eChapters

Introduction

We come across a variety of chemicals every day in a laboratory. While some of them are relatively safer, others are extremely hazardous. Thus, it is very important to know the potential hazards that can be caused by the chemicals present in the laboratory and the safety measures needed to be followed to avoid the hazards. Additionally, we should also be aware of the steps necessary to be taken on such hazardous situations. According to IUPAC, a hazardous chemical mean the chemical which has the potential to cause damage in various ways. In a laboratory, there are chemicals that might be irritant, carcinogen, respiratory fibrogen, systemic poison, asphyxiant, flammable, etc. which have the potential to cause hazard to the workers or environment. Therefore, it is important to use appropriate procedure to reduce the risk and protect the health/safety of laboratory personnel, the public and the environment.

Types of Hazards Associated with Chemicals

Chemical hazards: The hazards caused by chemicals can be broadly classified into three categories.

1. Health hazard: This is also known as toxic effects of chemical. The risk associated with a chemical in laboratory depends on the extent of exposure and the inherent toxicity of the chemical. Many chemical reactions form the product that might be much more toxic than the reacting chemicals. For example, inadvertent mixing of formaldehyde (a common tissue fixative) and hydrogen chloride results in the generation of bis(chloromethyl) ether, a potent human carcinogen. For most of the chemicals, the route of exposure (through skin, eyes, gastrointestinal tract, or respiratory tract) is more important (Figure 17.1) that must be considered during risk assessment.

The ultimate success of commercial propagation depends on the capacity to transfer plants out of culture on a huge range, at low cost and with high survival rates. The plants multiplied in vitro are exposed to a unique set of growth conditions (high levels of inorganic and organic nutrients, growth regulators, sucrose as carbon source, high humidity, low light, poor gaseous exchange) which may support rapid growth and multiplication but also induce structural and physiological abnormalities in the plants, rendering them unfit for survival under in vivo conditions. Poor control of water loss and heterotrophic mode of nutrition are main cause of deficient growth of in vitro plants.  Hence, gradual acclimatization is necessary for these plants to survive transition from culture to the greenhouse or field. During acclimatization the in vitro formed leaves do not recover but the plant develops normal leaves and functional roots. Once roots are well formed the plants are ready to be transferred into soil.The procedure of acclimatization of regenerated plantlets are: 

In a large random-mating population both gene frequencies and genotype frequencies remain constant from generation to generation in absence of migration, mutation and selection and the genotype frequencies are determined by the gene frequencies. These properties of a random mating population were first explained by G. H. Hardy and W. Weinberg independently in the year 1908 and are generally known as Hardy-Weinberg law. The operational understanding of this law involves three steps as follows:

1. From parents to the gametes they produce.
2. From union of the gametes to the genotypes in zygotes produced.
3. From genotypes of the zygotes to the gene frequencies in the progeny generation.

The gene and genotype frequencies in the original parent generation are assumed as follows:

Introduction

Resource management balances human needs with environmental preservation, focusing on sustainable development, responsible use, and conservation of natural resources. It involves environmental stewardship, economic efficiency, and social equity, ensuring equitable access for all societal segments while meeting present and future demands (Study Smarter, N.D; Mohd Akhter Ali et al., 2023).

There are specific areas such as water, soil, forests, waste, and sustainable harvesting practices. Each area presents unique challenges and opportunities, requiring tailored strategies and interventions to promote sustainability. The interplay between human activities, environmental impacts, and socio economic dynamics through the lens of resource management highlights the need for sustainable practices that balance development with ecological preservation, ensuring equitable resource distribution and long-term economic stability. Emphasis is placed on holistic approaches, participatory decision making, and capacity building to enhance resource governance and promote sustainable practices.

