eChapters

Introduction

Man’s intervention in the evolution of plants, to adapt them to suit his needs, constitutes the practice of plant breeding. Historically regarded as an art and still too empirical to be accepted universally as a science, it has recently been described as a technology (Riley 1978). Whether art, science or technology, it certainly draws on a wide range of disciplines and embodies all those principles of organisation and management that determine success in any production-oriented programme.

Perhaps the biggest contribution that the plant breeder has made to increased production during the past 50 years has been in helping to alleviate the effects of natural hazards such as lodging, pests and diseases on crop production. While most of this progress has been through the manipulation of biotic stresses, much is still to be achieved under non-biotic stresses such as drought, salinity, temperature, etc. This argument is strengthened by the fact that in spite of the spectacular achievements made possible by the ‘Green Revolution’, the productivity level of most crop plants, including wheat and rice, has remained both low and static under stress conditions. Concerted efforts are needed through an approach of interdisciplinary research, since not much has been done to define criteria for stress assessment and evolving breeding approaches for incorporating stress tolerance in crop plants.

Introduction

Global food productivity will have to rise significantly to satisfy an expanding world population. Increased vegetable production is one option towards the efficient conversion of natural resources into food stuffs. As a group, vegetables are a diverse range of herbaceous plants that do not belong to any particular botanical species, genus or family. Individual members may be at various stages of domestication. Vegetables are typically annual herbaceous species, whose plant parts (leaves, stems, flowers, fruits, roots or tubers) are consumed as fresh or as cooked product, and as an additional source of vitamins, minerals, fibre, phytochemicals, protein and/or calories. Health benefits are also claimed for some vegetable species, mainly due to antioxidant activity and capacity to scavenge free radicals.

Domesticated plants have been fundamentally altered from their wild relatives; these species have been moved into and adapted to new environments. They have become dependent on the farmer’s hand and they have been reshaped to meet human needs and wants. Modern crops are the results of thousands of years of these evolutionary processes. Like all biological evolution, crop evolution involves two fundamental process; the creation of diversity and selection (Harris and Hillman, 1989). Crop evolution is distinguished by two types of selection; one natural and another artificial or conscious. These evolutionary processes must continue in order for agriculture, a living and evolving system to remain viable.

In the hands of plant breeder’s sexual hybridization is a powerful tool for producing superior plants by combining characters distributed in different members of a species or different species of a genus. Genetic variability within the species has been efficiently utilized by breeders in their efforts to improve crops. However, the existing variability in a breeding population may not be sufficient for modern plant breeding purposes, and thus great efforts have been made to broaden the existing gene pool of crops through utilization of wild germplasm.

The current status of advances in fruit breeding is through the development of different scientific approaches augmented by ever-increasing knowledge and application of genetics, statistics and biotechnology. These innovative approaches very specific for a species in most of the cases, are the major tools of the fruit breeders to tackle the different objectives of fruit improvement programme at present Fruit improvement is a very slow process due to the long generation cycle varying from species to species, thereby reducing the chances of exploiting genetic recombination. Besides this factor, most of the fruit species are either highly heterozygous or polyploidy in nature. Due to this reason the asexual propagation of fruit plants is a conventional means while wide segregation occurs upon sexual reproduction. Such expectation is not unlikely because the types selected as commercial varieties are definitely to be vigorous ones, and a positive correlation exists between vigour and heterozygosity.

This discussion on breeding of fruit plants involves different aspect of the species concerned is so essential as well as fundamental that discussion of them must procede any consideration of breeding methods themselves. The plant species are grouped into two-self-pollinated and cross-pollinated. These two groups have emerged on the basis of pollination mechanism which plays significant role in the method of breeding application. To emphasize the difference in the reproductive systems of these two groups one should know the details about floral biology, mechanism of pollination control, reproduction by asexual and sexual means and self and cross-pollinated plants.

Transgenic crops, developed through genetic engineering techniques, have revolutionized modern agriculture by conferring novel traits that enhance yield, quality, and resilience. This chapter delves into the intricate interplay between the scientific advancements in breeding approaches for transgenic crops and the critical ethical concerns and regulatory frameworks that accompany them. The chapter begins by introducing the concept of transgenic crops and provides an overview of the diverse breeding techniques employed to manipulate plant genomes. These techniques include Agrobacterium mediated transformation, biolistic transformation, CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats–associated protein 9) genome editing, RNA interference (RNAi), and site-specific integration methods. Each method is presented within the context of its potential benefits and limitations. The subsequent sections address the ethical considerations that arise from the creation and deployment of transgenic crops. The potential ecological and biodiversity impacts, cross-contamination risks with conventional crops, and issues related to patenting genetically modified organisms (GMOs) are explored. Furthermore, the chapter examines the ethical implications of genetically modified crops on human and animal health and questions surrounding the monopolization of seed resources. Looking to the future, the chapter outlines emerging breeding technologies and anticipates potential challenges in ethical consideration and regulation.

All hybrids and varieties perform better under conventional farming in response to excess use of chemical fertilizers and pesticides, which are harmful to humans, animals and environment. Hence, there is a need to develop varieties/hybrids exclusively for organic farming. Breeding aspects of organic farming include breeding tools/methods which are used to breed varieties/hybrids including testing and multiplication under organic conditions duly following the principles of organic farming as defined by IFOAM. These cultivars should have high nutrient use efficiency, resistance to diseases and pests, competitive ability against weeds, higher yield and stability across environments along with enhanced nutritional quality. This book chapter briefly discusses the aspects of breeding that are involved in generating cultivars suitable for organic farming.

1. Introduction

Currently, organic farmers rely heavily on conventionally developed and produced varieties. Nevertheless, in order to optimize their production under organic agriculture, it is necessary to develop cultivars that are more suitable for organic cultivation. According to some studies, the naturalness of organic agriculture should go beyond simply by avoiding chemical inputs and substituting natural and organic components during the transition from conventional to organic farming.

