eChapters

SOIL WATER

Soil water and oxygen share the pore space in soil and generally the oxygen content is determined by the water content, which is added by irrigation or rains and then keeps on changing due to evapotranspiration. Water is the vehicle by which most nutrients move from the soil to root surface. But for the lowland rice, nutrients are most available to plants at ?eld capacity moisture (about 0.3 atmosphere soil water tension) and the availability decreases as the moisture content decreases to wilting point (about 15 atmosphere tension). That is why rainwater or irrigation increases nutrient availability, while extremely dry condition decreases it. There is thus a signi?cant interaction between water and nutrient availability in soil (Singh et al., 2014). In a study in India (Singh et al., 1980) the yield of wheat was signi?cantly affected by irrigation water and nitrogen treatments; maximum yield was obtained with irrigation at 50% available soil water in 60 cm soil depth and 120 kg ha ^–1 nitrogen addition. A study on wheat at Delhi (Kumar et al., 2015) very well shows the effect of irrigation water on yield and uptake of nutrients (NPK) (Table 5.1).

Introduction

Nitrogen constitutes 78% of the atmospheric gases and there is about 75,000 Mg N on each hectare of land. However, 99% of the atmospheric N is as N₂ and is inert and non-reactive, while the rest 1% or even less is the reactive-N. Reactive-N is linked with H, O and C and is responsible for the creation and sustenance of all life on the planet Earth. Nitrogen is the key nutrient that separates proteins from carbohydrates and fats, the three major macronutrients for humans. As a component of proteins, N is present in DNA and RNA, which carry the hereditary characters and then as the major constitute of the body muscles of humans (and animals). Plant growth and crop production are also very much dependent on the adequate availability of N in soil.

Fertilizer N has been the key input in increasing cereal production throughout the world. In India, it made possible to achieve the yield potential of high-yielding dwarf varieties of wheat that led to ‘Green Revolution in 1968’. Nitrogen fertilization also increases protein content in wheat grains (Rajeswara Rao and Prasad, 1987) and leads to increased production of proteins in cereals (Prasad and Shivay, 2015). Cereal production in India increased from 42.4 million tonnes (Mt) in 1950–51 to 259.6 Mt in 2017–18, while fertilizer N application increased from 0.05 Mt to 16.96 Mt. However, the average agronomic ef?ciency of N (AEn) in India for cereals is only 9.5 kg grain kg–1 N (Sharma and Batra, 2011) as compared to global average of 24 kg grain kg–1 N for maize, 22 kg grain kg–1 N for rice and 18 kg grain kg–1 N for wheat (Ladha et al., 2005). Besides this, more disturbing is the fact that in irrigated areas the AEn declined from 13.4 to 3.4 kg grain kg–1 N during 1970–2005 (Biswas and Sharma, 2006). This is due to poor N management. Bulk of fertilizer N is applied broadcast on surface in most crops.

As compared to total N soil total P is present in much smaller amounts in soil; it is roughly about 10% of total N. Further, while N in soil is in the largest amount in surface 0 to 15 cm layer, soil P may be the same or in larger amounts in the sub-soil. Again, organic P constitutes only a small portion of total P. Thus, the Chemistry of soil P is generally centered on inorganic P. Total and organic P in some Indian soils is given in Table 8.1; hill soils had the highest and the desert soils the least total as well as organic P.

FRACTIONS OF INORGANIC P

All P in soils has originated from apatites [3 (Ca₃ (PO₄)₂.Ca×₂, where ×₂ could be F, Cl, (OH) or CO₃). Large deposits of apatites form phosphate rocks, which are the major materials for making phosphate fertilizers. As the soil weathering proceeds, P in apatite reacts with Al, Fe and other cations and forms compounds of different solubility. A knowledge of these can help in understanding the P-supplying capacity of soils. A number of chemical extractants and resins are used for determining different fractions. In general, 7 fractions of inorganic soil P are mentioned. These are: saloid-P (soluble and loosely bound P extractable by NH₄Cl), labile P (determined by using anion-exchange resins), Al-P (NH₄F extractable), Fe-P (NaOH extractable), Ca-P (H₂SO₄ or HCl extractable), reductant-soluble- P (CDB or sodium citrate-sodium dithionite-sodium bicarbonate extractable) and occluded P (CTB followed by NaOH extractable)

Out of the three primary plant nutrients (NPK), potassium (K) is taken up by crop plants in the largest amount, yet as compared to N and P, only a tiny fraction of it goes in the grain or seed. For example, Shivay et al. (2015) reported from a study on rice that about 20 kg N, 6 kg P (13.7 kg P2O5) and 46 kg K (55.2 kg K2O) was taken up by the crop to produce each Mg or tonne (1,000 kg) of rice kernel; however, only 4.3% of K taken up by the crop was found in the rice kernel as compared to 44% of N and 66% of P taken up by the crop. Some information on N, P and K removed per tonne of grain/ seed for some crops is given in Table 9.1.