Introduction
In the ever-evolving landscape of agriculture, the intersection of science and technology continually reshapes the way we approach crop improvement. Among the most revolutionary advancements in recent years is the advent of genome editing technologies. These powerful tools offer unprecedented precision and efficiency in modifying the genetic makeup of plants, holding immense promise for revolutionizing the field of plant breeding. Genome editing plays a crucial role in plant breeding by enabling plant breeders to make precise and targeted changes to the DNA of crops, offering significant advantages over conventional breeding methods. Besides, crop improvement, these new breeding tools shorten the time needed to introduce desirable traits into crops, from decades to just a few years. They have revolutionized plant breeding by providing breeders with the ability to efficiently create crops that are more resilient, better adapted, and can produce higher yields with fewer resources, ultimately contributing to sustainable food production and addressing the challenges posed by climate change and population growth.
This comprehensive review aims to explore the transformative potential of genome editing technologies in genetic improvement of crop plants. The review will commence by elucidating the underlying mechanisms of genome editing technologies, offering insights into the molecular machinery that drives precise DNA modifications mediated by ZFNs, TALENs, CRISPR/Cas, base editing, prime editing and other new variants of CRISPR/Cas systems, highlighting their respective strengths and limitations. From enhancing crop productivity and quality to conferring resistance against biotic and abiotic stresses, these technologies offer a versatile toolkit for addressing pressing agricultural challenges. Case studies and examples from recent research will illuminate the successes and potential pitfalls of employing genome editing in crop improvement efforts. Besides, the regulatory and ethical considerations surrounding the deployment of genome editing in agriculture will be addressed. In conclusion, this comprehensive review seeks to provide a holistic perspective on harnessing genome editing technologies in plant breeding. By elucidating the scientific principles, applications, regulatory challenges, and ethical considerations, we hope to facilitate informed discourse and decision-making surrounding the integration of these transformative tools into agricultural practices. As we stand at the precipice of a new era in crop improvement, embracing the potential of genome editing holds the promise of unlocking sustainable solutions to global food security challenges.

Introduction
Crop improvement is critical for tackling global food security challenges caused by population growth, resource scarcity, and climate change (Singha and Singha, 2024). Traditional breeding techniques, such as Sanger sequencing, have been around for a long, but their accuracy, speed, and usefulness are typically limited. Sanger sequencing is useful for small-scale inquiries, but its laborintensive procedures and limited throughput make it unsuitable for large-scale genome analysis. Molecular marker-based breeding strategies have proven to be effective tools for addressing these difficulties by increasing plant growth and overall quality (Bohar et al., 2020). In this respect, molecular markers like as single nucleotide polymorphisms (SNPs), insertions/deletions (indels), simple sequence repeats (SSRs), and structural variations (SVs) are expected to be useful for future breeding operations (Panahi et al., 2024). The discovery and characterization of these molecular markers is strongly reliant on advances in sequencing technology, namely next generation sequencing (NGS). Furthermore, NGS technologies have shown to be crucial for functional genomics, allowing for large-scale transcriptome and whole genome sequencing across plant taxa (Singh et al., 2024). These vast databases give a comprehensive picture of gene expression and genetic variation, making it easier to identify functional markers linked with certain features (Figure 1). The integration of NGS and bioinformatics technologies has simplified the study of these datasets, enabling more efficient discovery of markers and improving the use of marker-assisted selection (MAS) in breeding programs (Panahi et al., 2024).
The development of high-throughput genotyping technology has enabled substantial SNP-based research, which has improved our understanding of genetic diversity, population structure, and disease association (Yirgu et al., 2023). With the progress of genotyping by sequencing (GBS), SNPs have emerged as the most extensively utilized DNA markers in the twenty-first century (Thomson, 2014). SNP markers have significantly advanced plant breeding across a variety of crops, including tomato (Peterson et al., 2012), maize (Junta et al., 2020), rice (Razak et al., 2020), wheat (Wei et al., 2011), soybean (Kim et al., 2010), oil palm (Maryanto et al., 2020), cassava (Karim et al., 2020), and taro (Helmkampf et al., 2018). Overall, SNP markers have emerged as critical tools for genetic improvement and precision breeding across a wide range of crop species. SNPs initially trailed behind SSRs in DNA fingerprinting because they have fewer polymorphisms

