eChapters

Introduction

Drought is one of the primary factors responsible for depressing rice yield in chronic areas and in destabilising rice production in drought-prone areas. It is a production constraint common to all rainfed rice cultures: wetland, upland, and deepwater (O’Toole and Chang 1979). Breeding for drought resistance, a major component of the International Rice Research Institute’s (IRRI) Genetic Evaluation and Utilization (GEU) Program since the early 1970s, aims at countering the adverse effects of drought in unfavoured rice production areas.

Rice germplasm has such remarkably rich diversity that a continuous spectrum of genotypes differing in the various physiological mechanisms can be found and is available for genetic manipulation (Chang et al. 1982a). However, effective evaluation methods are essential for unravelling the specific mechanism(s) involved and for devising eficient selection criteria in a breeding program. Moreover, the broad spread in growth duration among rice cultivars makes it impractical to obtain uniform evaluation of a large number of cultivars when they differ in physiological responses that are specific to certain growth stages. Methods that can accommodate large numbers are essential to breeding program.

Introduction

Man’s intervention in the evolution of plants, to adapt them to suit his needs, constitutes the practice of plant breeding. Historically regarded as an art and still too empirical to be accepted universally as a science, it has recently been described as a technology (Riley 1978). Whether art, science or technology, it certainly draws on a wide range of disciplines and embodies all those principles of organisation and management that determine success in any production-oriented programme.

Perhaps the biggest contribution that the plant breeder has made to increased production during the past 50 years has been in helping to alleviate the effects of natural hazards such as lodging, pests and diseases on crop production. While most of this progress has been through the manipulation of biotic stresses, much is still to be achieved under non-biotic stresses such as drought, salinity, temperature, etc. This argument is strengthened by the fact that in spite of the spectacular achievements made possible by the ‘Green Revolution’, the productivity level of most crop plants, including wheat and rice, has remained both low and static under stress conditions. Concerted efforts are needed through an approach of interdisciplinary research, since not much has been done to define criteria for stress assessment and evolving breeding approaches for incorporating stress tolerance in crop plants.

Introduction

Drought is the most common adverse environmental factor which limits crop production in different parts of the world. Often drought is accompanied by relatively high temperatures, which promote evapotranspiration, and hence could accentuate the effects of drought and thereby further reduce crop yields. Since these events occur more frequently in tropical and semitropical regions where most of the developing countries are situated, droughts are often associated with food shortages and an overall setback to developmental activities. Therefore, raising of drought-resistant crops is common sense to achieve stability in production and to enhance the possibility of self-suficiency in food. Consequently, breeding for drought resistance is a major objective of many research programmes in the international and national institutions. This has been so for the past several decades. But, it is disappointing that, there has not been any measurable success in these programmes compared with the success achieved in breeding for yield; or breeding for disease resistance or breeding for quality attributes. In fact, this was amply expressed by Arnon (1980) when he stated “Breeding for drought resistance has been a consistent theme for as long as I remember and probably the greatest source of wasted breeding efforts in the whole field of plant breeding.” However, the fact remains that we do hear of drought resistant varieties in many crops. For example, C-306 in wheat, Lalnakanda in rice and M 35-1 in Sorghum are some of the better known examples in India. It is also claimed that a large number of cultures among the Assam Rice Collection exhibit a considerably high degree of drought tolerance. Many land races and wild relatives of several crop species are said to contain drought resistant traits, which could be profitably utilised in breeding programmes. This situation is not unique to India alone but is a common experience in different parts of the world. However, to afirm a conviction a short questionnaire to assess the current state-of-art on breeding for drought resistance was distributed to 75 distinguished plant breeders and plant physiologists all over the world. The questionnaire and a summary based on the responses is as follows:

Expression of genetic potential for growth and yield of a crop variety is directly dependent upon the environment comprising both climate (weather) and soil components. As discussed in the preceding chapter, the term ‘salt-affected soils’ encompasses a broad group of adverse but distinct soil conditions, namely, saline, alkali (sodic) and acid soils with further variations such as coastal and inland locations as well as arid and water-logged situations (Swaminathan 1977; Bresler et al. 1982). Factors limiting growth and yield of crop plants in various categories of problem soils are different and specific. Likewise, adaptive strategies evolved by plants to cope with the prevailing edaphic stresses, such as salt stress, also vary a great deal as indicated in Table 1. It is not unexpected therefore, that even varieties within a crop often show notable differences regarding tolerance to adverse soil conditions (Epstein et al. 1980; Devine 1982; Shannon 1984; Sayed 1985). Hence, it is essential that the breeder must understand the inherent charaderistics of the problem soil with which he is concerned and should also simultaneously appreciate that basically it is the sensitivity of crop variety, rather than the soil parameters per se, that essentially determines the occurrence as well as the magnitude of actual soil problem (Rana 1977). Since the degree of tolerance (adaptation) of crop varieties to different kinds of salt affected soils is genetically controlled, it is axiomatic that it can be improved through genetic manipulations by adopting suitable breeding procedures.