Secondary nutrients is a triad of three essential plant nutrients namely, Calcium (Ca), Magnesium (Mg) and Sulphur (S). Of these three, Ca and Mg are taken up by plants as cations, while S is taken up as anion SO4 2–. Among the secondary plant nutrients, sulphur is emerging as a major plant-nutrient de?ciency in crops grown in the Indo-Gangetic Plains, spread over 13 million ha in Pakistan, India, Nepal, and Bangladesh (Khurana et al., 2008). From the Indian point of view, S de?ciency has emerged in a large part of the country and needs to be attended. Uptake of Mg and S by some crops is given in Table 10.1.

There are nine essential micronutrients, namely, iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl), vanadium (V) and nickel (Ni). Out of these, Fe, Mn, Zn, Cu and Ni (Dominic et al., 1978) are taken up by plants in their ionic form X²⁺, Mo as MoO^2-, chlorine as Cl^– form and boron as boric acid (H₃BO₃) or as its ionic form B (OH)₄ ^–. The absorption of vanadium by plants has received only limited attention (Lepp et al., 1983); it may be absorbed as cation V or vanadyl (VO²⁺) and anion vanadate (VO₄ ^3–). Bulk of the information is available on Fe, Mn, Zn and Cu, because of the acceptability of the single DTPA (Diethylene triamine pentaacetic acid)–CaCl₂ extraction test of Lindsay and Norvell (1978) for availability of all these four nutrients followed by their estimation on Atomic Absorption Spectrometer (AAS). Available B is estimated by hot 0.15 M CaCl₂ extraction method (Saha and Singh, 1997). Molybdenum data base is poor, because its determination is dif?cult and Mo de?ciency in crops has not been much noticed in India. Chloride is available in plenty in irrigation water and soil in India and has not received much attention in India.

Internationally maize (Zea mays) and citrus (Citrus sp.) are reported to largely suffer from Zn de?ciency, for which these are considered as marker plants. Zinc de?ciency in maize results in pale or whitish top young leaves and the de?ciency is referred to as 'white bud' (Camberato and Maloney, 2012). In citrus, Zn de?ciency results in ‘rosette’ (cluster of stiff leaves at the end of young shoots) formation (Brennan, 1993). Zinc de?ciency in India was ?rst reported in rice by Nene (1966) at the Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, and given the name ‘khaira’ disease due to dark-brown-coloured spots resembling kattha (Acacia catechu extract used in paan – the betel leaves) on the leaves of zinc de?cient plants. Soon All India Coordinated Project on Micronutrients was launched by the Indian Council of Agricultural Research (ICAR) with headquarters at the Punjab Agricultural University, Ludhiana, which was later shifted to the Indian Institute of Soil Science, Bhopal, Madhya Pradesh. About half of the cultivated soils in the India are de?cient in available zinc. Zinc de?ciency is most in Maharashtra and Karnataka and rice-growing states of north and northeast (Table 12.1). A good response of cereals to Zn fertilization has been reported (Rattan et al., 2008).

Boron (B) de?ciency has been realized as the second most important micronutrient constraint in crop production after that of Zn in the world (Ahmed et al., 2012). However, in Nepal, B de?ciency is more wide-spread than Zn de?ciency, as 80 to 90% of soil samples were de?cient in B, 20 to 50% in Zn and 10 to 15% in Mo (Anderson, 2007). In India, B de?ciency has increased from 2% of the soil samples de?cient in B in 1980s (Katyal and Vlek, 1995) to 52% soil samples in 2000s (Singh, 2012). Total B content in Indian soils varies from 7 to 630 mg kg^–1 soil (Kanwar, 1976); being the highest in arid regions of the country and the lowest in wet humid regions of the country (Behera et al., 2009; Prasad et al., 2014). Boron de?ciency is most in the heavy rainfall areas of Western Ghats of Maharashtra, Karnataka and the eastern states of Bihar, Odisha, Jharkhand and Chhattisgarh states of India (Fig.13.1). The wide-spread de?ciency of B in India can be seen from the fact that B fertilization recorded the highest bene?t : cost (B : C) ratio in rice–wheat cropping system at Palampur (Himachal Pradesh), Ludhiana (Punjab), Faizabad, Modipuram and Varanasi (Uttar Pradesh), Pantnagar (Uttarakhand) and in rice–rice cropping system at Maruteru (Andhra Pradesh), Karjat (Maharashtra) and Jorhat (Asom) (Singh and Goswami, 2014). Response of wheat to B fertilization is also reported from Bangladesh (Halder et al, 2007).