Introduction
Angiosperms produce attractive and intricately structured flowers, within which their reproductive process occurs. In flowering plants, as in other plant groups, a diploid spore-producing generation (sporophyte) alternates with a haploid gamete-producing generation (gametophyte). The flower contains specialized structures, such as the stamen (or androecium) and the pistil (or gynoecium), where the respective male and female gametophytes are formed. The pollen grain serves as the male gametophyte, while the embryo sac serves as the female gametophyte. These gametophytes are responsible for producing sperm and egg cells, respectively facilitating their union during fertilization. The pollen grain contains the male gametophyte in angiosperms or gymnosperms. Conversely, spores function as a resting and dispersal phase for cryptogams (Moore et al., 1991). The study of pollen grains (produced by seed plants, angiosperms and gymnosperms) and spores (produced by pteridophytes, bryophytes, algae and fungi) is known as palynology. This discipline examines the structure and formation of pollen grains and spores, their dispersal and their preservation under various environmental conditions. Palynology serves as a valuable research tool for understanding many aspects of plant and animal metabolism. Moreover, a deeper understanding of pollen can aid plant breeders in enhancing efforts to improve global food and fiber supplies. In the anthers of higher plants, neither the developing pollen nor the surrounding tissues exhibit autonomous growth and development. Instead, the developing anther functions as a system where the gametophytic and sporophytic generations of the plant communicate, coordinate and co-participate in development. This chapter aims to understand the various aspects of gene activity that occur during pollen development.

Introduction
Plant being sessile are subjected to a myriad of biotic and abiotic stresses that impede growth and resulting significant losses in crop productivity globally (Bhat et al., 2019; Ganie & Reddy, 2021). In this context, there is an immediate need to develop high yielding climate-resilient crop varieties for ensuring food security in the face of increasing population growth. Although conventional breeding has achieved notable success in the development of high-yielding crop varieties (Bhat et al., 2020), but this approach is slow to maintain pace with ever increasing population. In this regard, more recent approach of genomics-assisted breeding (GAB) has emerged as a pivotal approach to develop the high-yielding climate resilient crop varieties (Bhat et al. 2021). Although, low-throughput sequencebased markers like simple sequence repeats (SSRs) have been extensively utilized in molecular breeding programs, but they have the limitations of reduced genomic coverage and high cost (Varshney et al., 2014; Zargar et al., 2015). In this context, the emergence of second-generation DNA marker systems has provided higher genomic coverage and low cost in marker-assisted breeding. For example, recent advancements in next-generation sequencing (NGS) and genotyping platforms have substantially enhanced marker density and genomic coverage while reducing costs (Przewieslik-Allen et al., 2019); thus rendering them commercially available for both model and non-model crop species (Huang & Han, 2014; Rasheed et al., 2017). These high-throughput genotyping platforms provides millions of DNA polymorphisms (Bassi et al., 2016; Ganal et al., 2012), thereby enhancing gene mapping resolution and prediction accuracy in genomic selection (GS) (Robertsen et al., 2019; Yu et al., 2019). Most of the agriculturally important crop traits, such as yield, quality, and stress tolerance, possess complex inheritance i.e., governed by multiple genes with minor effect on trait of interest as well as are highly influenced by genotype-by-environment (G × E) interactions (Voss-Fels & Snowdon, 2016). The conventional linkage mapping approach has elucidated the genetic basis of agriculturally important complex traits but this approach involves the use of bi-parental mapping populations which are constrained by the limited genetic diversity, low resolution, and restricted recombination events (Brachi et al., 2011; Collard et al., 2005). Consequently, the genome-wide association study (GWAS) has emerged as a powerful approach for dissecting the genetic basis of complex quantitative traits in crop plants, resulting higher resolution and allelic diversity (Varshney et al., 2020; Zhu et al., 2008). Moreover, owing to the availability of cost-effective and high-density genotyping platforms, has allowed the routine use of GS in the crop breeding which is more recent approach of GAB (Crossa et al., 2017). In recent years, the advent of next-generation sequencing (NGS)-based genotyping techniques has significantly allowed the genotyping of extensive germplasm collections, enabling comprehensive GWAS and GS analyses (Annicchiarico et al., 2017; Zargar et al., 2015). Nonetheless, the predominant limitations impeding the utilization of SNPs in the GWAS and GS approaches encompass their inherently biallelic nature, the occurrence of rare alleles, and the prevalence of linkage drag (Voss-Fels & Snowdon, 2016; Wray et al., 2013). In

Heliconia is a tropical ornamental crop valued for its striking inflorescences, vibrant colours and long-lasting cut stems. This chapter presents the origin, distribution, species, botanical characteristics and commercially important types of Heliconia. It discusses climate, soil, shade, propagation, planting, irrigation, nutrition and cultural management. Pest and disease problems are described together with suitable management practices. The chapter also addresses harvesting stages, postharvest handling, grading, packaging, vase life and yield. Its emphasis on tropical production makes Heliconia particularly relevant to growers seeking to diversify high-value floriculture enterprises in warm and humid regions of India. commercially.

