eChapters

Nitrogen is the most important element on which depends growth and productivity of plants. It is also the most abundant molecule in the atmosphere (80%), yet it cannot be utilized by plants. The plant utilizable form of nitrogen is either, its most oxidized form, the nitrates or the most reduced state, the ammonia.  The indiscriminate use of nitrogenous fertilizers amounts to depletion of non-renewable fossil fuels used in fertilizer production. Sustainable agriculture depends largely on renewable resources and on-farm nitrogen contributions are achieved largely through biological nitrogen fixation (BNF), which helps in maintaining and/or improving soil fertility by using atmospheric nitrogen. Annually BNF is estimated to be around 175 million tonnes of which close to 79% is accounted for by terrestrial fixation.

Phosphorus is one of the essential nutrients for plant growth. It is an integral part of the cellular activities of the living organisms. It has a defined role in plant metabolism such as cell division, development, photosynthesis, break down of sugar, nutrient transport within the plant, transfer of genetic characteristics from one generation to another and regulation of metabolic pathways. Phosphorus is a frequently limiting macronutrient next only to nitrogen for plant growth and makes up about 0.2% of plant dry weight. The plants obtain their P requirement from the soil pool. It occurs in soil as inorganic phosphates, produced by weathering of parent rock or as organic phosphate derived from decayed plant, animal, or microorganisms.

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

Emphasis of present day agriculture is to produce more with lesser land, water and man power. Apart from natural calamities like drought, flood etc., biotic stresses like pests, diseases and weeds also influence the crop productivity greatly. Sixty to eighty per cent of the total crop losses are attributed to the devastations caused by pests and diseases. Farmer’s income in recent years is decreasing gradually due to increased cost of inputs particularly in plant protection. The excessive dependence on chemical pesticides leads to the development of resistance in insect pests and pathogens, out breaks of secondary pests and pathogens / biotypes and occurrence of residues in food chain. To avoid this situation the concept of Integrated Pest Management (IPM)/ Integrated Disease Management (IDM) approach should be considered on top priority.

The adoption of modern agricultural technologies has culminated into serious problems of pesticide resistance in major pests, resurgence in minor pests, elimination of populations of natural parasites, predators and pollinators, environmental pollution, pesticide residues in food chain and health hazards. World Health Organization (WHO) estimates one million pesticides poisoning cases and 20,000 deaths every year globally. This is due to high pesticide residues in food chain including cereals, pulses, vegetables, fruits, milk and milk products (including mother’s milk), fishes, poultry, meat products and water. Twenty five per cent of Indian food products contain pesticide residues above tolerance level compared to only 1.2% globally.

Herbicides are the chemical substances used to kill weeds, i.e., unwanted plants that compete with crop plants for soil nutrients. Chemical herbicides are the most effective immediate solution to most weed problems. Use of chemicals, however, can be harmful to wildlife, to the environment and to humans. Chemicals are also expensive, and weeds develop resistance to the chemicals. For these reasons, there is now a move toward alternative methods of controlling the weeds. One of the most promising is biological weed control, which involves using one living organism to control the activities of another organism.

Sustainable agriculture or organic farming wherein biological inputs are maximum and chemical inputs are minimal, is drawing the attention of farmers across the world including India. For replacing chemical fertilizers, which supply plant nutrients by organic manure, the basic requirement is the availability of raw material i.e. the organic matter or biomass that can be decomposed to organic manure. The question that is often asked is what are the different sources of available biomass and how much of it is available? Different sources of biomass can be categorized as

Microbial inoculants in agriculture, horticulture and forestry can be defined as preparations containing strains of microorganisms which can augment the microbiological process such as nitrogen fixation, phosphate mobilization, excretion of growth promoting substances, decomposition of organic wastes, biocontrol of insect pests and diseases etc. Thus they become an important component of sustainable agriculture. Microbial inoculants are based on renewable sources available in soil and nature and are low cost input and eco-friendly. These inoculants carrying the microorganisms when applied to soil/plant promote plant growth and productivity.

