eChapters

Weeds are unwanted and undesirable plants which interfere with the utilization of land and water resources and thus adversely affect crop production.

Classification of Weeds

Weeds can be classified in three different manner based on morphology, life cycle, habitat and origin.

Most of the insect pest and disease (insects, mites, diseases, nematodes, etc.) management problems arise from relying entirely on pesticides for control. Integrated pest management (IPM) is a strategy that draws on a range of management tools with the goal of using the least ecologically disruptive techniques to manage pests within economically acceptable levels. IPM considers the production system in a holistic manner and looks at all aspects of the farming enterprise as potentially increasing or decreasing pest numbers and, where possible, enhancing the activities that reduce these pest populations.

Strategy for Integrated Pest and Disease Management

The basic IPM strategy involves routine crop monitoring to ensure that pesticides are only applied when needed, as well as to ensure appropriate timing of pesticide applications. The most developed bio-intensive IPM relies primarily on beneficial organisms to manage insect pests. When greater pest control is needed, interventions chosen are complementary to the survival of these beneficial organisms. As other pests are incorporated more and more prevention strategies are adopted which reduces the need for direct control practices.

Relationship Between Plant and Water

Water is the most vital component of the living cells and the basis of plant feeding. Water is also characterized with extraordinary physical properties: it has high specific heat, biggest latent heat of vaporization, very high thermal conductivity and greatest surface tension. Large amounts of heat are tied up with water because of very high specific heat, which contribute to both climatic stability and to heat budgets of the plants and other organisms. Water molecules are integral part of living systems being the solvent for metabolites and structural component of proteins and nucleic acids. In fact, biological macro-molecules cannot exist in their complicated secondary folding or spiralled helixes without the support of hydrogen bonding within their water matrix. The water matrix is also critical for metabolic activity because its properties of hydration permit ready reactivity between molecules in solution as well as between enzymes and their substrates, and the biochemical processes are sensitive to tissue hydration. A reduction of only 20-25 per cent below maximum hydration is sufficient to cause metabolic malfunctioning of many enzymes. It is the substrate for photosynthesis and a product of respiration. Water also helps to buffer plant tissue against fluctuations in the external environment. Plant growth including leaf expansion, organ enlargement, reproductive development and stomata function are all clearly associated with moisture status. Hormonal changes (abscisic acid and cytokinins) in plant body occur with brief reduction in water potential. Water is the also major force in shaping the climatic patterns.

Plant nutrition is the study of the chemical elements and compounds necessary for plant growth, plant metabolism and their external supply. In 1972, Emanuel Epstein defined two criteria for an element to be essential for plant growth:

In its absence the plant is unable to complete a normal life cycle.

The element is part of some essential plant constituent or metabolite.

This is in accordance with Justus von Liebig’s law of the minimum. The essential plant nutrients include carbon, oxygen and hydrogen which are absorbed from the air, whereas other nutrients including nitrogen are typically obtained from the soil.

It is said that “Success of any production system depends on the kind of seed which are sowing”. It is true for the seedlings also beacause healthy seedlings grown in a well managed nursery will decide the yield and consequently the profit.

Definition of Vegetable Nursery

A vegetable nursery is a place or an establishment for raising or handling of young vegetable seedlings until they are ready for more permanent planting.

Why vegetable nursery is needed

Some vegetable crops require special cares during their early growth period. There are some vegetables with very small sized seeds. Seedlings of many seed propagated vegetable crops like, tomato, brinjal, chillies, sweet pepper, cauliflower, cabbage, knolkhol, broccoli, Brussels sprout, kale, endive, chicory, celery, lettuce, parsley, onion, etc. are first raised in the nursery beds before transplanted in the main field. Many seed propagated vegetable crops viz., okra, peas, beans, radish, carrot, beet, turnip and all the cucurbits (e.g. bitter gourd, bottle gourd, pumpkin, cucumber, watermelon, muskmelon, snake gourd, sponge gourd, ridge gourd, etc.) are conventionally grown through direct seeding in the main field. However, many cucurbits, particularly in the early season are also grown in India using the seedlings raised in polythene packets.

