eChapters

Introduction

Plant growth in agricultural soils is inf luenced by a myriad of abiotic and biotic factors. As a routine practice growers normally use physical and chemical approaches to manage the soil environment to improve crop yields while the application of microbial products for this purpose is less common. An exception to this is the use of rhizobial inoculants for legumes to ensure efficient nitrogen fixation; a practice that has been occurring in North America for over 100 years (Smith, 1997). The region around the root, the rhizosphere, is relatively rich in nutrients, in expense of as much as 40% of plant photosynthates from the roots (Lynch and Whipps, 1991). Consequently, the rhizosphere supports large and active microbial populations capable of exerting beneficial, neutral, or detrimental effects on plant growth. The importance of rhizosphere microbial populations for maintenance of root health, nutrient uptake, and tolerance of environmental stress is now recognized (Bowen and Rovira, 1999; Cook, 2002). These beneficial microorganisms can be a significant component of management practices to achieve the attainable yield for in other words a crop yield limited only by the natural physical environment of the crop and its innate genetic potential (Cook, 2002).

The prospect of manipulating crop rhizosphere microbial populations by inoculation of beneficial bacteria to increase plant growth has shown considerable promise in laboratory and greenhouse studies however, responses have been variable in the field (Bowen and Rovira, 1999). The potential environmental benefits of this approach, leading to a reduction in the use of agricultural chemicals are fitting the sustainable management practices. Realizing the biological interactions occurring in the rhizosphere, recent progress are in need to fulfill the practical requirements of inoculant formulation and timely delivery which would increase the technology’s reliability in the field and facilitate its commercial development.

Plant Growth Promoting Rhizobacteria (PGPR) are root-colonizing bacteria that form symbiotic relationships with many plants. The name comes from the Greek rhiza, meaning root. Though parasitic varieties of rhizobacteria exist, the term usually refers to bacteria that form a relationship beneficial for both parties (mutualism). They are an important group of microorganisms used in biofertilizer. Biofertilization accounts for about 65% of the nitrogen supply to crops worldwide. The term PGPRs was first used by W. Kloepper in the late 1970s and has become commonly used in scientific literatures. PGPRs have different relationships with different species of host plants. The two major classes of relationships are rhizospheric and endophytic. Rhizospheric relationships consist of the PGPRs that colonize the surface of the root, or superficial intercellular spaces of the host plant, often forming root nodules. Endophytic relationships involve the PGPRs residing and growing within the host plant in the apoplastic space.Some common examples of PGPR genera exhibiting plant growth promoting activity are: Pseudomonas, Azospirillum, Azotobacter, Bacillus, Burkholdaria, Enterobacter, Rhizobium, Erwinia, Mycobacterium, Mesorhizobium, Flavobacterium, etc.An ideal PGPR should possess high rhizosphere competence, enhance plant growth capabilities, have a broad spectrum of action, be safe for the environment, be compatible with other rhizobacteria, and be tolerant to heat, UV radiation, and oxidizing agent.

Abstract

The greatest challenge facing us in the coming years is to produce adequate amounts of basic necessities of food, feed, fibre, fuel and raw materials for the rapidly shrinking per capita agricultural land. One alternative is to make a sustainable use of existing marginal lands. In many regions of the tropics and sub-tropics, the need to use marginal low-input soils with usually inadequate nutrient(s) supply permits only very low or unreliable yields to be achieved. It is frequently not possible  to supply required amounts of mineral fertilizers or chemical pesticides because of the low purchasing power of the marginal farmers. In particular, it is not possible to compensate for the deficient nutrient supply and this constitutes a yield limiting factor. The role of soil microorganisms in sustainable productivity has been well construed. In recent years, root inhabiting (rhizozosphere) bacteria (rhizobacteria) is gaining importance.

Introduction

Lithosphere, including the earth’s crust, is helpful in providing the base or medium for sustenance of most life processes and forms, interwoven in fine network interdependencies within themselves and the environment surrounding them i.e. ecosystems. Terrestrial ecosystem contains an important dynamic living matrix termed soil, which is critical for agricultural production and food security. Soil forms the medium for growth and maintenance of a variety of plant species while the plant roots in the soil represent a four dimensional region in space and time of profuse activity relative to the bulk soil, revolving around pH, nutrient, redox potential, and exudate gradients changing as distance from the root increases (Marschner, 1995). The soil region adhering the plant roots is being strongly influenced by the presence of these roots and is characterized by high rates of microbial population and activity and referred as rhizosphere (the soil adhering to plant roots).