Introduction

Accumulation of excess soluble salts in the root zone of soils resulting in partial or complete loss of soil productivity is a worldwide phenomenon. The problems of soil salinity are widespread in the arid and semi-arid areas but salt-affected soils also occur extensively in the sub-humid and humid climates particularly in the coastal regions where the ingress of sea water through estuaries and rivers and through ground water movement causes large scale soil and water salinisation. Soil salinity is also a serious problem in areas where ground waters of high salt content are the only source of water available for irrigation. By far the most serious problems of salinity are being faced in the irrigated, arid and semi-arid regions of the world. Our ability to manage salt-affected soils and waters both in the irrigated and in the unirrigated regions will constitute a major effort in meeting potential food requirements. The magnitude of the problem can be appreciated from the following.

Object: Effect of ethylene on regulation of stomata.

Material required: Plant leaves, ethaphon, ACC, double distilled water, measuring cylinder, beaker and electric balance.

Theory: Ethylene is a plant hormone that regulates many aspects of growth and development. Despite the well-known association between ethylene and stress signalling, its effects on stomatal movements are largely unexplored. Here, genetic and physiological data are provided that position ethylene into the Arabidopsis guard cell signalling network, and demonstrate a functional link between ethylene and hydrogen peroxide (H₂O₂). In wild-type leaves, ethylene induces stomatal closure that is dependent on H₂O₂ production in guard cells, generated by the nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase AtrbohF. 

Object: Yield estimation of kharif crops.

Material required: Polythene bags, balance, gunny bags or baskets, pans and harvesting equipment like sickle, knife etc.

Theory: Yield is the ultimate objective of cultivating agricultural plants. Different plant parts constitute the economic yield in different crops, like grain in cereals, pulses and oil seeds, vegetative parts or fruits in record yield at the correct maturation stage. Do not allow excessive wilting or drying of the material. Estimate yield in a sufficiently large sample. Materials required only a representative crop to estimate yields. (Do not select plants of any particular type. Do not damage any plant part vegetable crops; bark or out growth in fiber crops (jute, cotton); and the entire plant in fodder crops. The yield per unit area (per M₂ or ha) is the product of yield per plant multiplied by the number of plants per unit area. It is, therefore, essential to know the yield components per plant as well as per unit area.

Object: Growth analysis: Calculation of growth parameters. 

Material required: Primary data collected from individual plants or derived from whole canopies. 

Theory: The growth analysis study provides information on the growth of plants or of a plant community in a precise way with the available’ raw data. The study also provides precise information on the nature of plant and environment interaction in a particular habitat.

Object: To demonstrate the measurement of growth in plants with the help of Arc auxanometer. 

Material required: Potted plant, Arc auxanometer, rope and weight.

Theory: Growth is a permanent change in plants with respect to its size, form, weight and volume.

Object: Determination of the viability of seeds by tetrazolium test. 

Material required: Healthy seeds, tetrazolium solutions, beakers, water and petridishes. 

Theory: Viability of seeds shows their potential towards germination.

Object: Breaking of seed dormancy to facilitate germination.

Material required: Seeds, water, sharp needle, sharp razor, sandpaper, acids, Potassium nitrate and gibberellic acid. 

Definition: Inability of a viable seed to respond the favorable environmental conditions for germination is known as dormancy.

Object: To demonstrate the optimum conditions for seed germination. 

Material required: Beaker, glass slide, bean seeds, thread and water.

Theory: Germination is a process by which the embryo in the seed becomes activated and begins to grow into a new seedling under favorable conditions. Food is stored in the seeds in dry conditions but the developing embryo cannot utilize this dry food. Food can be utilized in liquid form only and seeds can utilize only dissolved oxygen. Excess water stop germination because once all the dissolves oxygen is utilized by the seed, further germination is not possible as the life supporting oxygen is lacking. Suitable temperature is necessary because low temperature retards the embryo activity and high temperature destroys the delicate embryo tissue. Seed usually germinate between 0oC to 50oC temperature and the optimum temperature is lies between 25 to 30oC. During germination rapid cell division takes place. Energy is required for cell division. This energy is obtained from oxidation. The oxygen is required for oxidation is supplied by the air.

Object: To determine respiratory quotient of different types of respiratory substrates.

Object: To demonstrate that oxygen is used up during respiration. 

Material required: A conical flask, some germinating seeds, glass tube having two bends at right angles, mercury, beaker, small tube and caustic potash (KOH).