INTRODUCTION

The ultimate objective of forest tree breeding is to develop fast growing high yielding genetically improved superior strains in order to replace the wild natural forest stands so as to obtain higher forest productivity per unit area and time. A breeding programme, in fact, involves purposeful management of genetic variability present in a taxon. The variation is regulated through controlled mating. This obviously, needs detailed information on the nature and extent of genetic variation on one hand and equally on the reproductive biology of the species. A clear understanding of phenological behaviour, time of anthesis, time and duration of stigma receptivity, fertilization, mode of pollination, seed development etc. is necessary for attempting crosses between genetically different forms which is invariably involved in the breeding programmes. Although, tree breeding work has been done to a great extent on the temperate species (Devey et al. 2002; Murat et al. 2006; Gotzenberger et al. 2007), no serious efforts were made in the past on tropical forest species including Jatropha (Jatropha curcas), presumably due to the consideration that similar breeding methods may perhaps, be applied to the tropical trees as well. This, however, is not applicable, as the phenological and reproductive features are typical different to each species. It was in this background that the present research article was planned to collect information on floral biology, breeding behaviour and hybridization programme in Jatropha for subsequent application in its genetic improvement.

Crops plants are broadly classified into two groups based on their mode of reproduction viz. sexually propagated and asexually propagated. In sexually propagated crops seeds are the primary propagules and it is produced by the fertilization of male and female gametes. Whereas, asexual reproduction or clonal reproduction covers all those modes of multiplication of plants where normal gamete formation and fertilization does not take place and vegetative propagules are the means of reproduction. Since sexual reproduction involves meiosis, segregation and recombination, the creation of variation is a continuous process which is inevitable in these crops. On the other hand, in asexual propagation progenies are identical to the parent clones and they are genetically similar without any variation and they reproduce via mitosis. The most important vegetatively propagated food crops are potato, sugar cane, cassava, sweet potato, yam, plantain/banana, and fruit trees. Other crops with asexual propagations are some ornamentals, grasses, and forages.

Introduction
Based on the mode of reproduction, plants are broadly classified into sexually propagated and asexually propagated crops and some of the agricultural crops and a large number of horticultural crops are asexually propagated. The most important asexually propagated crops cultivated on a global basis are potato (Solanum tuberosum), cassava (Manihot esculenta), sweet potato (Ipomoea batatas), sugarcane (Saccharum spp), yam (Dioscorea spp.), taro (Colocasia esculenta), banana (Musa paradisiaca), etc. In sexually propagated crops, seeds are the primary propagules and it is produced by the fertilization of male and female gametes. Whereas, asexual reproduction or clonal reproduction covers all those modes of multiplication of plants where normal gamete formation and fertilization do not take place and vegetative propagules are the means of reproduction. Since sexual reproduction involves meiosis, segregation and recombination, the creation of variation is a continuous process which is inevitable in these crops. On the other hand, in asexual propagation, progenies are identical to the parent clones and they are genetically similar without any variation and they reproduce via mitosis.
Characteristics of asexually propagated crops
• Majority of the asexually propagated crops are perennials, e.g., sugarcane, fruit trees, etc. The annual crops are mostly tuber crops, e.g., potato, cassava, sweet potato, etc.
• Many of these crops show reduced flowering and seed set, and some varieties of these crops do not flower at all. But many of these crops flower regularly and show satisfactory seed set.
• They are invariably cross-pollinated and highly heterozygous and show severe inbreeding depression.
• A vast majority of asexually propagated crops are either polyploids. eg., sugarcane, potato, sweet potato, etc., or have polyploid species or varieties.
• Many cultivated crops are interspecific hybrids, ex., banana, sugarcane, etc.
• These crops consist of a large number of clones, that is, progeny derived from a single plant through asexual reproduction. Thus, each variety of an asexually propagated crop is a clone.

Expression of genetic potential for growth and yield of a crop variety is directly dependent upon the environment comprising both climate (weather) and soil components. As discussed in the preceding chapter, the term ‘salt-affected soils’ encompasses a broad group of adverse but distinct soil conditions, namely, saline, alkali (sodic) and acid soils with further variations such as coastal and inland locations as well as arid and water-logged situations (Swaminathan 1977; Bresler et al. 1982). Factors limiting growth and yield of crop plants in various categories of problem soils are different and specific. Likewise, adaptive strategies evolved by plants to cope with the prevailing edaphic stresses, such as salt stress, also vary a great deal as indicated in Table 1. It is not unexpected therefore, that even varieties within a crop often show notable differences regarding tolerance to adverse soil conditions (Epstein et al. 1980; Devine 1982; Shannon 1984; Sayed 1985). Hence, it is essential that the breeder must understand the inherent charaderistics of the problem soil with which he is concerned and should also simultaneously appreciate that basically it is the sensitivity of crop variety, rather than the soil parameters per se, that essentially determines the occurrence as well as the magnitude of actual soil problem (Rana 1977). Since the degree of tolerance (adaptation) of crop varieties to different kinds of salt affected soils is genetically controlled, it is axiomatic that it can be improved through genetic manipulations by adopting suitable breeding procedures.

Introduction

Stress is any unfavorable condition for a plant’s normal growth and development. In the case of crop plants, such adverse conditions are caused by biological (biotic) and non-biological (abiotic) environmental factors. Abiotic stress is the negative impact of non-living factors on living plants in a specific environment. Usually, abiotic stress is unavoidable, and we can only go for its management.

The most basic stresses include:

• Extreme (high/low) temperatures

• Soil-chemical properties

• Water deficiency

• Excessive moisture

• Element toxicity or deficiency

A. Salinity

Salinity is a predominant problem affecting crop productivity. Over 800 million hectares of land on earth are saline. This accounts for more than 6% of the total land mass on earth. Salinity is a global problem and is prevalent especially in the arid and semiarid regions, where leaching of salts is poor due to low rainfall or irrigation. Brine-affected soil occurs due to natural causes such as weathering and deposition of oceanic salts (eg. recently tsunami in India). In addition, human interference with the environment such as deforestation and/or desertification has resulted in the rising of water table, thus increasing the salt concentration in the root zone. This excess salinity poses a threat to sustainable crop production.