Plants have been a major source of therapeutic agents since time immemorial. The increasing acceptance of traditional herbal systems of medicine, like Ayurveda, within India and outside has resulted in the revival of ancient traditions of medicine. Medicinal plants and their derivatives are thus looked upon not only as a source of affordable healthcare but also as an important commodity item of international trade and commerce. As per World Health Organization estimates, traditional medicines, mostly plant drugs, cater to the health needs of nearly 80% of the world population. The medicinal plant related trade is growing rapidly every year due to the growing recognition of natural products being non-narcotic, with relatively less side effects and being easily available at affordable costs.

In India, medicinal plant sector has traditionally occupied an important position in the socio-economic, cultural and spiritual arena of rural and tribal lives. About 8000 flowering plants, 650 lichens, 650 algae, 200 pteridophytes and 150 bryophytes are attributed with medicinal properties. The Indian coded systems encompasses a large number of treaties on recognized systems of medicine viz. Ayurveda, Unani and Siddha. The Ayurvedic system of medicine, which cater to the health needs of a major segment of population currently utilizes as many as 1000 single drugs and over 8000 compound formulations of recognized merit. Other systems of medicine viz. Siddha, Unani and Amchi (Tibetan) systems of medicine together utilize about 1800-1900 medicinal species. Many medicinal plants are the source of clinically useful prescription drugs being used in modern systems of medicine. Also incredible knowledge on phyto medicine is acquired in non-coded form by tribals and rural community, as is clear from evidences related to folklore medicine. Recognizing their importance, medicinal plant sector has been identified as one of the key areas by the Government of India and the Department of Indian System of Medicine and Homeopathy.

Phytochemistry

Pytochemistry is concerned with enormous variety of organic substances that are elaborated and accumulated by plants and deals with chemical structures of these substances and biosynthesis, and their natural distribution and biological function. Chemical constituents of plants can be classified in different ways. Based on biosynthetic origin, solubility properties and presence of certain key functional groups, it is classified as phenolic compounds, substances that are readily recognized by their hydrophilic nature and by their common origin from aromatic precursor shikimic acid. Terpenoids share lipid properties and a biosynthetic origin from isopentenyl pyrophosphate (Fig. 1). Organic acids, lipids, alkenes and related hydrocarbons, polyacetylenes and sulphur compounds are derived biosynthetically from acetate. Nitrogen compounds of plants like amino acids, amines, alkaloids, cynogenic glycosides, indoles, purines, pyramidines and cytokinins and chlorophyll are basic substances recognized by their positive responses to either ninhydrin or Dragendorff reagent. Monosaccharides, oligosaccharides, sugar alcohols and cyclitols are water-soluble carbohydrates and their derivatives. Macromolecules of plants such as nucleic acids, proteins and polysaccharides are easily separated from other constituents by their high molecular weights (Harborne, 1984). Some of the therapeutically active compounds are discussed below:

Medicinal plants and their various products are extensively utilized not only in traditional systems of medicine but also in modern medicine throughout the world. In recent times, they have also attracted attention of scientists encompassing various disciplines of medicine and biotechnology for search of new drug molecules and modern drug development. Although several research strategies are followed for drug development only the traditional, empirical and molecular methods/strategies are mostly applied. There is also need of scientific validation for safety, efficacy and rational use of traditional form of medicine along with development of standards for identity, purity and strength (Singh and Bagchi, 2002).

Approaches of Drug Developement

Following approaches are generally employed to discover and invent new therapeutic agents from plants viz. screening of plant materials, identification of active constituents, pharmacological and clinical evaluation and drug design.

Good Agricultural Practices

Guidelines for Good Agricultural Practices of Medicinal and Aromatic Plants is intended to apply to the growing and primary processing of all such plants traded and used in food, feed, pharmaceutical, flavouring and perfume industries. The main aim is to ensure that the raw material meets the demands of the consumer and maintains standards of the highest purity. Important aspects are that, these are produced hygienically, in order to reduce microbial load to a minimum, and are produced with care, so that the negative impacts affecting plant during cultivation, processing and storage can be minimised. The guidelines provide guidance for producers to reduce raw material contamination to the lowest level. This document can be used in bilateral relationship between the supplier and the customer and the products documentation is regarded confidentiall (EUROPAM).