Theory: Plants at some stage have a capacity to respire more rapidly in presence of oxygen i.e. aerobic respiration. In this process, oxidation of carbohydrate occurs resulting in conversion of carbohydrate into carbon dioxide (CO₂) and water with release of large amount of energy.

Object: To demonstrate anaerobic respiration. 

Material required: Soaked pea or gram seeds, mercury, test tube stand, forceps and KOH pellets. 

Theory: Generally, plants at certain stage have the capacity to respire in absence of oxygen i.e. anaerobic respiration. In this process, oxidation of carbohydrate takes places, ethyl alcohol and CO2 being end products and only a little amount of energy is liberated-

Object: To demonstrate that O₂ is evolved during photosynthesis. 
 

Material required: Hydrilla plant, beaker, test tube, funnel, pond water and pyrogallol. 
 

Theory: Oxygen is a byproduct of photosynthesis, which is evolved in presence of light and chlorophyll during photosynthesis.

Object: To demonstrate that light and carbon dioxide are essential for photosynthesis (Moll’s half leaf experiment). 

Material Required: A potted plant, a wide mouthed bottle, caustic potash, splits of rubber Cork and vaseline etc. 

Object: To demonstrate unequal transpiration by the two leaf surfaces from four leaf method. 

Material required: four leaves of china rose or any dorsiventral leaves, two stands, thread and grease or vaseline. 

Theory: Transpiration is a process in which loss of water occurs in the form of water vapour from the aerial parts of the living plant. 

Method: Take four leaves of equal size from a plant (e.g. China rose). Now apply or smear the vaseline on the four leaves as follows:

Object: To find out the relation between transpiration and absorption. 

Material Required: Wide mouthed glass bottle, with a narrow graduated side tube, split rubber cork, water and a plant with intact root system.

Theory: The loss in weight of plant indicates the amount of water transpired. And fall in water level of the side tube indicates the amount of water absorbed. This shows that amount of water transpired is normally equal to the amount of water absorbed by the plant roots.

Object: To measure the rate of transpiration by using Ganong’s potometer

Material required: Ganong’s potometer, beaker, wax or vaseline, stop watch and twig or a branch of a plant.

Theory: The amount of water absorbed is almost equal to the amount of water transpired. The difference between the two amounts is negligible. 

Method: Potometer consists of wide mouthed tube fitted with a hard cork in which a twig or branch of a plant is inserted. Other end of tube is dipped in beaker. One half of the tube is graduated. The apparatus is filled with water using the reservoir. An air bubble is inserted in the tube as shown in figure.

Object: To measure rate of transpiration of potted plant by gravimetric (Lysimeter) method. 

Material required: Potted plants, Polythene sheet, Platform and electric balance etc.

Method: Select same size and same type well watered potted intact plants. Seal the pots and the root system with a sheet of polythene so that the water loss to the atmosphere occurs only from the shoot system not from the soil (To check evaporation losses). Immediately record the weight of the potted plant and keep them in different environment such as (1) warm environment (2) cool environment (3) Calm environment.

Object: To demonstrate that water is lost from a living plant during transpiration. 

Material Required: A potted healthy plant, a bell jar, a rubber sheet or oil cloth, a glass sheet and grease.

Theory: Transpiration: Loss of water in the form of water vapour from the internal tissues of living plants through aerial parts of the plant is known as transpiration.

Object: Demonstration of leaf anatomy or structure of C₃ and C₄ Plants (demonstration by already prepared slides).

Material required: Already prepared slides of corn and wheat leaves and microscope.

Object: Measurement of leaf area by graph paper method.

Material required: leaves, graph paper and pencil or pen.

Object: To demonstrate chlorophyll fluorescence.

Material required: Spectrophotometer, fresh green spinach, mortar, pestle, acid washed sand, acetone, funnel, filter paper and test tubes.

Principle: Chlorophyll molecule absorbs light in the blue (450nm) and red (660nm) region and get into excited state and emits an electron. The electron drops back to the ground state within 10-9 seconds and some energy (which is not used in biochemical reaction) are given out as the observed fluorescent far red light.

Procedure and observation: Take some soft green spinach leaves. Grind these with a pestle -mortar in acetone adding a pinch of acid washed sand. Make a fine paste. Filter to get a clear solution in a test tube. Take the test tube in bright sun light.

Object: Measurement of absorption spectrum of chloroplastic pigments.

Material required: Spectrophotometer, plant leaves, ethanol, electric balance, beaker, test tubes and water.

Objective: Estimation of photosynthetic pigment from plant leaves.

Material required: Plant leaves, test tube, test tube stand, spectrophotometer, balance, centrifuge machine, mortar and pestle, acetone and distilled water.