Unlike root-free soil, the rhizosphere around growing plants is a very dynamic environment that hosts a much higher number of microbes, in particular bacteria. Microbes interact with each other and with plants in symbiotic, associative, neutral or antagonistic ways. A plant colonized or penetrated by a microorganism can either result in asymptomatic or disease or form an association or symbiosis, depending on the cells’ perception of each other and how the environment affects that interaction. Microbes that penetrate and colonize plants have developed elaborate strategies to subvert plant defenses.

INTRODUCTION

Biological control involves the suppression of pests/organisms with other organisms.  It is an eco-friendly method for management of plant pathogens which can be done exploiting the fungi (Ampelomyces, Trichoderma, Coniothyrium, Candida etc.) or bacteria (Agrobacterium, Bacillus, Pseudomonas and Streptomyces) from rhizosphere,  as well as phylloplane and endophytes (Jayaraman and Verma, 2002). The rhizosphere microfloras are predominantly composed of gram negative pseudomonads.  The fluorescent pseudomonads constitute a large proportion of the rhizosphere microflora presumably due to their nutritional variability being able to use a large number of organic substances (Stolp and Gadkari, 1981). However earlier workers used fluorescent pseudomonads extensively they now prefer Bacillus sp. due to their spore forming ability and heat tolerance which make its formulation easier.

The rhizosphere is the narrow zone of soil surrounding the root that is under the immediate influence of the root system. This zone is rich in nutrients when compared with the bulk soil, due to the accumulation of a variety of organic compounds released from roots by exudation, secretion and deposition. Organic compounds released by plant roots include amino acids, fatty acids, nucleotides, organic acids, phenolics, plant growth regulators, putrescine, sterols, sugars and vitamins. Because these organic compounds can be used as carbon and energy source by microorganisms, microbial growth and activity is particularly intense in the rhizosphere.

Abstract

Rhizobia are soil bacteria that fix atmospheric dinitrogen after establishing symbiotic relationship inside the root nodules of legumes (Fabaceae). Plant Growth Promoting Rhizobacteria are the group of bacteria which thrive in the rhizosphere region and enhance the plant growth through direct & indirect mechanisms. Pulses are being inoculated with specific rhizobial strains to have better nodulation in India. The native rhizobial strains from the root nodules of legumes from different agroclimatic zones of Odisha was isolated, characterised and screened for PGP activities. Out of all eleven isolates showed similar characteristics with the family Rhizobiacae. Among them six isolates contained nif-gene and PGPR activity (B2, B4, B5, B6, B7 and B8) were applied to seeds, that helped in faster germination and better elongation of root and shoot. The observations were statistically significant.

Any substance or mixture of substances intended through physiological action, for accelerating or retarding the rate of growth or maturation, or otherwise altering the behaviour of plants or the produce thereof are known as plant growth regulators. It does not include plant nutrients, trace elements, nutritional chemicals, plant inoculants and soil amendments.

Plant hormones are organic compounds other than nutrients, synthesize by plants and regulate plant growth and development. They are active in very low concentrations, produced in certain parts of the plants and are usually transported to other parts where they elicit specific biochemical, physiological and morphological responses. They are also active in tissues where they are produced. The term plant growth regulator is usually used to denote a synthetic plant hormone, but most of the synthetic compounds with structures similar to those of the natural hormones have also been called hormones. For instance, the synthetic cytokinin, kinetin is considered a hormone.

Introduction

Plant growth regulators are defined as small, simple chemicals produced naturally by plants to regulate their growth and development and are essential for regulating their own growth. They act by controlling or modifying plant growth processes, such as formation of leaves and flowers and elongation of stems.

In modern forest nursery raising, the benefits of extending the use of plant hormones to regulate the growth of economically important plants have been established. There are two possible goals in inducing trees to form floral buds, in particular, female buds. The first is to achieve precocity. Precocious flowering in normally immature trees can provide advantages in breeding and seed production because it overcomes a substantial seed production delay intrinsic to late-maturing conifers. The second reason is the phase change from juvenile growth to mature growth. The induction of either precocity or increased male flower and female cone formation are generally the result of applied treatments. A few studies have focused on the intrinsic physiological differences between high and low producing clones.