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.

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.

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.

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.

The commercial exploitation of heterosis started only after the rediscovery of Mendel’s law of inheritance and consequent understanding of the theoretical basis of hybrid vigour. Heterosis is considered as a major revolution in classical plant breeding era. Utilization of heterosis has substantial influence in genetics to provide hybrid vigour, consequently high yielding hybrids in different crops and plants. Yield increase from heterotic hybrids due to the expression of heterosis is up to 30% superior to conventional varieties. The term heterosis was first used by Shull (1914) and represents the increase or decrease in fitness and vigour of the F₁ hybrid over the mean or mid parent values, produced by crossing two genetically different individuals for one or more traits. Generally, positive heterosis is desirable but in some cases like maturity duration and presence of toxic substances, negative heterosis is condiderable as desirable. Heterosis can be estimated in three different ways. When the heterosis is estimated over mid parent, it is called as relative heterosis or mid parent heterosis. Estimation of heterosis over better parent out of the two parents involved in the cross is referred as “Heterobeltiosis”, the term which was coined by Fonseca and Patterson (1968). “Standard Heterosis”, often called as useful heterosis which was coined by Meredith and Bridge (1972) and denotes the superiority of F₁ over the standard commercial check.

Hybrid vigor or heterosis is opposite and complementary to inbreeding depression (reduction in fitness as a direct result of inbreeding). In theory, the heterosis observed after crossing is expected to be equal to the depression upon inbreeding, considering a large number of crosses between lines derived from a single base population. In practice, plant breeders are interested in heterosis expressed by specific crosses between selected parents, or between populations that have no known common recent origin. Furthermore, because heterosis is subject to the interactions between genotype and environment, it is desirable to describe the heterosis of a particular hybrid line for a specific trait at a specific location or under specified environmental conditions.

Hibiscus (Hibiscus rosa-sinensis) is a vigorous tropical evergreen flowering shrub valued for its large, colourful and attractive blooms. In India, its flowers are widely used for religious offerings, particularly in temple worship, as well as for ornamental and loose flower purposes. The chapter introduces its origin, distribution, genetics, botanical characteristics and important varieties. It also highlights the crop’s medicinal and food-related importance, including the use of hibiscus products in herbal beverages and processed foods. Detailed production practices cover climate, soil, propagation, field preparation, nutrient management, irrigation and cultural operations. Major pests and diseases, harvesting, postharvest management and yield are also included for commercial cultivation.

With the sharp development of urban and industrial growth, the area under agriculture is declining year by year. On the other hand, human and animal population is increasing at a very fast rate. So, to meet the growing demand of food and fodders, a vertical increase in yield is required. Crop productivity per unit area can be enhanced with the manipulations of some agronomist practices such as sowing the crops at appropriate time, selection of suitable field for raising a crop, adoption of best planting techniques, use of appropriate seed rates, adoption of proper irrigation schedule, proper and need based application of fertilizers, adoption of zero till technology, green manuring, mulching, addition of well decomposed farm yard manure, timely and proper weed management, selection of recommended crops and crop varieties, proper control of insects and pests, adoption of marketing tips etc.

1.1 Introduction

With the rise in the global population, the demand for increased supply of food has motivated scientists and engineers to design new methods to boost agricultural production. With limited availability of land and water resources, growth in agriculture can be achieved only by increasing productivity through good agronomy and supported with an effective use of modern technology. Advanced agronomical methods lay stress not only on boosting agricultural produce through use of more effective fertilizers and pesticides, but also on the hygienic storage of agricultural produce. The detrimental effects of modern agricultural methods on the ecosystem have raised serious concerns amongst environmentalists. The widespread use of persistent pesticides globally over the last six decades has contaminated groundwater and soil, resulting in diseases and hardships in non-target species such as humans and animals. The first step in the removal of disease causing microbes from food products or harmful contaminants from soil and groundwater is the effective detection of these damaging elements. Nanotechnology can augment agricultural production and boost food processing industry through applications of these unique properties.