Before the discovery of chemical fertilizer in early 20^th century, organic manures and growing of legumes were the ways of replenishing soil fertility. The only other way was leaving land fallow for a few years before its re-cultivation, a practice followed in shifting cultivation (jhuming) (Garbyal, 1999). This was also true for India, where although the ?rst single superphosphate plant was set up in 1906 in Ranipet (Tamil Nadu), the real use of fertilizer started with the manufacture of urea, the ?rst plant for which was set up in 1959 at Sindri (Bihar) (Tandon, 2014). Organic manures could meet crop-nutrient needs in early days because the average grain yield of most cereals was about 1.5–2.0 t ha^–1, while the average yield of pulses was 0.5–0.75 t ha^–1. However, the crop production scenario changed rapidly after the introduction of dwarf, high-yielding varieties of wheat from Mexico, which led to the “Green Revolution” (Swaminathan, 2013). This was followed by the development of semi-dwarf, high-yielding varieties of rice and hybrids of maize, sorghum and pearl millet. These varieties/ hybrids of cereals needed 100–150 kg N ha^–1 in one growing season, and this could be met only by urea or other N fertilizers; organic manures had no chance and their use became almost nil over a period of next 25 years or so. Well-off young farmers cannot even think of making manure heaps or compost pits, the job is too hard and not a clean one. However, what is ignored is the fact, that organic manures not only supply plant nutrients but also build up soil organic matter, which improves soil physical properties, helps in storing moisture and is the elixir of life for the soil biota (Lal, 2014). A large numbers of reports are available on the effect of adding organic manures and crop residues on improving soil physical (Hati et al., 2007; Brar et al., 2015) and chemical and biological properties of soil (Prasad et al., 1999; Prasad and Mishra, 2001;Sharma et al., 2009; Prasad et al. 2014). Thanks for the organic farming (Prasad, 2005), the interest in organic manures and composts has increased in India and it is now a sought after material. However, it has not entered the main stream of crop production.

Soil-rejuvenation power of legumes in crop rotations has been known in several parts of the world since ages. It is mentioned in the Indian agriculture of the Chalcolithic period (ca 1000 BC) (Raychaudhuri and Mira, 1993), in Chinese agriculture in the Han dynasty (ca 2nd century) (Hsu, 1980) and in Roman agriculture (White, 1970). Legumes can be ?tted in cropping systems in India in a number of ways, such as, a crop in a cropping system, a catch crop in an intensive cropping system, an intercrop and as a green manure. A brief discussion on these follows.

Fertilizer recommendations are generally made on the basis of soil test. Recommendations of fertilizer for top-dressing are best made on tissue testing.

SOIL TEST

A number of approaches have been adopted to increase the precision of soil-test values in making fertilizer recommendations. Four most important ones are discussed.

Low-Medium-High Approach

Making fertilizer recommendations based on soil test for a nutrient involves conducting a large number of ?eld experiments on soils similar to those which are intended for making recommendations. For an individual nutrient (say P for example) experiments are conducted with graded doses of P on a crop for which the fertilizer recommendations are to be made. Thus, agronomic experiments are to be conducted for each crop on each kind of soil. The response curve can then be divided into three sections: a, low soil-test value and high response to fertilizer zone; b, medium soil-test value and medium response to fertilizer zone; and c, high soil-test values and no response to fertilizer zone. In India, this was done

The introduction of high-yielding varieties of wheat and rice, the development of intensive cereal–cereal rotations (rice–wheat, rice–rice, hybrid maize–wheat), application of high doses of N (above 100 kg N ha^–1 to each crop) without adequate P and K application, increased use of high-analysis fertilizer (urea and diammonium phosphate in place of ammonium sulphate and superphosphate) and ignoring the application of organic manures led to heavy depletion of P, K, S, Zn and other plant nutrients, which led to wide-spread de?ciencies of P, S and Zn in Indian soils. These de?ciencies of nutrients led to focus on integrated nutrient management.

Plant nutrients are important for increased production of food for the ever-increasing world population. Of the plant nutrients, primary nutrients N, P and K are applied to ?elds each season in fairly large amounts. In addition to increasing crop yields, they also impact the environment. This is briefly discussed in this chapter; only main points are made here.

NITROGEN

Nitrogen is blamed the most for environmental degradation. It contributes to eutrophication of inland and sea-waters, enrichment of air with NH₃ and N₂O and even with global warming. However, it is almost impossible to grow more food without additional nitrogen. It is estimated that by 2050 about 250 million tonnes (MT) of fertilizer nitrogen may be needed to meet global increased food demands as against an estimated current consumption of 116 MT

1.1 Introduction

Fungi are chlorophyll-less thallophytic plant. Due to absence of chlorophyll, they are heterophytes which depend on other form of life for food. They grow in various habitats and show much diversity in their structure, physiology and reproduction. They evoloved long back from the ancient time.