Plant growth regulators are organic substances other than nutrient, which is required in minute quantity to modify the plant growth processes. PGR has very important role in fruit breeding which is used in every facet of crop improvement e.g. multiplication of hybrids/selection through asexual means or by micro propagation, breaking of seed dormancy, growth control, regulation of flowering, fruiting and induction of sterility in reproductive organs etc (Dhatt, 1985). Details of the various uses of plant growth regulators are given as under.

Growth

Growth means quantitative increase in the planwt body e.g., increases in the length of stem, roots, number of leaves, fresh and dry weight of fruits etc.

Development

It refers to the qualitative changes from the initiation of growth to the death of a plant or plant parts like seed germination, formation of flowers, fruits and seeds, emergence of buds, leaves and falling of leaves and fruits.

Plant hormone is an organic compound synthesized in one part of the plant body and translocated to another part where in very low concentration it causes a physiological response. However, this definition could not demarcate the vitamins and other growth influencing substances from hormones. For this reason, the term Phytohormone was introduced with included vitamins, growth hormones and flowering hormones. Phytohormone can be defined as an organic substance produced naturally in higher plants, controlling growth or other physiological functions at a site remote from its place of synthesis and active in minute amounts, whereas, an organic substance, which promotes growth, i.e., irreversible increase in height or volume, when applied in low concentration to the shoots of plant is known as growth hormone.

The plant hormones are naturally occurring as they are synthesized by the plant. On the other hand, there are several manufactured chemicals, which often resemble the hormones in physiological action and molecular structures, are called growth regulators. Generally, there are five classes of phytohormones.

The phytohormones universally present in all plants are classified as under:

Plant hormones (phytohormones) are chemicals that regulate plant growth and are termed as ‘plant growth substances’. Plant hormones are signal molecules produced within the plant, and are present in extremely low concentrations. Hormones regulate cellular processes in targeted cells. Hormones also determine the formation of flowers, stems, leaves, the shedding of leaves, and the development and ripening of fruit. Every cell is capable of producing hormones in plants. They shape the plant, affecting seed growth, time of flowering, the sex of flowers, senescence of leaves, and fruits. Plant hormones affect gene expression and transcription levels, cellular division, and growth.They direct which tissues grow upward and which grow downwards. Hormones are vital to plant growth. Hence, they are also known as growth factors or growth regulators.

The quantitative increase in plant body such as increase in the length of stem and root, the number of leaves etc., is referred to as plant growth whereas, the qualitative changes such as germination of seed, formation of leaves, flowers and fruits, falling of leaves and fruits is referred as development. Utilization of these substances for proper development of the plant is regulated by certain chemical messengers called plant growth substances or plant growth regulators, which in minute amounts increase or decrease or modifies the physiological process in plants. Plant growth substances are the chemical other than nutrient which required in very small amount but without which plant can not complete their physiology.

The two sets of internal factors, viz., nutrition and hormone control the growth and development of the plant. The raw material required for growth is supplied by nutritional factors which include the minerals, organic substances the protein, carbohydrates, etc.

Plant hormones and growth regulators are compounds that influence flowering, aging, root growth, prevention or promotion of stem elongation, prevention of leaf emergence and/or leaf fall and many other physiological processes. These substances produce major growth changes at a very low concentration.

Hormones are endogenously produced substances in plants while plant growth regulators may be synthetic compounds (i.e. IBA and Cycocel) that mimic naturally occurring plant hormones or they may be natural hormones that are extracted from plant tissue (e.g. IAA).

These growth regulating substances, most often, are applied as a spray to foliage or as a liquid drench to soil around a plant’s base. Generally, their effects are short-lived and they may need to be re-applied in order to achieve the desired effect.

Plant growth regulating substances are normally classified into five groups viz.: (i) Auxins, (ii) Gibberellins; (iii) Cytokinins; (iv) Ethylene; and (v) Abscisic acid.

For the most part, each group contains both naturally occurring hormones as well as synthetic substances. Physiological functions of each and every group of growth regulating substances are given below in brief:

Plant growth

Definition: The quantitative increase in plant body such as increase in the length of stem and root, the number of leaves etc., is referred to as plant growth.