The term ‘Phyto-hormone’ was coined by Thimann in 1948. Phyto-hormones are organic compounds, which are produced naturally in plants, synthesised in one part and usually translocated to the other part where in every small quantity affect the growth and other physiological function of the plants. Auxin was the first hormone to be discovered in plants. At one time, auxin was considered to be the only naturally occurring plant growth hormone however, four other classes of phyto-hormone viz., gibberellins, cytokinin, ethylene and abscisic acid was later discovered. Plant growth regulators include both five specified classes of phyto-hormones (auxin, gibberellins, cytokinin, ethylene and abscisic acid) and other synthetic organic compounds (for example, polyethylene glycol, dinoseb-2-sec butyl 4,6dinitrophenol, proteins and/or amino acids, carboxylic, phenolic acid, humic acids, etc.) having properties of bio-stimulants or bio-inhibitors. Plant growth regulators (PGRs) modify plant physiological processes either by stimulating or inhibiting specific enzymes or enzyme systems to help regulate plant metabolism and thereby enhance yield and product quality. They normally are active at very low concentrations in plants.

Importance of PGRs was first recognized in the 1930s. Since then, wide array of natural and synthetic compounds that alter function, shape and size of crop plants have been discovered. Of the many uses of PGRs, effects on yield are often indirect. A wide range of beneficial effects of PGRs on crop growth and yields are: 1. promotion of germination and/or emergence, 2. stimulation of root growth, 3. promotion, mobilization and translocation of nutrients within plants, 4. modification of flowering, 5. increase in stress tolerance and improvement of water relations in plants, 6. promotion of early maturity, 7. increase in disease resistance, 8. retardation of senescence and 9. improvement of crop yields and/or quality.

Development can be defined as the process and timing of differentiation of the component events causing qualitative changes in form and function of the plant and therefore, manifestation of economic plant parts. Sowing is the beginning of the process, after which plants emerge, grow and develop with or without transplanting and may be harvested in vegetative (e.g., cole, bulb, tuber, root, salad crops) or reproductive phase (solanaceous fruits, peas and beans, cucurbits, okra, etc.). Growth and development of plants is dependent on abiotic (physical) and biotic (biological) factors. Abiotic factors include the physical environmental conditions and biotic factors include animals, insects, and diseases. Each plant has certain environmental requirements. To attain the highest potential yields a crop must be grown in an environment that meets these requirements. A crop can be grown with minimal adjustments if it is well matched with its climate or growing condition. Unfavourable environmental conditions can produce a stress on plants resulting in lower yield. In such cases the environment can be artificially modified, as done in protected structures like poly house, shade net house, etc. to meet the crop requirements.

Different abiotic environmental factors viz., light, temperature, water and soil greatly influence plant growth and geographic distribution. These factors determine the suitability of a crop for a particular location, cropping pattern, management practices, and levels of inputs needed. A crop performs best and is least costly to produce if it is grown under the most favourable environmental conditions. To maximize the production of any crop, it is important to understand how these environmental factors affect plant growth and development.

Classification of Vegetable Crops

Vegetables are defined as herbaceous plant origin product with no calorific value and providing micronutrients, vitamins, antioxidants, fibre and alkaline reaction inside human body. Vegetable crops are not only botanically different but also their cultural and climatic adaptation also shows wide variability. It is, therefore, necessary to classify the vegetable crops for their easy recognition. Vegetable crops can conveniently be classified “Botanically” for the purpose of vegetable breeding and according to “Method of culture” from the point of crop husbandry.

Botanical Classification

Botanical classification involves grouping of plants into kingdom, division, sub-division, phylum, sub-phylum, class, sub-class, order, family, genera, species, sub-species and variety. The broadest group in which vegetables are discussed is family. The genus and species constitute the scientific name. Scientific names are accepted worldwide and there cannot be any confusion as per their nomenclature. All vegetable crops belong to the division Angiospermae. The division Angiospermae has two classes: Monocotyledoneae and Dicotyledoneae.

The crops used for vegetable purpose in the world belong to 1200 species under 78 families and of them, more than 860 species under 59 families belong to dicotyledoneae and about 340 species under 19 families belong to monocotyledoneae. In the tropical and subtropical parts of the world, about 90 species of vegetable crops are cultivated, but hardly 25 of them are commercially important in terms of market demand, development of variety/hybrid and seed production. In the present botanical classification, over 140 different kinds of vegetable crops under 7 monocotyledoneae and 20 dicotyledoneae families have been included.