Theory: Photosynthetic pigments, namely, the chlorophylls are present in green leaves and shoots of plants. There are at least five types of chlorophylls in plants. Chl’a’ and ‘b’ occur in higher plants, ferns and mosses. Chl ‘c’,‘d’ and ‘e’ are found only in algae and in certain bacteria. Chlorophylls are extracted from plant leaves. The absorption peaks of chl ‘a’ at 663 nm and ‘b’ at 645 nm are characteristic measures from which amount of chlorophylls can be calculated.

Object: Estimation of water potential of plant tissue by Chardakov’s method.

Material required: Test tubes, sucrose or polyethylene glycol (PEG) 6000, methylene blue and dropper.

Principle: Concentration of the solution in which a plant tissue is immersed changes. If the solution is hypertonic (with lesser yw) the tissue loses water and the solution becomes dilute. If the solution is hypotonic (with higher yW) the tissue absorbs water and the Solution becomes concentrated. If the solution is isotonic (with yw equal to the tissue sap) the tissue neither loses nor absorbs water and the solution concentration does not change. Thus the yw of this solution gives the yw of the tissue.

Object: Methods of measurement of water status and water saturation deficit in plant parts. 

Material required: Leaf samples, leaf borer, water, petridishes, forceps, oven and blotting paper. 

Theory: Plant water status strongly influences plant growth and biomass production through its effects on leaf and root expansion and on photosynthesis. Therefore, measurement of plant water status is an important component of understanding plant processes and maximizing yield under different ecosystems. 

Method: Plant water status can be measured and computed by any one of the following methods

Object: To demonstrate the process of diffusion.

Material required: Beakers, copper sulphate, distilled water and sugar solution.

Object: To demonstrate the phenomenon of endosmosis and exosmosis by using grapes and raisins.

Material required: Grapes, raisins, beaker or petridish, water and sugar solution.

Object: To demonstrate the phenomenon of osmosis using potato osmoscope. 

Material required: A potato tuber, sugar solution, beaker, water, petridish, knife, measuring cylinder, and stand.

Theory: Osmosis is a phenomenon in which water molecules diffuse through the semi permeable membrane from region of its higher concentration to the region of lower concentration.

Object: Preparation of solutions. 

Material required: Volumetric flask, measuring cylinder, beakers, pipettes, balance, distilled water and chemicals. 

Theory: The use of solution is common in experimental procedures of plant physiology. It is very important for a student to be familiar with their preparation. The substance dissolved in a solution is called solute and the medium in which it is dissolved is known as solvent. Solutions of two liquids (e.g. alcohol in water) and solid in liquid (e.g. NaCl in water) are most common. Solutions are thus a homogenous mixture of a solute in a solvent. 

A. Bhattacharya
    
8.1.    Glycolysis in Plants
    
    8.1.1.    Oxidative Decarboxylation of Pyruvate
    
8.2.    Citric Acid Cycle
    
8.3.    Oxidative Phosphorylation
    
    8.3.1.    Efficiency of ATP Production
    
8.4.    Photorespiration
    
8.5.    Effect of Abiotic Stresses 
    
8.6.    Effect of Drought on Respiration
    
8.7.    Effect of Waterlogging on Respiration
    
    8.7.1.    Plant Metabolism and Energetic Alteration Under 
        Waterlogging
    
8.8.    Effect of Low Oxygen on Respiration
    
8.9.    Effect of Higher Day and Night Temperature on Respiration
    
8.10.    Respiration Under Low Temperature Stress
    
8.11.    Effect of Salt Stress on Respiration
    
    8.11.1.    Reactive Oxygen Species
    8.11.2.    Physiological and Biochemical Processes
    
8.12.    Effect of High CO2 Concentration on Respiration
        
References

7.1.    Single Action Gene
    
    7.1.1.    Osmoprotectants
    7.1.2.    Detoxifying Genes
    7.1.3.    Late Embryogenesis Abundant (LEA) Protein
    7.1.4.    Transporter Genes
    7.1.5.    Multifunctional Genes for Lipid Biosynthesis
    7.1.6.    Heat -shock Protein Genes
    
7.2.    Regulatory Gene
    
    7.2.1.    Transcription Factors
    7.2.2.    Signal Transduction Genes
    
7.3.    Choice of Promoters
    
7.4.    Physiological Evaluation of Stress Effect
    
7.5.    Conclusions
        
References

A. Bhattacharya

6.1.    Macronutrients (Primary)
    
6.2.    Macronutrients (Secondary and Tertiary)
    
6.3.    Micronutrients
    
6.4.    Inter-relationships Between Nutrient Elements
    
    6.4.1.    Synergism
    6.4.2.    Antagonism
    
6.5.    Potassium Inter-relationships with Macronutrients
    
    6.5.1.    Potassium Inter-relationships with Secondary Nutrients
    6.5.2.    Potassium Inter-relationships with Micronutrients
    