Their existence was recorded from Pre-cambrian period. Information from ancient literature indicates that the fungi were used as food by men. At present, the fungi are used in medicine as well as food in addition to other aspects. The fungi cause diseases in crop plants (spots, rusts, smuts etc.) and on human beings (Aspergillosis, Blastomycosis etc.).

At present biologists use the term fungus (fungus mushroom, from Greek, sponagos = sponge) to include eukaryotic, spore bearing, achlorophyllous organism that generally reproduce sexually and asexually and whose usually filamentous, branched somatic structure are typically surrounded by cell wall containing chitin or cellulose or both of these substances, togather with many other complex molecules

More than 1.5 million species (Hawksworth 2001; Kirk et al., 2001) of fungi have been recorded, but their number may be much more than the actual record. The subject which deals with fungi is known as Mycology (mykes — mushroom; logos—study) and the concerned scientist is called mycologist. The various definitions of fungi as proposed by mycologists are:

Alexopoulos (1962) defined fungi as “nucleated, spore-bearing, achlorophyllous organisms which generally reproduce sexually and asexually and whose usually filamentous, branched somatic structures are typically surrounded by cell walls containing cellulose or chitin or both”.

Alexopoulos and Mims (1979) defined fungi as eukaryotic spore bearing, achlorophyllous organisms that generally reproduce sexually and asexually, and whose usually filamentous, branched somatic structures are typically surrounded by cell walls containing chitin or cellulose, or both of these substances, together with many other complex organic molecules.

According to G.C. Ainsworth (1973) the fungus is free-living, parasitic or mutualistic, saprotrophs, necrotrophs or biotrophs and devoid of chlorophyll. Cell wall composition very variable, majority contain chitin and glucans, reserve materials glycogen, oil and mannitol, characteristic disaccharide and trehalose. Some yeast-like but majority with thread-like filaments, hyphae, branched profusely to form the vegetative mycelium on which spores are produced, asexually or sexually, free on hyphae or enclosed in complex reproductive structures. Separated mainly on morphology of the latter.

2.1 Divisions: Myxomycota

These are wall-less and quite unusual organisms only included in the fungi as mostly studied by mycologists. Possess either a plasmodium, a mass of naked, multinucleate protoplasm, which feeds any ingesting particulate matter and moves by amoeboid cells. Both of slimy consistencies hence slime molds. Four classes:

2.1.1 Class: Acrasiomycetes (Cellular slime molds)

Assimilative phase, free living amoebae which aggregate to form a pseudoplasmodium before reproduction.

Fungi are achlorophyllus so they have to depend on other organisms hence heterotrophic nutrition. Depending on the nutrition, fungi are classified as Saprophytes, Parasites and Symbionts.

3.1 Saprophyte (sapros = rotten; phyton = plant)

Fungi which get their nutrition only from dead organic are called saprophytes ex: Saprolegnia, Rhizopus, Mucor, Alternaria etc.

3.1.1 Facultative saprophyte (Facultas = ability)

Ability of a fungus to become saprophyte. It is a parasite ex. Ustilago

3.1.2 Obligate saprophyte (obligate = to bind itself)

When they strictly get their food only from dead organic matter and can never become parasites are called obligate saprophyte ex. Mucor.

Reproduction in fungi is the formation of new individuals having all the characters of species. It is of two types. Asexual, somatic, or vegetative reproduction does not involve the union of nuclei of sex cells or sex organs. Sexual reproduction is characterized by the union of two opposite nuclei. During reproduction entire thallus is converted into one or more reproductive units. It is called holocarpic fungi (holo = whole, korpos = fungi) ex. Plasmodiophora and Synchytrium. In Plasmodiophora vegetative body is plasmodium, which is transformed into reproductive structure. In some fungi only a part of thallus is transformed into one or more reproductive structures. (eu = true, good, carpus = fruit). These fungi are known as eucarpic. Both somatic and reproductive structures coexist. Ex. Rhizopus, Puccinia and Helminthosporium.

There are great variations in the life cycles of fungi. Raper (1954, 1966b) recognizes seven basic types.

5.1 Asexual cycle

In which sexual reproduction apparently lacks and diploidy is restricted to somatic diploids. The entire groups known as Fungi Imperfecti and numerous other species which clearly belong to various groups of the perfect fungi such as Penicillium notatum have this life cycle. Certain benefits of sexuality are provided here in many of the sterile forms by para sexual recombination.

In the classification given below only those groups have been given emphasis which contain plant pathogenic fungi or which are important from taxonomic point of view. The description includes only critical features.