Food, at the fundamental level, is viewed as a source of nutrition to meet daily requirements at a minimum in order to survive but with an ever greater focus on the desire to thrive. Nutritional security denotes the consumption and physiological use of adequate quantities of safe and nutritious food by every member of the family and encompasses the process of equitable distribution among members of household and communities. This would entail the need to ensure a varied food intake, comprising all the essential macro- and micronutrients (protein, carbohydrates, minerals and vitamins), plant pigments (lycopene, β- carotene, anthocianin, lutein, capsanthin, zeaxanthin, etc.) and other functional phytochemicals (secondary metabolites, like flavonoids, isothiocyanates, glucosinolates, etc.) through a diversified diet. The growing awareness in recent years of the health promoting food has directed increased attention to vegetables as vital components of daily diets.

Main Nutrient Components of Vegetables

Nutrient components of our food can be grouped into five main divisions, namely, (i) Carbohydrate, (ii) Protein, (iii) Fat, (iv) Vitamins and (v) Minerals. Balanced diet is the food containing all these nutrient components in balanced form to run the physiological process in good tune. So, only eating to one’s heart’s content may not be the criterion of a balanced diet. Our dietary constitution which is mostly cereal based is really alarming. Cereals, which supply chiefly carbohydrate, constitute only a part of the diet. Moreover, the present average carbohydrate supply through cereals is also not adequate. Chief deficiencies in our diet are calories, protein, vitamin A and riboflavin. According to the studies of Indian Council of Medical Research, New Delhi and National Institute of Nutrition, Hyderabad, meager intake of vegetables, the low cost protective foods, is largely responsible for malnutrition among the majority of our population. The dieticians advocate intake of 125g leafy vegetables, 75g other vegetables and 100g root and tuber vegetables (total 300g) everyday to make our diet balanced. In households below the poverty line, per capita vegetable consumption is very low, apprehended to be even lower than 40g per day.

Historical Account on Vegetable Cultivation in India

The vegetables have chequered history in India which dates back to prehistoric period before the arrival of Aryans in India (c. 1500-1000 BC). During the pre-historic times before the arrival of Aryans in India, the Proto-Australoids (Nisada) used brinjal, bottle gourd and watermelon as vegetables. Pea existed in India much before the Aryans came to the country and it was already present in Western Asia prior to its cultivation. The pea, most likely the field pea (Pisum sativum subsp. sativum var. arvense L.) was eaten during the Harappan civilization as evidenced from the archaeological excavations of Mohenjo-daro and Harappa (2500-1750 B.C.) in which carbonized pea seeds were discovered. Pea seeds were also found from Neolithic site (last stage of the Stone age) of Chirand in Bihar (situated 10 Km south-east of Chapra), Chacolithic site (period or Copper Age) of Maheshwar Nevdatoli (c. 1200 BC.) in Madhya Pradesh and part of Osmanabad district in Maharashtra. The presence of seeds of melon along with wheat was also recorded from the Harappan excavation. Plant remains of Chenopodium album, Portulaca oleracea and a few species of Solanaceae, Polygonaceae and Labiatae family during Mesolithic times (Middle Stone Age) were found at Mesolithic site of Damdama, Uttar Pradesh (c. 7000-6000 BC). Wood charcoals of plant remains of Lablab purpureus were found from the early phase of Indus-Saraswati (Sarasvati) or Indus Ghaggar-Hakra civilization (c. 3100-2800 BC). Kundru (Coccinia indica), cowpea and field pea were recorded from Hulas in Saharanpur district, Uttar Pradesh, late Indus valley civilization archeological site. Carbonized seeds of hyacinth bean (dolichos bean), peas, Phaseolus, Vigna and melon from Rojdi in Gujarat and Chenopodium and amaranth from Surkotada, Gujarat (c. 2300-1800 BC), both being the archaeological sites belonging to the Indus valley civilization also suggested the existence of vegetables in India in the pre-historic times. Among the vegetables eaten during the pre-historic period, like brinjal, bottle gourd, watermelon, peas and melon as mentioned earlier, only brinjal has its origin in India while the other were brought from other countries much before the arrival of the Aryans. It is difficult to understand how a few important Indian native vegetables, like cucumber, Luffa (smooth and ridge gourd), pointed gourd and Dolichos bean (Lablab purpureus) were not known at that time. Similarly okra which has a secondary centre of origin in India has not been mentioned in any ancient literature. However, Abelmoschus moschatus called “Lata kasturika” in Sanskrit as a source of perfume has been recorded in Carak Samhita. The use of bottle gourd, which is not a native vegetable, is known from pre-historic times. Its dried fruit-shell is used as a hand jug (utensils) by saints and monks and in musical string instruments, like ektara, tamboora, tanpura, sitar and veena. Even mythological paintings have always delineated Naradmuni with tamboora in his hand and the goddess Saraswati with Veena which suggest the antiquity of bottle gourd in India. However, its date of introduction and the place from where it came remain unrecorded. It is also not mentioned in any iconography of the Medieval period (9^th and 10^th Century AD).