6.6.    Nutrient Deficiency
    
6.7.    Role of Mineral Nutrition Against Environmental Stress
    
6.8.    Role of Mineral Nutrition Against Drought Stress
    
6.9.    Role of Potassium in Abiotic Stress Resistance
    
    6.9.1.    Potassium and Drought Stress
    6.9.2.    Cell Elongation and Cell Membrane Stability
    6.9.3.    Aquaporins and Water Uptake
    6.9.4.    Osmotic Adjustment
    6.9.5.    Stomatal Regulation
    6.9.6.    Detoxification of Reactive Oxygen Species
    6.9.7.    Potassium and Salt Stress
    6.9.8.    Potassium and Low-Temperature Stress
    6.9.9.    Potassium and Waterlogging Stress
    
6.10.    Partition of Photosynthates under Nutrient Deficiency
        
References

A. Bhattacharya
    
5.1.    Chlorophyll
    
5.2.    Response to Drought Stress
    
5.3.    CO2 Fixation Under Drought
    
5.4.    Response to High Temperature Stress
    
5.5.    Response to Low Temperature Stress
    
5.6.    Effect of Cold Stress on CO2 Fixation
    
5.7.    Cold Acclimation and its Role in Providing Freeze-tolerance
    
5.8.    Response to Salinity Stress
    
5.9.    CO2 Fixation Under Salinity Stress
    
5.10.    Response to High Light Intensity Stress
    
5.11.    Stress-induced Changes
         
    5.11.1.    Effects on Photosynthetic Pigments
    5.11.2.    Effects on Photosystems
    5.11.3.    Effects on Gas-exchange Characteristics        
    5.11.4.    Effects on Activities of key Photosynthetic Enzymes
    
5.12.    Improvement in Photosynthetic Capacity Under Stress by Engineering Photosynthesis-related Genes or Transcription Factors
    
    5.12.1.    Transfer of C4 genes/traits to C3 plants
    5.12.2.    Role of Transcription Factors in Regulation of Genes Involved in Photosynthesis
    
5.13    Role of Mitogen-activated Protein Kinases (MAPKs) in Photosynthesis
    
5.14    Conclusion and Future Prospects
        
References

A. Bhattacharya    
    
4.1.    Factors of Abiotic Stress
    
4.2.    Light
    
4.3.    Temperature
    
    4.3.1.    Heat-stress Threshold
    4.3.2.    Low Temperature Stress
    4.3.3.    Plant Responses to Heat Stress
    
4.4.    Water
    
    4.4.1.    Drought
    4.4.2.    Flooding
    
4.5.    Soil
    
    4.5.1.    Soil Type
    4.5.2.    Soil pH
    4.5.3.    Soil Fertility
    4.5.4.    Soil Salinity
    
4.6.    Growth and Development
    
    4.6.1.    Phases of Development Sensitive to Temperature or Photoperiod
    
4.7.    Phenology
    
    4.7.1.    Changes in Phenology of Cropping Systems
    4.7.2.    Effect of CO2 on Flowering
    4.7.3.    Temperature and Effects on Phenology
    4.7.4.    Effect of Salinity
    
4.8.    Molecular/Genetic Aspects of Flowering Response to Climate Change
    
4.9.    Simulation of Phenology for Future Climate
        
    References

Raj Bahadur
    
3.1.    Nitrogen Fixation in Saline Soil
    
3.2.    Legumes and Nitrogen Fixation
    
    3.2.1.    Legumes in Saline Agriculture; Nitrogen Fixation Capabilities
    3.2.2.    Legumes in Saline Agriculture; Salinity Tolerance of Legumes
    3.2.3.    Improvement of Salinity Tolerance of Legumes
    3.2.4.    Legumes of the HALOPH Database
    
3.3.    Perspective for Saline Agriculture
    
3.4.    Impacts of Agriculture and Global Climate Change Terrestrial Biogeochemical Cycle of Nitrogen
    
    3.4.1.    Nitrogen Chemistry and Terrestrial Life
    
3.5.    Nitrogen Fixation
    
    3.5.1.    Decomposition
    3.5.2.    Nitrification
    3.5.3.    Denitrification
    3.5.4.    Bio-geochemical Linkage of Nitrogen and Carbon
    3.5.5.    Soil Organic Matter
    3.5.6.    Perturbations and N and C Biogeochemistry
    3.5.7.    Organic Nitrogen
    3.5.8.    Mineralization
    
3.6.    Factors Influencing Biological Nitrogen Fixation in Legumes
    
    3.6.1.    Temperature
    3.6.2.    Soil Water Status
    3.6.3.    Nitrogen Concentration in the Root Zone
    3.6.4.    Carbon Demand for Fixation
    3.6.5.    Seasonal Regulation of Legume Biological Nitrogen Fixation
    