Aloe, known for laxative property is one of the old natural remedies that have emerged as modern miracle drug. Popularly known as ‘nature’s sun screen’ has growing use as skin tonic in cosmetic industry and as a nutraceutical. Aloes are also quite popular among succulent ornamental plants because of their stiff, harsh and rugged habit and are commonly grown in deserts and other dry situations. Genus Aloe is indigenous to African continent and Mediterranean countries such as Greece and Southern Italy, and got naturalized in arid tracts of India. In India, Aloe barbadensis is cultivated on a small scale in Rajastan, Andhra Pradesh and Gujarat (CSIR, 1998).

Botany

Genus Aloe belonging to Liliaceae comprises 275 species distributed in Africa, Asia and America. Forty-two species belong to Madagascar region, 12-15 to Arabian Peninsula and rest are distributed over tropical South Africa. Aloe barbadensis, A. ferox and A. arborescens are used as herbal drugs. In India, only four species occur and of these, Aloe barbadensis is the most widely naturalized species. These taxa comprise several varieties viz., officinalis, chinensis, littoralis and they cross freely and several intermediary forms occur in semi wild state.

Aconites, the tuberous roots of which contain highly toxic alkaloids, are deadly poisons. In small doses, aconites are beneficial in nasal catarrh, sore throat, gibbous, paralysis and chronic fevers. Aconitum is a genus of perennial, erect or rarely twining herbs distributed over North temperate regions of world. The mountains of Eastern Asia form the primary centre, presenting the greatest diversity of genus. About 28 species are reported from India, mostly confined to alpine and subalpine belts of Himalayas. Of the Aconitum spp. occurring in India, roots of nine species are obtained in Indian market. In fact, aconite sold in Indian market is a mixture of 304 species. Still, A. ferox, known as Indian Aconite, is considered the most important.

A. ferox is a perennial herb with tuberous roots. Roots are paired, daughter tuber, ovoid oblong to ellipsoid, with filiform root fibres. Leaves are scattered, orbicular-cordate to reniform, palmately 5 lobed, resembling melon leaves. Petioles are pubescent. Flowers are pale dirty blue, borne in a dense terminal raceme, 10-25 cm long. Follicles are oblong with long, obovoid winged seeds.

Allard (1960) defines germplasm as “the sum total of the hereditary  materials in  species” The word germplasm in context of plants is now referred to as plant genetic resources i.e. PGR.PGR is a component of the world’s biological diversity. The term biological diversity is a vast and often undervalued resource. Biological diversity includes every form of life, from the smallest microbe to the largest beast. Biodiversity is the variety and variability of all plants, animals and microorganisms and the ecological complexes of which they are part. The earth’s biodiversity – its ecosystems, species and genes – are the product of over 3000 million years of evolution. Throughout this time, small changes have accumulated in populations, resulting in a multitude of living forms closely adapted to the physical conditions they face and to each other. They supply all our food, much of our raw materials and energy and many of our medicines. Intact eco-systems also play a central role in the functioning of biosphere. Plants are of crucial importance in stabilizing climate, protecting watersheds on soils and maintaining the chemical balance of the earth. When key species are lost, vital ecological services are disrupted (Zedan, 1995).

The National Bureau of Plant Genetic Resources, commonly known as NBPGR was established by the Indian Council of Agricultural Research (ICAR) in 1976 with its main campus at New Delhi. Being the nodal organization in India it has been given the national mandate to plan, conduct, promote and coordinate all activities concerning plant exploration and collection and also for safe conservation and distribution of both indigenous and introduced genetic variability in crop plants and their wild relatives. The Bureau is also vested with the authority to issue Import Permit and Phytosanitary Certificate and conduct quarantine checks on all seed materials and plant propagules (including transgenic material) introduced from abroad or exported for research purposes.

Plants are vital part of the world’s biological diversity and essential resource for human well being. Besides meeting our basic food and fibre requirement, many thousands of wild plants have immense economical and cultural importance and potential for providing food, medicine, fuel, clothing and shelter for vast number of people at the global  level. Traditional Chinese medicines use around 5000 plant species and about 7000 different plants are used in traditional medicines in India. Plants play an important role in maintaining basic ecosystem functions essential for survival of animal life. Thus, it is of vital importance to collect and conserve the plant genetic resources on a global basis. It is all the more important as several cases of genetic vulnerability of plants that are grown for food and other uses have been recorded (National Research Council, 1972, Granett et al., 1991). Genetic diversity in the germplasm of crop plants is an effective defense against genetic vulnerability. The genetic diversity is strategically used as modern plant breeding intervention to help increase stability and sustainability of food production using modern cultivars.

