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Resistance to disease in a host plants is a condition in which the plant conquer the pathogen’s attack and thus suffers small or no injury. Resistant hosts prevent or slow the development and reproduction of the majority of pathogen propagules that they come into contact with. Different plants defend themselves in different ways. Each kind of plant, probably, employ different defense mechanism against each of the pathogens that attack it. The defense barriers erected by plants are a co-ordinated system of molecular, cellular and tissue-based responses to pathogen attack.

There are various mechanisms of defense used by plants. For convenience, such mechanisms can be considered under two broads heads;

1. Pre existing or passive defense (Defense present on or inside the plant since beginning)

a. Pre existing structural defense

b. Pre existing biochemical defense

2. Post infection or active defense (Defense in response to attack by the pathogen)

a. Post infection structural defense

b. Post infection biochemical defense

Plant disease epidemiology is the study of how plant diseases develop and spread. It involves understanding the causes of diseases, how they spread, and their impact on plants and crops. This knowledge is used to develop strategies for managing and controlling plant diseases, such as predicting outbreaks, breeding resistant plants, and implementing cultural and chemical controls.

Element of an epidemic: Plant disease epidemics develop as a result of the timely combination of the element in plant disease: Susceptible host plant, a virulent pathogen and favourable environmental conditions over a relatively long period of time. Humans may unwillingly help initiate and develop epidemics. Thus, the chance of an epidemic increases when the susceptibility of the host and virulence of the pathogen are greater, as the environmental conditions approach the optimum level for pathogen growth, reproduction and spread and as the duration of all favourable conditions.

CONCEPT

The word “epidemic” is derived from the greek word, epi= (on) and demons=(people) and in true sense applies to those disease of human being which appear very virulently among a large section of population. To carry the same sense in the case of plant diseases the term epiphytotic has been coined. an epiphytotic disease is one which occur widely but periodically. it may be present constantly in a locality but assumes severe form only on occasions. Of late, the term “epidemiology” has come to have a broad meaning within plant pathology. The term has been variously defined as the study of disease in populations; the study of environmental factors that influence the amount and distribution of diseases in population, and the study of either increase or decrease in the amount of disease in time, in space, or both.

Elements of An Epidemic

Generally, the elements of an epidemic are referred to as the “disease triangle”: a susceptible host, pathogen, and favorable environment. For disease to occur all three of these must be present. Where all three items get together there is disease. As long as all three of these elements are present disease can commence, an epidemic will only arise if all three continue to be present. Sometimes a fourth factor of time is added as the time at which a particular infection occurs, and the length of time conditions remain viable for that infection, can also play an important role in epidemics If all of the criteria are not met, such as a susceptible host and pathogen are present but the environment is not conducive to the pathogen infecting and causing disease, disease cannot occur.

Factors that affect the development of epidemics

DEFINITION

Fore casting involves all the activities in ascertaining and notifying the grower of community that conditions are sufficiently favourable for certain diseases, that application of control measures will result in economic gain or on the other hand, and just as important that the amount expected is unlikely to be enough to justify the expenditure of time , energy and money for control. The above statement made explicit distinction between positive forecast and negative forecast and both have value for growers as well as society in general.

Positive forecast: Employs need based chemical sprays, provides adequate protection to crop and reduces damage to environment.

Negative forecast: Avoids unnecessary chemical sprays, no risk to the crop health and no disruption of environment.

Methods for plant diseases control were first classified by Whetzel (1929) into exclusion, eradication, protection and immunization.

Two more principles - avoidance and therapy were created (NAS, 1968).

4.1. Physical methods

Employed for reduction or elimination of primary inoculums that may be present in seed, soil or planting material.

Introduction

In Organic farming; agricultural management system uses eco-friendly management practices and biological fertilizers derived largely from plant residue, animal excreta and nitrogen-fixing cover crops. It favorably affects the quality and yield attributes of crops. In modern agriculture system, development of organic farming in relation with the environmental hazard triggered by the huge application of inorganic pesticides and synthetic fertilizers in conventional agriculture, and it has abundant ecological aids. Spent mushroom substrate (SMS) can be used as such fertilizer. It is an organic mass that can be converted into humus in the soil.

Mushrooms are a fleshy, macroscopic, saprophytic, spore-bearing fruiting structure of a fungus (edible fungus) belonging to class Basidiomycetes except few which belong to Ascomycetes. It grows on dead and decaying organic materials derived from the agriculture, horticulture, poultry, brewery waste materials for its cultivation. Mushrooms are delicate, nutritional and medicinal fruit bodies of fungus which are used as an important ingredient of human dishes. It contains protein, minerals, vitamins and essential amino acid. Mushroom industries does not only produce edible mushroom but also produces virtually in-exhaustible supply of a co-product called spent mushroom substrate (SMS). Mushroom industry is flourishing day by day and not just mushroom as a whole is being used but many of its other uses are also studied and performed like using mushroom production for bioremediation or using mushroom waste which is known as SMS for different purposes. Therefore, growing mushrooms just for consumption is not true but its growth has many underlying purposes through which not just humans but the entire ecosystem is benefitted (Staments, 2005; Phan and Sabaratnam, 2012).