For growing fungi, a wide range of media are used. Media affect colony morphology and color. For utilizing different carbon sources some fungi lack the necessary enzymes. For growth and reproduction all fungi require several specific elements. The requirements for growth are generally less specific than for sporulation, so it is often necessary to try several types of media when attempting to identify a fungus in culture. Sporulating cultures should be used because repeated transfers of a pathogen on artificial media usually result in loss of sporulation or pathogenicity or both. Transfer should be made using spores and cultured alternately on nutrient rich and poor culture media. Most fungi thrive on potato dextrose agar (PDA), but in some fungi excessive mycelial growth is obtained at the expense of sporulation. Similarly, wood-inhabiting fungi and dematiaceous (dark pigmented) fungi often sporulate better on Corn meal agar (CMA) or Oat Agar, both of which have less easily digestible carbohydrate than PDA. Cellulose-destroying fungi grow on a weak medium such as Water Agar (WA) or Potato Carrot Agar (PCA). By adding pieces of tissue, such as filter paper, wheat straw, rice, grains, leaves or dung, often produces good sporulation dependent on the organism grown. Some special methods of inducing sporulation in fungi.

Diagnosis of plant diseases require some knowledge of light microscopy to examine infected tissues for the presence of plant pathogens. Most of the pathogens and the diseases caused by them can be identified quickly by using different methods such as section or cutting of infected tissue, squashes of scrapping of plant surface. Homecare, the detail study enquires ultrastructural examination of the pathogen.. Electron microscope rely on a beam of electrons produced from a hot filament (e.g. tungsten) and its power of resolution is much greater than light microscope. Electron microscope are of two type

When any serious work is undertaken involving the use of living cultures it is necessary to keep these alive for use during the work and for future reference.

This can be done either by growing on a suitable substrate and transferring to fresh media, as the nutrient is used up or by treating the cultures in some way, which halts metabolism until they are revived for use. The former method is time consuming and cultures are at risk whenever they are handled, so various means are devised which can lengthen the periods between sub culturing. The latter methods tend to be complex and expensive.

Agriculture has been the base of human livelihood since ancient time when the man started planting of seeds of some edible plants now called Agricultural crops. Domestication of food plants and animals was started with the development of human civilization. Thus agriculture can be explained as science and technology of growing food crops and rearing of animals. Still in several countries of the world, most of population is based on agriculture for their livelihood particularly in rural areas of that country. According to Williams and Haq (2002) there are over 7000 species of plants that can be used for food. The edible plants species grown for food are called agricultural crops. The crops grown in garden are known as garden cops or Horticulture crops. Horticulture is a branch of agriculture, which deals with intensive cultivation of garden crops such as fruits, vegetables, f lowers, ornamental plants, plantation crops, spices, medicinal and aromatic plants, and mushroom. It also deals with post-harvest technology of horticultural crops. Processing and Preservation of fruits and vegetables is a part of Post-harvest Technology of horticultural crops which deals with methods of processing and preservation of these crops to extend the shelf life of fruits and vegetables after harvesting.

All horticultural crops have their own importance in our society. Fruits, vegetables and spices are major ingredients of our meal. Spices add taste and flavor to our food and also have high medicinal values. Flowers and ornamental plants are used for decoration of environment and landscape. Aromatic and plantation crops have become industrial crops. Mushroom growing is a great enterprise. Among these crops fruits and vegetables are major crops and have been considered presently as highly economical and important food crops. There are 1200 crop species are used for vegetable purpose in the world (Hazra and Som, 2006). Fruits and vegetables are richest and cheapest source of all essential nutrients (carbohydrates, fat, protein, vitamins and minerals) required by our body for proper functioning of body organs and maintaining good health. Besides these nutrients they also supply water and fibers to our body which play vital roles in our body. Fruits and vegetables have important place in our daily diet and based on survey made by experts FAO WHO (2003) has recommended 400 g/capita/day of fruit and vegetables (fruits -100 g/capita/day and vegetables -300 g/capita/day) to be consumed for good health and prevent chronic diseases. Therefore, the demand of these food commodities has increased in the modern society due to increased awareness of the nutritional importance of fruits and vegetables. So that people must be aware that what part of fruit and vegetable is to be consumed?

World Scenario

The world climatic conditions are divided into Tropical; Sub-Tropical and Temperate climates. Fruits and Vegetables suited to these climatic conditions are grown successfully. Considering the nutritional and economic importance of fruits and vegetables, there is tremendous increase in area and production of fruits and vegetables throughout the world. The present global scenario of fruit and vegetable crops (areas harvested, production and productivity (yield) has been given in Table 1. It shows that the fruits 865.88 million tones has been harvested from 65.24 million Ha land with productivity 13.27 t/ha (Table 1) where as vegetables produced 1075.20 million tonnes from area 57.00 million ha with yield 18.86 tonnes/ha (Table 1) during 2016.

