Ebooks

Acervulus: A saucer-shaped, spore-producing body of a fungus embedded in host tissue. Actinomycetes Filamentous bacteria that produce several antibiotics and give soil its earthy smell. Active ingredient: In pesticides, the chemical responsible for the desired effect. Aggressiveness: Virulent forms of pathogen cause differing degrees of symptom severity. Alternate Host One of two kinds of plants on which a parasitic fungus must develop to complete its life cycle. Anamorph: Asexual stage of a fungus. Antagonism: The counteraction between organisms or groups of organisms. Antibiotic: A complex chemical substance produced by one microorganism that inhibits or kills other microorganisms. Antiseptic: A substance that prevents, retards, or destroys microorganisms. Apothecium: An open, cuplike, or saucer-shaped sexual fungal fruiting body containing asci. Asexual: Vegetative without sex organs, sex cells, or sexual spores, as the anamorph of a fungus.  Autoecious: The need of only one host for completing the life cycle of a rust.

Plant Pathology The term Plant Pathology is derived from greek words- pathos (suffering) + logos (study) i.e. the study of the suffering plant. Plant Pathology has two phases broadly- • Science- Understanding of the disease i.e. the theoretical consideration of the suffering plants and how do pathogens invade, how do plants defend themselves, what causes symptoms etc. • Art- The application of the science to the field problems i.e. Diagnosis and Control. Plant pathology or phytopathology is the branch of agricultural, botanical or biological science which deals with the cause, etiology, resulting in losses and management methods of plant diseases.  Plant pathology can also be defined as the study of the nature, cause and prevention of plant diseases. Plant pathology is related to most of the old and new sciences like biology, physics, chemistry, physiology, mathematics, genetics, soil science, biochemistry, biotechnology etc.

Disease Disease is one of those terms that are very difficult to define. It is realized that disease (literally dis-ease) implies lack of ‘comfort’and therefore, involves deviation from normal functioning. From time to time several definitions which have been proposed, in fact descriptive but not simultaneously exclusive. The definitions for the term disease are: • Disease is a malfunctioning process that is caused by continuous irritation, which results in some suffering producing symptoms. • Disease is an alteration in one or more of the ordered sequential series of physiological processes culminating in a loss of coordination of energy utilization in a plant as a result of the continuous irritation from    the presence or absence of some factor or agent. • Disease is any morphological or physiological abnormality in a plant or any of its parts caused by continuous irritation and results in economic losses to human beings. • Any deviation from normal growth or structure of plants that is sufficiently pronounced and permanent to produce visible symptoms or to impair quality and economic value. • A plant is said to be diseased when there is a harmful deviation from normal functioning of physiological process .

For the accurate identification and diagnosis of plant disease and plant problems a foundational knowledge of terms and definitions is vital for developing concepts, doing research, discussing and communicating issues and providing clarity to your work. The following terms and definitions are basic to the study of plant pathology. They are, however, just a brief introduction to the vocabulary of the science. If you have limited or no background in the subject and you are just getting started, the concepts and terminology of plant problems can seem somewhat daunting. However, your vocabulary and skill will develop through exposure to diagnostics, experience and correct use of the appropriate terms. Plant pathology (gr., path -“suffering”- “logy”, the science of) is the study of plant diseases and the abnormal conditions that constitute plant disorders. Etiology is the determination and study of the cause of disease. A pathogen can be living or non-living, but usually refers to a live agent. A pathogen is an organism which causes a disease. Pathological is a condition of being diseased. Pathogenic is having the characteristics of a pathogen and pathogenicity is the capability of a pathogen to cause a disease.

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, plant virology and plant disease control has been described in chronological order for easy and better understanding of the student in following sub-headings.  

Plant diseases are classified on the basis of type of pathogenic or nonpathogenic causes of the disease. The classification is based on the plant pathogenic organisms as follows. 1. Parasites They include both biotic and mesobiotic agents. The diseases are incited by parasites under a set of suitable environment. Association of definite pathogen is essential with each disease. i. Biotic agents: They are also called as animate causes. They are living organisms.Biotic agents include 1. Prokaryotes a. True bacteria or bacteria (Facultative parasites) e.g. Citrus canker. b. Rickettsia-like bacteria (RLB) e.g. Citrus greening, Pierce’s disease of grape. c. Mollicutes or wall-less prokaryotes i. Mycoplasma-like organism (MLO) e.g. Sesame phyllody, Egg plant little leaf. ii. Spiroplasma e.g. Corn stunt, Citrus stubborn.

There are thousands of diseases, which attack crop plants. Classification can be made based on several criteria. The various ways of classifying diseases of plants are given below. A. Based on type of infection 1. Localized disease: Affecting only a part of the plant; leaf spots and anthracnoses caused by different fungi. 2. Systemic disease: affecting the entire plant. B. Based on symptoms: Rusts smuts, wilts, blights, cankers, mildews, rots, damping-off, die-back, scab etc. C. Based on the host plant 1. On the basis of host e.g. Diseases of apple, diseases of wheat, diseases of rose, diseases of coconut, diseases of coffee, diseases of cotton. 2. On the basis of host group- e.g. cereal crop disease, pulse crop diseases, oilseed crop diseases, root crop disease, forage crop disease, plantation crop disease etc.

Parasitism The term parasitism refers to a parasite’s taking of food from its host. Without chlorophyll, fungi are unable to synthesis their own sources of food. Fungi are classified into three main biological groups according on the basis of mode of the nutrient uptake . Parasites, Saprophytes and Symbionts, The term saprophytes, or saprobes, refers to those fungi that feed on dead and decaying organic matter (Gr. sapros rotten + bios life). Some of them have evolved farther, but they are still unable to grow on other living things and can only exist as saprobes. We refer to them as obligate saprophytes(L. Obligare = to bind sapros) . On the other hand, some species live as saprophytes, but under certain circumstances, they can infect another living entity. We refer to them as facultative parasites (Greek parasitos + Latin facultas ability). Many fungus infect living hosts and deprive them of their food. They are called parasites (Greek: parasitos, which means to eat beside). Additionally, a few of them developed into facultative soprophytes (L. facultatas ability + Gr. sapros) after diverging as obligatory parasites (L. Obligar? to bind + Gr. parasitos table mate). Obligate parasites can only grow in culture on living media; in the wild, they can only feed on living protoplasm. On the other hand, facultative saprophytes are basically parasitic organisms but also capable of growing on dead organic matter under some conditions.

Most often, a plant gets diseased when it is harmed by an abiotic agents or attacked by a pathogen. As a result, in the first scenario, interaction and contact between the pathogen and the plant are required for the occurrence of a plant disease. No disease develops even though a pathogen and a plant come into contact if the weather is too extreme at the time of the pathogen’s contact with the plant and for a while afterwards. This could be because the plant is able to fend off the pathogen’s attack or because the pathogen is unable to attack at all. Therefore, it would appear that in order for disease to manifest, a third component—a set of environmental factors falling within a favorable range—must also exist. The degree of disease severity in both individual plants and plant populations is impacted by changes in any one of the three components, which can each show significant fluctuation. Plants can exhibit genetic uniformity over a wide area, be of a species or variety that may be more or less resistant to the pathogen, or they may be too young or too old for the pathogen to prefer. All of these factors can either accelerate or slow down the rate at which a particular pathogen causes disease. The way the three elements of disease interact has frequently been represented as a triangle (Fig. 2-1), which is commonly known as the “disease triangle.”

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. General Characteristics of Fungi 1. Thallus The body of the fungus is called as Thallus, which is without stem, root and leaves. It may be Plasmodial, Pseudoplasmodial , Pseudomycelial or Mycelial. A single thread like filament is called as hypha. A hypha is made up of a thin, transparent tabular wall filled or lined with a layer of protoplasm. A group of hypha constituting the body of fungus is called as mycelium may be septate or aseptate. i.e coenocytic. (a) Coenocytic or Nonseptate or Aseptate Mycelium: When mycelium is not divided by cross walls called as Coenocytic mycelium. Depending upon the nature of parasitism with the host plant, mycelium is either ecotophytic or endophytic. b) Septate Mycelium: When mycelium is divided by cross walls or septa called as septate mycelium.

Definition Bacteria belong to proakaryota 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. Structure of bacteria 1. A bacterial cell consists of a cell wall and a compound membrane enclosing protoplasm. 2. The protoplasm contains the nucleus, vacuoles, mesosomes, lipids, polysaccharides, mitochondric granules, and spores. 3. Bacterial cells may have flagella, pili, fimbrae, and capsules on the outside. 4. The bacterial cell contains a characteristics cell wall. The cell wall of bacteria is composed of a peptidoglycan. It is composed of acetyleglucosamine and cetyle-muramic acid . 5. The rigid peptidoglycan layer is located. 6. The latter layer is composed of lipoprotein . It is common in gram negative bacteria. 7. Many bacteria possess other intracellular membrane systems such as mesosomes and chondrioids. 8. The mesosome structure is formed by an invagination of the cytoplasmic membrane. 9. Mesosomes serve for compartmentalization and integration of biochemical systems.

Definition of Virus Viruses are very small (submicroscopic) infectious particles (virions) composed of a protein coat and a nucleic acid core. They carry genetic information encoded in their nucleic acid, which typically specifies two or more proteins. Translation of the genome (to produce proteins) or transcription and replication (to produce more nucleic acid) takes place within the host cell and uses some of the host’s biochemical “machinery”. Viruses do not capture or store free energy and are not functionally active outside their host. They are therefore parasites (and usually pathogens) but are not usually regarded as genuine microorganisms. Mathwas (1981) considers a virus as a set of one or more template molecules normally encased in a protective coat or coats of protein or lipoprotein, which is able to organize its own replication only within suitable host cells where its production is: i) Dependent on hosts protein synthesizing machinery (ribosomes). ii) Organised from pools of required material rather than binary fission and iii) Located at sites which are not separated from the host cell contents by a lipoprotein bilayer membrane.

Introduction The goal of plant disease management is to reduce the economic and aesthetic damage caused by plant diseases. Conventionally, this has been called plant disease control, but current social and environmental values believe “control” as being absolute and the term too rigid. More multifaceted approaches to disease management, and integrated disease management, have resulted from this shift in attitude, however. Single often severe measures such as pesticide applications, soil fumigation or burning are no longer in common use. Further, disease management measures are often determined by disease forecasting or disease modeling rather than on either a calendar or prescription basis. Disease management might be viewed as proactive whereas disease control is reactive, although it is often difficult to distinguish between the two concepts, especially in the application of specific measures. Plant disease management practices rely on anticipating occurrence of disease and attacking vulnerable points in the disease cycle (i.e., weak links in the infection chain). Therefore, correct diagnosis of a disease is necessary to identify the pathogen, which is the real target of any disease management program. A thorough understanding of the disease cycle, including climatic and other environmental factors that influence the cycle, and cultural requirements of the host plant, are essential to effective management of any disease.

Principles The principles involved in thermotherapy is that the pathogens present in seed material are inactivated or eliminated at temperatures nonlethal for the host tissues.The exact mechanism by which heat inactivates the pathogen is not fully understood. However, it is universally accepted that heat causes inactivation and not immobilization of the pathogen by heat. Th rate at which the pathogen is inactivated is determined by temperature, the higher the temperature, the faster is the inactivation. At constant temperature, the drop in the density of pathogenic inoculum. Methods Following physical methods are employed for reduction or elimination of primary inoculums that may be present in seed, soil, or planting material. i. Hot water treatment (HWT) Hot water treatment is widely used for the control of seed borne pathogens, especially bacteria and viruses. A list of various important diseases claimed to have been controlled by hot water treatment is given in Table-1.

Introduction. The Cultural practices which includes manipulation /or adjustment of crop production techniques have been as old as possibly agriculture itself. In early stages 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 diseases. By proper crop rotations they had been avoiding such diseases. As a matter of fact, in the present day agriculture, cultural practices are being considered as essential backup methods for plant disease management. Cultural practices often offer the opportunity to alter the environment, the condition of the host, and/or the behavior of the causal agent, to achieve economic management of disease. Most cultural practices used to control plant disease are preventive in nature. Integration of cultural practices, host resistance and pesticides or biocontrol agents may be necessary to provide options for controlling economically important plant diseases.

Managing plant diseases is necessary to preserve the quantity and quality of food, feed, and fiber that producers worldwide produce. To avoid, lessen, or manage plant diseases, several strategies may be employed. Aside from using effective horticultural and agronomic techniques, growers frequently largely depend on chemical pesticides and fertilizers. The remarkable increases in crop productivity and quality over the past 100 years have been largely attributed to such agricultural inputs. However, fear-mongering by certain opponents of pesticides and environmental degradation from excessive and improper use of agrochemicals have prompted significant shifts in public perceptions toward pesticide usage in agriculture. Political pressure is present to remove the most dangerous chemicals from the market, and there are stringent limits on the use of chemical pesticides today. Furthermore, because of the potential scale at which such applications could need to be made, the proliferation of plant diseases in natural ecosystems may make the successful application of pesticides impossible. As a result, several researchers studying pest management have concentrated on creating substitutes for artificial chemicals in the management of diseases and pests. Biological controls are one type of alternative among them.

Definition of Host Plant Resistance (HPR) 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. or Those heritable characteristics possessed by the plant which influence the ultimate degree of loss done by the disease. or The inherent ability of an organism (i.e., the crop plant) to resist or withstand the pathogen is called resistance Classification of Resistance Each plant species is affected by hundreds of kinds of pathogen. Frequently a single plant is attacked by hundreds of individuals of a pathogen. Yet, those plants survive which are resistant, adapting a number of mechanisms classified variously. 1. Based on existence a. Preformed When the resistance is already present in the plant even I the absence of the pathogen, it is known as preformed, axenic or passive

Plant Quarantine The term ‘Quarantine’ is derived from the Latin word quarantum, meaning 40. It refers to the 40 days period of detention of ships from countries with bubonic plague and cholera in the Middle Ages. The first such quarantine was imposed in Venice in 1374.Present quarantine laws now include plants. Plant quarantine , restrict entry of plants, plant products, soil, cultures of living organisms, packing materials, and commodities, as well as their containers and means of conveyance to protect agriculture and the environment from avoidable damage by hazardous organisms.They exclude dangerous organisms while permitting plants and plant products to enter. The term exclusion convey this objective more clearly than plant quarantine. Exclusion relates to keeping organisms out; plant quarantine relates to keeping plants out. In strict sense ‘Plant Quarantine’ refers to the holding of plants in isolation until they are believed to be healthy. Now, broader meaning of the plant quarantine covers all aspects of the regulation of the movement of living plants, living plant parts/plant products between politically defined territories or ecologically distinct parts of them. Intermediate quarantine and post entry quarantine are used respectively to denote the detention of plants in isolationfor inspection during or after arrival at their final destination.

Anti-pathogen Chemicals The chemical substances that help to retard the activity of pathogens like fungus, bacteria and nematodes are said to be anti-pathogen chemicals. Aim of use of chemicals in plant disease control The aim and of use of chemicals in plant disease control are • To create a toxic barrier between the host surface or tissue and the pathogen . • To eradicate the pathogen present at a particular site on the host, such as seed, foliage, roots etc. Functions of chemicals in plant disease control • Reduction in inoculum density or eradication of inoculum from source of growth, multiplication and survival. • Inactivaion or destruction of the pathogen when it lands on the treated surface, and • Cure of the diseased plant.

The overuse of chemical pesticides and farmers’ improper application of them have resulted in a number of issues, including residue in food, feed, and fodder; resistance developing; resurgence, secondary outbreaks; and, most importantly, pollution of the environment. This has caused a condition known as Pesticide Treadmill, which is characterized by the need to apply ever-increasing amounts of chemical pesticides. Integrated Pest/Management was developed as an environmentally sound substitute for the exclusive use of chemicals after Rachel Carson’s book “Silent Spring” in 1962 sparked widespread concern about the overuse of pesticides. The IDM Concept In disease management, every alternative control strategy—cultural, biological, mechanical, resistant varieties, physical, etc.—is applied in combination to keep the disease below the threshold of economic injury . In order to control the disease, pesticides are employed if it spreads and hits the economic threshold. With consideration for the agro-ecosystem, this approach to integrated disease management uses the minimum amount of pesticides possible. In reality, we don’t aim for complete control while managing diseases—rather, we let them progress below what is tolerable, such as the economic threshold. Additionally, it offers agents the chance to endure by controlling the diseases and maintaining a particular state of equilibrium. Therefore, the goal of the integrated disease management concept is to manage the disease using all available strategies while achieving positive effects on the environment, society, and economy.