Historically, Indian scientists have recognized the importance of conserving plant biodiversity with particular reference to indigenous     and naturalized crops and their wild relatives. Indian scientists have recognized the importance of conserving plant biodiversity as early as 1935 by the ‘Crops and Soil Wing’ of the then Board of Agriculture and Animal Husbandry. Late Dr. B. P. Pal, in his classic paper ‘Search for New genes’ published in 1937 emphasized the importance of germplasm augmentation and utilization in crop improvement programmes. The need was reiterated in a meeting of the Indian Society of Genetics and Plant Breeding in 1941, which inter alia discussed the subject of economic crops. Dr. B. P. Pal, working at the then Imperial (now Indian) Agricultural Research Institute approached the then Imperial (now Indian) Council of Agricultural Research (ICAR) to set-up a unit for assembly of global germplasm under phytosanitary conditions in India. The ICAR scheme for plant introduction started functioning in 1946 under the leadership of late Dr. Harbhajan Singh as the first ‘Operational Scientist’. The scheme was further expanded and strengthened as ‘Plant Introduction and Exploration Organization’ in the Botany Division in 1956 and later established as a separate Division of Plant Introduction in IARI in 1961 headed by Dr. Harbhajan Singh.

IPGRI founded in 1974 is the world’s largest international institute dedicated solely to the conservation and use of plant genetic resources. It is located at Rome in Italy. The institute is funded by the Consultative Group on International Agricultural Research (CGIR) which is an informal association of 45 public and private sector donors. CGIAR supports a network of 16 International Agricultural Research Centres. The Group was established in 1971. It is cosponsored by the Food and Agriculture Organization (FAO), the World Bank, United Nations Development Programme (UNDP), and the United Nations Environment Programme (UNEP).

The place of origin of the crop plant can be found out on the basis of genetic affinities. This would mean to find out the geographical distribution of the wild progenitors of the cultivated plants. If one can locate the distribution of a given progenitor, one can delimit the area in which domestication could have occurred. Vavilov based his judgment on variation patterns in cultivated plants. Information on wild plants in those days was much more fragmentary than what it is today. Even today, genetic and ecological information on wild relatives of several cultivated plants is incomplete and in such cases assessment of a place of origin is difficult to make. However, in most cases required information is available on genetic affinities between wild and tame, on distribution areas and on ecological affinities of the wild progenitors. On this basis it is possible to determine the initial place of origin.

Biodiversity is the foundation stone of human survival on the earth. Very appropriately, the theme of the World Food Day celebration, 16 October, 2004 was “Biodiversity for Food Security” Biological diversity is fundamental to agriculture and food production. Scientists have identified so far about 1.4 million of the plant and animal species that exist on earth. A rich variety of cultivated plants and animals serves as the foundation for agricultural biodiversity. Yet people depend on just 14 mammal and bird species for 90 % of their food supply from animals. Just four plant species, namely, wheat, maize, rice and potato provide half of our energy from plants (FAO, 2004).

India is located between 8^°- 38^° N and 68^°- 97^ºE and exhibits extreme variation in altitude — from sea level to heights above vegetational limits in the Himalayas (ca 4500 m), and climate — from monsoon- tropical in south to temperate and alpine in the north-western Himalayas and extremely arid to semi-arid in the north-western plains. It is floristically extremely rich with about 33 percent of its botanical wealth (over 15,000 species of higher plants) being endemic. There are about 141 endemic genera distributed over 47 families. Further, of the 4,900 endemic species, larger percentage is localised in the Himalayas (about 2,532 species) than in other regions, namely, the peninsular tract (1,788 species), and the Andaman and Nicobar Islands (185 species). It is also estimated that floristic richness is maximum in the north-eastern region, which holds about 50 percent of India’s total species diversity, i.e., more than 7,000 species, and is considered as the cradle of flowering plants. Of 990 species of orchids, 700 species occur in this region (Nayar, 1989). This, thus, makes the Indian region botanically unique and interesting (Arora, 1991).

