eChapters

Although thousands of plant species exist on the earth, only those that were found to be useful for humans as food, feed, fiber, timber and other utility materials have been selected for domestication. When these plant species were affected by various biotic and abiotic causes, the necessity arose to determine the ways and means of protecting the valuable plants species and to understand the host plant defense mechanisms and pathogenic potential of the microbial pathogens causing enormous losses to the cultivators. All plant species have built-in resistance to most microbial plant pathogens existing in the environment. Susceptibility of plants to some of them is an exception, since they are endowed with genes which effectively nullify the possible adverse conditions created by the microorganism. Likewise, microbial pathogens possess genes for survival and pathogenicity to survive in the absence of susceptible plant species and to successfully establish infection in suitable plant species. The microbial pathogens have evolved highly specialized tactics to overcome the defense responses and to rapidly multiply in plants for their survival and perpetuation in a geographic location / ecosystem

Plants are exposed to microbial pathogens at all growth stages from seeds to harvested produce. But they are resistant to numerous pathogens that are present in the environment and susceptible only to some of them. In other words, a plant species has built-in resistance mechanism to avoid or resist the invasion by many microbial pathogens. A pathogen may reach several plant species, but it can infect only a few plant species in the particular location or region. The process of pathogenesis or disease development is initiated when the pathogen reaches the plant surface that allows the initiation of infection. An organism is able to derive its nutrition from the susceptible host plant and becomes pathogenic. The physiological functions of such infected plants deviate from those of the healthy (normal) plants and suffer irreversibly to different magnitudes. The organism adversely affecting the plant growth and other functions to obtain nutrition is the pathogen. It develops rapidly or slowly in proportion to the levels of susceptibility / resistance of the host plant to the pathogen species concerned. Thus a plant species may be susceptible to some pathogens, while remains resistant / immune to other organisms that may be pathogenic to some other plant species. Depletion of compounds from the plants to meet the nutritional requirement of the pathogen leads to different kinds of external symptoms and internal changes due to derangement of normal metabolic functions of the host plant. The process of disease development in a susceptible host plant species is known as pathogenesis.

Detection and identification of the causes and diagnosis of the diseases rapidly and precisely are the basic requirements for developing effective crop disease management systems suitable for different ecosystems. Incorrect diagnosis leads to failure to contain the disease spread and consequent additional expenditure to the growers. Hence, it is essential that proper diagnostic procedures are followed to achieve the goal of reducing both quantitative and qualitative losses of agricultural and horticultural produce. Morphological, biological, biochemical, physiological, immunological and genomic characteristics of microbial plant pathogens have been carefully considered to develop rapid, sensitive and reliable methods of detection and identification of cause(s) of newly observed disease (s) in the locations concerned. Various methods of establishing the nature of microbial plant pathogens are discussed in detail in earlier publications

Occurrence of various diseases affecting agricultural and horticultural crop is known for several centuries. However, critical examination of crop diseases to understand the nature of the causative agents and extent of losses induced by diseases and development of effective disease management systems were possible much later. Any deviation from normal form and function of plants is considered as ‘disease’. Both pathogenic (biotic) and physiogenic (abiotic) causes are involved in diseases of plants. Adverse environmental conditions such as extremes of temperature, light and oxygen, soil moisture, pH and polluted air may alter the physiological conditions of the plants. Nutritional deficiencies also affect various crops leading to considerable losses. Microbial plant pathogens–fungus-like oomycetes, fungi, bacteria, phytoplasmas, viruses and viroids–form the major group of biotic agents that induce different diseases of crop plants in the field as well as during transport and storage (Narayanasamy 2002,2006). Presentation of information in this book is confined to various aspects of the microbial plant pathogens and the diseases caused by them.

Microbial pathogens may induce symptoms that may be visible externally and also in the deep-seated internal tissues which have to be examined using light or electron microscope. In the case of some diseases, the symptoms may be localized in different plant parts such as roots, leaves, stems, floral parts or seeds / fruits / vegetables. Such infections are known as local infection. On the other hand, the pathogen may spread from the point of entry into the host to other plant parts which exhibit characteristic symptoms. These diseases are termed as systemic diseases. In some cases, no recognizable visible symptom is produced although the pathogen is able to develop without inconveniencing the host plant species which are called as carriers and the infection is designated latent infection. Plant viruses are carried symptomlessly by many weed plant species which may serve as sources of infection for crop plants.

Human beings, considered to be the highly evolved living organisms, have been making consistent and constant efforts to lead comfortable life without much concern for the conservation of nature and adversities to other living and nonliving entities existing in the universe. To meet the requirements of food, feed, fibre, timber and other needs, the plants that could supply the above were selected and domesticated. When the useful plant species were cultivated over large areas repeatedly year after year, the problems afflicting plants that were not recognized earlier as constraints for crop cultivation, assumed monstrous proportions wiping out entire crops and ruining the livelihood of the people of that geographical location/country. World history is replete with numerous instances of huge crop losses caused by microbial plant pathogens resulting in malnutrition, hunger and death. Migration of millions of people to other countries for their survival, became unavoidable. Such historical evidences threatening the existence of humans necessitated to investigate the causes of destructive diseases like late blight and heliminthosporiose diseases affecting respectively potato and rice, the staple food of the largest populations of the world. In order to take appropriate measures for minimizing losses due to crop diseases and to mitigate the sufferings of man and the animals, application of various short- and long-term disease management strategies has become indispensable for the profitable cultivation of crops

Marketing is one of the most important factors in determining the success of any vegetable farming enterprise. Marketing includes all the operations and decisions taken by the producers. These decisions range from determining the most marketable crops for production to deciding how to best deliver quality produce to the consumers at a profit. However, contrary to popular belief, marketing does not begin after a crop is produced. Instead, marketing alternatives need to be considered even before the start of production.