Plant development

Definition: The qualitative changes such as germination of seed, formation of leaves, flowers and fruits, falling of leaves and fruits is referred as developement.

Phytohormones

Definition: These are the organic substance or hormones produced by plants which in low concentrations regulate plant physiological process. It is synthesized in one part of plant and translocated to other parts. These are endogenous substance means naturally occurring in the plant.

The quantitative increase in plant body such as increase in the length of stem and root, the number of leaves etc., is referred to as plant growth whereas, the qualitative changes such as germination of seed, formation of leaves, flowers and fruits, falling of leaves and fruits is referred as development. Utilization of these substances for proper development of the plant is regulated by certain chemical messengers called plant growth substances or plant growth regulators, which in minute amounts increase or decrease or modifies the physiological process in plants. Plant growth substances are the chemical other than nutrient which required in very small amount but without which plant can not complete their physiology.

The two sets of internal factors, viz., nutrition and hormone control the growth and development of the plant. The raw material required for growth is supplied by nutritional factors which include the minerals, organic substances the protein, carbohydrates, etc.

Phytohormones: These are the hormones produced by plants which in low concentrations regulate plant physiological process. These usually move within the plants from a site of production to a site of action.

Plant growth regulators: These are organic compounds other than nutrients, which in small amounts promote, inhibit or otherwise modify any physiological process in plant.

It may be defined as any organic compounds which are active at low concentrations (1-10 ml) in promoting, inhibiting or modifying growth and development in plants. The naturally occurring (endogenous) growth substances are commonly known as plant hormones, while the synthetic ones are called growth regulators.

Plant hormones: It is an organic compound synthesized in one part of plant and translocated to other parts, wherein very low concentration causes a physiological response.

The plant hormones are identified as promoters (auxins, gibberellin, and cytokinins), inhibitors (abscisic acid and ethylene) and other hypothetical growth substances (Florigen, death hormone, etc.).

Plant growth regulators are defined as chemicals other than nutrients and vitamins which regulate (or) modify the physiological process ofthe plant. A plant hormones or phytohormones are chemical substances which are naturally produced by plant in specific organs and are translocated from site of synthesis to the site of action. They bring about specific physiological response, even in very low concentration. The quantity of synthesis of these hormones differ from plant to plant, plant internal and external factors. They are readily absorbed and these chemicals move rapidly through the tissues when applied to different parts of the plant. A plant growth hormone may be termed as a plant growth regulator, but not vice - versa, since other than natural plant hormones, plant growth regulators are synthetically manufactured chemicals.

Plant growth regulators have a diverse chemical composition. Based on the general response the chemical mediates in the plant system, they are classified as growthpromoters and growth inhibitors/retardants. However, a particular growth regulator may be growth promoter at a lower concentration and growth inhibitor at higher concentration.

Plant growth regulators or phytohormones are organic substances produced naturally in higher plants, controlling growth or other physiological functions at a site remote from its place of production and active in minute amounts. Thimmann in1948 proposed the term Phytohormone as these hormones are synthesized in plants (Thimmann, 1963).

1. Introduction

In the field of sustainable agriculture our main aim to produce high quality, safe and affordable food for ever-increasing worldwide population. Today, global agriculture is at crossroads and this is the consequence of climatic change, increased population pressure and detrimental environmental impacts. Furthermore, agricultural growers and producers have the additional constraints of economic profitability and sustainability. During the last couple of decades excessive amounts of chemicals are used to improve plant health, productivity and for management of plant pathogens, which has disturbed the ecological balance of soil and has led to the depletion of nutrients. Therefore, there has been ever-increasing interest to develop new mechanisms to ensure food security through sustainable crop production system that will supply adequate nutrition without harming the agroecosystem. Plant growth in agricultural soil is influenced by many abiotic and biotic factors. There is a thin layer of soil immediately surrounding plant roots that is an extremely important and active area for root activity and metabolism which is known as rhizosphere.