The food we eat contains nourishing substances called nutrients which are required by human body for proper functioning and maintenance of body health. They are classified into five groups such as:

Carbohydrates,

Protein,

Fats,

Minerals

Vitamins

Fruits and Vegetables are highly perishable in nature due to which huge spoilage (damage) takes place during the period between harvesting and consumption. Fruits and Vegetables after harvesting are often poorly handled and in many cases neither cleaned nor washed. Improper handling may cause physical damage due to tissue breakdown which results mechanical damages and physiological changes in harvested fruits and vegetables. Mechanical losses include bruising, cracking, cuts, microbial spoilage by fungi and bacteria and physiological losses include changes in respiration, transpiration, pigments, organic acids and flavour.

Processed fruit and vegetable are considered as staple food products throughout the world, and are becoming more popular with the increase of the global urban population. As a result, demand for processed fruit and vegetable products tends to increase with population growth in the world. There is strong demand for processed fruits and vegetables in the developing world over the past few years. In poor countries, people consume less fruits and vegetables due to the relatively high prices. All forms of preserved fruits and vegetables are available only to the urban elite people. But rural mosses producing more than 90 % of these fruits and vegetables are usually deprived of their uses.

Demand of Processed Fruits and Vegetables

Demand of processed fruits and vegetables is increasing in the developing as well as under developing countries of world. The following reasons are responsible for day by day increasing demand of processed fruits and vegetables.

After harvesting the quality of fruits and vegetables begins to diminish and products is edible for only a limited time then products begin to spoil or rot. Losses occur during harvesting and handling of fruits and vegetables can be minimized by proper techniques but processed food spoilage is bit difficult to control and stop after infection and contamination of microorganism.

Spoilage

Spoilage is deteriorative process which results reduction in quality of food (fruits and vegetables) which become inedible. The changes in food that cause it to lose its desired quality and eventually become inedible is called food spoilage or rotting. After harvesting, the quality of fruits and vegetables begins to diminish and product is edible for only a limited time. The deterioration and spoilage of fruits and vegetables may occur at different ways.

The losses in harvested products begin immediately after detachment of products from their parental plants. After some time, theses products begin to spoil or rot. Spoilage can be defined as the deteriorative process which renders the food inedible or results in reduction in quality. Spoilage of fresh fruits and vegetables usually occurs during storage, transportation and during processing. They also get contaminated with spoilage organisms either from each other or from the containers. Mechanical injuries during harvesting and transportation further aggravates the deterioration process.

The fruits and vegetables are highly perishable in nature. The losses in harvested fruits and vegetables start immediately after harvesting and the resulting spoilage caused by biochemical changes (enzymatic) and activity of microorganisms such as bacteria, moulds and yeast. The losses caused by the microorganism in fruits and vegetables products can be prevented by controlling or destroying these organisms in order to preserve fruits and vegetables by processing and preservation means. The processing and preservation is one of the most important activities among various types of activities of Horticultural Science.

Processing: The processing can be defined as an activity, which is performed to maintain or improve the quality or to change the form or characteristics of the product. Processing operations are undertaken to add value to horticultural produce after their production. The main purpose of processing is to minimize the qualitative and quantitative deterioration of produce after harvest.

Preservation: Preservation can be defined as the science which deals with the methods of prevention of decay or spoilage of produce and allow it to be stored in a fit condition for future use.

Fruits and vegetables can be preserved for short and long term. For short term preservation can be achieved by proper handling of produce and low temperature storage. Long term preservation can be achieved by canning, drying and dehydration, fermentation and by using chemical preservatives.

The basic processing and preservation techniques such as canning, freezing, dehydration, salting, pickling and freeze drying are designed to change perishable foods into more usable form and prevent undesirable changes caused by microorganisms, or by chemical, physical and biochemical reactions in the food itself. Hence an ideal processing technology would involve prevention of growth of microorganisms and at the same time retention of f lavor, texture, nutritive value and palatability of the products.

Processing and Preservation

Processing and preservation is the best way of utilizing surplus production of fruits during seasonal gluts.

In the physical methods of preservation, fruits and vegetables are preserved by (i) adding heat, (ii) removing moisture content of produce to prevent spoilage and (iii) irradiated by Gama rays which kill the microorganisms responsible for spoilage of foods. These methods are described below.

Processing and Preservation by Adding Heat or Heating

In this method, heat treatment is given to destroy the microorganisms which are responsible for spoilage of the produce. Heat treatment is given by many methods.