A plant is said to be healthy or normal when it carries out its physiological functions to the best of its genetic potential. These normal functions include division, differentiation, development, absorption of water and mineral from soil and translocation of these throughout the plants, photosynthesis and translocation of photosynthetic product to areas of utilization or storage, the metabolism of synthesized compounds, reproduction and storage of food supplies.

A plant becomes diseased when it is disturbed by pathogen under certain environmental conditions which interfere with one or more of its essential functions. Diseased plant refers to any disturbance brought about by living organism under environmental factors, which interfere with normal function of plant or in other words when any organ and part of plant is not doing their work properly and when either the growth or reproduction is not going forward in natural or regular manner.

Crop production is challenged by abiotic and biotic stresses results in low yield and high production costs.

Magnitude and intensity of stresses are increasing dramatically due to climate change causing recurrent droughts, increased temperature (heat) and emergence of new diseases and pests.

Diseases of plants are produced by a variety of organisms from plant and animal kingdoms viz., fungi, bacteria, viruses, nematodes and insects. The diseases reduce total biomass (dry matter) production and consequently yield of the crop by general stunting, damage to the leaf tissues, fruits and seeds or by killing the plants. The degree of damage would depend upon the intensity of infection but both need not be proportional. One serious effect of disease is the disappearance from cultivation of otherwise excellent but susceptible varieties.

Vegetable crops have been found to be highly susceptible to biotic stresses from the disease causing microorganisms and insects-pests. The ability of pathogen and insect-pests to attack and proliferate in the host plant is highly specific. There are wide differences in the host plants in response to the attack by pathogens and insects. Although control of the diseases and insects by the use of chemicals is possible to certain extent but indiscriminate use of fungicides or insecticides over the crop has several disadvantages. Besides increasing cost involved in chemical control, residual toxicity of the chemicals such as fungicides, antibiotics and insecticides in food chain and development of resistance against pathogens and insect-pests to different chemicals are serious problems.

Genetic improvement of host plants conferring resistance to diseases and insect-pests is considered to be the best approach in the management of diseases and insect-pests, and this is more particularly true in case of vegetable crops. Indiscriminate use of chemicals in the vegetable sector has led to health hazard. This has resulted in switching towards organic vegetables. However, cost of production of organic vegetables naturally will not permit the common people to consume these products. Therefore, the best option is to induce resistance in the host varieties. The resistant varieties could in turn be an important component in the organic vegetable farming, thereby reducing cost of production to certain extent.

In general, disease means an impairment of health or a condition of abnormal functioning. Plant disease is an abnormal deviation from the normal physiological functioning of the plants their by it causes quantitative and/or qualitative losses. Disease may caused by biotic agents (infectious) like fungi, bacteria, viruses, viroids, phytoplasma, spiroplasma, fastidious bacteria, protozoa, nematodes and parasitic higher plants or abiotic agents (non-infectious) like extreme environmental factors includes temperature, light, soil moisture, atmospheric humidity, environmental pollutants, carbon-dioxide concentration, soil nutrient deficiency, acid rain, soil pH and herbicides. 

Plant diseases, in spite of the various measures adopted to control them, continue to be a major cause of crop losses. At times these losses have been so heavy that they have caused severe famines. Diseases are caused by a wide variety of organisms such as fungi, bacteria, viruses, mycoplasma and nematodes. The diseases may be partially or completely controlled by chemical, cultural and genetic methods. When no single method is effective in controlling a disease, integrated control constituting a combination of the three methods of disease control (chemical, cultural, genetic) may be effective. If host resistance alone is sufficient to check a disease, then it is to be preferred to other methods because it is the least expensive, has no adverse environmental effects and involves no specific action on the part of the farmer, even when only partial, genetic resistance supplements chemical control and makes it more effective in comparison with chemical control on a completely susceptible cultivar.

Many plant diseases have been successfully controlled by exploiting genetic resistance especially where differentiation in the pathogen with respect to resistance genes in the host is lacking. In some cases, even when pathotype differentiation occurs in the pathogen, genetic resistance in combination with other methods has given adequate control. Breeding for resistance to highly variable air-borne fungal pathogens has claimed much time and effort of plant breeders and success has often been transient. The reasons for the shortlived success have become clear from research during the last quarter of a century.

This chapter starts quoting first para of the book entitled Disease Resistance in Plants by Van Der Plank (1968). “In 1958 the American Phytopathological Society met to celebrate its Golden Jubilee and review the problems and progress in plant pathology during the 50 years, 1908 to 1958. J. C. Walker was elected to review the problems and progress in controlling plant diseases by host resistance, a fitting tribute to one who perhaps more than any other had contributed during those 50 years both to understanding of nature of resistance and to the practical application of resistance to problems in horticulture and agriculture. In his summary Walker wrote “By and large the development of resistant varieties must be looked upon as a continuing program. The potential variability of most pathogens (including viruses) will not permit any currently successful variety to remain so for an indefinite period”. This opening para tells the importance of breeding for resistance to diseases in crop plants on a continuous basis as the fight between host and the pathogen will go on and on.

Vegetable crops are highly susceptible to biotic stresses incited by different diseasecausing micro-organisms (fungi, bacteria, phytoplasma, virus), insect pests, nematodes, arachnids and weeds. In contrast to abiotic stresses caused by the environmental factors such as drought, heat, soil salinity, alkalinity, etc., biotic stress-causing agents directly deprive their host of its nutrients leading to reduced plant vigour and, in extreme cases, death of the host plant. In vegetable crops, different biotic stresses are the major cause of pre- and post-harvest losses.
Indiscriminate use of chemicals for the control of diseases, insect pests and nematodes has several disadvantages particularly, increasing cost involved in chemical control, residual toxicity of the chemicals (fungicides, antibiotics, insecticides) in food chain and development of resistance against pathogens and insect pests to different chemicals. Management of diseases and insect pests involve the use of resistant varieties and integration of cultural and chemical control measures.