Failure in timely diagnosis of diseases and other pests has often been responsible for devastating losses. Reducing crop losses by keeping pests at bay is crucial to food security. Plant clinic is an innovative paradigm which plays a vital role in assuring food security and ushering prosperity by providing timely diagnosis and rendering necessary advice to the growers, gardeners and other stakeholders for managing pest problem in India. Plant clinics are all about plant health. Though the major role of plant clinic lies in diagnostics and advisory, the activities of plant clinic extend beyond plant clinic, with emphasis on extension, working more closely with farmers and organizations involved in promoting food production. The role of plant clinics beyond diagnostics and advisory. These are:

The term “plant health” has two overlapping meanings. In the more specific meaning, plant health refers to plant quarantine, while in the less specific use, it covers all areas of plant protection, such as plant pest management, plant quarantine, and pesticide regulation and application.

Thiamann (1948) designated the plant hormones by the term ‘phytohormones’ in order to distinguish them from animal hormones. He defined a phytohormone as “an organic compound produced naturally in higher plants, controlling growth or other phy-siological functions at a site remote from its place of production and active in minute amounts.”

According to Johannes van Over-beek (1950), the plant hormones are defined as “organic compounds which regulate plant physiological process – regardless of whether these compounds are naturally occurring and/or synthetic; simulating and/or inhibitory; local activators or substances which act at a distance from the place where they are formed.”

When crops are grown in either intercropping or sequential cropping interaction between different component crops occurs which is essentially a response of one species to the environment as modified by the presence of another species is commonly referred to as interference or interaction.

The interaction are classified into three groups

1. Competitive interaction: One species may have greater ability to use the limiting factor and will gain at the expense of the other and this is called competitive interaction or when one or more growth factors are limiting, the species that is better equipped to use the limiting factor(s) will gain at the expense of the other and this is called competitive interaction.
2. Non competitive: If the crops are grown in association and the growth of either of the concerned species is not affected, such type of interaction is called non competitive interaction or if resources (growth factors) are present in adequate quantities, as a result of which, the growth of either of the concerned species is not affected, then it is non-competitive interaction or interference.
3. Complementary: If one species is able to help the other, it is known as complementary interaction or if the component species are able to exploit growth factors in different ways (temporal or spatial) or if one species is able to help the other in supply of factor (like legumes supplying part of N fixed by symbiosis to non-legumes), it is complementary interaction or interference and also referred to as Annidation.

16.1 Introduction

Plant introduction is the process of introducing plants from their growing locality to a new locality. Introduction of plants from a foreign country is called foreign introduction or exotic collection. Introduction from one state to another within a country is called indigenous collection or indigenous introduction. With introduction, the process of acclimatization is associated. Acclimatization is the adaptation or adjustment of an individual plant or population of plants under the changed climate for a number of generations. Plant introduction is an oldest method of plant breeding. It is used in self-pollinated, cross-pollinated and asexually propagated crops. The material of seed-propagated crops is introduced in the form of seed and that of vegetatively propagated crops in the form of cuttings or propagules. The introduced material may be a new crop, a wild relative or a new cultivar of a crop already grown in the area. There are five important sources of plant collection, namely, (1) centres of diversity, (2) gene banks, (3) gene sanctuaries, (4) seed companies, and (5) farmers’ fields.

Plant mineral nutrition is a sub branch of plant physiology which addresses issues on uptake of elements that plant needs to absorb from air or water or soil to grow and to live. Besides function of nutrient elements in plants, it also includes deficiency symptoms and how to address deficiency symptoms in a plant. Plant mineral nutrition and mechanism of uptake has two major aspects:

Plants are responsible for highly useful molecular reactions. All the enzymatic  reactions  that  occur in the cell are  termed  as metabolic reactions.  They  take place within organisms in an orderly and regulated way.  They  are  the  metabolic pathways and the compounds  resulting from the process, namely,  metabolism are called  the metabolites. Metabolism in Greek means change. It is the set of life sustaining chemical transformations within the cells of living organisms. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to the environments around them.
 
Metabolism is a highly organized,   coordinated and purposeful enzymatic activity inside a cell. Metabolism has four functions: 1. To obtain energy from the environment, 2. To convert molecules into building blocks, 3. To convert the building blocks into proteins, lipids, sugars, nucleic acids and other cell components and 4. To synthesize and degrade organic molecules for specific needs of the cell.

