eChapters

Introduction

India is the second most populous country in the world. The per capita cultivable land resource is shrinking day by day. To meet the food, fibre, fuel, fodder, and other needs of the growing population, the productivity of agricultural land has necessarily to be increased. It requires increased use of agricultural inputs like quality seeds, fertilizers, water, agro-chemicals, etc. in such a manner that do not create any environmental problems.

Plant needs different chemical elements to grow and thrive. The most important chemical elements include (i) carbon, hydrogen and oxygen, which are basic life building blocks and are available in plenty from air and water (ii) nitrogen, phosphorus and potassium which are the macro nutrients and affect the plant growth significantly (iii) sulfur, calcium, and magnesium as secondary nutrients and (iv) boron, chloride, copper, iron, manganese, molybdenum and zinc as micronutrients in very small quantities.

What is Precision Farming?

It is information and technology based farm management system to identify, analyze and manage variability within fields for optimum profitability, sustainability and protection of the land resource without disturbing the environment. It is basically means adding the right amount of treatment at the right time and right location within a field.

Introduction

Plant hormones (also known as phytohormones) are chemicals that regulate plant growth, which are termed ‘plant growth substances’. Plant hormones are signal molecules produced within the plant and occur in extremely low concentrations. Plant hormones are small, simple molecules of diverse chemical composition: indole compounds, terpenes, adenine derivatives, steroids, aliphatic hydrocarbons and derivatives of carotenoids or fatty acids. In the context of rooted habit and iterative mode of growth, plant hormones are not produced in specialized glands, but in most parts of the plants. Plant hormones are required in minicule quantities and their concentrations at sites of activity are precisely regulated. Changes in hormones concentration and tissue sensitivity mediate a whole range of development processes in plants, many of which involve interaction with environmental factors. First five hormones discovered from the plants were gibberellins, abscisic acid, cytokinins, indole-3-acetiv acid, and ethylene as well as some compound shown more recently to have a regulatory role in plant development, namely, brassinosteroids, polyamines, jasmonic acid and salicylic acid.

Introduction

Plant needs nutrients for their growth and development. In a systemic agriculture, nutrients are supplied to the plant in different amount, form and time for the economic and optimum crop production. Green revolution realized in the late sixties of the last century is an outcome of efficient use of improved varieties and nutrient management. Success of the green revolution has increased use of chemical fertilizers in the post green revolution era. Soon the chemical fertilizers become indispensible from all the crops including vegetable and plantation crops. Non judicious use of chemicals in the agriculture has lead to the serious health, soil and environmental hazards. Biofertilizers are considered to be the most safe, promising and economic component of sustainable agriculture. Biofertilizer is a substance which contains living or latent microorganisms which, when applied to seed, plant root or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by providing and essential nutrients or increasing the supply or availability of primary nutrients to the host plant. They can applied in all the agronomic, horticultural and plantation crops.

Mineral Nutrition and Nutritional Deficiency

The normal green plant is autotrophic that means it can synthesise all its organic substances; provided it is supplied with all the inorganic elements and growth under normal condition. The nutrition of green plant is therefore, solely inorganic. It is, in fact, commonly called mineral nutrition. Element absorbed from the soil by the roots are generally known as Plant nutrition or Mineral nutrients.

Introduction

The horticulture sector has been a driving force in stimulating a healthy growth trend in Indian agriculture. This sector contributes around 28 per cent of the GDP from about 13.08 per cent of the area and 37 percent of the total exports of the agricultural commodities (Rather et al., 2013)  India is currently producing 257.2 million tonnes of horticulture produce from an area of 23 million ha. Over the last decade, the area under horticulture grew by about 3.8% per annum but production rose by 7.6% per annum. The higher growth rate in horticulture was brought about by improvement in productivity of horticulture crops, which increased by about 28% between 2001-02 and 2011-12. (Anonymous, 2012)

Introduction

Green house is a structure in which external climatic factors can be controlled for cultivation and protection of crops. It has mainly two parts. (a)  a frame or the basic structure and (b) the cladding or covering material (U.V. film) Frame can be made of G.I. pipes, bamboos, woods or iron rods while the cover can be of glass or plastic films. In India the technology is primarily used. Greenhouse technology is more suited to vegetables crops (such as tomato, cauliflower, capsicum, cucumber, leafy vegetables etc.), and flowers (like rose, gerbera, carnation, etc).  This technology is mainly suitable for commercial farming, as it requires investment in setting up the entire framework.  Based on cooling systems of the greenhouse, it can be classified as naturally ventilated and fan-pad type greenhouse.

Introduction

In horticulture crops, plant materials has been  propagated through vegetative propagation methods for its superiority in growth as well as yield for centuries. Among vegetative propagation methods, micropropagation is most advance technique which made a significance in the horticultural crops to increase quality and yield. It can produce many plants from a single individual.

Current Trends in Fruit Exports from India

Fruit culture in the Indian subcontinent dates back to the Harappan civilization when datepalm, pomegranate and lemon were domesticated. Fruits such as aonla, bael, jackfruit, karonda, phalsa, mango, pomegranate, almond, walnut and pistachio are mentioned in Charaka Samhita (300 BC) and Sushruta Samhita (400 BC), the oldest known texts on ayurveda. Owing to diverse agro climatic conditions, India can produce a wide range of tropical, subtropical, arid and temperate fruits. In the past few decades, India had made rapid strides in fruit production and is currently the second largest producer of fruits in the world, next only to China. The annual production is estimated to be about 81 million tonnes for about 12.6% of the total world production. However, India’s share in the global export of fresh fruits is less than 5 per cent. The major fruits exported in terms of quantity are grape, mango, banana and pomegranate. In value terms, grapes and mango earn the maximum foreign exchange for India.

Introduction

Agriculture is highly dependent on environment, and it’s very difficult to get favourable climate and other conditions for optimum crop growth and development as per crop need. Open field conditions are having a high direct affect of the prevailing weather conditions on crop growth, and also on population dynamics of viruses, fungus, bacteria, insects, etc. With time crops has adopted themselves to specific seasons, but the fast changing climatic conditions happening across the globe has changed the climatic characteristics of a season. This has resulted in untimely rains, high temperature fluctuations and changes in other abiotic and biotic factors in geographically varied locations where it was not supposed to be earlier based on various geographical factors deciding the climatic conditions of that area. Therefore, there is need to develop suitable technologies to sustain these challenges. How to address these issues, can we manipulate the climatic conditions or can we provide protection to the crops against climatic fluctuations and various other related stresses.

Introduction

Citrus spp. grown in almost all the states of India. Citrus fruit, consisting of mandarin oranges (Citrus reticulata Blanco), sweet orange (Citrus sinensis Osbeck) and lime (Citrus aurantifolia Swingle) are grown commercially in tropical, sub-tropical, arid, irrigated and mountainous regions in varying soil and weather condition. The citrus tree on the whole do well in dry climate, with a rainfall between 75 and 125 cm but certain species such as pummel and certain mandarin oranges thrive in heavy rainfall areas of Konkan, Assam and Coorg. It is grown almost all kinds of soil, varying from heavy black soil to shallow open soils. A hard substratum or a sticky impervious layer is very injurious. Soils having a high water table should be avoided. Although the citrus industry in India has faced many challenges, there has been a consistent increase in area and production owing to the awareness for sustained production (Table 1).

Introduction

Vegetable crops are an important component of Indian Agriculture. They are known for their short cycle and high productivity per unit area providing a valuable source of income leading to improve livelihood. The prosperity and advancement of a nation largely depend on achieving nutritional security to its people. The vegetables play a vital role as major supplement to food and nutritional security of our people. They are important source of nutrients like b- carotene, vitamin B, C, E as well as folic acid, iron, magnesium, etc. and they also supply fair amounts of carbohydrate, protein, fiber, antioxidants and energy.

Introduction

India (8^o-30^o N and 68-97.5^ºE) exhibits a wide range in topography and climate, which has a bearing on its vegetation and floristic composition. This subcontinent is one of the World’s 12 leading Biodiversity Centres, encompassing 16 different agro-climatic zones, 10 vegetation zones, 25 biotic provinces and about 426 habitats of specific species. It has been estimated that about 45,000 plant species (nearly 20% of the global species) occurs in the Indian Sub-continent. About 3,500 species of both higher and lower plant groups are of medicinal values. More than 80 per cent of medicinal and aromatic plants (MAPs) are collected from 17 million hectares of Indian forest land. However, many of these, due to over-exploitation have become rare (Rheum emodi, Aconitum deinorrhizum), threatened (Rauvolfia serpentina, Berberis artistata) or endangered ones (Sassurea lappa, Dioscorea deltoidea). Problems arising out of rapid genetic loss of medicinal plants forced the need for international co-operation and co-ordination to undertake programmes for conservation of medicinal plants to ensure that adequate quantities are available for future generations.

Introduction

Beauty, purity, love and passion are some of the emotions symbolized by the flowers. The feelings of love, affection and joy are conveyed effectively with these non-speaking beauties of nature, for example a lotus conveys purity, rose love, pansy thoughts and narcissus egotism. Flowers have a definite role to play at almost all occasions of human affairs like birth, marriage, worship, adornments and death. Besides flowers, other ornamental plants also play an important role in environmental planning of urban and rural areas and from wasteland development to overcoming pollution. An important aspect of floriculture is that it is a good avenue to generate gainful employment for youth and women of peri-urban and rural areas.

Introduction

Vegetables are the vital sources of minerals, vitamins and dietary fibres and play an important role in supplying nutrition to human health. Vegetables require comparatively lesser quantities of agro-inputs to grow. Vegetables are rich source of vitamins, minerals and plant fibres which provide food and nutritional security. These also generate high income and employment, particularly for small farmers. Vegetables being a rich and cheap source of vitamins and minerals, occupy an important place in the food basket of Indian consumers, a majority of whom are vegetarian. This persistent vegetarianism coupled with rising per capita income is fuelling a rapid growth in consumption of vegetables. Presently, India is producing more then 70 types of vegetables which are capable of meet out the economic and nutritional requirement of the country (Table 1). There has been a revolution in the production of vegetables in the country in the last four decades.

Introduction

Horticulture is the science of cultivation, management, postharvest handling, value addition and marketing of fruits, vegetables, ornamental, aromatic and medicinal plants, spices and plantation crops. Looking to its important role in nutritional security, poverty alleviation and employment generation, it has rightly been emerged in form of horticulture industry and as one of the most significant sectors in the world. The production of fruits, vegetables and flowers has acquired much importance in recent times due to their increasing demand. Changing lifestyles of people across the globe, attempts to overcome the stressful lifestyle, inclination towards healthy and balanced eating habits have made people include fruits and vegetables in their daily diet. In the case of flowers, the demand for fresh flowers has steadily increased not only for decoration but also for many other purposes like essential oils, cosmetics, aroma therapy, dry flowers, pot-pourries, natural dyes, medicines, etc. Rising incomes and growing consumer interest in a variety of fresh fruits and vegetables year-round is stimulating international trade in horticulture.

Okra/Ladies finger/Bhindi
1. Leaf blight/Spot
Pathogen
Cercospora abelmoschi Ell. & Ev.
Symptoms
The fungus grows as shooty to dark olivaceous, ectoparasite covering entire leaf lamina. Pathogen initiates as small isolated fungal growth on lower side of leaf but very soon it spreads on both sides. Pathogen reduces severely the photosynthesis area. Infected leaves fall down very quickly after dropping and rolling. It causes severe loss in seed production crop as well as in the late sown crops.

1. Damping off
Pathogen
Pythium spp
Phytophthora spp
Fusarium spp
Sclerotium spp
Symptoms
It is a term used to describe the damage caused by various fungi to the seed and emerging seedling in the reduced plant stand and sometimes it is so serious that  resowing becomes inevitable. Major symptoms are the failure of the seedlings decay or sudden death of the emerged seedlings roots and lower stems of emerged seedlings become soft and watery and may be reddish brown in colour.

Cauliflower, Cabbage and Knol khol
1. Leaf spot
Pathogen
Alternaria brassicae (Berk.) Sacc.
Symptoms
Alternaria leaf spot usually appear in early stage in cauliflower while at later stage symptoms in cabbage appear as circular light brown spot in leaves. Concentric rings are clearly visible on the spots. In older plants on leaves, petioles and stem, brown to black circular to slightly elongated spots appear.

Tomato
1. Damping off
Pathogen
Pythium aphanidermatum
Fusarium spp.
Sclerotium spp.
Symptoms
Damping off is the most important disease of tomato. Several seed and soil borne fungi can kill before the tender redical and plumule establish in the nursery bed. The pre emergence damping off and seed rotting is the usual cause of poor seedling stand. This type of damping off causes hidden loss but the post emergence damping off is more serious problem. Seedlings get infected near the soil line (collar region) after emergence and give wire stem symptoms. The tissue become soft, water soaked and weak causing the seedlings fall over and later on they die. The entire action is so fast that leaves remain green but they are unable to stand further.

Vegetables
Peas
1. Rust
Pathogen
Uromyces fabae (Pers.) de Bary
Symptoms 
The fungus produces characteristics rust pustules on the host. Pustules are mostly found on the leaf blade, though often they may be found on the petiole and stem of pea plants. The sori are small, roundish, open, and powdery as well as brown coloured. In severe infections, the leaf may wither, resulting in considerable damage to the crop. As the plants near maturity, the fungus produces the telial stage on the host.

1. Damping-off
Pathogen
Pythium aphanidermatum (Edson.) Fitz.
P. debaryanum                  
Rhizoctonia solani Kuhn.
Fusarium spp.
Sclerotium spp.
Symptoms
Damping-off of onion seedlings occurs in two stages:
    (i)    Pre emergence
(ii)    Post emergence
In pre emergence stage, plumules are killed before they reach the soil surface. They may be infected, killed even before the hypocotyls have broken the seed coat.

Tremendous genetic diversity occur within different crops of this family with respect to their adaptability. Some cucurbits are grown in tropical, subtropical or arid deserts whereas other prefer to grow in temperate conditions. Harvested fruits and vegetables can be potentially exposed to numerous abiotic stresses during production, handling, storage and distribution (Hodges, 2003). However, when the abiotic stress is moderate or severe, quality losses almost always are incurred at market (Toivonen, 2003). Annually about 42% of the crop productivity is lost owing to various abiotic stress factors (Oerke et al., 1994). One of the key factors for abiotic stress in crop plants is the ill effect of global warming which may cause reduced precipitation, less snow pack, and earlier snow melt, leading to drought conditions. In addition about 20% of the world’s irrigated lands are affected by salinity (Zhu, 2001), a situation worsened by climate changes.

2.1 Insect Pests

Insects are often a major obstacle to the successful production of cucurbits (York, 1992). They can severely reduce yield, injure or kill plants, spread diseases and adversely affect fruit quality. A number of insect pests, mites and nematodes have been found to infest cucurbitaceous vegetables but fortunately, in India, fruit flies and a few species of beetles are of economic importance; aphids and blister beetles though of regular occurrence, seldom cause severe damage.
 
Other insect pests reported to infest the cucurbitaceous vegetables are pumpkin caterpillar, Diaphania indica (Sounders), snake gourd semilooper, Plusia peponis Fab., white fly, Bemisia tabaci Genn., stink bugs, Apspongopus spp. and flea beetle, Phyllotreta spp. etc. These biotic pressures on the crops are increasing day by day due to round-the-year intensive cultivation of photo and thermo insensitive cultivars as well as indiscriminate use of toxic agro-chemicals in the present era of chemicalized agriculture.

1.1 Introduction

‘Cucurbits’ is a term coined by Liberty Hyde Bailey for cultivated species of the family Cucurbitacae. During this current century the term has been used not only for cultivated forms, but also for any species of the family Cucurbitacae. Cucurbits are frost sensitive, predominantly tendril-bearing vines which are found in subtropical regions around the globe. A few numbers of species those are native to or cultivated in temperate climate are prolific seed producing annuals or perennials that live for one season until killed by frost (Robinson and Decker-Walters 2004). Other vernaculars applied to the family Cucurbitacae and several of its members are ‘gourd’, ‘melon’, ‘cucumber’, ‘squash’ and ‘pumpkin’.

Current status of researches on VA mycorrhiza and their benefits to the plants carried out by the mycorrhizasts of the country has been described in detail in chapters II to X.

Prior to the establishment of any specific forum, the pace of research on VA mycorrhiza in the country was not of desired level. However, the activities related to research on VA mycorrhiza gained unexpected momemtum when Mycorrhiza network came into exixtence in the year 1989. The network provided not only assistance and guidance of various types to the scientists working on VA mycorrhiza in the country but also offered them periodical platforms to exchange their informations and thoughts on status of researches on VA mycorrhiza and to propose future strategies of research. During the National conferences held in different parts of the country the panel of experts made certain observations regarding future prospects and strategies for research on VA mycorrhiza. They have been mentioned in the present chapter.

The understanding of VAM symbiont and VAM symbiosis is of prime importance in manipulating VAM associations for the welfare of plants. Many contributions have been made worldover in the areas of taxonomy, morphology, anatomy, histology, cytology and genetics of VAM fungi and/or their associations with the plants. However, the share of Indian mycorrhizasts in such contributions is negligible. The following description gives an account of work done by the mycorrhizasts of the country in these areas.

Since a method to cultivate VAM fungi in pure culture is not available as yet, clean and high quality VAM inoculum production is not possible. However, VAM technology is gradually getting a place in agriculture as well as reclamation and afforestation programmes. The inoculum currently being used includes infested fields soils, sievings from such soils, soil and roots of greenhouse plants, or pot culture inoculum derived from surface disinfected spores of a single VAM fungus on a host plant grown in a sterilized growth medium. Attempts are being made to manipulate VAM fungi, rooting media, hosts and fertilizers in order to secure superior quality of inoculum by these methods on a large scale. In addition, other techniques like tissue culture, hydroponic system etc. are also being attempted to cultivate VAM fungi in pure culture. The Indian mycorrhizasts have also attempted to devise and develop improved methods for production and storage of commercial VAM inoculum. The following description gives an account of Indian work related to production and storage of consistently high quality disease free VAM inoculum.

During the last thirty years, there has been a growing appreciation of the impor tance of VAM fungi in improving the plant growth and yield. They have been extensively studied also in India. Considering the potential importance of these organisms in the recovery of disturbed sites and their possible use in land reclamation, researches regarding their relationship to ecosystem recovery have now been initiated also in India.

Large areas of land in the country called wastelands are degraded and lying unutilized due to various constraints. Part of it called culturable, has the potential for the development of vegetation cover. On the other hand, part of it called unculturable, has no potential for the development of vegetation cover. In addition to these natural wastelands, there are large tracts of wastelands created due to human activities such as mining, deforestation etc. Such wastelands are also culturable and a vegetation cover can be developed on them after removing the constraints with some efforts.

Extensive studies have been carried out to explore the possibility of using mycorrhizal model system in inducing suppressions of potential soil-borne pathogens. Its relevance becomes all the more important since most of the soil-borne diseases, by and large, are not easily controlled by conventional methods.

Diseases due to Fungal Pathogens

Most of the studies conducted on the interaction of VAM fungi and fungal pathogens suggest that mycorrhizae decrease the severity of disease, while a few studies suggest that there is either no effect or there is an increase in the severity of disease. It has been pointed out that in view of the fact that VAM fungi deter the severity of disease they may be used as biocontrol agents. Various mechanisms by which VAM could suppress the fungal pathogens have been suggested on the basis of experimental evidences.

Factors which influence the colonization and life cycle of VAM fungi have important bearing on the extent to which they may benefit their host. As we move closer to using mycorrhizal fungi to increase growth and productivity of different plant communities, a thorough understanding of the factors which influence their survival, germination, root colonization an d sporulation will be critical. Seasons, physico-chemical characters of the soil, agronomic practices, plant protection chemicals, pollutants and genotypic characters of the host may affect VAM fungi and their potentiality to colonize and provide benefit to the host. In view of this, the effect of such factors on the VA mycorrhizal symbiosis and its benefit to diverse plant communities has been extensively investigated worldover.

Of the various microorganisms present in and around roots, VAM fungi occupy unique ecological position as they are partly inside and partly outside the host. Their internal phase encounters competition and antagonism from other beneficial symbiotic microbes while their external phase faces competition and antagonism from beneficial non-symbiotic microbes present around the roots. Since they have an ensured source of nutrients from the host, they have comparatively better conditions for their growth and may exert greater effect on plants with other symbiotic and non-symbiotic microbes in and around their roots. It has been pointed out that investigations are needed on the interactions between VAM fungi and these beneficial microbes, and their effect on growth and productivity in plants. A bulk of information has been collected related to this aspect; however, authentic generalization has not been possible as yet. Following description gives an account of the work done by Indian mycorrhizasts on the interactions between VAM fungi and other beneficial symbiotic/non-symbiotic microbes in and around the roots.

Favourable effect of VAM association in plants has been attributed to an increased nutrient uptake by mycorrhizal roots. The transfer of ion from the soil to the roots by mass flow or by diffusion depends on the mobility of that particular ion in the soil. Ions such as NO₃^- ,SO ₄^— and Ca⁺⁺ may move rapidly through the soil to the roots by mass flow, and uptake would be limited by the absorbing capacity of the roots. On the other hand, ions such as H₂PO₄^-, NH₄⁺, Zn⁺⁺ and Cu⁺⁺ are poorly mobile and move to the roots by diffusion, the rate limiting steps is likely to be the movement to the root surface. Under such conditions, it is expected that uptake would be increased if ions could be moved rapidly through extramatrical hyphae of the VAM fungi rather than diffusing slowly through the soil. It is now well established that VA mycorrhizae enhance the uptake of phosphate by the roots but it is likely that they can also assist in the uptake of other ions. The following account provides an information on the findings of Indian mycorrhizasts on the effects of VA mycorrhizal association on nutrient uptake in the plants and its physiological implications.

In recent years the importance of VAM fungi for plant growth in most soils has been accepted and acknowledged by soil chemists, agronomists, horticulturists and farmers. Ever since it was shown that VAM could increase nutrient uptake and water uptake from soil in plants, researchers have been trying to extend and manipulate this effect of mycorrhiza in improving the growth and productivity in various groups of plants. Mycorrhizasts of the country have also explored the possibility of utilizing this tool for improving the performance of various crops including cereals, millets, pulses, vegetables, oilseeds and fruit crops. In addition, they have tried to explore the possibility of utilizing this biotool also for improving the growth of various types of trees including forest trees. Following account is related to the work done by the mycorrhizasts of the country on the effect of VA mycorrhiza on the growth and productivity of various groups of plants including cultivated crops.

VAM fungi are of worldwide distribution. They are present in the soil in form of chlamydospores, zygospores and azygospores and have been recovered from the soils of a variety of habitats e.g. agricultural fields, nutrient deficient soils, sand dunes and deserts, industrial wastes, sodic soils, polluted sites, sewage, eroded sites and others like forests, open woodlands, scrub, savana, heaths, grasslands, anthracite and bituminous coal wastes. There are several reports of VAM fungi from diverse habitats from India.

VA-mycorrhizal associations occur widely throughout the plant kingdom. They have  been reported to be present in Bryophytes, Pteridophytes, Gymnosperms and Angiosperms in nearly all the geographical regions of the world. Most of the agricultural and horticultural crops belonging to diverse families have been shown to form VA-mycorrhizae. Many species of plants of economically important families have been reported to be mycorrhizal. Likewise, many of the plantation crops like coffee, tea, citrus, timber trees, many of the fruit trees and medicinal plants have been shown to form VA-mycorrhiza.

Mycorrhiza research is relatively recent. Although, it was in 1885 that A.B. Frank made reference for the first time to the term “Mycorrhiza”, it took him nine more years to establish the symbiotic relationship between the fungus and its host plant. It took a much longer time to convince the rest of the scientific community of the validity of Frank’s theory. Researches carried out between 1917 to 1950 confirmed that “Mycorrhizal colonization is a beneficial symbiosis between tree and fungus”. It is an unique partnership in nature, where the higher plants share their photosynthates with their fungal partners and provide them shelter, the fungal partners in return provide protection to the root system and assist it in performing its functions especially anchorage and absorption of nutrients / water from soil more efficiently.

The ectomycorrhizal fungi have been in use as a biological tool in improving the performance of forest trees since long. Better performance of forest trees is ensured by making them mycorrhizal, employing efficient strains of ectomycorrhizal fungi.

Abstract

Cyanobacteria were first oxygen evolving photosynthetic organisms on Earth, which not only survived under harsh conditions of primitive Earth but are also dominant and efficient photosynthesizers and N₂ fixers of present time which significantly contribute to fertility of paddy fields as natural biofertilizers. Cyanobacteria require solar radiation to carry out photosynthesis and nitrogen fixation. The stratospheric ozone depletion which has resulted in an increase in ultraviolet-B (UV-B; 280 - 315 nm) radiation on the Earth’s surface has been reported to inhibit a number of photochemical and photobiological processes in cyanobacteria. However, they have evolved mechanisms such as synthesis of photoprotective compound scytonemin and their derivatives to counteract the damaging effects of UV-B. In addition to Photoprotection, scytonemin has biotechnological potentials and several applications in biology and allied sciences.

In factorial experiment it may sometime happen that certain factors require bigger plots than other for convenience of operation of the experiment.  For example, in an agricultural experiment involving two factors, say, irrigation and fertilizer, it is organizationally very inconvenient to apply different levels of irrigation to small neighbouring plots.  But there is no such difficulty for the application of different levels of fertilizer. To meet such situations it is desirable to have different sizes of the experimental units in the same experiment.

In the foregoing experiments performed either in CRD or RBD or LSD. We were primarily concerned with the comparison and estimation of the effects of a single set of treatments like varieties of paddy, different methods of cultivation etc., and such experiments which deal with one factor only may be called simple experiments. In factorial experiment the effects of several factors of variation are studied and investigated simultaneously in a single experiment, such experiments are known as factorial experiments. In these experiments an attempt is made to estimate the effects of each factors and also the interaction effects i.e. the variation in the effect of one factor as a result to different levels of other factors.  These experiments provide an opportunity to study not only the individual effects of each factor but also interactions.  In many biological and clinical trials factors are likely to have interaction. Therefore, factorial experiments are more informative in such investigations.

In many situations, experiments may not known in advance which contrasts they wish to compare, or they may be interested in more than (m – 1) possible comparisons.  In many exploratory experiments, the comparisons of interest are fixed only after preliminary examinations of the data.
 
13.1 Scheffe’s Method for Comparing All Contrasts

Scheffe (1953) has proposed a method for comparing any all possible contrasts between treatment means.  In the Scheffe method, the type I error is at most a for any of the possible comparisons.

12.1 Introduction
 
The design of the experiment includes (i) planning of the experiment (ii) obtaining the relevant information from it regarding the statistical hypothesis under study and (iii) making a statistical analysis of the data. Design of experiment may be defined as the logical construction of the experiment in which the degree of the uncertainty with which the inference is drawn may be well defined. It may also be redefined as the choice of treatments, the method of assigning treatments to experimental units and arrangement of experimental units in varies patterns to suit the requirement of particular problems, are combined known as the design of experiment.

11.1 Introduction

The analysis of variance is a powerful statistical tool for tests of significance.  The test of significance based on t-distribution is an adequate procedure only for testing the significance of the difference between two sample means. In a situation when we have three or more samples to consider at a time an alternative procedure is needed for testing the hypothesis that all the samples are drawn from the same population, i.e., they have the same mean. For example five fertilizers are applied of four plots each of wheat and yield of wheat on each of the plot is given we may be interested in finding out whether the effect of these fertilizers on the yields is significantly different or in other words, whether the samples have come from the same normal population. The answer to this problem is provided by the technique of analysis of variance. Thus basic purpose of the analysis of variance is to test the homogeneity of several means.

10.1 Introduction

In previous lessons we have been dealing with problems connected with variation occurring in any one variable, say the income of a person, the height or weight of an individual, the wage of a worker in a factory, the sales of a shop, demand of a commodity etc.  The values of a single variable were obtained from every member of the population and the different characteristics were described by certain descriptive constants after grouping into frequency distribution.  In this lesson, we shall be dealing with problems wherein there are paired variables and every individual or member of the population exhibits two values, one for each of the variables under consideration.  Example of the two variables which are to be studies together are (i) the income and expenditure of a household, (ii) the price and demand or supply of a commodity, (iii) the height and weight of a student, and (iv) the grain yield and straw yield of paddy, (v) Height of father and height of son, etc.

We have seen the procedures of testing hypothesis about population parameters in chapter 11. Frequently our interest is to test whether a set of observed values are in agreement with those which would occur if some specified hypothesis were true. The X² statistic provides a measure of agreement between such observed and expected frequencies.

The X² distribution has a number of applications in testing of hypotheses. It is used to test, (1) the independence of attributes, (2) the  goodness of fit, (3) the homogeneity of variances, (4) the homogeneity of correlation coefficients, and (5) the linkage in genetic problems. For applying X² test procedure we have to use only the actual observed frequencies and not the percentages or ratios. Further, the samples should be independent and the observations within a sample should be non-overlapping. The expected frequency in each category should be more than 5. The number of observations should be large, say, more than 50.

8.1 Statistical Hypotheses

in attempting to reach decisions about the populations, it is useful to make assumptions or guesses about the populations involved. When the assumption or statement about a phenomenon occurring under certain conditions is formulated as proposition it is called a scientific hypotesis. We can construct criteria by which a scientific hypothesis may be ‘the  yield of a new paddy variety will be 3500 kg per hectare’. In statistical language it may be stated as ‘the random variable (yield of paddy) is distributed normally with mean 3500 kg/ha’. Such a statement or proposition about the probability distribution of a random variable is called the statistical hypothesis.

7.1 Meaning of Sampling
    
Before we consider sampling theory, we first define the terms population and sample.
 
The word ‘population’ or ‘universe’ in statistics is used to refer to any collection of individuals or of their attributes or of results of operations which can be numerically specified. For example the assemblage of heights of all the individuals in the population is called a population of heights.  Similarly we may consider the population of weights, wages, yields of grain; prices of wheat, mileages of automobile tyres, etc. a population containing a finite number of individuals or members is called a finite population.  For instance the population f ages of the workers in a factory constitute a finite population of ages. A population with infinite number of members is known as infinite population.  For example the population of pressures of temperatures at various points in the atmosphere is an infinite population. 

It has been a general notion that if an experiment is conducted under identical conditions, values so obtained would be similar. But the experiences of people have dispelled this belief. Observations are always taken about a factor or character under study, which can take different values, and the factor or character is termed as variable.
Hence, we have a set of outcomes (sample points) of a random experiment. A rule that assigns a real number to each outcome (sample points) is called random variable. The rule is nothing about a function of the variable, say, X, that assigns a unique value to each sample point of the sample space.

In day-to-day life, one comes across many statements which create doubt about certain happenings and one may want to determine the chance of occurrence of a particular happening, e.g., if one desires to know the chance of rain based on some metrological observations.  In the case of coin tossing, one wants to know what will be the chance of winning if a person always stakes for head in a fixed number of tossing. There can be innumerable such queries which one would like to make and meanwhile evaluate mathematically the chance of the occurrence of such possibilities.  This invoked the need of probability theory. The theory of probability came in existence when problems of games were referred to mathematicians like Karl Pearson, Laplace and others. Complicated applications involving advanced theory of probability and axionmatic approach of probability are not dealt within this book.

4.1 Introduction and Measuring

A measure of central tendency exhibits only one of the important characteristics of distribution, namely they typical representative figure to the whole set of its values. This measure alone will not adequately describe a set of observation unless all the observations are alike. Moreover one cannot understand completely about the data set with a measure of central tendency.  Because in real practical situation there may exits a number of sets of observations (or different distributions) whose measures of central tendency are same but they may differ individually from each other in a number of ways.  In particular two sets of values have the same mean but whilst one set of data is grouped close to the mean the other one is more spread out.  The following examples will illustrate this view point clearly.

3.1 Introduction

One of the most important objectives of statistical analysis is to summaries the information contained in the data which may be considered either as a population or as a sample (or sub-population). If the set of data consists of all conceivably possible (or hypothetically possible) observations of a certain phenomenon or a variable, we call it as population. If a set of data contains only a part of these observations, that is selected values of a variable, we call it as sample. Frequency distribution and graphical representation summarize to some extent.  They reduce a mass of data to a more understandable form but not to a single value. The aim of this lesson is to determine descriptive measures or statistical constants which will describe the nature of the data.