Definitions

Selection, integration and implementation of disease control means on predicted economic, ecological, and sociological consequences.

A comprehensive approach to disease control that uses combined means to reduce the status of diseases to tolerable levels while maintaining a quality environment.

The optimization of disease control in an economically and ecologically sound manner, accomplished by the coordinated use of multiple tactics to assure stable crop production and to maintain disease loss below the economic injury level while minimizing risks to man and the environment.

A sustainable approach to manage diseases by combining biological, cultural, physical and chemical tools in a way that minimizes economic, health and environmental risks.

Proper selection of a fungicide and its application at the correct dose and the proper time are highly essential for the management of plant diseases. The basic requirement of an application method is that it delivers the fungicide to the site where the active compound will prevent the fungus damaging the plant. The fungicidal application varies according to the nature of the host part diseased and nature of survival and spread of the pathogen. The method which are commonly adopted in the application of the fungicides are discussed

Fungicide Formulation

Fungicide formulation is the process by which the fungicide is put into a form which can be easily produced, stored, transported and applied by practical methods in order to achieve a safe, convenient economic and effective method of disease control.The mixture of active ingredient and inert (inactive) ingredients is called a fungicide formulation.

Introduction and Concept

The word fungicide has originated from two Latin words: viz. fungus and caedo (to kill). So literally, a fungicide would be any physical or chemical agency which kills a fungus. However, the word is restricted to chemicals. Hence, the word fungicide should mean a chemical capable of killing fungi. However, there are a number of compounds which do not kill the fungus. They simply inhibit growth or spore germination temporarily. If the fungus is freed from such substances, it would revive. Such a chemical is called a fungistat. and the phenomenon as fungistasis. Some other chemicals, like certain phenantherene derivatives and bordeaux mixture may inhibit spore production without affecting vegetative growth. These are called antisporulants. There are other groups of chemicals which exhibit very poor or no antifungal activity in vitro condition but provide protection to the plants either by inhibiting the penetration of host surface by the fungi or by inducing the host defense system. The former type of chemicals are termed as antipenetrants and later as antipathic agents. Even though fungistats, antisporulants, antipenentrants, and antipathic agents do not kill fungi, they are included under the broad term fungicide because by common usage, the word fungicide has been defined as chemical substance which has ability to prevent damage caused by fungi to plants and their products. Fungicide which is effective only if applied prior to fungal infection is called protectants. On the other hand, fungicide which is capable of eradicating a fungus after it has caused infection, and thereby curing the plant, is called therapeutant.

Definition

Those characters that enable a plant to avoid tolerate or recover from attacks of pathogens under conditions that would cause greater injury to other plants of the same species.

Definition

Garret (1970) defined biological control as any condition under which or practice whereby survival or activity of a pathogen is reduced through the agency of any other living organism (except man) with the result that there is a reduction in the incidence of the disease caused by that pathogen.

Baker and Cook (1974) stated that the biological control is the reduction of inoculum density or disease producing activities of a pathogen or parasite in its active or dormant stage, by one or more organisms, accomplished naturally or through manipulation of the environment, host or antagonists, or by mass introduction of one or more antagonists.

Biocontrol can be simply defined as the application of living organism to control diseases.

1. Biosecurity

Biosecurity is strategic and integrated approach encompasses policy frameworks to analyze and manage risks for food safety, animal life and health and plant life and health including environment.

Introduction

Cultural management is defined as manipulation /or adjustment of crop production techniques for management of plant diseases. Cultural practices have been as old as possibly agriculture itself. In early stage of agriculture development, the growers through their experiences and observations had known that repeated cultivation of a particular crop species or variety on a piece of land often resulted in crop sickness. As a matter of fact, in the present day agriculture, cultural practices are being considered as essential backup methods for management of plant diseases. Adequate adjustment in crop production techniques can modify the environment in such a manner that it becomes unfavorable for the pathogen and pathogenesis. Based on this the disease control affected by cultural practices are preventive, these practices aim at reducing the activity and density of inoculum. It offer the opportunity to alter the environment, the condition of the host, behavior of the causal agent to achieve economic management of disease.