Introduction

Plants are considered as immobile organisms with poor sensitivity and limited ability to respond. Within the plant kingdom, Mimosa pudica (also called the sensitive plant), Drosera (sundews), Dionea muscipula (flytraps) and tendrils of climbing plants which showed rapid and purposeful movements were considered as exceptions. These sensitive plants attracted attention of outstanding pioneer researchers like Pfeffer (1845-1920), Burdon-Sanderson (1828-1905), Darwin (1809-1882), Haberlandt (1854-1945) and Bose (1858-1937). Stahlberg, 2006 reported the presence of various mechanoreceptors in such species which could trigger action potentials (APs) which activated these sudden movements.

The first extracellular recording of a plant action potential (AP) development was initiated by Charles Darwin; later, the animal physiologist Burdon-Sanderson in 1873 performed similar studies on leaves of the Venus flytrap (Dionea muscipula Ellis). Haberlandt (1884) demonstrated that phloem strands were the actual paths for excitation by destroying the external, non-woody part of vascular bundles. This notion was confirmed in Mimosa and other plant species by a number of recent studies. Houwink (1935) carried out experiments with two species of Vitis (grape) and obtained electrical fluctuations which was similar and comparable with the action potentials he obtained with Mimosa. In 1907, Bose, used a D’arsonval galvanometer to demonstrate propagating electrical effects in different genera of plants such as Ficus, Artocarpus, Cucurbita, Corchorus, “fern” etc. APs have their largest amplitude in phloem sieve cells and cells adjacent to this area (Sibaoka, 1969). Other studies found that AP-like signals are propagated with equal rate and amplitude throughout the cells of vascular bundles.

The essential plant nutrients, or essential elements, are listed in the Table 41. It enumerates 16 chemical elements of which the essentiality for plant growth and reproduction has been established according to the criteria formulated by D.I. Arnon and P.R. Stout, 1939. This listing has existed since 1954 with chlorine as the latest addition (cited by Hopkins 1999).

These plant nutrients are classified into various groups:

1.    Major elements and trace elements : Of the 16 listed, 9 are major elements or macronutrients and 7 are trace elements or micronutrients. Major elements are those which are needed by plants for their growth and reproduction in relatively large amounts while trace elements are needed in smaller amounts compared to the former. The major elements are further sub classified into structural elements (carbon, oxygen and hydrogen), primary macronutrients (nitrogen, phosphorus and potassium), and secondary macronutrients (calcium, sulfur, and magnesium). Micronutrients are Zn, Cu, Mn, Fe, Mo4 and boron (Table 41).

Plant nutrient disorders result from nutrient imbalances in soils. Nutrients are considered essential for plants, when it satisfies the following criteria (Arnon and Stout,1939):
    1.    The deficiency of the nutrient element makes it impossible for the plant to complete its life cycle
    2.    The deficiency of the element is specific and can be corrected only by supply of that element
    3.    The element is directly involved in the nutrition of the plant

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.

7.1. Introduction

Like all other living organisms such as humans, animals, and microorganisms, plants also need elemental nutrients for their growth and development. They assemble the nutrients from soil, water and air. However, to obtain economical crop yield, nutrients are also supplied to the crops from external sources such as chemical fertilizers and manures and using biofertilizers. It is the present-day need to handle the soil fertility status in a more realistic and careful way to obtain maximum crop harvest. Under poor management practices, soil may become infertile and loose its importance in agricultural use. In modern days, huge food demand for the burgeoning human population does not permit to show luxury to use only fertile soil. Moderately fertile soil or even degraded soil should also be managed properly so that they may be used to grow crops. For this, plant nutrients status of the soil plays a significant role along with other soil properties. For sustainable soil fertility management, parameters such as crop to be raised, its nutrient demand at various growth stages, current nutrient status of the soil, amount of nutrient application based on the soil testing results etc are important to be considered. Balanced nutrition to the plants is the prerequisite to obtain maximum benefit. If nutrients supplied to the plants are low in quantity than their requirement, crop production is lowered down. Similarly, if the nutrients are provided in more amount in the soil or unbalanced way through fertilizer or manure applications, total crop yield is suffered. It is a very common example that excess of phosphorus leads to zinc deficiency in most crop plants and it has been observed that excess N is responsible for potassium starvation in potato. Again, excess of iron, manganese, zinc, copper shows plant toxicity. Addition of nutrients to soils in excess also causes environmental pollution when the excess nutrients are lost from soil by leaching, surface run-off and volatilization. Unscientific way of soil fertilization leads to increasing cost of cultivation and imparts adverse effect to the environment instead of doing any good. Therefore, one should have a clear knowledge on soil fertility to obtain a sustainable productivity.