Understanding Immunogenetics
The study of genetic basis of the immune response is known as immunogenetics. The term was introduced with the discovery of ABO blood groups and were first demonstrated through the existence of “natural” antibodies i.e., isoantibodies. The broad field of immunogenetics include study of normal immunological pathways as well as identification of genetic variations that result in immune defects, which may facilitate detection of new therapeutic targets for immune diseases. Hence, understanding and subsequent manipulation of host immune response (immunomodulation) is the most precise and effective tool to reduce disease incidences and nullify the limitations associated with antibiotic treatment or vaccination. Therefore, breeding for disease resistance has gained considerable attention from researchers in the recent past.
Immune Response Genes
Often it was observed that individuals respond differently to same infectious agent. A possible explanation may be the genetic variability between them. Indeed, many studies have looked for associations between genes involved in immunity and disease outcome and it has been found that certain immune response (Ir) genes play the crucial role. This concept was discovered in the mid-1960s and this discovery introduced an apparently new level of antigen recognition whose diversity and specificity had to be explained in addition to those of familiar immunoglobulins. Hence immune response (Ir) genes were defined as antigenspecific genes that control the ability of an animal to raise an immune response, either humoral or cellular to a particular antigen .

High temperature stress
Abiotic stresses either individually or in combination cause morphological, physiological, biochemical and molecular changes that adversely affect plant growth and ultimately yield. The major forms of abiotic stress plants are exposed to in nature are heat, drought, cold and salinity. Of these abiotic stresses, heat stress has an independent mode of action on the physiology and metabolism of plant cells. High temperatures above optimal have generally damaging effects on plant development which has led to the prediction that Global warming have a negative effect on plant growth. High temperature regimes may cause severe yield reduction leading to even famine. High temperature stress has wide range of effects on plant in terms of physiology, biochemistry and gene regulation pathways. The susceptibility to high temperatures in plants varies with the stage of plant development and genotype.
Mechanisms of heat tolerance
Heat tolerance is generally defined as the ability of the plant to grow and produce economic yield under high temperature conditions. Several plant physiological parameters and mechanisms that contribute to heat tolerance in the field include:

In practical agriculture, resistance represents the ability of a certain variety to produce larger crop of good quality than an ordinary variety at the same level of insect population. During the 19^th Century, the French wine industry survived a major set-back largely due to the use of resistant root stocks imported from America and which still maintain their resistance levels against the beetle pest (Painter, 1951). Another important example of resistant variety is the U-4 variety of cotton possessing high level of resistance to the jassid, Emposasca spp. (Parnell, 1925). The excessive use of pesticide on oilseed crops needs to be minimized owing to several reasons: (i) most of the pesticides are lipophilic and are likely to be carried in the oil (ii) in a few cases like Brassica, leaves and inflorescence are consumed as saag (pot herb), (iii) the oilseed crops provide the raw material for the vanaspati industry, cosmetics, etc., (iv) many of the oilseeds and oils are directly consumed without further processing, and (v) the oil cakes are used as cattle feed. Thus there is an urgent need to exploit the non-pesticidal methods of pest control, among which the use of resistant varieties assumes a great significance. The details of each oilseed crops are given below:

Crop varieties are domesticated since civilization, and their continued cultivation depends on continuous breeding programmes for insect, disease and other stress resistance. World wide, insects and their associated problems cause threat to crop production. Many crops suffer from insects, which may be in the form of direct damage by feeding or indirectly by the transmission of diseases by insects as vectors. Until now, chemical crop protection is seen as the major way to combat these problems. However, insects develop resistance to the insecticides very quickly. Apart from controlling pest insects, insecticides also affect beneficial insects, such as predators and parasitoids of the pest insect, pollinators, and harmless fauna, thus upsetting ecological balance results in many unwanted problems. Hence, the best strategy is to prevent the problems that occur. The most economical and environmental friendly way of controlling the insect pests of crops would be through host-plant resistance (HPR). Resistant plants help farmers to grow crops with minimal use of chemicals. This will lead to a reduction in the cost of production, thereby increasing the profit margin for farmers and thus importance of breeding for pest resistance is manifested.

Genetic resistance is the more efficient and the more environmentally friendly way to protect crops against phytonematodes. Nematode management is complex, hence, the prevention of an initial phytonematode infestation in pathogen-free areas is of fundamental importance. However, after the entry of the nematode into an area, it is virtually impossible to eradicate because it is a soil-dwelling organism. In this regard, the genetic resistance of plants to nematodes is considered one of the most efficient and economically feasible methods to prevent production losses (Matsuo et?al?, 2012). Thus, breeding for nematode resistance is essential in crop management to obtain a high yield and stable production.

The immediate and long-term objective of modern plant breeding in all countries irrespective of the state of their advancement is increasing the availability of food to meet the calorie-protein requirement of their people. In the past, breeders have concentrated their efforts on increasing the yield of the important crop species. Better adaptation to local environmental conditions, high production and better resistance to the major pests and diseases have been among the priority goals of genetic plant improvement. Yielding ability and stability undoubtedly deserve high priority but enough attention also needs to be paid to improving nutritional characteristics of the plant produce for their maximum utilisation. Awareness of nutritional requirements and the optimal characteristics of crop products to be utilised as food and feed, therefore, becomes an important parameter of breeding effort.

The main source of food in the developing world is cereals which provides 45 to 85 per cent of the total calories and 50 to 80 per cent of the total protein requirements. The consumption of animal proteins, which are nutritionally well balanced, is low and costly and beyond the reach of the low income groups. On the other hand, plant proteins are cheaper to produce and easier to store and transport. All these factors go in favour of increasing the quantity and quality of cereal proteins in order to improve the dietary and nutritional status of the masses in the developing world.