Introduction

Cultural management is defined as manipulation /or adjustment of crop production techniques for management of plant diseases. Cultural practices have been as old as possibly agriculture itself. In early stage of agriculture development, the growers through their experiences and observations had known that repeated cultivation of a particular crop species or variety on a piece of land often resulted in crop sickness. As a matter of fact, in the present day agriculture, cultural practices are being considered as essential backup methods for management of plant diseases. Adequate adjustment in crop production techniques can modify the environment in such a manner that it becomes unfavorable for the pathogen and pathogenesis. Based on this the disease control affected by cultural practices are preventive, these practices aim at reducing the activity and density of inoculum. It offer the opportunity to alter the environment, the condition of the host, behavior of the causal agent to achieve economic management of disease.

Defintion

Management of plant diseases using physical means is called physical management.

Also called physical therapy or thermotherapy.

It is mostly curative in nature.

The techniques used in disease management mainly based on two principles: Prevention or prophylaxis and cure. The first principle prevention includes disease management tactics applied before infection i.e., the plant is protected from disease. It includes: avoidance, exclusion, eradication, resistant & protection. Second principle curative action: functions with any measure applied after the plant is infected i.e., the plant is treated for the disease. It includes therapy.

Disease Forecasting

Definition

Forecasting 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.

Epidemiology

Vanderplank has called epidemiology the science of disease in population. Epidemiology puts its emphasis on population phenomena. The important populations are those of the host, on the one hand, and of the pathogen, on the other. But further, epidemiology is concerned with host-pathogen interactions that lead to disease and crop losses. These interactions are often environmentally dependent. So epidemiology deals with effects of the biotic and abiotic environments. Finally , man has had important effects on hosts, pathogens and the environments, effect that today are increasing in magnitude and scale of importance. Epidemiology therefore also deals with the effects of man on disease and sometimes with the effects of plant disease on mankind. All of this can be symbolized by the disease tetrahedron.

Introduction

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, employs 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.

Pathogenesis: Role of enzymes

The chain of metabolic events that bring about the disease is pathogenesis. It involves the virulence of the pathogen, susceptibility of the plant and impact of the environment. It is called disease triangle. Penetration infection, invasion, colonization and reproduction are the events that occur during pathogenesis, and lead to development of disease.

The establishment of pathogen in the host and consequent development of disease involves a chemical interaction between the host and the pathogen. The pathogen employs offensive chemical weapons to break host barriers, which the host resists with all its might. Parasitism and disease resistance run parallel and are inseparable, A biochemical ‘tug of war’ ensures between the host and the pathogen, in which one tries to outwit the other. Enzyme, toxins and growth regulators are the important chemical weapons of the pathogen. Viruses, however, because of their basic nature, do not produce any of these chemicals.

Pathogens produce these substances either in normal course of their activities (constitutively) or when, they grow on certain substrates such as their host plants (Inducible). Plant pathogenic enzymes disintegrate the structural components of host cells, breakdown inert food materials in the cell, or affect components of the protoplast directly and interfare with its functioning system. Toxins seem to act directly on protoplast component and interfare with the permeability of its membrane and with its function. Growth regulators exert a hormonal effect on the cells and either increase or decrease their ability to divide and enlarge. Polysaccharides seem to play a role only in the vascular diseases, in which they passively interfere with the translocation of water in the plants or they may also be toxic.

A. Types of parasitism

An organism that lives within or upon another living organism from which it derives nourishment and in which it may cause various degrees of injury is called as parasite. The removal of food by a parasite from its host is called parasitism. Among the parasite one can distinguish different degree of parasitism

Definition

The availability of a plant pathogens in given area depends upon its ability to survive not only during its parasitic relations with hosts but also during those seasons in which the hosts are not growing. The latter part of continued existence of plant pathogens in which they remain in dormant condition to overcome the unfavourable condition of non availability of hosts is called “survival”. Pathogens may survive between crop seasons by means of specialized resting structures , by functioning as saprophyte in or on the soil or in diseased plant debris, or by living in some intimate association with living plants or other organism.

Definition

To make a healthy plant sick or diseased, primary requirement of a pathogen is spread of its inoculums from the source of survival to the susceptible host. The spread of a plant pathogen within the common area in which it is already established is called dispersal or dissemination. Moving the inoculum only a few inches and transporting it for hundreds of kilometers both represent its dispersal. Nevertheless, the pathogen dispersal is not necessarily only for spread of diseases but also for continuity of the life cycle and development of the pathogen. A detail knowledge of pathogen dispersal is necessary to find out effective control measures for diseases because the possibilities of preventing dispersal and thereby breaking the infection chain always exist.