In the previous chapter the physical methods of fruit and vegetables processing and preservation have been discussed. The present chapter deals with chemical method of fruit and vegetable preservation. In this method of preservation of fruits and vegetables, chemicals as preservatives are used to prevent the spoilage of fruit and vegetable products. These preservatives react with food (produce) constituents or microorganisms and create unfavourable conditions which hinder growth, activities and multiplication of microbes responsible for spoilage of food products. These chemical agents have maximum permissible limit of their use as law. They can be classified into two classes class I and class II.

Class I: Sugar, Salt and Oils

Class II: Sodium benzoate, Potassium metabisulphite (K M S) and Sorbic acid

Sugar also acts as preservative at high concentration 70% or more in food products (fruit and vegetable products). High concentration of sugar in food materials create unfavourable conditions for microbial survival and prevent spoilage. Based on this principle of preservation, sugar based products are prepared from fruits and vegetables so that they can be preserved for long time. This method of preservation with high sugar concentration is principally based on the reduction in moisture content to arrest or stop microbial spoilage. Preparation of sugar based products is one of the most important aspects of home scale as well as industrial level processing of fruits and vegetables. Sugar based value added products include.

Fermentation

The decomposition of carbohydrates by microorganisms and enzymes is known as fermentation. During fermentation process of food organic acids and alcohol etc are produced which act as preservatives and also provide fine flavor and aroma that increase the value of raw materials. Most fermented foods contain a complex mixture of carbohydrates, proteins and fats etc. Fermentation occurs when microorganisms consume susceptible organic substances as a part of their own metabolic processes. Natural fermentation is probably oldest form of food preservation.

Preservation of food (fruits and vegetables) in common salt sand vinegar is called pickling. It is one of the most ancient method of preservation of fruits and vegetables. Pickling is the result of fermentation by Lactic acid forming bacteria which are found in large number on the surface of fruits and vegetables. They can grow in acidic medium and in the presence of 8-10 percent salt solution. The growth of majority of undesirable bacteria is inhibited. Lactic acid most active at 30 °C temperature. This temperature should be maintained during the process of pickling.

Preparation of pickles

Pickles are prepared with salt, vinegar and oil or combination of these ingredients. Spices are also used for pickle preparation.

Process of preservation of food stuffs such as fruits and vegetables whole or in pieces in sugar syrup or brine by heating them in hermetically sealed containers for long storage is known as canning. In other words canning is the process of sealing food stuffs hermetically in containers and sterilizing them by heat for long storage.

Several products of fruits and vegetables are prepared on commercial and home scale. Products development from fruits and vegetables is the best way to utilize excess produces and save them from post harvest losses..

Value Addition

This is the process of improving the value of a commodity through processing by changing its form, increasing its shelf life or better presentation like packaging. Value addition can be done through the ways.

Packaging

Packaging is a mean or system by which a fresh or processed product will reach from the production center to consumer in safe and sound condition at an affordable price.

Objectives of packaging and packaging materials

The primary objective or packaging is to protect the contents during storage, transportation and distribution against deterioration. It may be physical, chemical or biological. However, followings are objectives of packaging and packaging materials.

Several fruits and vegetables are unexploited for proper utilization and product development. Due to lack of utilization, there is a lot of wastage and ultimately the great loss to the people as well as nation. Some unexploited fruits and vegetables have potential for introducing new products. Therefore unexploited fruits and vegetables have to be exploited for new product development especially from underutilized sub-tropical and tropical fruits and vegetables. Research and development should be undertaken to utilize these fruits and vegetables.

Unexploited Fruits

Unripe Green Mango: Although pickles are prepared but droped green mango fruits are not preferred for pickle preparation. They can be dried and utilized for preparation of dried slices or amchur. Amchur is used to develop flavor and taste in Ice cream. These products are used to develop flavor and taste in meal or food. It is also used to prepare chatney. But utilization of Amchur is not known to common people.

Avocado: It is found in tropical and sub-tropical climatic regions having more humidity and rainfall. In Ethiopia it is found throughout the country but not utilized properly by people. They prefer to eat ripe fruits with salt and lime juice. It is very healthy fruit for chronic disease like cardiac and diabeted diseases. This is seasonal use but no product is available for off season. Therefore researches should be carried out for different products development of Avocado products.

Of the 7 billion global population, about 800 million do not have enough food to eat and majority of the them live in developing countries. By 2050, the world population is estimated to reach 9 billion. Plant pests and diseases are responsible for losses of 20 to 40% of global food production. Due to increasing global trade and a changing climate, plant diseases pose a major threat to food security today than ever before. Agriculture will have to cope with weather fluctuations that can affect the survival, distribution and multiplication of plant pathogens apart from shift in pathogenic microbial flora. Emergence of new races of pathogen potentially threaten the production of food. To cite an example, migration of 13 -A2 clonal lineage of Phytophthora infestans from Europe, during 2013, devastating tomato and potato in India. Plant pathogens also impact on environment sustainability, forest health, recreational horticulture, human and animal health.