Proteins are made up of about twenty different amino acids. For man, eight of these amino acids, valine, methionine, leucine, isoleucine, threonine, phenylalanine, lysine and tryptophan, are essential (EAA) for constituting a well balanced diet. In impioving the grain quality of cereals consideration should, therefore, be given apart from the content of carbohydrates, fats, minerals and vitamins in the grains, to improving the protein content as also the amino acid composition of the protein.

I. Introduction
Abiotic stress refers to the detrimental impact of environmental factors such as temperature, light intensity, humidity, and salinity on plants, leading to damage or hindered growth. Unlike biotic stresses caused by living organisms, these abiotic stresses arise from physical conditions like extreme temperatures, droughts, floods, high winds, air pollution, soil erosion, and other natural phenomena. The severity of these stressors varies depending on the plant species and their ability to adapt to changing surroundings. Gaining insights into how plants react to abiotic stress is essential for devising strategies to enhance crop productivity in unfavorable conditions (Huang et al., 2014; Zhu, 2016).
A. Definition and types of abiotic stress
Abiotic stress pertains to the adverse effects of non-living elements on organisms within a particular habitat. These stressors surpass the usual scope of environmental fluctuations and have the potential to damage both plants and animals. In contrast to biotic stress triggered by living disturbances, abiotic stress factors are intangible and encompass factors such as intense sunlight, extreme temperatures, wind, and various other natural phenomena.

Introduction
Biological stress factors such as bacteria, fungi, viruses, and pests can lead to losses in yield and quality before and after harvest. An estimated10 to 23 percent loss is caused by fungal pathogens, along with an additional 10 to 20 percent post-harvest loss. Unlike animals, plants do not possess a highly developed immune system or mobile immune cells. They possess highly sophisticated defense mechanisms based on their structural, chemical, and protein composition. The defense responses of plants to different pathogens are influenced by factors such as the stage of plant development, the pathogenicity of the pathogen, and the environmental conditions. Recognizing the importance of genes that resist biotic stressors, it becomes clear that they are invaluable natural resources for sustaining agricultural productivity and minimizing crop losses36. Any physiological abnormality or significant disruption in the average health of a plant is considered a disease. Living agents, like fungi and bacteria, and environmental factors such as nutrient deficiency, drought, and lack of oxygen, excessive temperature, ultraviolet radiation, and pollution can all contribute to disease development. Plants have developed diverse constitutive and inducible defenses to safeguard themselves from harm. Disease resistance is decreased pathogen growth on or within the plant11. It indicates a lower disease occurrence in one genotype than the susceptible variety and is a relative characteristic. Typically, the reproduction rate is significantly decreased, which restricts disease transmission. Plants have varying levels of resistance to different pathogens, with some being more susceptible to specific pathogens while being resistant to others. This resistance is often specific to particular species or strains of pathogens.

When conditions in the plant growing environment are less than the optimum, the plants experience stress which is broadly termed as abiotic stress. Major abiotic stresses impacting crop yield significantly are as follows (Grover et al., 2004; Acquaah, 2007):

Drought: This is the environmental condition caused by lack of adequate rainfall. This is also termed as water stress or desiccation stress. Effects of drought on crop plants are complex and variable and are greatly accentuated by a number of interacting factors. The onset of drought in general has been observed to reduce germination, emergence, hypocotyl length, water uptake and the mobilization of dry matter reserves even at the early growth stages. Drought stress causes a marked reduction in leaf area. Soil moisture availability at the seed germination, anthesis and at post-anthesis growth stages determines as to what extent production potential of crops would be expected in drought-prone situations.

The yield losses in field crops may be attributed to inadequate water availability at the critical growth stages. Crops therefore differ in their susceptibility of growth stages to water stress. Stress exposed plants immediately lower down relative water content (RWC) of their leaves, leaf water potential, osmotic potential. Turgor pressure may also be decreased unless plants have finally adapted to drought by opening of stomata again and improving the water potential. It has been reported that low leaf expansion rate at the early stage and accelerated leaf senescence accompanied by mortality of older leaves at later stage decreases total leaf green area.

29.1 Introduction

An environmental factor that interferes with the complete expression of genotypic potential of a crop is called stress. The stresses may be biotic (pathogens, insect-pests, etc.) or abiotic. The main abiotic stresses are drought, mineral deficiency/toxicity and heat or cold. The losses due to abiotic stresses can be minimized by:

Crop management: The degree of stress can be reduced by suitable agronomic/soil management practices, e.g., irrigation to relieve drought stress, soil amendments to reduce salinity.

Development of resistant cultivars: This offers the cheapest, easiest to apply and most eco-friendly approach to reduce losses due to any stress.

Indirect breeding: Evaluation of materials under stress often helps in identification of a resistant line that may become an important commercial cultivar.

???????Direct breeding: It is deliberate breeding of materials for stress resistance. When a genetically variable material is grown under the stress environment, selection can be based on survival, yield and other traits contributing to stress resistance.

Plant abiotic stresses are external and nonliving factors that have harmful effects on plants. A non-living factor must exert influence on the normal range of environmental variation to adversely and significantly affect the plant performance or the physiology of the organism. Abiotic stresses are the most harmful factors affecting the growth and productivity of crops worldwide, resulting in a yield reduction ranging from 10% to 100%. They are most harmful when occurring together with other abiotic stresses and their effect in yield will only worsen with the climatic changes experienced now and expected to be more severe in the future.

28.1 Introduction

The stress that is caused by biological agents or factors such as diseases, insect-pests and parasitic weeds is called biotic stress. The term disease can be broken into two words: “dis” (means negative, reverse or opposite) and “ease” (means comfort, or freedom from pain or discomfort). Hence, plant disease can be defined as any harmful alteration from the normal functioning of physiological processes. Diseases may be bacterial, fungal or viral. A wide range of insects infests various crop plants. The extent of damage caused to crop plants by various organisms is usually in the order fungi > bacteria > viruses > nematodes = insects. But the relative importance of these organisms varies to a great deal in different crops. Breeding of cultivars resistant to diseases and/or insect-pests is the cheapest, safest and most dependable means of limiting the losses due to them. Resistant cultivars form an important component of integrated management of diseases and insect-pests.