Definition

Neamtode may be defined as triploblastic, bilaterally symmetrical, unsegmented, pseudocoelomate individual invertebrate, with 4 main hypodermal chords, a triradiate oesophagus, circum oesophageal nerve ring, and lacking specialized organs for respiration and circulation.They have tubular gonads which open separately in females but join alimentary canal in males to open through a cloacal aperture.

The parasitic flowering plants are also important pathogens. There are few seed plants, which are parasitic on living plants and are called parasitic higher plants or Phanerogamic parasites. These parasitic higher plants attack some valuable crops and trees causing considerable losses. They produce flowers and seeds and belongs to several widely separated botanical families they differ to each other on their dependency on host plants. These parasites have haustoria as absorbing organ, which sent deep into the vascular bundle of the host to draw water and nutrients. More than 2500 species of higher plants are known to live parasitically on other plants.

Definition of Virus

According to Luria and Darnell (1968), Viruses are entities whose genome is a nucleic acid, either DNA or RNA, which reproduce inside living cells and use their synthetic machinery to direct the synthesis of specialized particles- the virions, which contain the viral genome and transfer it to other cells.

Nature of Virus

The physical and chemical nature of viruses eluded scientists until the 1930s. Stanley (1935) announced crystallization of Tobacco mosaic viruses, a feat for which he got a Nobel Prize. Stanley thought the crystals to be pure proteins. It was the pioneer work of F.C. Bawden and N.W. Pirie of England which showed that the viruses consists of proetein and nucleic acid. The chemical nature of viruses was settled. It consisted of nucleic acid and protein. The viruses chemically were proved to be nucleic acid. The mature particle of a plant virus is generally called virion and the whole infective particle is called as Nuclcocapsid.

Bacteria

Definition

Bacteria belong to prokaryota which encompasses organisms with a primitive type of nucleus lacking a clearly defined membrane. The bacteria are smaller than fungi and measure about 0.5 to 1.0 x 2.0 to 5.0µ.

Taxonomy

Taxonomy is the science that deals with the identification, nomenclature and classification of organisms.

Systematics

It is scientific study of organisms with the ultimate object of characterizing and arranging them in an orderly manner.

Classification

Classification is the ordering of organisms into groups and systems, based on their morphological, phylogenetic and physiological relationships.

Nomenclature

It is the system of assigning names to the taxonomic groups or organism according to international rules.

Introduction

Plant pathogens induce diverse reactions in the body of their hosts. This result in creation of abnormalities which become visible on the plants. A visible or otherwise detectable expression of abnormal physiology, development, or behaviour in a plant resulting from disease is called symptoms. Normally, a distinction is made between symptoms and signs A symptom of disease is expressed as a reaction of the host to a causal agent, whereas, a sign is evidence of disease other than that expressed by the host. Signs are usually the structures of the pathogen. A disease is first noticed by the presence of symptoms and /or signs, and recognition of specific type of symptoms or sign aid in the eventual diagnosis of the disease.

a) Definition

Fungus is Latin word meaning ‘mushroom’

Alexopoulus and Mims 1979 defined fungus as eukaryotic, achlorophyllous organism generally produced by sexual or asexual method and whose filamentous branched somatic structure is typically covered by cell wall.

Definition

Plant disease in which no pathogens or parasitic is associated with the cause is known as Non-parasitic disease. They are also called as noninfectious or physiological disorders.

General Characteristics

Occurs in the absence of pathogen and therefore, cannot be cultured or transmitted.

Caused by the lack or excess of something that supports life from diseased to healthy plants.

Effect plant in all stages of their lives, such as seeds, seedlings, mature plants or fruits.

Symptoms may range from slight to severe & affected plants may even die.

These disease cause damage in field, in storage or at the market.

Fungi

Definition

Fungi are eukaryotic, spore bearing, achlorophyllus, heterotrophic and thallophytic plants with varied forms and habitats, representing heterothallic or homothallic types of sexuality with characteristic sexual and /or asexual means of reproduction without tissue differentiation.

Plant diseases are classified on the basis of type of pathogenic or non-pathogenic causes of the disease. The classification is based on the plant pathogenic organisms as follows.

A. Parasites

The diseases are incited by parasites under a set of suitable environment. Association of definite pathogen is essential with each disease. They include both biotic and mesobiotic agents.