However, vegetable marketing in India has not yet been organised so far. The long route from the grower to the retailer and ultimately to the consumer involves a chain of middlemen, transport contractors and wholesale merchants. Very often, there arises stagnation of the produce in the peak season or in the year of good production. The large number of intermediaries in the vegetable marketing channel grab maximum share of the consumer’s price and as a result, the producers’ profit becomes marginal. Vegetable cultivation is a capital intensive venture, and huge production alone cannot fetch profit for the growers. Organised marketing, storage and transport facilities are the key factors for making vegetable farming profitable which ultimatily boost vegetable cultivation.

Quality Components of the Produce

Various components of quality are used to evaluate the products in relation to specific grades and standards and responses to various environmental factors and post-harvest treatments. The relative importance of each factor depends upon the commodity and its intended use, fresh or processed. The main quality components of vegetables are mentioned below

Cropping system is defined as the cropping pattern followed on a farm and its interactions with farm resources, other farm enterprises and production technology. The yearly sequence and spatial arrangement of crops and fallow on a given area is termed as cropping pattern.

India has over 17% of world’s population living on 2.4% of the world’s geographical area. Per capita agricultural land has reduced by 67% from 0.48 ha in 1951 to 0.16 ha in 2008 due to explosive increase in population. In this situation, it is very difficult to get horizontal expansion in vegetable cultivation. Hence, total production per unit area can be increased by increasing the productivity per unit area through (a) growing improved high yielding varieties and hybrids, (b) adequate and scientific crop management practices and (c) increasing cropping intensities following different cropping patterns.

Potato

Potato, Solanum tuberosum L. under the family Solanaceae (Chromosome No. 2n = 4x = 48) is the most important non-grain food crop in the world, ranking 3rd in terms of total production with over 381 million tonnes per year in (FAOSTAT, 2017), after rice and wheat. It is grown in 150 countries spread across both temperate and tropical regions and at elevations from sea level to 4,000 m. It is extensively cultivated in China, Russian Federation, Ukarine, Poland, Ireland, Great Britain, Germany, Netherlands, France, Spain, South America, India and USA. Potato was brought from Peru to Spain by the Spaniards in 1565 when it was widely grown in Spain and Italy. They were probably brought to England in 1586 by Sir Francis Drake. Potato was introduced in India in early 17^th century probably by the Portuguese. Now it is one of the principal cash crops of India.

The crop

The subsection Potato is distinguished from all other subsections within the genus Solanum by “true potatoes whose tubers are borne on underground stolons, which are true stems, not roots”. The series tuberosa is characterised by “imparipinnate or simple leaves, forked peduncle, rotate to pentagonal corolla and round berries”.

The species S.tuberosum is characterised by “pedicel articulation placed in the middle third, short calyx lobes arranged regularly, leaves often slightly arched, leaflets always ovate to lanceolate, about twice as long as broad, tubers with well marked dormancy period”

Potato is an annual herbaceous plant and growth habit varies between and within species. The plant has a rosette or semi-rosette habit. The stem is erect in the early stage but becomes spreading and prostrate later on. The leaves are compound and alternate, irregularly odd pinnate. The tuber is an enlarged portion of an underground stem or stolon. Tuber eyes are the buds from which next season’s growth will emerge. Eyes are concentrated near the apical end of the tuber, with fewer near the stolon or basal end. Eye number and distribution are characteristic of the variety.

Potato is mainly propagated vegetatively by means of tubers and sometimes by botanical seeds, i.e., true potato seeds. Potato has a terminal inflorescence consisting of 1-30 (but usually 7-15) flowers, depending on the cultivar. The five petals give the open flower a star shape. A flower also has a pistil that generally protrudes above a cluster of five large, bright yellow anthers. The corolla colour varies from white to complex range of blue, red and purple. Flowers are self-pollinated but also cross pollination take place by insect. Seeds are produced in the fruit which is botanically called berry. Potato fruits, stems and leaves contain glycoalkaloids, the toxic compounds, of which the most prevalent are solanine and chaconine.

Protected cultivation can be defined as a cropping technique wherein the micro-climate surrounding the plant is controlled partially or fully as per the requirement of the plant species during their growth period. This cropping technique is the most modern approach to grow different horticultural crops mainly, vegetable crops and flowers for enhancement of both productivity and product quality. This technology has spread extensively the world over in the last few decades. This technology involves the cultivation of different crops particularly, horticultural crops in a controlled environment wherein the environmental parameters like the temperature, humidity, light, soil, water, plant nutrition, etc. are manipulated for enhancement of production as well as product quality even during off-season which ensures additional return to the growers.

Green revolution technologies such as greater use of synthetic agrochemicals like fertilizers and pesticides, adoption of nutrient-responsive, high-yielding varieties of crops, greater exploitation of irrigation potentials etc. has boosted the production output in most cases. However, continuous use of these high energy inputs indiscriminately now leads to decline in production and productivity of various crops as well as deterioration of soil health and environments.

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