Marshall and Brown (1975) have considered the subject of optimal sampling strategies for use in the genetic conservation of crop plants. The theme of this paper has been relatively narrow. These authors have defined a strategy for populations under imminent threat of extinction applicable to particularly the traditional landraces of some major crops such as wheat, rice and barley on account of danger of replacement of the landraces on a very broad scale due to the spread of modern cultivars. According to Brown and Marshall (1995) the emphasis in collecting of crop genetic resources has  changed radically over the years. Instead of crisis-driven broad scale crop specific programmes, the collection of plant genetic resources now involves 3 important elements as given below :

The diversity collection and making it available for future use is one of the most important activities related to management to plant germplasm resources. The collection of plant germplasm from their natural habitat is broadly known as plant germplasm exploration. The main reasons for collecting germplasm of given gene pool in a given geographical location are as follows (Engels et al., 1995)

Active plant breeding programmes call for continuous search for new genes to be incorporated into advanced breeding lines to face the new problems and the challenges. The rapid technological developments in gene transfer technology in recent years have opened new avenues for introducing useful genes from wild and weedy relatives of crop plants. It is also a fact that due to genetic erosion, wild species, are getting lost. Therefore, systematic collection of germplasm of wild and weedy species have become more relevant today then ever before for the following reasons (Bothmer and Seberg, 1995).

The most important root and tuber crops cultivated on a worldwide scale are potato (Solanum tuberosum), cassava (Manihot esculenta), sweet potato (Ipomoea batatas), yams (Dioscorea spp.) and taro (Colocasia esculenta), but there are many others that are of regional, national or local importance, in a total of over a dozen dicot and monocot families. Most of these originated in tropical or subtropical areas and are mainly used as sources of carbohydrates. Many minor root and tuber crops, such as turmeric (Curcuma longa) and arrowroot (Maranta arundinacea, Tacca leontopedaloides), are also used in folk medicine and as spices (Sastrapradja et al., 1981). All these crops are vegetatively propagated. There are also vegetatively (or clonally) propagated crops that are not roots or tubers, e.g. bananas and sugarcane. A selection of the more important crops is given in Table 13.1 (Huaman et al., 1995).

Molecular characterization involves the use of techniques that are available to analyze variation in plants and animals at the DNA level. Differences in gene sequences can be directly observed and described with a precision previously impossible to achieve. Many of the techniques that have been developed have already been used in evolutionary and taxonomic studies. They have immense value in studies of accessions identity and for the detection of novel useful variation in the plant germplasm. Molecular markers provide genetic information of direct value in key areas of conservation both ex situ and in situ. For ex situ conservation the key issues are:

Aplant collector and conservationist faces many problems. These include adverse weather, limited availability of personnel, insufficient material because of poor growing season, general scarcity of the plant in the target region, grazing of the plant by animals, damage by pests or diseases or immaturity of the material. These problems are common to both seeds and vegetative propagules. The vegetatively propagated plant material face another unique problem related to excessive weight and bulk. The cost and inconvenience of transporting large amounts of material can be a limitation on the scope of a plant exploration mission. There is additional need to maintain selected clones in a disease-free condition for distribution to national programmes.

The methods of plant germplasm preservation or conservation depend  upon type of germplasm i.e. seed or non-seed clonal materials. 

Storage of Seeds

According to the storage tolerance of seeds to low temperature and dry environments seeds are further divided into storable (orthodox) and non-storable (recalcitrant) types. The orthodox seeds are those seeds which are fully desiccation tolerant. These basically include small seeded grain crops and vegetables. They can be stored for a long time under low temperature and low humidity environment and are separately stored in long, medium and short term storage conditions in accordance with the purpose of storage.

International Board for Plant Genetic Resources (IBPGR) now known as International Plant Genetic Resources Institute (IPGRI) uses the following items in genetic resources documentation. 
    i)    Passport (accession identifiers and information recorded by collectors) 
    ii)    Characterization (consists of recording those characters which are highly heritable, can be easily seen by the eye and are expressed in all environments) 
    iii)    Preliminary evaluation (consists of recording a limited number of additional traits thought to be desirable by a consensus) of users of the particular crop
Characterization and preliminary evaluation will be the responsibility of the curators while further characterization and evaluation should be carried out by the plant breeders. The data from further evaluation should be fed to the curators who will maintain a data file.