Biotic agents: They are also called as animate causes. They are living organisms.

There are number of diseases which attacks crop plants. Therefore It is mandatory to classify plant disease into more manageable and more specific group based on several criteria for easy and better understanding. Let us discuss one by one.

1. On the basis of type of infection

On the basis of type of infection disease can be classified into two types

The Disease Triangle and Disease Pyramid

The disease triangle is one of the first concepts encountered by students in an introductory plant pathology course and often may be encountered in higher level classes. The interactions of the three component namely (1) susceptible host (2) virulent pathogen and (3) favorable environments have been visualized as a triangle, generally referred to as the “DISEASE TRAINGLE”. Each side of the traingle represent one of the three components. The length of each side is proportional to the sum total of the characteristic of each component that favor disease. For example, the more virulent and abundant the pathogen, the longer the pathogen side would be and the greater the potential amount of disease. Similarly if the plant are resistant, the widely spaced or wrong age, the amount of disease would be small or zero. Where as if the plants are susceptible, at a susceptible stage of growth, or densely planted, the host side would be long and the potential amount of disease could be great. Also, the more favourable the environmental conditions that help the pathogen, or that reduce host resistance, that longer the envirnmental side would be and greater the potential amount of diseases. If the three component of the disease traingle could be quantified, the area of the traingle would represent the amount of disease in a plant or in plant population. If any of three component in zero, these can be no disease.

Definition

Pathogenesis can be defined as the chain of events leading to the development of a disease. In another words it is also called disease cycle.

It tells us about

There is a very impressive and extensive number of terms and definitions used in plant pathology, many of which you will not come in contact with. With interest, study and practice, terms and names will come to light and become familiar to you. When you start out, don’t worry too much about the terms; but also don’t be afraid of them. The more exposure you have to the subject the more comfortable you will be when dealing with your peers and the public. With these you are going to be exposed to some terms and definitions that will be a good ice breaker and prepares you for the information to follow

History in general reveals chronological account of important events, contribution of persons who significantly influenced the thinking of their era and the interpretations of the observed facts or phenomenon over the period of time. The progress in plant pathology leading to the major land mark in mycology, plant bacteriology and plant virology will be discussed in chronological order for easy and better understanding.

Of the 7 billion global population, about 800 million do not have enough food to eat and majority of the them live in developing countries. By 2050, the world population is estimated to reach 9 billion. Plant pests and diseases are responsible for losses of 20 to 40% of global food production. Due to increasing global trade and a changing climate, plant diseases pose a major threat to food security today than ever before. Agriculture will have to cope with weather fluctuations that can affect the survival, distribution and multiplication of plant pathogens apart from shift in pathogenic microbial flora. Emergence of new races of pathogen potentially threaten the production of food. To cite an example, migration of 13 -A2 clonal lineage of Phytophthora infestans from Europe, during 2013, devastating tomato and potato in India. Plant pathogens also impact on environment sustainability, forest health, recreational horticulture, human and animal health.

The science of plant pathology can play a much needed role in alleviating hunger and malnutrition through development of affordable solutions for devastating plant diseases leading to increase in food production. It hold promise to ensure quality produce by containing microbial invasions and toxin contamination of food crops. Plant Pathologists have an important role to play in meeting the food security need of the nation by developing technologies for ensuring proper crop health. There is an urgent need to produce more food per unit area for feeding rapidly increasing human population. We need to act ahead of pathogens in our efforts to ensure normal crop yields. Cutting edge biotechnologies such as CRISPR gene editing systems and RNA interference are being exploited to rapidly developed crop varieties having resistance to specific pathogen races.

Crop protection has come a long way from predominantly chemical based approaches to more environment friendly IDM technologies including green chemistry. There is a need to develop bio-intensive modules for management of diseases. Decision support system need to be developed for important diseases for their timely, more efficiently management. There is need to adopt information technology at a larger scale to facilitate quick dissemination of new crop protection solutions among the farmers and other stakeholders.

6.1 INTRODUCTION

Water in soils is essential to plant growth, being the medium through which inorganic nutrients are translocated to the root surface and carried through the plant. Most of the water in soils at or near field saturation can be considered as equivalent to bulk water, and only bulk properties need be considered in discussing its movement through soil interstices and its retention in soil capillaries; this is the field with which soil physics deals. But, in the first molecular layer in contact with soil particles, and perhaps for several molecular layers beyond, the behaviour of water molecules is very different from that in the bulk. Strong adsorptive forces can reduce the volatility of these molecules and restrict their mobility. Such an adsorbed layer of water competes with other polar molecules for adsorption sites, and so has an important role in determining the release and retention of fertilizers and pesticides. Such strongly adsorbed layers confer wettability on soils, but hydrophobic surfaces can also be present and these lead to non-wettable soils with serious consequences in run off and inefficient use of precipitation. This region of distinctive molecular interactions between water and soil particles falls within the field of soil chemistry.

