms and interchangeable.

13.2 Types of Heterosis

Depending on the nature, origin, adaptability, reproducibility and non-reproducibility, heterosis can be categorized into two: (1) euheterosis (true heterosis) and (2) pseudo-heterosis (false heterosis, i.e., luxuriance).

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:

The information under this section is primarily based on Yordanov (1983). It is almost unanimously accepted that heterosis manifestation in tomato is in the form of the greater vigour, faster growth and development, greater earliness, and productivity, higher resistance to disease and adaptability unfavourable environmental conditions. The first step towards a large scale extension of hybrid tomato cultivars in the practice and proper organization of hybrid seed production took place in Bulgaria. After the second world war tomato heterosis breeding developed quickly in the Netherlands, England France, USA, Japan and other countries. In India, tomato hybrid cultivar on commercial scale was introduced in 1973 by Indo American Hybrid Seed Company.

10.1. Heterosis

Occurrence of a genetically superior offspring from mixing the genes of its parents.

Superiority of F₁ hybrids over its both parents in terms of yield and vigour.

20.1 Introduction

A hybrid cultivar (also called hybrid) is the F₁ progeny of a planned cross between inbreds, cultivars, clones or populations. Depending upon the breeding approach, the hybrid cultivar may involve two or more parents. A critical requirement of hybrid production is that the parents are divergent. This divergence is the cause of superior performance of hybrids. The outstanding performance of crops is due to the exploitation of the phenomenon of heterosis (hybrid vigour) which is high when parents are divergent. Much of what we know about heterosis breeding (also called hybrid breeding) came from the work on maize hybrid cultivar development. However, commercial hybrids are now available in many crops including self-pollinated crops.

Abstract
The analysis of variance showed significant differences for all the traits studied. The best two combinations out of the 28 F1s produced by crossing eight diverse lines of capsicum in diallel fashion (excluding reciprocals) with respect to most of the traits were Osh Region x EC-119058 and California Wonder x Bonali.

Keywords: Heterosis, Capsicum annuum L.

Bell pepper (Capsicum annuum L.) also known as Sweet pepper or Spanish pepper is an important vegetable used in various delicacies and salads, the world over. The crop originated in New World tropics and subtropics (Greenleaf, 1986), and introduced in India by the British. Because of its excellent quality as obtained under Shimla hills conditions, it came to be called as Shimla Mirch. Its most notable feature is flavour and hence is appreciated worldwide. It is also an excellent source of pro-vitamin A and vitamin C. Bell pepper assumes a special significance in the mid hills of Himachal Pradesh as it is grown as an off season crop during summer and rainy seasons, which brings lucrative returns to the growers. 

Introduction
Definition of heterosis
The word “heterosis” was coined by G.H. Shull in 1914 as a convenient abbreviation for awkward phrases like ‘stimulation of heterozygosis’. When two genetically diverse parents are crossed, the resulting F1 or hybrid progeny has superior performance over both of its parents which is known as heterosis. The F1 or hybrid has superiority in vigour, adaptability, stress tolerance, growth rate, population fitness, biological and economic yield. Luxuriance on the other hand is a more general term often confused with heterosis, used to describe plant’s overall healthy and abundant growth, regardless of its genetic background (Allard, 1960). Charles Darwin introduced the concept of hybrid vigour in 1876, a term closely related to heterosis. The exceptional hybrid vigour in the F1 generation stems from the theory of dominance and codominance, offering numerous advantageous characteristics, particularly economically significant ones.
Heterosis is confined to F1 or hybrid generation only. The F2 and subsequent generations do not show heterosis due to factors like recombination and segregation, which lead to shuffling of the genes and produce variety of new combinations, hence they are neither homogenous like F1 nor have hybrid vigour. One of the main characteristics of heterosis is that it is highly variable from crop to crop as well as from cross to cross. So, some of the crosses will exhibit higher heterosis than the other crosses. This is because heterosis is controlled by many factors which include the genetic diversity of parents, combining ability of parental lines, genetic background, additive, dominance, epistasis nature of gene imparting heterosis which will be dealt in detail in next sections of the book.
Heterosis, manifested in positive (yield, quality, disease resistance) or negative (plant height, maturity duration) aspects, is more prevalent in crosspollinated species than in self-pollinated ones. It can be fully exploited in hybrids or partially exploited in synthetic and composite varieties. The performance of hybrids relative to parents exhibits distinct features, as illustrated in Figure 1, including better-parent heterosis with optimal trait values surpassing either parent. Mid-parent heterosis exceeds the parental average but holds limited agronomic relevance. Phenotypes are broadly categorized as additive (similar to parental average) or non-additive, further subdivided into partially dominant, dominant, and over/under dominant. Factors influencing heterosis include genetic diversity, combining ability, genetic background, and the interplay of additive, dominance, and epistatic genetic factors, explored in detail in subsequent sections.

INTRODUCTION

Heterosis has contributed significantly towards increased crop production and it has become the basis of multibillion dollar agro-businesses in the world (Phillips, 1999). Hybridization is the important way that can create genetic variability and make new options. The F₁ population is obtained from the crossing of two homozygous but genetically dissimilar gametes or individuals (purelines in self pollinated crops or inbred lines in cross pollinated crops) that shows increased or decreased vigour over the better or mid parent value. Heterosis is maximum in F₁, generation which diminishes gradually in later generations. Hence, production of F₁, hybrid seeds of different flower crops is considered as the extreme focused area in floriculture industry.

Production of F₁ hybrids in ornamental crops was carried out even before Shull’s classical theory of hybrid vigour which was reported in 1971 for the first time in plant breeding. Benary Seed Company in Germany released F₁ hybrid in begonia (Begonia semperflorens) in the name of Prima Donna in 1909 (Reimann-Philip, 1983). But that time it did not attract the attention of plant breeders. It was during Second World War in 1942, when flower breeders were attracted towards heterosis breeding and started systematic F₁ hybrids. From 1950 onwards, numerous outstanding hybrids have been developed in many other flower crops in several countries like USA, The Netherlands, Denmark, Germany, United Kingdom and Japan, etc. First hybrid in single geranium was produced in 1960, in other flower crops like antirrhinum, pansy, marigold and zinnia in 1965, ageratum in 1966, geranium double in 1970, dianthus, begonia, impatiens and portulaca in 1976-77, gerbera in 1980 and carnation in 1981. In the present scenario of developed floriculture industry, in many countries F₁, hybrids are available in a number of annual flowers like ageratum, antirrhinum, anemones, calceolaria, dianthus, hollyhock, gazania, marigold, flowering tobacco, pansy, portulaca, stock, wall flower, zinnia, etc.

As emasculation is having the maximum share in cost of hybrid seed production, researchers have found several techniques in different flower crops as the alternative of emasculation and that can help in reducing the cost of hybrid seed production. The list of techniques being utilized commercially in different flower crops (Janakiram, 2004) is as follows: