eChapters

INTRODUCTION

Plant pathogens can spread rapidly over great distances, vectored by water, wind, insects, and humans. Across large regions and many crop species, it is estimated that diseases typically reduce plant yields by 10% every year in more developed nations or agricultural systems, but yield loss to diseases often exceeds 20% in less developed settings, an estimated 15% of global crop production.

Disease control is reasonably successful for most crops. Disease control is achieved by use of plants that have been bred for good resistance to many diseases, and by plant cultivation approaches such as crop rotation, pathogen- free seed, appropriate planting date and plant density, control of field moisture and pesticide use. However, the most attractive form of control is provided by disease resistance, for as long as it remains effective, it provides protection at no cost to the farmers or the community. So plant resistance is a highly useful strategy that can be applied in the control of diseases. It does not require any special action from growers and constitute cheap and practical input in the integrated disease management system. The use of resistant varieties cannot only ensure protection against diseases but also save the time, energy and money spent on other measures of control. In addition to these advantages, resistant varieties, if evolved, can be the only practical method of control of such diseases as viruses, phytoplasmas wilts, and rusts etc. in which chemical control is very expensive and impractical. In crops of low cash value, chemical and other methods of control are often too expensive to be applied. In such crops development of varieties resistant to important diseases can be an acceptable recommendation for the farmer.

Plant diseases need to be controlled to maintain the quality and abundance of food, feed, and fiber produced by growers around the world. Different approaches may be used to prevent, mitigate or control plant diseases. Beyond good agronomic and horticultural practices, growers often rely heavily on chemical fertilizers and pesticides. Such inputs to agriculture have contributed significantly to the spectacular improvements in crop productivity and quality over the past 100 years. However, the environmental pollution caused by excessive use and misuse of agrochemicals, as well as fear-mongering by some opponents of pesticides, has led to considerable changes in people’s attitudes towards the use of pesticides in agriculture. Today, there are strict regulations on chemical pesticide use, and there is political pressure to remove the most hazardous chemicals from the market. Additionally, the spread of plant diseases in natural ecosystems may preclude successful application of chemicals, because of the scale to which such applications might have to be applied. Consequently, some pest management researchers have focused their efforts on developing alternative inputs to synthetic chemicals for controlling pests and diseases. Among these alternatives are those referred to as biological controls.

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 sickness. By proper crop rotations they had been avoiding such sickness. 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

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. Thrate at which the pathogen is inactivated is determined by temperature, the higher the temperature, the faster is the inactivation.

INTRODUCTION

Plant diseases have caused severe losses to humans in several ways. Starvation and uprooting of families resulted from the Irish famine caused by potato late blight . A valued resource was lost with the virtual elimination of the American chestnut by chestnut blight. And direct economic loss such as the estimated one billion dollars lost in one year to American corn growers from southern corn leaf blight . Many plant diseases cause less dramatic losses annually throughout the world but collectively constitute sizable losses to farmers and can reduce the aesthetic values of landscape plants and home gardens.

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.

DEFINITION

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

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

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

CONCEPT

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

Elements of An Epidemic

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

Factors that affect the development of epidemics

INTRODUCTION

Variability in different organisms is common feature and is an important process for the continuity of life under stress conditions. Plant pathogens especially fungi, bacteria, virus and nematode show variations in their pathogenic potential (virulence) and physiological functions that support their survival and perpetuation in different environmental conditions. These variations may be largely due to genetic factors that may be conditioned by environmental factors. Various studies on genetic variability of microbial plant pathogens have shown that variations may occur in characters which affect their ability to infect host plants and also other characters that do not alter the pathogenic potential, but they may be concerned with their survival. Knowledge of variation in pathogenic characteristics is valuable in planning effective measures for disease management. In addition, development of resistant to fungicides has been a serious concern to growers, researchers as well as the administrators, since the decision to continue application or withdrawal of a fungicide can affect both the growers and industry.

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

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

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

a. Pre existing structural defense

b. Pre existing biochemical defense

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

a. Post infection structural defense

b. Post infection biochemical defense

Pathogens are different from parasites, Parasites penetrate into the host and obtain nutrients from the host. They live inside the host without causing any other damage. They may be at times symbionts also i.e. they may be beneficial to the host. The examples for parasites are Rhizobium spp. which form nodules in leguminous plants and mycorrhizal fungi. Pathogens not only take nutrients from the host but also damage the host severely. They induce numerous symptoms of the disease and even kill the plants.

Pathogens in their life cycle enter into two distinct phases. One is biotrophic and the other is necrotrophic phage. In the biotrophic phase they invade the host cells inter and intracellularly and establish themselves in the living cells. In the second phase, they kill the cells and obtain nutrition from the dying cells. This phase is called necrotrophic phase. In case of obligate pathogens the biotrophic phase may be much longer while in case of facultative saprophytes, long biotrophic phase may be followed by necrotrophic phase. In case of facultative parasites necrotrophic phase will be much longer with short biotrophic phase. However in case of all pathogens, both the phases may exist either as a short or long spell.

In the biotrophic phase the pathogens establish themselves in the host cells. The first barrier between host plant and the attacking pathogen is the cuticle. Host cells have cell wall, structure surrounding the protoplast. Cell wall is divided into three regions: middle lamella, primary wall and secondary wall. Below the cell wall membranes are found. The membrane provides a semi permeable barrier between the cell and its external environment. The membrane consists of lipids and proteins. During the biotrophic phase, the pathogen invade the cells by degrading cuticle, middle lamella,cell walls and cell membranes, by producing a series of enzymes.After the biotrophic phase, the pathogens produce toxins which kill the cell and enter into the necrotrophic phase. Thus, enzymes, toxins, growth regulators are important tools of the pathogens for their pathogenesis.

A parasitic must establish an intimate relationship with the host tissues to absorb the desired nutrients. Successful establishment of this relationship is called infection. The chain of events that takes place in the causation of disease is called pathogenesis or infection process. It encompasses the germination or multiplication of an infective propagule in or on a potential host through to the establishment of a parasitic relationship between the pathogen and the host. The process of infection is influenced by properties of the pathogen, the host and the external environment. If any of the stages of the infection process is inhibited by any of these factors, the pathogen will not cause disease in the host. While some parasites colonise the outside of the plant (ectoparasites), pathogens may also enter the host plant by penetration, through a natural opening (like a stomatal pore) or via a wound. The symptoms of the diseases produced by these pathogens result from the disruption of respiration, photosynthesis, translocation of nutrients, transpiration, and other aspects of growth and development. The “infection process”can be divided into three phases:

The availability of a plant pathogens in given area presupposes 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 insome intimate association withlivingplants or otherorganism.

Modes of Survival: The modes of survival of plant pathogens are described below:

1. Parasitic Survival

Organisms, parasitic on perennial plants (fruits, plantation and forest trees) survive in or on their hosts actively or passively depending on the environmental conditions. Certain bacterial pathogens viz, X. campestris pv citri, X. campestris pv jugalandis, X. campestris pv. Pruni and Erwinia amylovora are known to be carried over perennially in holdover cankers or blighted twigs, which may produce bacterial ooze in favourable weather to fresh inoculums. Similarly several fungal plant pathogens like Colletotrichum gloeosporioides (anthracnose of mango), Oidium mangiferae (powdery mildew of mango), Podosphaera leucotricha (powdery mildew of apple), etc survive on infected organs of the plants. Along with cultivated crops, several undesirable plant (weeds, etc) both annual and perennial, grow independently in the nature. Such plants which belong to the same botanical family to which cultivated hosts belong , are known as collateral hosts. Some important examples include the survival of three Puccinia spp. causing wheat rusts in Indian subcontinent . These fungi survive in active sporulating stage on wild species of Triticum, Aegilops, Horedeum and Agropyron repens. Similarly, Rice tungro virus survive actively on Oryza spp., Echinocloa spp. and Leersia hexandra .

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.

Plant pathogen dispersal generally occurs through two key groups:

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, where as, 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.

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.

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 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.

A plant disease is an abnormality in the structure and/or function of the host plant cells and/or tissue as a result of a continuous irritation caused by a pathogenic agent or an environmental factor. A disease is not static; it is a series of changes in the plant. All plants, to some extent, are subject to disease. Plant disease is the result of an infectious, or biotic agent or a noninfectious, abiotic factor. Plant injury is an abrupt alteration of form or function caused by a discontinuous irritant. Plant injury includes insect, animal, physical, chemical or environmental agents.

A causal agent is a general term used to describe an animate or inanimate factor which incites and governs disease and injury. A causal organism is a pathogen of biotic origin. When a pathogenic agent is virulent it can cause disease and if the agent is avirulent it is a variant of a pathogen that does not cause severe disease.

DEFINITION

Plant disease in which no pathogens or parasites is associated with the cause is known as Non-parasitic disease. They are also called as non-infectious or physiological disorders. When no pathogen is found, cultured from or transmitted from a diseased plant, then the disease is said to be caused by a non-living or environmental factor. These diseases occur because of disturbances in the plant system by the improper environmental conditions in the air or soil or by mechanical influences.

Fungi, nematodes, bacteria, and viruses are probably the first things that come to mind when thinking of plant pathogens. These organisms certainly do cause damage to plants of economic importance, but it may surprise you to know that 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.

INTRODUCTION

1. Nematodes belong to the animal kingdom, and phylum Nematoda.
2. The body of nematodes is elongate ( thread like; nema in Greek means thread) without any segment.
3. It is cylindrical, tapering at each end especially towards the tail.
4. Most of the important parasitic genera belong to the order Tylenchida and few under Dorylaimida.

VIROIDS

Defnition

Viroid is circular, encapsulated, low molecular weight (1.1-1.3x105), self replicating, highly infectious ssRNA molecules .

General Characters

1. The viroid exists in in vivo as unencapsulated RNA.
2. They never contain any protein coat (capsid).
3. Genome of the viriod naked, single stranded ( RNA) with 250-400 nucleotide, either linear or mostly circular. Viroids are smaller in size than viruses i.e 50 nm or 1.1 to 1.3 X 103 molecular weight.
4. Despite its small size, the infectious RNA is replicated autonomously in susceptible cells; that is, no helper virus is required for multiplication.
5. The infectious RNA consists of one molecular species only.
6. Viroids are notable to synthesize protein and replicase enzyme required for replication.
7. Viroids replicate by direct RNA, copying in which all components required for viroid multiplication including RNA polymerase are provided by the host.
8. They cause diseases only in plants.
9. Viroids concentration and translocation is higher in growing parts of the plants (up to 0.2 mm from the apex)
10. Most of the types of symptoms observed with viral diseases also occurs viroids like epinasty, leaf distortions, vein clearing, localized chlorotic or necrotic spots, mottling of leaves, necrosis of leaves, and death of the whole plants.

PHYTOPLASMA OR MYCOPLASMA

Definition

Phytoplasmas are unicellular, ultramicroscopic, walless, prokaryotic, self- replicating, highly pleomorphic, filterable organisms or entities.

Mycoplasma lack rigid cell wall, being surrounded only by single triple unit membrane which allows them to be highly plemorphic. They assume vast array of shapes and size. They require sterols (Lipoproteins) for growth. Mycoplasma cannot be grown on artificial media and they reproduce by budding and binary fissions.

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:

1. Dependent on hosts protein synthesizing machinery (ribosomes).
2. Organised from pools of required material rather than binary fission and
3. Located at sites which are not separated from the host cell contents by a lipoprotein bilayer membrane.

Bos (1983) defines virus as an infectious agent often causing disease, invisible with the light microscope (Sub-microscopic), small enough to pass through a bacterial filter, lacking a metabolism of its own and depending on a living host cell for multiplication. Viruses are small packages of host alien genetic information of one type. (RNA or DNA), either in one strand or in a few segment. Encapsulated together or separately and enclosed in a coat of one or more types of protein, some time with an extra coat (envelope) and some other constituents.

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.

Structure of Bacteria

1. A bacterial cell consists of a cellwall and a compound membrane enclosing protoplasm.
2. Inside the protoplasm, nucleus, vacuoles, mesosomes, polysaccharides, lipids, mitochondric granules and spores are found.
3. Externally bacterial cells may show capsules, pili, fimbrae and flagella.
4. The bacterial cell contains a characteristics cell wall.
5. The cell wall of bacteria is composed of a peptidoglycan. It is composed of acetyle-glucosamine and cetyle-muramic acid.
6. The rigid peptidoglycan layer is located between the cytoplasmic membrane and an outer multiple tract layer.
7. The latter layer is composed of lipoprotein . It is common in gram negative bacteria.
8. Many bacteria possess other intracellular membrane systems such as mesosomes and chondrioids.
9. The mesosome structure is formed by an invagination of the cytoplasmic membrane.

PROKARYOTES

Prokaryotic organisms are that in which nucleus is primitive type and nuclear material is not enclosed within the nuclear membrane.

Bacteria are placed in the kingdom “Prokaryotae” because of the prokaryotic cellular organization of the members. However, extremely diverse groups of microorganisms differing in morphological, physiological and ecological properties are found within this kingdom. In the beginning, description and information of bacterial systematics or classification was being published in the comprehensive volumes of “Bergey’s Manual of Determinative Bacteriology” (1923, first edition). The 9th edition of Bergey’s Manual, published in 1984 was the last of such comprehensive manual and from 1984 onwards it was renamed as “Bergey’s Manual of Systematic Bacteriology”. It is the most widely accepted and used reference document or book for classification and identification of bacteria. In the 9th edition, the kingdom Prokaryota (Monera) is divided into 4 divisons based on nature of the cell wall.These are : Gracilicultes; Firmicutes; Tenericutes and Mendosicutes .

GENERAL CHARACTERS

• Deuteromycotina includes the fungi in which the ‘perfect stage’(zygote, ascus, basidium) is either lacking or has not been discovered so far. Because of the apparent absence of any perfect stage or sexual phase, these fungi are commonly called ‘imperfect fungi’ or technically ‘Fungi imperfecti’.
• The characteristic feature of Deuteromycotina is the absence of sexual reproduction. The members reproduce only be asexual methods, and that too also chiefly by conidia, which develop on conidiophores.
• The conidia are produced either directly on the conidiophores or in some special types of fruiting bodies such as synnemata, acervuli, sporodochia or pycnidia.
• Fungi possess branched, septate and multinucleate mycelium except the unicellular yeast like members of Blastomycetes.
• Sexual reproduction is completely absent.
• Parasexuality is shown by some Deuteromycotina. Under this phenomenon, the process of plasmogamy, karyogamy and haplodization take place, but not at specified time or specified points in the life cycle of the fungus.

GENERAL CHARACTERS

• The members are terrestrial, and saprophytic or parasitic.
• The mycelium is well developed, branched and septate. The mycelium is of primary, secondary and tertiary type.
• Dolipore septum is present except rusts and smuts.
• Clamp connections present.
• Cell wall consists of chitin and glucans.
• Basidiomycetes reproduce asexually by conidia, arthrospores, oidia, fragmentation or budding.
• No specialized sex organs develop in Basidiomycetes.
• Plasmogamy takes place by somatogamy or spermatization.
• Sexual spores are basidiospores.
• They are exogenously produced on basidium.
• Usually four basidiospores are develop on basidium.
  The Basidiomycotina includes rusts, smuts, mushrooms, jelly fungi, puffballs, shelf fungi, toadstools, bird’s nest fungi, bracket fungi and earth stars.

GENERAL CHARACTERS

• Ascomycotina includes only such fungi in which the zygospores are absent and the perfect state spores are the ascospores.
• The Ascomycetes and Basidiomycetes are sometimes combindly called ‘higher fungi’.
• Cell wall is made up of chitin.
• Mycelium is well developed branched and septate.
• Asexual spores are non-motile conidia.
• Sexual spores are ascospores.
• Ascospores are usually 8 in an ascus.
• They are produced endogenously inside the ascus.
• The asci are usually grouped to form a definite type of multicellular fruiting body called ascocarp.
• The ascocarps are either cup or saucer shaped ( apothecium), flask shaped (perithecium), or closed, spherical and indehiscent (cleistothecium).
• The characteristic ascospores are present in sac- like body, called ascus and therefore these fungi are also commonly called ‘sac fungi’
• Yeast is single celled organism.

GENERAL CHARACTERS

• The majority of the members are saprobic. A few Zygomycetes are weak parasites, attacking plants and animals.
• Most Zygomycetes produce a well developed and branched mycelium, consisting of coenocytic hyphae.
• Cell wall is mainly composed of chitin.
• Motile cells or zoospores are absent.
• Asexual reproduction takes place by non motile sporangiospores called aplanospores.
• Sexual reproduction takes place by gametangial fusion.
• Gametangial fusion results in the production of a thick walled resting spore, called zygospore.

GENERAL CHARACTERS

• The Mastigomycotina includes all eumycota fungi which produce flagellated cells during their life cycle.
• Majority of them are with filamentous hyaline coenocytic mycelium.
• Cell wall contains cellulose.
• They show centric nuclear divison.
• The mode of nutrition is typically absorptive, because a majority of mastigomycotina contains some or other type of haustoria.
• They produce asexual spores called zoospores.
• Oospore is the sexual spores.
• Members of the class oomycetes are mostly aquatic but some are facultative or obligate parasites of vascular plants.

Taxonomy

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

Nomenclature

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

Systematics

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

GENERAL CHARACTERISTICS OF FUNGI

1. Thallus

The body of the fungus is called as Thallus, which is without stem root and leaves. It maybe 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 Cornocytic 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.

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.

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:

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.

DEFINITION

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.

Study of plant pathology includes the study of sciences viz, microbiology, bacteriology, virology, mycology, nematology, protozology, phycology, unfavorable environmental factors, nutritional deficiencies and flowering plant parasites.

Plants make up the majority of the earth’s living environment as trees, grass, flowers, etc. Plants are the only higher organisms that can convert the energy of sunlight into stored, usable chemical energy in carbohydrates, proteins and fats. Directly or indirectly, plants make up all the food on which humans and all animals depend. Plants however also gets sick, grow and exhibit various types of symptoms and sometimes whole plant die. It is not known whether diseased plant feel pain or discomfort. If a plant is looking different from its community then it is equal to be disease one. Any biotic or abiotic agents which induce the disease in plant is referred as the cause of diseases.The causative agents of disease in plants are pathogenic such as fungi, bacteria, viruses, protozoa and nematodes and environmental conditions such as lack or excess of nutrients, moisture, light, etc to presence of toxic chemicals in air or soil. These biotic constraints can, at times, seriously compromise food security, For example, potato late blight, caused by Phytophthora infestans, struck Europe like ‘a bolt from the blue’ in the 1840s. In Ireland, about a million people died of starvation and more than a million attempted to emigrate. The reasons for this calamity were the arrival in Europe of a virulent strain of the pathogen, the high dependence of much of the Irish population on potato for sustenance, the lack of resistance in the plant to the pathogen, and weather conditions favorable to epidemic development. There have been other disasters caused by plant diseases such as the Great Bengal Famine of 1943 and the southern corn blight epidemic of 1970-71 in the USA, to name but two. In the former, an estimated 2 million people died owing to the high dependence of most of the population on a single crop, rice, which was attacked by the fungus Cochliobolus miyabeanus. In the USA, by contrast, although in some genus, Cochlobolus heterostrophus, alternative sources of nutrition were plentiful so no one died, although the effect on the agricultural economy was severe.

The first two of these heartbreaking examples demonstrate with brutal clarity that in areas of the world where a large proportion of the population is dependent on a single crop or a few crops, they are at risk should that crop fail owing to one or more devastating diseases. At the present time, the threat is partially great in developing countries, where populations are growing fastest, poverty is endemic , the population depends upon on locally produced staples, and the infrastructure of extension and R&D is often poorly resourced. The losses due to weeds, disease and insects have been estimated to around 40% in the developing and underdeveloped countries. If the post harvest losses (15-20%) are also added , the situation becomes even more alarming.

The transition from conventional to organic farming requires numerous changes. One of the biggest changes is in the mindset of the farmer. Conventional approaches often involve the use of quick-fix remedies that, unfortunately, rarely address the cause of the problem. Transitioning farmers generally spend too much time worrying about replacing synthetic input with allowable organic product instead of considering management practices based on preventative strategies. Here are a few steps new entrants should follow when making the transition to organic farming:

20.1. Understand the Basics of Organic Agriculture and the Organic Farming Standards

Since organic production systems are knowledge based, new entrants and transitional producers must become familiar with sound and sustainable agricultural practices. Transitional producers should be prepared to read appropriate information, conduct their own trials and participate in formal and informal training events. As mentioned, switching from conventional to organic farming is more than substituting synthetic materials to organic allowed materials. Organic farming is a holistic system that relies on sound practices focused on preventative strategies. Since there are often few organic remedies available to organic producers for certain problems, prevention is the key element in organic production.

In food production remarkable progress has been made in the last fifty years in agricultural production and self – sufficiency (Food security) has been reached. Yet nutritional security seems to be a distant goal. With depleting natural resources and increasing threat to the environment, sustainable crop production is attracting the attention of the scientists, farmers and administrators. Due to over exploitation of natural resources and indiscriminate use of agro chemicals, green revolution also brought in quite a lot of miseries which focus the urgent need to have EVERGREEN REVOLUTION that is sustainable, leading to food and nutritional security to the rural poor. At this juncture it will be more appropriate to practicing organic agriculrure through the integration of traditional wisdom and modern scientific knowledge in synergy with nature.

19.1. Eco-friendly Technologies for Rice Cultivation

A sound package of eco-friendly technologies to grow rice is being successfully adopted by a few progressive farmers in Puliangudi village in Tirunelveli district of Tamil Nadu. “The technologies work well with indigenous rice varieties such as Kitchili Samba. The cost of cultivation is substantially reduced and the organic rice fetches a premium price in the market,” says Mr. P. Gomathinayagam, a pioneer in organic farming in Puliangudi.

In India, there are two accreditation systems for authorizing Certification and Inspection agencies for organic certification. National Programme on organic Production (NPOP) promoted by Ministry of Commerce is the core programme which governs and defines the standards and implementing procedures. National Accreditation Body (NAB) is the apex decision making body. Certification and Inspection agencies accredited by NAB are authorized to undertake certification process. The NPOP notified under FTDR act and controlled by Agricultural Processed Foods Export Development Authority (APEDA) looks after the requirement of export while NPOP notified under APGMC act and controlled by Agriculture Marketing Advisor, Directorate of Marketing and Inspection looks after domestic certification. Currently 20 certification agencies have been authorized to undertake certification process.

National Programme on Organic Production

National Program on Organic Production (NPOP) was launched during 2001 under the Foreign Trade & Development Act (FTDR Act). The document provides information on standards for organic production, systems criteria, and procedures for accreditation of Inspection and Certification bodies, the national organic logo and the regulations governing its use.

Realizing that nematodes cannot be eliminated, and that we must live with them, the overall goal is to keep the population density as low as possible. The economic threshold is the density of nematodes where the losses incurred exceed the cost of nematode management. It is not advisable to depend on a single method to control nematodes. Efficient management requires judicious and careful integration of several which will result in reduction of nematode populations. Important components of non chemical methods of nematode management program are considered in this chapter.

17.1. Organic Amendments

Manure and fertilizer applications are essential part of growing any crop. Besides supplying required essential nutrients theyhelp in many ways directly or indirectly by suppressing harmful organisms including phytonematodes. The use of organic amendments against nematodes was demonstrated by Linford et al., in as early as 1938. FYM and cattle urine have found to reduce nematode population. Biogas plant waste slurry was found to be effective for nematode management. Compost of water hyacinth, oilcakes, cellulose amendments like sawdust, wheat straw, rice husk, rice hull ash, green manuring with legumes, green leaf incorporation are useful to keep nematode populations low. Non - edible oilcakes like those of neem, karanj, mahua, caster, cotton as well as edible oilcakes groundnut, mustard sesame, coconut have been recommended at 2 - 2.5 t/ha for reduction of root knot and other nematode population in soil. Miscellaneous substances like decaffeinated tea waste, rice hull ash, chicken manure, tannery and food and fruit processing waste, market and domestic organic refuse, dead vegetation and crop stalks, wood shaving, etc. have been recommended for root knot nematode management. Castor leaves (40g/kg) along with NPK at 75:25:37.5 kg/ha achieved reduction of M. javanica population on tomato.

Paddy is cultivated about 45 m ha in India, less than 1% is under organic cultivation.

16.1. Varieties

Good quality fine varieties like Ponni, Super ponni, insect and disease resistant varities must be selected for getting higher yield and returns.

16.2. Seeds

Organically produced seeds only must be used.

16.3. Seed Treatment

For 1 kg of seeds 20 g Azospirillum, Pseudomonas and 10 g Phospobacteria must be used with rice gruel.

Panchagavya spray @ 1% for treating the seeds.

15.1. IFS Components Tested for Wetlands

Area Allocation;

In 1 ha of land

75 % - Cropping

10 % - Fodder cultivation

3 % - Goat shed

12 % - Fish pond

Possible Integrations:

14.1. Water Source Identification

• In places where Ficus religiosa tree is found, underground water will be more.
• Underground water will be more in places where the neem tree with more knots is found.
• In places where termite hills are found, underground water will be more.
• Farmers are practicing traditional method of using neem stick, metals etc. for finding the water resource in underground for digging wells. While they are walking with this stick on hand it will be rottate automatically at the place where underground water is surplus.
• Some farmers are using the magnetic stones for identifying water sources. Magnet is tied with a thread and held like a pendulum while walking over the fields. The magnet will rotate automatically at the place where underground water is more and this is taken as the indication for digging wells.

13 1. Rishi Krishi

Drawn from Vedas, the Rishi Krishi method of natural farming has been mastered by farmers of Maharashtra and Madhya Pradesh. In this method, all on-farm sources of nutrients including composts, cattle dung manure, green leaf manure and crop biomass for mulching are exploited to their best potential with continuous soil enrichment through the use of Rishi Krishi formulation known as “Amritpani” and virgin soil. 15 kg of virgin rhizosperic soil collected from beneath of Banyan tree (Ficus bengalensis) is spread over one acre and the soil is enriched with 200 lit Amritpani.

It is prepared by mixing 250 g ghee into 10 kg of cow dung followed by 500 g honey and diluted with 200 lit of water. This formulation is utilized for seed treatment (beej sanskar), enrichment of soil (bhumi sanskar) and foliar spray on plants (padap sanskar). For soil treatment it needs to be applied through irrigation water as fertigation. The system has been demonstrated on a wide range of crops i.e. fruits, vegetables, cereals, pulses, oilseeds, sugarcane and cotton.

12.1. General Practices for Storage

• Lime juice is mixed with grains and then sun dried before storage to prevent insect pests (Farmers in Nigeria).
• Seeds are safely stored in earthern pots after mixing with the leaves of neem and Vitex negundo (Farmers in Gujarat, India).
• Drying seeds and grains of all the crops on the new moon day before storing to avoid pest attack.
• Store seed materials in earthen pots which are kept on the ‘Paran’ directly above the furnace in kitchen. The smoke acts as a repellent.
• Grains, trees etc. harvested on full moon day are raqre prone to storage pest attack.
• Mixing the dried leaves of neem with seeds while storing them.

Change in weather affects growth and development of plants. The extent of these effects depends upon the range or severity of change of weather. It is very much possible to change the weather in relatively small area to reap better harvest. Micro weather modification is defined as, “The manipulation of weather elements at increasing or decreasing the duration, intensity, quality etc., for desired effects at microlevel of crop under investigation”.

The climate near the ground can be managed partly by influencing the moisture status and temperature of the upper soil layers, e.g. by mulching and partly by action above the ground e.g. by shading or use of wind breaks.

Soil regeneration is about bulding or making topsoil. It is a particular form of ecological regeneration within the field of restoration ecology is the act/idea of replenishingthe top soil with beneficial nutrients casing natural methods. Time required from inorganic to organic would be about 60 to 200 days depending upon the situation. Once the inorganic fertilization is stopped, following actions facilitate quick conversion:

• Apply Farm yard/Poultry manure available in the farm as a basal dressing.
• Sow 25 kg of multi varietal seeds (MVS) in one acre.
• Allow it to grow up to 60 days.
• Inoculate the soil with the bio-agents like Azospirillum, Phosphobacterium, Pseudomonas flouresens, Trichoderma viride on 30 days after sowing (DAS).
• Incorporate in situ 60 DAS (30 t ha^-1 biomass is generated on 60 DAS) green manures.

9.1. ITKS for Seed Treatment and Sowing

• Yield of almost all the crops depends on seed quality.
• Even if it is a quality seed, it should be a dried one because well dried seeds will have higher longevity and keeping quality.
• It better to change the seeds at least once in two years.
• To maintain the seed viability and prevent it from outside damage, the outer shell is not separated.
• The seeds are generally stored along with the leaves of neem (Azadirachta indica), pungam (Pongamia pinnata), notchi (Vitex negundo) and thumbai (Leucas aspera).
• Six weeks nursery period is enough for six months duration of the crop.
• Shallow sowing is followed in dry lands.
• Severing the broadcasted seeds in dry lands with soil.
• Dragging, over the fields, the thorny branches with weight over them for covering seeds the sown on dry lands.
• It is better to start planting from ‘Sani moolai’ (north east) of the field to get higher yields.
• It is better to perform sowing and planting operations during evening hours.

8.1. Documented ITKs on Moisture Conservation

The ITKs were documented under following specific categories

• Agronomic Measures
• Tillage
• Bunding & Terracing (Mech. & Vegetative barrier)
• Land Configuration
• Soil Amendment / Mulching
• Erosion Control & Runoff Diversion Structures
• Water Harvesting, Seepage Control & Ground Water Recharge

7.1. Rice

• Treatment of paddy seeds in diluted bio gas slurry for 12 hours increases resistance of seedlings to pests and diseases.
• During panicle formation in paddy, the flowers of Cycas circinalis are placed on sticks in paddy fields @ 4/ac. Its unpleasant odor repels ear head bugs.
• About 30 kg of tamarind seeds are applied for an acre of paddy field 1 day after transplanting to boost up the crop growth and yield.
• Soaking the paddy seeds in diluted cow’s urine before sowing, considerably reduces the incidence of leaf spot and rice blast
• Presoaking of paddy seeds in milk increases its resistance against ‘tungro’ virus and ‘stunt’ virus
• For control of red leaf spot disease in paddy, the seeds are soaked in ‘Pudina’ leaf extract (Mentha sativa) for 24 hours
• ‘T’ shaped bamboo stands are placed in many places in the paddy fields so that birds can sit on them and feed on the larvae and adults of rice pests.
• Sowing on eighteenth day (Aadipperukku) of Tamil month Aadi (Jul-Aug.) ensures good harvest.
• Daincha (Sesbania spp.) seeds are sown on paddy main fields when paddy nursery is raised and the grown up daincha is ploughed in-situ during field preparation.
• Plough the main field for four to six times for better yield.

Indigenous Technical Knowledge (ITK) based inputs (Most of the ITK’s needs scientific validation before large scale adoption)

Is the systematic body of knowledge acquired by local people through the accumulation of experiences, informal experiments, and intimate understanding of the environment in a given culture (Rajasekaran, 1993). Learning from ITK can improve understanding of local condition and provide a productive context for activities designed to help the communities. In addition, the use of ITK’s assures that the end user of specific agricultural development projects are involved in developing technologies appropriate to their needs’. Yet, ITK is still an underutilized resource in the development activities. It needs to be intensively and extensively studied, and incorporated into formal research and extension practices to make agriculture and rural development strategies more sustainable.

Many of our indigenous practices in agriculture and allied fields have been replaced by the so-called modern technologies and they have become obsolete, especially among the younger generations. Now these indigenous practices are endangered ones and these are a possibility for them to become extinct particularly during this era of globalization, liberalization and commercialization. Now the need has come to re-examine and then gradually re-introduce the effective traditional technologies of crop production.

Therefore, there is a need to systematically document the ITK as they are the unwritten body of knowledge. There is no systematic record to describe what is, what it does, how it does, means of changing it, its operations, it boundaries and its applications. It is held in different brains, languages and skills in as many groups, cultures and environments. Tamil Nadu is also a treasure land of indigenous practices in agriculture. However, only a few attempts have been undertaken by social scientists to document the available indigenous agricultural practices but none has evaluated scientifically. The documented ITK practices are given below.