Sixteen chemical elements are known to be important to a plant’s growth and survival. The sixteen chemical elements are divided into two main groups: non-mineral and mineral.  The Non-Mineral Nutrients are hydrogen (H), oxygen (O), and carbon (C). These nutrients are found in the air and water.
  
In a process called photosynthesis, plants use energy from the sun to change carbon dioxide (CO₂ - carbon and oxygen) and water (H₂O- hydrogen and oxygen) into starches and sugars. These starches and sugars are the plant’s food. Since plants get carbon, hydrogen, and oxygen from the air and water, there is little the farmers and gardeners can do to control  how much of these nutrients a plant can use.

Involved in plant metabolic functions and the plant cannot complete its life cycle without the element.

7.1. Plant nutrient concentration and plant growth

1. Deficient

Lowest concentration of an essential element that limit yield severely and cause distinct deficiency symptoms.

In the realm of natural elements, there exist approximately one hundred and three distinct elements. Among them, nearly ninety elements are absorbed by plants. To differentiate essential elements from those that plants can assimilate but are not vital, Arnon (1954) established the following criteria:

1. The plant must be incapable of normal growth or completing its life cycle in the absence of the element

2. The element is specific and irreplaceable by another

3. The element directly participates in plant metabolism

By applying these criteria, molybdenum and chlorine are not deemed essential, even though they serve a functional role in plant metabolism. This is because they can be substituted by vanadium and halides, respectively. Subsequently, D. J. Nicholas refined the definition of essential elements, replacing the term “functional or metabolic nutrient” to encompass any mineral element that contributes to plant metabolism, regardless of whether its action is specific.

Plant nutrition is the study of the chemical elements and compounds that are necessary for plant growth, and also of their external supply and internal metabolism. The criteria for an element to be essential for plant growth:

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

That the element is part of some essential plant constituent or metabolite.

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.

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.

Prologue: The Issues

Farmers lose a significant portion of their income when their crops and products become infested with various insects, diseases and weeds, resulting in much lower crop productivity and lower actual yields than the attainable yield of crops. Yield losses due to pests, pathogens and weeds are responsible for 20-40% losses in global agricultural productivity. India reports crop losses of 20-25% annually due to pest infestations. Without the use of crop protection solutions, there could be a 78% loss in fruit production, 54% loss in vegetable production and 32% loss in cereal production. According to the Ministry of Agriculture, India loses INR 1.48 billion worth of agricultural production annually due to pests, weeds and plant diseases.

1. ………… is the father of plant pathology.

   a) T J Burril

   c) Anton De Barry

   b) Needham

   d) E J Butler

2. ……… first time reported that plant diseases are caused by bacterium.

   a) Robert Koch

   c) Kuhn

   b) E F Smith

   d) T J Burril

Important Points to be Remember

• Father of Indian plant pathology – E.J.Butler
• Father of Plant virology – Beijerinck
• Wheat rust is associated with Indian scientist – K.C.Mehta
• Kresek phase of rice is due to – Bacterial leaf blight
• Bakanae disease of rice is also known as – Foot rot and Foolish seedling disease

Plant physiology is a sub-discipline of botany concerned with the functioning, or physiology of plants. Closely related fields include plant morphology (structure of plants), plant ecology (interactions with the environment), phytochemistry (biochemistry of plants), cell biology, genetic, biophysics and molecular biology. Fundamental processes such as photosynthesis, respiration, plant nutrition, plant hormone functions, tropism, nastic movements, photoperiodism, photo-morphogenesis, circadian rhythms, environmental stress physiology, seed germination, dormancy, stomata function and transpiration, both parts of plant water relations, are studied by plant physiologists. The field of plant physiology includes the study of all the internal activities of plants those chemical and physical processes associated with life as they occur in plants. This includes study at many levels of scale of size and time. At the smallest scale are molecular interactions of photosynthesis and internal diffusion of water, minerals, and nutrients. Major sub disciplines of plant physiology include phytochemistry (the study of the biochemistry of plants) and phytopathology (the study of disease in plants). The scope of plant physiology as a discipline may be divided into several major areas of research.