6.1. Fungicides

Fungicide originated from two latin words viz., fungus and caedo.

Word caedo means to kill.

Fungicide is a chemical agent which has the ability to reduce or prevent the damage caused to plants and their products.

Physical agents like ultra violet light and heat should also be considered as fungicides.

Antisporulant and fungistatic compounds do not kill the fungi, they are included under the broad term fungicide

What is Plant Disease Resistance and Its Mechanisms

There are two main types of plant disease resistance:

Innate Resistance (Non-Host Resistance): This is a broad-spectrum resistance that prevents most potential pathogens from infecting the plant. It is often due to the lack of essential factors required for the pathogen’s survival or the presence of preformed physical and chemical barriers.Plant disease resistance is the ability of a plant to prevent or reduce the damage caused by pathogens (disease-causing organisms) like fungi, bacteria, viruses, and nematodes. It involves a complex interplay between the plant’s defense mechanisms and the pathogen’s virulence factors.

History

 • The fossil evidence also indicates the presence of plant diseases 250million years ago.

 • The diseases caused by fungi and nematodes were discovered by Monocernin 1735.

 • Johan Needham (1743) identified wheat gall caused by a nematode.

 • Adolf Mayer (1886), demonstrated the transmission of Tobacco mosaicvirus (TMV).

 • EF Smith (1890) described bacterial wilt in cucurbits.

• The thrips (Thysanoptera) as vectors of plant viruses were identified thescientific studies made by Samuel and his team.

 • Karl Maramorosch (1952) demonstrated the multiplication of Asteryellows virus (AYV) in leafhopper vector.

 • The mite Aceriatulipae has been identified as a vector of Wheat streakmosaic virus by JT Slykhuis in 1955.

 • The term “vir

5.1. Cultural methods

5.1.1. Eradication

Elimination of pathogen after it has become established in the area where host is growing.

Disease is one of those terms that are very difficult to define. It is realized that disease (literally dis-ease) implies lack of ‘comfort’and therefore, involves deviation from normal functioning. From time to time several definitions which have been proposed, in fact descriptive but not simultaneously exclusive. The definitions for the term disease are.

Introduction

Indigenous Technological Knowledge (ITKs) refers to the knowledge that acceptable to all as absolute hearing and developed about the meticulous altitude by the people irrespective of gender that is women and men ancient to an a specific geographical area. This ancient technological knowledge that humans in an accustomed association accept developed over time and abide to advance it, is predicated on animal kingdom adventures on accumulation scale, activating and changing, activated throughout a lot of cases over centuries of use. Highest accessible knowledge to bounded knowledge and ambiance and put greater weightage on abbreviate risks instead of maximizing profit. The traditional technological knowledge (ITKs) covers a complicated sphere of subjects, viz. crop production, livestock rearing, accustomed knowledge management, ailment preparation, healthcare, insect administration, and others. The utilization of non-chemical methods for protecting lives and crop aegis is already accepting in several countries including India. The administration strategies developed and answer by the Governments is now supported the utilization of plant extracts. If an accomplishment is fabricated arise the cultivation of Indigenous Technological Knowledge (ITK) based articles on the small scale, it is often an economically applicable advantage for the appropriate development of eco-friendly chemicals.

Indian agriculture has been started over 10,000 years old, over millennia, farmers developed innumerable practices to auspiciously abound crops and accession animals within the awful adapted agro ecological regions of the Indian subcontinent. About 170 years of acceptance brought in new techniques, some advantageous in addition to a few harmful event of ancient Technological knowledge (ITK) systems, including administration of accustomed environment, has been a bulk of adaptation to the humans who generated these systems continued aback. Million of ITKs were supported to avail knowledge of actual and living assets to construct sure basal livelihoods for bounded people.

Biodiversity is the foundation stone of human survival on the earth. Very appropriately, the theme of the World Food Day celebration, 16 October, 2004 was “Biodiversity for Food Security” Biological diversity is fundamental to agriculture and food production. Scientists have identified so far about 1.4 million of the plant and animal species that exist on earth. A rich variety of cultivated plants and animals serves as the foundation for agricultural biodiversity. Yet people depend on just 14 mammal and bird species for 90 % of their food supply from animals. Just four plant species, namely, wheat, maize, rice and potato provide half of our energy from plants (FAO, 2004).