5.1 INTRODUCTION: THE PHYSICAL CHEMISTRY OF COLLOIDAL SUSPENSIONS

This chapter is concerned with understanding the factors which influence the partition of ions between solid surfaces and aqueous solutions. There are many aspects of soil science such as some of those concerned with soil formation, transfer of nutrient ions from soil particles to plant roots, soil pollutant interaction and soil management which are critically dependent on what happens in the space of the order of 1 nm wide between solid and equilibrium solution. A broad survey of the development of ideas on soil-electrolyte interaction shows that there have been two main avenues of approach. One views the soil as an electrically charged surface with its adsorbed hydrated ions as one phase in equilibrium with solution, which is seen as the second phase. The other approach focuses on the electrical double layer extending from the charged solid surface out into the solution. In the latter approach the solid surface, the outer equilibrium solution and the make up of the transition zone between these two phases must all be involved in any detailed consideration of the micro structure of the system. For a full and proper understanding of soil-electrolyte interaction anything less than a detailed analysis of the micro-structure is likely to be inadequate and in this it must be remembered that the interaction between electrical double layers which overlap with one another is likely to be important.

4.1 INTRODUCTION

It has been suggested that the relationship of surface chemistry to soil science is similar to that of biochemistry to biology. Certainly the fact that surfaces of soil particles are extensive and reactive leads to a dominance of surface chemistry in soil behaviour, but it is not an exclusive relationship, because many precipitation reactions, oxidation and reduction processes, and biological reactions take place more or less independently of the surface processes. Nevertheless it is difficult to understand soil properties fully without an appreciation of the nature and extent of the surfaces of the soil constituents, and this chapter is devoted to a discussion of this topic.

3.1 INTRODUCTION

The complete soil organic fraction is made up of live organisms, and their undecomposed, partly decomposed and completely transformed remains. Soil organic matter is the term used to refer more specifically to the non-living components which are a heterogeneous mixture composed largely of products resulting from microbial and chemical transformations of organic debris. These transformations, known collectively as the humification process, give rise to humus, a mixture of substances which have a degree of resistance to further microbial attack.

2.1 INTRODUCTION

Textural assessment has long been used to indicate quality in agricultural soil and although it contains an element of subjective judgement, a skilled surveyor can differentiate many grades of texture. Soil texture correlates with the distribution of particle size in the soil, though this is not the only component in texture. Although particle size distribution is an objective attribute of soils and can, in principle, be measured with accuracy, the determination is in practice quite difficult and certainly laborious, so that it is customary in soil mechanical analysis to divide the soil into several broad fractions: sand, silt and clay are the principal categories. The clay fraction, which comprises the smallest particles in the soil, is generally defined as the fraction smaller than a nominal diameter of 2 jam. The practical division is, however, based on the velocity of fall of soil particles through a fluid, calculating the diameter of the particles from the equation of Stokes

1.1 THE IMPORTANCE OF SOILS

Soils are the medium in which crops grow, and so they are essential to the provision of the food and fibre to sustain mankind. But besides the immense importance of this role they are an essential component to life as we know it because of their action as a buffer to control the flow of water between sky, land and sea. They are also a sink, and usually a safe sink, for many of the chemicals that might otherwise make life difficult or unpleasant.

As with other natural resources, it is important that soils are used conservatively, so that the advantages we enjoy from them now can continue to be enjoyed in the future. To do this we need to understand them, to understand the flow of nutrients from soil to plants, and back to the soil or the sea in food chains and water flow. We need to understand the processes by which rocks alter to form soils, and how fast or how slowly the process occurs in different conditions. We need to understand the decay of plant materials in the soil, and how the products of decay help to make the soil a better place for plants to grow.

The chemistry of the constituents of soils, and of the processes by which changes occur, is not simple. Nevertheless we have learnt much about it, and can apply that knowledge to ensure that soils continue their important functions, and are not exploited so that they become infertile, nor used in such a way that the fertile topsoil is lost by erosion by wind or water.