28.2 Breeding for Resistance to Biotic Stresses-Diseases

Agrios (1970) has defined disease as: “Disease is a series of invisible and visible responses of plant cells and tissues to a pathogenic microorganism or an environmental factor that result in adverse changes in form, function or integrity of plant and may lead to partial impairment or death of the plant or its parts.” The organism causing disease is called pathogen, while the plant affected by the disease is called host.

The principles underlying breeding for resistance to diseases are much the same as for other characters, except for one important difference, i.e., the diseases caused by pathogens are the product of interaction between two genetic systems, that of the host and that of the parasite. Both systems are capable of variation and evolution and affect the interaction between host and pathogen. Here the breeder is required to deal with the heritable traits of both the host plant and the pathogens invading it.

Biotic stresses include diseases and insect pests which cause serious damage to the crop plants and ultimately yield loss. Biotic stresses can be listed as follows:

• Diseases caused by pathogens which include fungi, bacteria, and viruses
• Insects
• Nematodes
• Parasitic weeds

Another category of stresses are called as abiotic stresses which are caused by environmental factors as:

• Water stresses (water logging, drought)

Introduction

Worldwide damage due to insect pest attack accounts for 15 per cent crop losses, despite the use of insecticides which represents over US $100 billion (Krattiger, 1997). The annual cost of insect control itself amounts to US $8 billion, thus warranting immediate and economical control measures. The crop varieties developed in the past 30 years were high yielders, but unfortunately had poor storage characteristics and were highly susceptible to pest damage. Insect-pests are capable of evolving to biotypes that can adapt to new situations, for instance they overcome the effect of toxic materials or bypass natural or artificial plant resistance, which further confounds the problem (Roush and McKenzie, 1987). Under these circumstances, provision of food to the rapidly expanding population has always been a challenge facing mankind. This problem is more acute in the tropics and sub-tropics, where the climate provides a highly conducive environment for a wide range of insects and necessitates massive efforts to suppress the population densities of different pests in order to achieve an adequate supply of food. In developing countries, the problem of competition from insect-pests is further complicated with a rapid annual increase in human population (2.5-3.0 percentage) against a meager 1.0 per cent increase in food production. In order to feed the ever expanding population, crop protection plays a vital and integral role in the present day agricultural production to minimize yield losses. Currently, the crop protection practice in agricultural systems relies exclusively on the use of agrochemicals, although a few specific cases do exist, where inherent varietal resistance and biological control have been successfully employed. The exclusive use of chemical pesticides not only results in rapid build-up of resistance to such compounds, but their non-selectivity affects the balance between pests and natural predators, and is generally in favour of pests (Metcalf, 1986).

Introduction

Within the very small portion of the plant kingdom that includes the world’s crop plants, the legumes are a large group second to the cereals as sources of human food. Legumes belong to the family leguminosae with a group of bacteria, Rhizobium, which is able to utilize atmospheric nitrogen. This symbiosis which occurs in the root hairs may be the key to the success of legumes worldwide distribution. The family leguminosae includes about 18,000 species, characterized by their fruits, which are pods, by their (usually) alternate, pinnate or trifoliate leaves (Cobley and Steele, 1976). The diversity in the family ranges from hardwood trees of the tropical rain forests to the herbs of temperate pastures.

Vegetables are considered protective foods and play an important role in human nutrition. These help to combat malnutrition and also diversify diets with variety of colours. The compounds imparting various colors to the vegetables are important antioxidants that also help to combat degenerative diseases like cancer. Over the years, vegetable sector has made an appreciable progress in terms of production and productivity and emerged as the better option to diversify agriculture, generate employment and enhance farmers’ incomes. The worldwide production of vegetables has doubled over the past quarter century and the value of global trade in vegetables now exceeds that of cereals.

Globally, India ranked second in vegetable production and contributed 15.8 and 14% to global vegetable area and production, respectively. The production of vegetables in India is estimated to be 212.91 million tonnes in the year 2022-23 compared to 209.14 million tonnes in the year 2021-22. India ranked first in production of okra in the world (73% of world production) and second in brinjal (27.55%), cabbage (13%) and tomato (11%). The major vegetable growing states in India are West Bengal (14.1%), Uttar Pradesh (11.4%), Bihar (9.3%), Madhya Pradesh (8.0%) and Gujarat (7.1%). Vegetables are especially important crops for farmers with small holdings because an appreciably higher income per hectare can be generated by growing vegetables than from conventional staple crops (Genova et al, 2006). However, vegetables are generally considered more vulnerable than staple crops to stressful environmental conditions including extremes of temperatures, drought, salinity, alkalinity, water logging, mineral nutrient excesses and deficiency (Chinnusamy et al, 2005). These environmental stresses are likely to be exacerbated by the prevalent climatic changes in many parts of the world.
Among environmental factors, soil salinity stress is one of the main factor reducing production and productivity of vegetables in arid and semi-arid regions where irrigation water has excessive salt and annual rainfall is low. In India, about 6.73 million ha of land (~2.1% area of the country) is salt affected, out of which 2.96 million ha is saline and 3.77 million ha is sodic (Arora & Sharma 2017). About 75% of salt-affected areas exist in four states, i.e., Gujarat, Maharashtra, West Bengal, and Rajasthan (Mandal et al., 2018).

INTRODUCTION

India has emerged as second highest producer of potato in the world, after China. The crop has been identified as the most important crop for ensuring food security for the developing countries, and a highly nutritious food providing more calories, vitamins and nutrients per unit area of cropped land than any other staple food. The crop has witnessed phenomenal increase over the seven decades of potato research in India. For a crop which was introduced in the country only in the early 17^th century, and was neither adapted, nor its staple food, the remarkable increase in potato production and productivity is an exceptional achievement of breeding this temperate introduction into the present day potato cultivars.