3.7.    Quantification of Biological Nitrogen Fixation
    
    3.7.1.    Estimation with Empirical Models
    3.7.2.    Potential N Fixation Rate
    3.7.3.    Impact of Soil Temperature
    3.7.4.    Impact of Soil Water Status
    3.7.5.    Effect of Soil Mineral N or Internal Substrate N
    3.7.6.    Influence of Plant Substrate C or C supply
    3.7.7.    Changes in N Fixation with Plant Growth Stage
        
    References

A. Bhattacharya

2.1.    Seed Germination
    
    2.1.1.        Drought Tolerance in Plants
    2.1.2.        Osmotic Adjustment
    2.1.3.        Cell membrane Stability
    2.1.4.        Epicuticular Wax
    2.1.5.        Partitioning and Stem Reserve Mobilization
    2.1.6.        Salt Stress and Seed Germination
    
2.2.    Seedling Drought Traits
    
2.3.    Seed Germination Under Abiotic Stress

2.4.    Salt Stress and Seed Germination

2.5.    Seedling Growth

2.6.    Stress Effects on Seedling Growth
    
    2.6.1.        Temperature
    2.6.2.        Nutrition, Salinity, and pH
    2.6.3.        Water
    2.6.4.        Under Flooding Condition
    
2.7.    Drought Stress and Abscisic acid (ABA)
    
2.8.    Salt Stress on Seedling Length
    
    2.8.1.        Salt Stress on Seedling Dry Weight
    2.8.2.        Mechanism of Salt Stress on Germination
    2.8.3.        Root Establishment Methods
    
2.9.    Root Development
    
    2.9.1.        Root System Development and Abiotic Stress
    
2.10.    Root Development Under Abiotic Stress
    
    2.10.1.        Drought Stress
    2.10.2.        Regulation of Root System Architecture by Water Availability and Salinity Stress
    2.10.3.        Regulation of Root System Architecture by Nutrients
    2.10.4.        Phosphate Starvation
    2.10.5.        Nitrogen
    2.10.6.        Potasium and Iron
    2.10.7.        Meristematic Activity Regulation by Abiotic Stress
    2.10.8.        Waterlogging Stress
    2.10.9.        Salt Stress
    2.10.10.    Temperature Stress
    2.10.11.    Illumination Stress
    2.10.12.    Nutrient Deficiency or Excess
    2.10.13.    Heavy Metal Stress
    2.10.14.    Elevated Atmospheric Levels of CO2
    2.10.15.    Mechanical Stress
    
2.11.    Biochemical Regulation of Root
        
References

A. Bhattacharya
1.1.    Specific and Unspecific Reactions to Stress

Nematodes are the most numerous metazoa on earth. They are either free living or parasites of plants and animals. Although currently only about 4100 species of plant parasitic nematodes have been described (i.e. 15 % of the total number of nematode species known), their impact on humans by inflicting heavy losses in agriculture is substantial. Most of the developing countries including India lie in tropical or sub tropical regions where climate is suitable for activity and multiplication of nematodes almost throughout the year. Sandy and warm soils such as found in India other developing countries in the arid zone are very favorable for nematode infection, especially in irrigated areas which are used for crop production continuously. The percentage of crop losses caused by plant pathogens, insect pests and weeds world wide has been estimated to 42% according for $500 billion worth of damage. The estimated overall annual yield loss of world’s major crops due to damage by plant parasitic nematodes has been reported to the extent of 12.3% (Sasser & Freckman, 1987). Estimated losses due to nematodes attack on different cultivated crops all over the world by FAO are around 400 million dollars. Annual crop losses in India is Rs. 242.1 billion. A large number of plant parasitic nematodes have been found associated with pulse crops in allover India but pathogenicity has not been proved for all. Plant parasitic nematodes are one of the most unwanted organisms in agricultural soils. They parasitize the roots of our carefully nurtured crops, reduce their ability to produce yields, make them weak and perhaps vulnerable to many pests and diseases. They reduce the crop yields that may equal those associated with more severe and easily identifiable plant diseases and we do not even realize their presence. Damage to crops by nematodes often goes unnoticed or attributed to other causes such as lack of fertility, deficient soil moisture. Sandy and warm soils such as found in India other developing countries in the arid zone are very favourable for nematode infection, especially in irrigated areas which are used for crop production continuously (Taylor, 1967).