Basic LabTechniques - This laboratory is intended to:

(1) Provide an introduction to basic techniques used in biology labs

(2) provide some experience with the equipment employed in future labs

2.1 Microscopy

The compound light microscope is a veryimportant tool in the study of biology. Typical compound light microscopes allow specimens to be viewed at 400 to 1000 times their actual size (total magnification is determined by multiplying the objective lens magnification by the ocularlens magnification). Thelight microscopeis made up of a system of lenses aligned in such a way thatallows magnification, as well as improved resolution. The resolution obtainable is also dependent on contrastin the specimen. Contrast can be adjusted with the iris diaphragm, located below the condenser lens,and can also be enhanced by the addition of stains to the specimen.

Scientific drawings of specimens observed under the light microscope are often used to provide a record of what was viewed. Proper scientific drawings should be neatly drawn,with smooth lines, in pencil (they should never be in colour). More than one cellshould be drawn to illustrate the cellularassociation to the observer(e.g.found singly or as part of a tissue). Labels should be added using straight horizontal lines to the right side of the drawing, and care should be taken with singular and plural forms of structural terminology. To demonstrate differences in density of specific structures, use stippling rather than shading. A figure caption thatindicates the specimen viewed, how viewed, and the to right side of the drawing, and care should be taken with singular and plural forms of structural terminology. To demonstratedifferences in densityof specific structures, use stippling rather than shading. Afigure caption thatindicatesthe specimen viewed, how viewed, and the magnification of the drawing is always necessary.

Significance in Agriculture

The Green Revolution resulted in many fold increase in the food grain production. Crop yields have increased steadily over time, but continuing these increases above the current high levels would be difficult. But in order to meet the demands of the increasing population, the crop production must increase in a sustainable manner. Sustainable increase in the total production without increasing cultivated area represents a huge challenge that can only be met by integrative investigations at the whole plant-plant community level. Improvement of crop production systems will require a thorough understanding of basic principles of yield production. This involves the study of the plant processes responsible for the growth, development and production of economic yield by crop plants, focusing on whole plants and plant communities and not individual plant parts, organs, or cells because most of the processes that control yield operate at the whole plant-plant community level.

The processes responsible for the primary productivity of crop communities are photosynthesis, respiration, transpiration, nutrient utilization and how the products of these processes are converted to economic yield and morphogenetic processes.

Crop physiology is the study of plants at the whole-plant and plant-community level of organization and Agronomy is the study of crops and cropping systems at the farm level over a period of time. At this level of organization, the complexity of the system is so large that comprehensive attempts are to be made to examine the mechanisms underlying the crop responses to management or climate.

The scientific approach to agriculture has been to isolate (i.e., the experiments in which everything else is equal except the studied phenomenon) and to reduce (i.e., the process by which, a phenomenon is quantified in terms of one or more essential molecular processes), because the production system is too complex. Whereas the unraveling of crop production systems to simple chemical and physical phenomena has improved our general understanding of the system, it is necessary to understand how these chemical and physically processes interact within a whole plant grown from seed to maturity under natural conditions for this information to be useful in agronomy.

1. A man supplied excess fertilizer and water the grass well. After sometime the leaves turn brown because

   a) Due to water logging

   b) It decreases photosynthesis

   c) Fertilizer is drained in lower layer of soil

   d) Osmosis occurs in root and root dies

2. If roots of plant are removed and plant is placed in water, then what will be happen?

   a) Passive absorption will continue

   b) Imbibition will continue

   c) Active absorption will continue

   d) None of these

Plant pigments impart colour to the different components like leaves, flowers, fruits etc. They in turn are responsible for the colour of raw food, we eat. Pigments like chlorophyll, anthocyanins, flavonoids, tannins, xanthones etc. are the different pigments that are present in plants. The primary function of pigments in plants is photosynthesis, which uses the green pigment chlorophyll along with several red and yellow pigments that help to capture as much light energy as possible. Chlorophyll is green in colour. Carotenoids like a, b, and g, carotenoids are yellow in colour. Lycopene is red in colour. Flavones and falvonols are also yellow in colour. Anthocyanins are purple and magenta in colour. Other functions of pigments in plants include attracting insects to flowers to encourage pollination. The assay of pigments is mostly based on their native colour.