Plant quarantine is a government endeavor enforced through legislative measures to regulate the introduction of planting materials, plant products, soil, living organisms, etc., in order to prevent inadvertent introduction of insect-pests, pathogens and weeds harmful for the agriculture of a country/state/region, and if introduced, prevent their establishment and further spread. Various methods of pest disease control are: exclusion, eradication, protection, therapy, resistance, and biological control. Exclusion or ‘keeping out’ is fundamental to the concept of plant quarantine while eradication methods are employed to eliminate a newly established pest/pathogen. Plant quarantine may, therefore, be defined as ‘Rules and regulations promulgated by governments to regulate the introduction of plants, planting materials, plant products, soil living organisms, etc. with a view to prevent inadvertent introduction of exotic pests, weeds and pathogens harmful to the agriculture or the environment of a country/region, and if introduced, to prevent their establishment and further spread’. Plant quarantine is designed as a safeguard against harmful pests/pathogens exotic to a country or a region (Ram Nath, 1991, Khetrapal et al., 2004).

No country is self-sufficient in plant genetic resources, and until recently this was thought to be sufficient to ensure the free flow of germplasm among nations. However, the concepts of ownership, sovereignty and intellectual property rights (IPR) have increasingly been invoked of late in discussions of how best to conserve and use plant genetic resources. This has resulted from the growing realization that germplasm has real economic value. At the same time, awareness has grown that the repercussions of overexploitation of natural resources, of the extinction of species and the disappearance of crop landraces, of environmental damage and of habitat destruction can be global, transcending national boundaries and short-term financial considerations (Anon. 1995). Therefore important international agreements/legislations on plant genetic resources management have been enacted from time to time. The important ones are as follows :

Seed is the most important component for productive agriculture. Significant advances have been made in production of food crops in India during the last four decades. The quantum jump in the food production primarily accounted for by increased productivity and production in rice and wheat was the result of introduction of improved varieties and their seeds often nicknamed as Green Revolution. The food production which was nearly 50 million tones during 1950 – 51 reached to a level of 210 million tones during 2003 – 04. During the same period the productivity increased about 3 folds (Table 20.1).

Issue

2004-2005 saw an upsurge in seed industry takeovers and a shake-up in rankings. Today, the top 10 companies control half of the world’s commercial seed sales. With a total worldwide market of approximately US$21,000 million [$21 billion] per annum, the commercial seed industry is relatively small compared to the global pesticide market ($35,400 million), and it is positively puny compared to pharmaceutical sales ($466,000 million). But corporate control and ownership of seeds – the first link in the food chain – has far-reaching implications for global food security. This chapter examines seed industry consolidation and other recent trends in the commercial seed industry.

Indian seed market is one of the largest in the world and entire supply is through almost locally produced seed. The value of currently marketed seed (excluding the major share of seed saved and used by the farmers) is about USD1 billion (Rs.4500/crore). Of this, roughly a third includes the traded seed making the seed business worth about Rs. 1500 crore. This figure is likely to touch Rs. 4500 crore (USD 1 billion) crore mark by 2010. In comparison to about USD 1 billion seed business in India, the worldwide market of seed is worth about USD 21 billion. The global pesticide market is worth USD 35 billion. These values, however, are much smaller in comparison to global sale of pharmaceuticals worth USD 466 billion.

Minimum field standards for seed production have been prescribed  for each crop. The major components to be looked into for meeting the field standards are: 
   Preceding crops 
   Isolation distance 
   Number of field inspections 

The minimum proceding crop requirement has been specified to minimize genetic contamination on account of volunteer plants germinating from the left over seeds in the previous season. The disease contamination is also possible from soil borne disease organisms if the previous crop was not certified. The preceding crop requirement would mean that for a prescribed minimum period the same crop or any other contaminating crop should not have been grown on the same field where seed production is to be taken up unless the preceding crop was a seed crop and had met the field/the seed standards.

Certified seed must meet certain seed standards in order to ensure an adequate level of seed purity along with the reasonable level of seed germination so that the farmer gets a good stand of the crop conforming to the varietal description. The components of the seed standard are as follows :
     The minimum percentage of pure seed 
     The maximum permissible limit for inert matter 
     Other crops seeds  
     Weed seeds 
     The maximum permissible limit for objectionable weeds 
     The maximum permissible limits of seeds of other distinguishable varieties (ODV) 
     Maximum permissible limits of seeds infected by seed bone diseases 
These standards are ensured in the seed crop by strictly adhering to field standards and careful harvesting, threshing, seed drying and then brining the same to the seed processing /seed conditioning plants. The Indian minimum seed standards for different crops are given in Tables 24.1-24.3 (Agarwal, 1995).