A large number of insect pests are associated with stored grains which are directly related to geographical and climatic conditions. There are different estimates on post harvest losses in food. During storage both quantitative and qualitative losses occur due to insects, rodents, and microorganisms. Almost all the insect species may destroy 10.0 - 15.0 % of grain and contaminate with undesirable odour. These pests also helps in transportation of fungi. Some insect pests initiate damage at the ripening stage of crops and continue during storage. Major sources of infestations are old gunny bags, storage structure and old containers (Pruthi and Singh, 1950). The spread and distribution of stored product pests are facilitated by movement of grains from one area to another and by flight of insect pests as some of the adult insects are strong fliers. The cracks and crevices are probable sites for cross infestation. Nearly one thousand species of insects have been associated with stored products in different part of the world. Majority of insect pests belong to the orders Coleoptera and Lepidoptera (Khare, 1994).

Inorganic pest management systems using external inputs such as chemical fertilizers, pesticides, high yielding varieties have resulted in increased yields in certain areas, but resulted in ecological degradation hence a decrease in productivity. Under organic farming systems, the fundamental components and natural processes of ecosystems, such as soil organism activities, nutrient cycling, and species distribution and competition are used to work directly and indirectly as farm management tools. For example, crops are rotated, planting and harvesting dates are carefully planned, and habitat that supplies resources for beneficial organisms are provided. Soil fertility and crop nutrients are managed through tillage and cultivation practices, crop rotations, cover crops, and supplemented with manure, composts, crop waste material and allowed substances.
 
Bio intensive IPM incorporates ecological and economic factors into agricultural system design and decision making and addresses public concerns about environmental quality and food safety. The benefits of implementing bio intensive IPM can include reduced chemical input costs, reduced on-farm and off-farm environmental impacts, and more effective and sustainable pest management. An ecology-based IPM has the potential of decreasing inputs of fuel, machinery, and synthetic chemicals—all of which are energy intensive and increasingly costly in terms of financial and environmental impact. Such reductions will benefit the grower and society.

Fruit Flies and Economic Importance

Fruit flies belong to order Diptera (true flies) with one of the largest, most diversified and fascinating acalypterate family Tephritidae. These are commonly called as fruit flies due to their close association with fruits and vegetables and are also known as peacock flies because of their habit of strutting about and vibrating spotted and striped wings. Of the 4500 known species of fruit flies worldwide, nearly 200 are considered as pests but 70 species are regarded as agriculturally important throughout the world (Clarke et al., 2005, Schutz et al., 2012). David and Ramani (2011) reported 325 species in the Indian subcontinent of which 243 in 79 genera are from India alone. Important fruits flies damaging fruit crops in India include Oriental fruit fly or mango fruit fly, Bactrocera dorsalis (Hendel); peach fruit fly, B. zonata (Saunders); guava fruit fly, 
B. correcta (Bezzi); melon fly, B. cucurbitae (Coquillett) and ber fruit fly, Carpomyia vesuviana Costa, whereas important fruit flies in Punjab include B. dorsalis and B. zonata. Important host plants of B. dorsalis are mango, guava, peach, citrus, pear, ber and loquat but most preferred host of B. dorsalis is guava while that of B. zonata are guava, peach, mango, pear, ber, citrus and loquat but C. vesuviana infests only ber (Mann 1990, Sharma et al., 2005, Singh 2008b, Singh 2012, Singh et al., 2014a,b and Singh et al., 2015). Bactrocera dorsalis is considered to be the most damaging and aggressive fruit flies in the world (Leblance and Putao 2000). They are strong fliers and can fly upto two kilometers in search of food (Butani 1979).

A systems approach to pest management based on an understanding of pest ecology is referred to as Biointensive Integrated Pest Management (BIPM). It is more dynamic and ecologically informed as compared to IPM that considers the farm as part of an agro ecosystem. Accurate diagnosis of the pest problem is the first step, which then relies on a range of preventive tactics and biological controls to keep pest populations within acceptable limits. It also considers ecological and economic factors into agricultural system design and decision - making and addresses public concern about environmental quality and food safety. As a last resort, the reduced – risk pesticides are used if other tactics have not been adequately effective.

The earlier concept of IPM has failed because of ease of applicability to easy availability of chemical pesticides. Hence, the present concept of BIPM, with more intensive use of biological and other biorational means has emerged. The flexibility and environmental compatibility of BIPM strategies make it useful in all types of cropping system. BIPM would likely decrease chemical use and costs entailing them. BIPM ultimately provides resistance / immunity to the entire system so that no foreign elements (insect pests or disease causing organisms) survive or gain upper hand. BIPM if followed for years shall enhance the natural control system, thus suppressing pest populations below those causing economic injury.

Solanaceous Vegetables

Solanaceous vegetables are also infested heavily by several major insect pests.

Brinjal Solanum melongena L.
 