India is located between 8^°- 38^° N and 68^°- 97^ºE and exhibits extreme variation in altitude — from sea level to heights above vegetational limits in the Himalayas (ca 4500 m), and climate — from monsoon- tropical in south to temperate and alpine in the north-western Himalayas and extremely arid to semi-arid in the north-western plains. It is floristically extremely rich with about 33 percent of its botanical wealth (over 15,000 species of higher plants) being endemic. There are about 141 endemic genera distributed over 47 families. Further, of the 4,900 endemic species, larger percentage is localised in the Himalayas (about 2,532 species) than in other regions, namely, the peninsular tract (1,788 species), and the Andaman and Nicobar Islands (185 species). It is also estimated that floristic richness is maximum in the north-eastern region, which holds about 50 percent of India’s total species diversity, i.e., more than 7,000 species, and is considered as the cradle of flowering plants. Of 990 species of orchids, 700 species occur in this region (Nayar, 1989). This, thus, makes the Indian region botanically unique and interesting (Arora, 1991).

2. 1. Plant domestication

Process of bringing wild species under human management.

2.1.1. Changes in plant species under domestication

Elimination or reduction in shattering of pods, spikes, etc.

Elimination of dormancy

Decrease in toxins of other undesirable substances. Eg. Bitter principle of cucurbits.

Cultivated plants show altered tillering, branching, leaf characters.

Decrease in plant height. Eg. Cereals and millets.

8.1 Introduction

In pre-historic times, people lived as hunters and gatherers. Then, gradually they began to produce the crops they ate on piece of land, and farming was born. Wild plants have certain traits that keep them protected and productive without human intervention. However, most of them are not desired for food or other use by humans. By spontaneous mutagenesis and hybridization, occasionally variant plants were found that lacked some of the undesired traits, such as bitter taste, thorns, or had particularly attractive features, such as larger fruits and more regular tuber shape. Consequently, as time passes such variation was picked up by humans by selection of such variants, keeping and advancing them. Thus, plant domestication is the process of bringing wild species under human management. In other words, plant domestication is the process by which genetic changes (shifts) in wild plants are brought about through a selection process imposed by humans. It is a method of plant breeding in the sense that, when successful, it provides domestic types that are superior to ones previously available.

Pre-historic man domesticated virtually all of our present-day crops. But, domestication of wild species continues even today and is likely to continue for a long time in the future. For example, in many countries there is an increasing emphasis on bringing forest trees producing timber, etc. under human management. A similar trend is seen for medicinal plants and plants producing specific compounds of interest, e.g., hydrocarbons, oils, etc. Kala jeera (Bunium persicum), a perennial spice, was domesticated during 1990s in Himachal Pradesh; it is being cultivated as an orchard crop. One important aspect of domestication at present is the use of particular genes from wild relatives in the improvement of cultivated species. When a plant breeder transfers one or a few desirable genes from a wild relative to a cultivated type, he is, in a sense, domesticating the wild species in part.

Food is the basic requirement for maintaining the life process. Plants supply the bulk of foods required for human and animal. With limited cultivable area and ever increasing pressure of human population, the demand for food is constantly rising which can not be alone met by conventional plant breeding technologies. Novel techniques like plant genetic engineering are gaining momentum for production of superior plants or yield enhancement of a species.  It has been observed that the most commercially successful application of recombinant DNA technology is in genetic engineering of plants, which led development of multinational seed companies deriving monetary benefit from genetically modified crop and food products. From production of herbicide resistant or insect pest tolerant plants to alter the inherent quality composition of human food, plant genetic engineering has established firmly the commercial viability of recombinant DNA technology.

Introduction
Plant genetic engineering has revolutionized modern agriculture, enabling the development of crops that not only meet the demands of a growing global population but also address the challenges posed by climate change, pests, and diseases. As traditional breeding methods often face limitations in terms of time, precision, and scope, genetic engineering offers a powerful alternative. By directly manipulating plant genomes, scientists can introduce specific traits with greater accuracy and speed, leading to significant improvements in crop quality and productivity. This chapter explores the protocols and methodologies employed in plant genetic engineering aimed at enhancing the quality of crops, providing insights into the techniques that have transformed agricultural practices.
The importance of plant genetic engineering cannot be overstated. With the global population projected to reach nearly 10 billion by 2050, the agricultural sector must find ways to increase food production while ensuring sustainability and environmental conservation (Tilman et al., 2011). Conventional breeding methods, which rely on the natural variation present in plant populations, can be slow and imprecise. In contrast, genetic engineering allows for the targeted introduction of desirable traits, such as disease resistance, improved nutritional content, and enhanced stress tolerance (Gurian-Sherman, 2009). These advancements are crucial for maintaining food security in the face of growing environmental challenges.