BREEDING REQUIREMENTS

The table potatoes introduced in India were adapted to long photoperiods of up to 14 hours and crop durations of 140-180 days allowing them to be cultivated only in the hilly regions of India. The unique and diverse agro-climatic condition of the country, comprising of contrasting conditions in the Indian plains, where potato could be grown in the winter months necessitated breeding efforts to develop the potato varieties suitable for the sub-tropical plains and the other potato growing regions. The winters in sub-tropical plains have short photoperiod (with about 10-11 hours sunshine) and the crop duration is limited to 90-100 days because of short and mild winter. Further constraints on photosynthetic activity due to early morning fog, posing a strong limitation on tuber bulking. This is followed immediately by a long hot summer period, which coincides with the post-harvest storage period of potato, creating challenging storage problems. The rapid degeneration of seed stocks, with concomitant decrease in yield due to accumulation of viral diseases and tuber storage and utilization in hot and humid climate thus needed to be addressed, in priority. Besides, these southern, north Bengal and Sikkim hills and the plateau offer agro climatic area specific problems related to the biotic and abiotic stresses prevalent in the regions. Moreover, the unique reproductive biology of the plant made it possible to flower only under the long day conditions of the hills, where hybridization was initiated at Kufri (Shimla), Himachal Pradesh. However, during the initial years, it was not possible to evaluate the breeding progenies in the warmer sub-tropical plains due to the quick degeneration of hill bred progenies and dormancy of hill potatoes.

Horticulture, which includes fruits and vegetables, plantation crops, spices, flowers, and medicinal and aromatic plants, has proved beyond doubt its potentiality for gainful diversification. One of the significant developments is that, horticulture has moved from rural confine to commercial production. Recently horticulture has emerged as one of the best option of diversification for effective land use planning and to achieve inclusive growth. The achievement in the development of horticulture through crop improvement is laudable, as the sector now contributes more than 30 percent to GDP of agriculture and has maintained the growth rate of more than 5 percent during the last two decades.

Breeding objectives genetic resources and techniques for breeding

• There are countries that consume 100 to 150 kg yearly per capita while others which do not even make it to 10kg.
• Genetic variability is the raw material of the plant breeder.
• International network for the improvement of Banana and Plantain (1 NIBAP), Prance to conserve the available germplasm.
• Only pathogen gene-free planting material can be used for construction or distribution from the gene bank for further multiplication or utilization in any breeding program.
• Fruit breeders have therefore tended to utilize single gene variants in performance to polygenic variation.
• In general, for most commercial requirements, homozygous is inadequate by six or seven generations of selling (56 or 37).
• In the dominance hypothesis, it is assumed that the deleterious gene is normally recessive.
• The simplest approach for the selection of our breeders is mass selection.

Indian jujube (Ber) belongs to the genus Zizyphus and family Rhamnaceae having more than 600 species. The family includes trees with spine, shrubs and climbers. The original home of Ber is Myanmar and India. Many workers have tried to classify it on the basis of leaf, flowers and fruits characteristics. Some tried to divide into two groups i.e. having smooth leaves on both surfaces and having leaves downy beneath. Ber as a tree has been described it as small, much branched or a large shrub with dense spreading habit, bark dark gray, branches elongated, leaves with glabrous shining upper surface densely covered beneath with whitish hairy growth.

Ber has attracted sustained breeding attention owing to its wide adaptability, good quality and nutritive value. However, problems like poor shelf life, incidence of powdery mildew disease, fruit fly and fruit borer have hindered the extension of the area under this crop. In Chinese jujube, the problem of fruit cracking and ‘witches broom’ disease are the major hindrances in its cultivation. There are two major cultivated species viz., Ziziphus mauritiana and Ziziphus jujuba, which are widely distributed covering vast regions in Asia. The wild population found is heterozygous and extremely variable. As a result, many local selections were made, some of which have become widely recognized as cultivars. The success of any breeding programme depends on the extent of genetic variability in the source population. The assessment of variability is therefore a basic requirement of breeding programme. Since most of the plant characters of economic importance are governed by the group of genes and are highly influenced by environmental variation, it is difficult to judge whether the observed variability is heritable or due to environment. This necessitates optimizing of phenotypic variation into its heritable and non heritable components, so that the selection of parents

5.1. Characteristics of asexually propagated crops

Majority of them are perennials

Many of them show reduced flowering and seed set.

Invariably cross pollinated.

Mostly polyploids.

Many species are inter specific hybrids.

4.1. Synthetic varieties

Produced by crossing in all combinations, a number of lines that combine well with each other.

The genetic organization of cross pollinated crops are different from that of self pollinated crops, because of differences in the reproductive system. Open pollinated populations are heterozygous with free inter mating individuals, heterozygous at most of the loci. Heterozygosity is an essential feature of commercial varieties of out breeders. It is maintained during breeding or is restored at the end. Population improvement involves selection, generation after generation, with recombination of selected individuals. Its aim to increase the frequency of favorable alleles in the population. The improved forms may be used for commercial cultivation or as a base germplasm for the derivation of inbred lines. The list of cross pollinated plants is presented in Table 10.1. The factors that promote the cross pollination are dicliny, dichogamy, herkogamy, self-incompatibility and male sterility. The breeding methods which are commonly used in cross-pollinated crops are population improvement, hybrid and synthetic varieties.

Population Improvement

In cross pollinated crops heterozygosity must be restored in the end product of any breeding programme. It is classified into the following types:

3.1. Selection

To isolate desirable plant types from a population.

3.1.1 Progeny test

Evaluation of growth of plants on the basis of performance of their progenies

Real value of plant could be known by studying the progeny.