Seed certification is a legal programme to maintain and make available to the public high quality seeds and planting material of genetically distinct crop varieties. Under seed production programme, quality seed is produced by govt. farms research stations, progressive farmers and seed producers using careful quality control, pedigreed plant stock, field inspections during the growing season and seed inspections after the harvest. Certification is an officially recognized method for maintaining varietal identity of the seed. In India certification is carried out by State Seed Certification Agencies.

Seed quality is a multiple criterion that encompasses several important attributes. A seed scientist may be concerned with each quality characteristic of an individual seed while the seed trader normally considers the quality components of a seed lot. Any individual seed may possess certain measurable seed quality components which include:

After harvesting and threshing, the seed usually arrives at the cleaning plant with trash, green leaves, weeds, other crop seeds and insects, etc. If the seed contains leaves, etc. and other high moisture materials, it cannot be accurately cleaned and safely stored until most of the foreign material has been removed. The process of removing the unwanted materials from a seed lot is known as seed conditioning. Seed conditioning is an essential component of seed technology to ensure that the farmers get the seed of high quality.

Seed enhancement is the process or technology to further improve seed performances under very specific regimes and with certain planting equipment. Three major seed enhancement technologies are as follows (Copeland and McDonald, 1995). 
        Seed hydration 
        Biological seed treatments 
        Seed coatings

The purpose of seed storage is to preserve planting seed from one season  to the next. Further, the objective of seed storage is to maintain seed quality for the longest duration possible. 

Relative Humidity and Temperature Influence Seed Storability

The two most important factors that influence the storability of seed are relative humidity and temperature. The effects of relative humidity and its subsequent effect on seed moisture and the temperature of the storage environment are highly inter- dependent. Harrington (1963) gave two useful thumb rules for relative humidity and temperature in reference to storage life of the seed. These rules are as follows :

Hybrid technology is one of the options to boost crop productivity. Hybrids give more yield than improved varieties under optimum crop production conditions. Further, uniform size, earliness, better adaptability to adverse environments, better transportability due to better keeping quality and resistance to stresses are certain additional advantages of growing hybrids with better monetary return to the growers. Hence in coming years, hybrid technology has to go a long way in our country to meet the future challenges (Kalloo et al., 2000). Thus, it is pertinent to have an overview of the methods of the hybrid seed production technology. Various methods are as follows:

Hybrid Rice

People’s Republic of China announced the successful development and use of F1 rice hybrids in the late 1970s. The first hybrid rice combinations were put into commercial production in China in 1976. Since then commercial exploitation of hybrid rice attracted the attention of researchers around the world. It is accepted that about 20% yield advantage of hybrid rice would be usually required to meet the extra cost of seed production and the future rice demands of a growing world population. Realizing the prospects of hybrid rice, IRRI intensified research on this and organized an ‘International Symposium on Hybrid Rice’ on 6-10 October 1986 at the Hunan Hybrid Rice Research Centre, Changsha, China where Prof. Yuan Longping and his co-workers had made their names in development of hybrid rice. The proceedings were brought out in form of a book entitled ‘Hybrid Rice’ in 1988 by International Rice Research Institute, Philippines. This book documents the information exchanged, and presents for the first time, in English, much of the Chinese literature on hybrid rice.

Floral Biology and Crossing

Pearl millet spikelets bear 2 types of florets, one being bisexual and the other staminate. A singIe pistil with 2 feathery and 3  anthers is enclosed between the lemma and palea. The unisexual staminate florets are sessile and borne below the bisexual flowers. These have 3 anthers and lack the female organs. Pearl millet is a highly protogynous species and thus  highly cross pollinated.
 