Fruit and shoot borer Leucinodes orbonalis Gunnee (Lepidoptera: Pyraustidae)

Economic importance: Most destructive pest of brinjal, found throughout the country. Besides brinjal, the pest is also known to infest potato, bitter gourd, pea pods, cucurbits and other solanaceous etc. The infestation on brinjal can be as high as 70 per cent. The pest is active throughout the year, except in severe cold weather in North India.
 
Mark of identification and life cycle: Moths wings are white with pinkish or black tings and are ringed with small hair along the apical and anal margins. The fore wings are ornamented with a number of black, pale and light brown spots. Female lays 80-120 creamy white eggs, singly or in batches of 2-4 on the underside of leaves, on green stems, flower buds or the calyces of fruits. Caterpillars are creamy when young, but light pink when full-grown in 9-28 days. Pupate in tough silken cocoons among the fallen leaves with period of 6-17days and adult survive for 2-5days of its life cycle. A single life-cycle takes 22 - 25 days extending up to 74 days during winter and there may be 8 - 12 generations in a year.

Okra Abelmoschus esculentus L.

Cotton Jassid Amrasca biguttula Ishida (Hemiptera: Cicadellidae)

Economic importance: Sucking pest cause damage during May to September. Adults are also found on plants such as potato, brinjal, tomato, etc.

Mark of identification and life cycle: Adults are about 3 mm long and greenish yellow during the summer, acquiring a reddish tinge in the winter. The winged adults jump or fly away at the slightest disturbance and are also attracted to light at night. Females lay about 15-38 yellowish eggs on the underside of the leaves, embedding them into the leaf veins. The eggs hatch in 4-5 days. Nymphs are wedge-shaped and are very active and complete five instars with 3-5 days in each instars. Adult live for 11days.

Nature of damage: Damage to the crop is caused by the adults as well as by the nymphs, both of which are very agile and move briskly, forward and sideways. They suck cell-sap from the underside of the leaves and pass through six stages of growth in 7-21 days. They feed constantly on the plant juice. The pest completes seven generations in a year. Damage symptoms: Injury to plants is due to the loss of sap and probably also due to the injection of toxins. The attacked leaves turn pale and then rust-red. With change in appearance, the leaves also turn downwards, dry up and fall to the ground.

Vegetables constitute a substantial part of human diet supplying vitamins and minerals, in which other food materials are deficient. India has emerged out as the second largest producer of vegetables in the world. More than 25% of fruits and vegetables are damaged by the attack of insect-pests (Pradhan, 1964).Vegetable crop is damaged by both sucking as well as chewing insect-pests. Sucking pests are aphids, whitefly, jassids and bugs attacking in initial stage whereas chewing pests like borers, infesting in flowering and fruiting stage. Sucking pests may transmit the viral diseases which cause severe loss in yield in tomato and okra crops. About 13-14 % of total pesticides used in the country are applied on vegetables. Average pesticide consumption in vegetables in India around 0.678 a.i. kg/ha. Maximum pesticide usage in chilli followed by brinjal, cole crops and okra. Global agro-chemical consumption dominated by fruits and vegetables, accounting 25 % of total pesticide market. Major insect-pests of different vegetable crops and their management are as follows:
 
Cole crops

Cabbage (Brassica oleracea var capitata) and Cauliflower (Brassica olercea var botrytis L) are grown in cold and moist climate. It is rich in minerals namely iron, magnesium, phosphorous and sodium. Cole crops were attacked by number of insect pests and cause heavy economic loss. The major insect pests are described below along with their management:

Vegetable is an important constituent of Indian diet. India is the second largest producer of vegetables which contributes 16.7% to global vegetable area with a production of 156.33 million tons (15.4%) (Table 1). The level of productivity of vegetable17.4 tons/ha is quite low (Rai et al., 2014). Majority of Indians are vegetarian, with a per capita consumption 135 g per day as against the recommended 300 g per day. It is still very less than recommended diet level. In near future, there is a need of around 5-6 million tons of food to feed our 1.3 billion Indian population expected by the year 2020 (Paroda 1999). The major biotic stress in vegetable production is due to increased insect pest. In many cases, there is 100 per cent yield loss due to viral diseases vectored by insects. Vegetables are more prone to insect pests and diseases mainly due to their tenderness and softness as compared to other crops and virtual absence of resistance characters because of intensive hybrid cultivation. The insect pests inflict crop losses to the tune of 10-30 per cent in vegetable production (Table 2). To overcome these losses farmers used indiscriminate doses of toxic chemical on vegetable. It accounts for 13-14 per cent of total pesticides consumption, as against 2.6 per cent of cropped area (Sardana, 2005). For the benefit of the farmer and other, application of BIPM is must. Bio intensive pest management involves every part of management that keeps pest below economic injury level so that pest does not cause any economic loss to the farmers or growers.