The science of plant pathology can play a much needed role in alleviating hunger and malnutrition through development of affordable solutions for devastating plant diseases leading to increase in food production. It hold promise to ensure quality produce by containing microbial invasions and toxin contamination of food crops. Plant Pathologists have an important role to play in meeting the food security need of the nation by developing technologies for ensuring proper crop health. There is an urgent need to produce more food per unit area for feeding rapidly increasing human population. We need to act ahead of pathogens in our efforts to ensure normal crop yields. Cutting edge biotechnologies such as CRISPR gene editing systems and RNA interference are being exploited to rapidly developed crop varieties having resistance to specific pathogen races.

Crop protection has come a long way from predominantly chemical based approaches to more environment friendly IDM technologies including green chemistry. There is a need to develop bio-intensive modules for management of diseases. Decision support system need to be developed for important diseases for their timely, more efficiently management. There is need to adopt information technology at a larger scale to facilitate quick dissemination of new crop protection solutions among the farmers and other stakeholders.

History in general reveals chronological account of important events, contribution of persons who significantly influenced the thinking of their era and the interpretations of the observed facts or phenomenon over the period of time. The progress in plant pathology leading to the major land mark in mycology, plant bacteriology and plant virology will be discussed in chronological order for easy and better understanding.

There is a very impressive and extensive number of terms and definitions used in plant pathology, many of which you will not come in contact with. With interest, study and practice, terms and names will come to light and become familiar to you. When you start out, don’t worry too much about the terms; but also don’t be afraid of them. The more exposure you have to the subject the more comfortable you will be when dealing with your peers and the public. With these you are going to be exposed to some terms and definitions that will be a good ice breaker and prepares you for the information to follow

Definition

Pathogenesis can be defined as the chain of events leading to the development of a disease. In another words it is also called disease cycle.

It tells us about

The Disease Triangle and Disease Pyramid

The disease triangle is one of the first concepts encountered by students in an introductory plant pathology course and often may be encountered in higher level classes. The interactions of the three component namely (1) susceptible host (2) virulent pathogen and (3) favorable environments have been visualized as a triangle, generally referred to as the “DISEASE TRAINGLE”. Each side of the traingle represent one of the three components. The length of each side is proportional to the sum total of the characteristic of each component that favor disease. For example, the more virulent and abundant the pathogen, the longer the pathogen side would be and the greater the potential amount of disease. Similarly if the plant are resistant, the widely spaced or wrong age, the amount of disease would be small or zero. Where as if the plants are susceptible, at a susceptible stage of growth, or densely planted, the host side would be long and the potential amount of disease could be great. Also, the more favourable the environmental conditions that help the pathogen, or that reduce host resistance, that longer the envirnmental side would be and greater the potential amount of diseases. If the three component of the disease traingle could be quantified, the area of the traingle would represent the amount of disease in a plant or in plant population. If any of three component in zero, these can be no disease.

There are number of diseases which attacks crop plants. Therefore It is mandatory to classify plant disease into more manageable and more specific group based on several criteria for easy and better understanding. Let us discuss one by one.

1. On the basis of type of infection

On the basis of type of infection disease can be classified into two types

Plant diseases are classified on the basis of type of pathogenic or non-pathogenic causes of the disease. The classification is based on the plant pathogenic organisms as follows.

A. Parasites

The diseases are incited by parasites under a set of suitable environment. Association of definite pathogen is essential with each disease. They include both biotic and mesobiotic agents.

Biotic agents: They are also called as animate causes. They are living organisms.

Fungi

Definition

Fungi are eukaryotic, spore bearing, achlorophyllus, heterotrophic and thallophytic plants with varied forms and habitats, representing heterothallic or homothallic types of sexuality with characteristic sexual and /or asexual means of reproduction without tissue differentiation.

Definition

Plant disease in which no pathogens or parasitic is associated with the cause is known as Non-parasitic disease. They are also called as noninfectious or physiological disorders.

General Characteristics

Occurs in the absence of pathogen and therefore, cannot be cultured or transmitted.

Caused by the lack or excess of something that supports life from diseased to healthy plants.

Effect plant in all stages of their lives, such as seeds, seedlings, mature plants or fruits.

Symptoms may range from slight to severe & affected plants may even die.

These disease cause damage in field, in storage or at the market.

a) Definition

Fungus is Latin word meaning ‘mushroom’

Alexopoulus and Mims 1979 defined fungus as eukaryotic, achlorophyllous organism generally produced by sexual or asexual method and whose filamentous branched somatic structure is typically covered by cell wall.