The time of panicle exertion from boot leaf varies in inbreds and hybrids. Bhatnagar and Kumar (1960) observed that spike takes 6 days to emerge from the sheath with the maximum emergence on the fourth or fifth day. The stylar branches protrude first from the florets at the tip of the head and gradually proceed downwards. Most of the stylar branches on the earheads emerge by the third day. There exists a great variation in the time taken for the complete emergence of the styles in the hybrids than in the inbred lines (Tewari et al.,1971). Anthesis in pearl millet is completed in two phases. The first involves the bisexual florets while the second involves staminate florets. It has been generally observed that the anthers in the sessile male florets emerge 2-3 days after the anthers have emerged in the bisexual florets. Thus most heads continue to shed pollen for 4-6 days.The largest number of anthers emerged between 8 PM and 2 AM. Environmental factors like temperature and humidity have significant role in the anther emergence.

The information under this section is primarily based on Yordanov (1983). It is almost unanimously accepted that heterosis manifestation in tomato is in the form of the greater vigour, faster growth and development, greater earliness, and productivity, higher resistance to disease and adaptability unfavourable environmental conditions. The first step towards a large scale extension of hybrid tomato cultivars in the practice and proper organization of hybrid seed production took place in Bulgaria. After the second world war tomato heterosis breeding developed quickly in the Netherlands, England France, USA, Japan and other countries. In India, tomato hybrid cultivar on commercial scale was introduced in 1973 by Indo American Hybrid Seed Company.

Hybrid vigour in plants has long been noted, and the first suggestion that it be exploited in vegetables was by Hayes and Jones in 1916. F1 hybrid eggplants were used on commercial scale in Japan before 1925. Demonstration of the value of hybrids in corn in the early 1920’s gave impetus to a few exploratory studies in other crops. Methods of its application to large scale field production of hybrids in vegetable crops were first proposed in 1932 using the self incompatibility system in cabbage and in 1943 using the cytoplasmic genetic male sterility system in onion. Today hybrid varieties are common in several vegetable crops viz., sweet corn, onion, tomato, summer squash, ordinary cabbage, cucumber, watermelon, muskmelon, asparagus, sweet pepper, chilli pepper, spinach, broccoli, Chinese cabbage, eggplant, Brussels sprout, Chinese radish, red beet, celery, bottle gourd, bitter gourd, okra, etc. India figures prominently in commercial exploitation of heterosis in vegetable crops like cabbage, tomato, okra, watermelon, muskmelon, eggplant, bottle gourd, bitter gourd and cucumber.

Squashes and pumpkins are vegetable crops of the genus Cucurbita. They are grown in temperate, subtropical and tropical regions of the world. These crops are common elements in home gardening and subsistence agro-ecosystems in most countries and are produced on commercial scale in some countries. The economic botany, genetics and evolutionary history of Cucurbita has been reviewed by Whitaker and Davis (1962) and Whitaker (1974).

Many developing countries, for example India, China, Thailand, Brazil, Mexico, Egypt and South Africa, utilise the so-called modern biotechnology, based on genetic engineering and genomics. Agricultural biotechnology is the most widespread biotechnology in developing countries, but only a few of them are able to carry out all of the research and development activities leading to the commercialization of genetically modified seeds. These include basic research in molecular and cell biology and genetics, greenhouse and field trials according to  internationally agreed biosafety standards, risk assessment and management, respect for intellectual property rights relating to the transferred genes and to the creation of new crop varieties, production of genetically modified (GM) seeds by private corporations or working in cooperation with the public agricultural research sector, extension activities aiming at delivering the new seeds to the farmers and biovigilance in the fields of GM crops so as to detect any abnormalities or any hazards caused to the environment and to conventional crops (Sasson and Elliot, 2004).

The genetically engineered (GE) seeds developed using recombinant DNA technology often referred to as transgenics or genetically modified organism (GMOs) provide an usually adaptable, scale neutral technology for the farmers. Even small farmers can benefit from such seeds provided the seeds are made available at reasonable cost. While growing such seeds the existing crop management practices are usually sufficient. The transgenics or GMOs are also defined as those organisms with a gene or gene construct of interest that has been introduced by molecular or recombinant DNA techniques. These exclude organisms produced by conventional breeding as well as organism produced by rearrangement of genetic materials by physical methods or by chemical means. Thus, GMO’s carry trangene(s) which when integrated and expressed stably and properly, confer either a new trait to the organism which was hitherto not present (such as insect resistance), or enhance an already existing trait such as nutritional quality (Prasana 2001).