The prime object of plant breeder is to develop high yielding variety with superior characteristics. Selection is based on the phenotypes of the plants. Consequently the effectiveness of selection primarily depends on the degree to which the phenotype of plants reflects their genotype. These are all self fertilizing species. In these species development of seed take place by self fertilization. Hence self pollinated species are also known as autogamous species. Various plant characters such as homogamy, cleistogamy, chasmogamy, bisexuality etc. promotes self pollination. The self pollinated crops with their description are given in Table 9.1. The breeding methods used in self and often-self pollinated crops are discussed below:

Plant Introduction

Plant introduction consists of taking a genotype or a group of genotypes of plants into a new area or region or environment, where they have not being grown earlier. It is very simplest and fastest method of developing new variety. It is of two types:

Reproduction that does not involve the union of male and female gametes is known as asexual reproduction. Reproduction in which sexual organs or related structures take part but fertilization does not occur, or crops which are propagated asexually or by vegetative means are known as asexually propagated crops. Most of the fruit plants are propagated asexually which consist of large number of clones. Example: sugarcane, potato, sweet potato, banana, mango, citrus, pears, peaches, litchi, crops that propagates by asexual means. The procedure of selection used for asexually propagated crops is known as clonal selection, since the selected plants are used to produce new clones or superior clones can be isolated from local variety, introduced variety or inter crossed population.

Important breeding methods can be classified as follows:
    1.    Introduction
    2.    Selection
    a.    Mass selection: Done in self pollinated crops, cross pollinated crops and dioecious crops.
    b.    Individual plant selection: Done in self pollinated crops, cross pollinated crops (line breeding) without control of pollination, artificially self pollinated lines, dioecious plants and clonally propagated lines.
    3.    Hybridization
    a.    Crossing in self pollinated crops.
    b.    Single crosses, double crosses and synthesized varieties.
    c.    Varietal crosses.

Introduction
In recent years, there has been a growing interest in alternative nutritious food sources (McClements, 2020) and such group of foods that has gained significant attention is millets. Millets are a diverse group of small-seeded grasses that have been cultivated and consumed for thousands of years. They are rich in essential nutrients such as proteins, fibers, vitamins, and minerals, making them an important addition to a balanced diet. Millets are not only rich in essential nutrients but also have several health benefits. They are known to have nutraceutical properties, low glycemic index, making them suitable for individuals with diabetes. Additionally, millets are a good source of antioxidants, which can help in reducing the risk of chronic diseases such as heart disease and cancer. The diverse range of millet varieties also provides flexibility in incorporating them into various dishes, making them suitable for different culinary preferences and dietary requirements. Therefore, the usage of millets can play a crucial role in promoting sustainable and healthy eating habits.
Malnutrition continues to be a pressing issue worldwide, particularly in developing countries (Ashok et al., 2020). The lack of access to nutritious food is one of the main causes of malnutrition, leading to various health problems such as obesity, diabetes, cardiovascular diseases, cancer, and celiac disease (Birania et al., 2020). To address this issue, millets have emerged as a promising solution. Despite being nutritionally superior to other cereals, millets have traditionally been limited to consumption by the poor and those with conventional dietary practices. However, there is a growing recognition of the potential of millets in combating malnutrition and improving public health. Millets, such as finger millet, pearl millet, and sorghum, are often referred to as “superfoods” due to their high nutritional content (Singh et al., 2020). These grains are rich in protein, carbohydrates, fats, vitamins, minerals, and dietary fiber, making them an ideal source of essential nutrients (Ashok et al., 2020). Additionally, millets are easily available and costeffective, making them a viable option for addressing malnutrition on a larger scale (Birania et al., 2020). Furthermore, millets are resilient crops that can withstand environmental changes and water shortages, making them an ideal choice for sustainable agriculture. In this chapter, we delve deeper into specific aspects of millet nutrition, examining their micronutrient profiles, health benefits, culinary versatility, and potential applications in combating malnutrition and promoting sustainable agriculture. By understanding the nutritional richness of millets, we can uncover innovative solutions for improving human health and fostering agricultural resilience.

4.1. Flower and flowering in pigeonpea

Growth habit: Primarily, there are two major growth types in pigeonpea. These are determinate and non-determinate. The determinate growth in the pigeonpea plants is characterized by flowers in bunches at the top of the canopy (Fig 17a). In this case the epical growing points are transformed in to reproductive buds and bunches of flowers appear on the top of the canopy. Such cultivars are not popular as the management of insects such as Helicoverpa and Maruca becomes very difficult. Most of the cultivated types belong to another growth category called as non-determinate. In such genotypes the apical growing points remain vegetative and the plants keep growing under favorable conditions and it results in tall canopy with many spreading or compact branches. The inflorescence in this case emerges from the axil of secondary and tertiary branches (Fig 17b); and hang sideways. These types show less susceptibility to insects due to non-clustering nature of flowers.

17.1 Introduction

Almond or badam is a high energy nut. Almond kernels contain lipids (52.2%), protein (20%), carbohydrate (20.4%) and water-soluble sugars (4.4%). Irrigation affects almond yield and quality. Almond quality is primarily genotype dependent. Maturity at harvest can also influence kernel quality.

Aonla has been regarded as a sacred tree in India. The tree is worshipped as mother earth and is believed to nurture humankind because the fruits are very nourishing. It is also known as Amrit phal. Aonla is mainly recognized due to its high nutritive, medicinal and therapeutic properties. It contains high amount of vitamin C (500-1500 mg/100 g), it is also rich in pectin, iron, calcium and phosphorous. Dried fruits of aonla can be is used in curing hemorrhage, diarrhea, chronic dysentery, diabetes, jaundice, dyspepsia, cough etc. Recently, aonla has gained more popularity in arid and semi-arid region of the country because of its hardy nature, prolific bearing capacity and ability to grow under various adversities as a remunerative crop (Shukla et al.2002). It may be an important fruit in future due to its high productivity, suitability in wasteland particularly salt affected soil and sandy soil of arid ecosystem. Aonla is the main ingredient of Chavanprash and Triphala powder which is used for curing different abnormalities. The fruit contains a chemical substance gallic acid and leucoanthocyanin which have antioxidant property.