eChapters

1. SEED GERMINATION

The process whereby seeds sprout and begin to grow is known as germination.

Germination is the onset growth of a seed, often following a period of dormancy, in response to suitable environmental conditions. During germination (the growth and development process) of a seed, the water is absorbed through micropyle, and the formerly dormant embryo resumes growth and emerges from the seed.

1. INTRODUCTION

In plants, seed dormancy is controlled by temperature, light and hormones. Unlike animals, which secrete hormones from special glands, hormones are always present in plant cells. Each plant hormone plays multiple roles, depending on the site of action, the life stage of the plant and the hormone’s concentration. A plant hormone is any chemical that is produced in one part of the plant that has a targeted function elsewhere. Certain hormones induce and keep seeds in a dormant state, while others cause seeds to break dormancy and initiate germination They are stored in regions where stimulus are and then released for transport through either phloem or mesophyll when the appropriate stimulus occurs. These are chemical messengers influencing many patterns of plant development

The first theory is that the five classic plant hormones, auxin, cytokinins (CKs), gibberellins (GAs), ethylene, and abscisic acid (ABA), plus the new plant hormones, brassinosteroids (BAs), and salicylates or salicylic acids (SAs) can be gathered into three groups. These are growth hormones, stress hormones and shock hormones. Auxin and CKs are growth hormones. Ethylene, GAs, and brassinosteroids are stress hormones. ABAs and SAs are shock hormones. All three types of hormones are similar in that they fall within the classic definition of an intercellular hormone. They are made by a cell and are meant to affect the behavior of other cells, either in nearby tissue or at the opposite end of the plant.

ABA, also known as abscisic acid plays a direct role in dormancy release and germination. Ethylene and the gibberellins group of hormones are indirectly involved.

1. INTRODUCTION

In general, seed dormancy refers to lack of growth due to any external or internal cause. It also refers to a state in which viable seeds fail to germinate even when given favourable environmental condition i.e. adequate moisture, appropriate temperature regime, a normal atmosphere and in some cases light.

There are various degrees of dormancy varying from very slight to very strong (deep). Sometimes the development or degree of dormancy changes during the lifetime of the seed, usually as a response to external conditions. Hence, dormancy may be innate, develop, be broken and redevelop in seed.

Several types of dormancy exist, and sometimes more than one type of dormancy occurs in the same seed. In nature, dormancy is broken gradually or by a particular environmental event. The type of event that may break dormancy depends on dormancy type. Dormancy caused by a hard seed coat may be overcome by a gradual or an instant abrasion, and darkness induced dormancy by exposure to light. In seed handling, the natural dormancy breaking mechanism is applied or simulated during the process of pretreatment. “Pretreatment” is a term used for conditions or processes applied to break dormancy prior to germination, while “treatment” is used for application of pesticides for control of pests and diseases.

The chemical composition of seeds is basically determined by genetic factors and varies among different species and seed parts (Table 1). However, it is influenced by environmental and cultural practices.

1. SEED MATURITY

Harvesting should be done after the attainment of physiological maturity, when the seeds reached complete maturity to avoid harvesting of immature and ill-filled seeds.

1.1. Physiological maturity

It is the stage of accumulation of maximum drymatter within the seeds. It is expressed by maximum seed weight, germination and vigour potential. The moisture content of the seed at this stage is around 25-30% depending up on the species.

1.2. Harvestable maturity

The physiological maturity is represented to a seed and this maturity will not be the same for all the seeds of a single plant / population, due to continuous differential flowering habit. Hence, the stage of attainment of physiological maturity by 80% of the population is considered as the harvestable maturity stage. The moisture content of the seed will be lesser than the physiological maturity stage (18-20%).

1. DEFINITION

Artificial seed technology involves the production of tissue culture derived somatic embryos encased in a protective coating. Artificial seeds have also been often referred to as synthetic seeds. However, the term ‘synthetic seed’ should not be confused with commercial seeds of a synthetic cultivar which is defined as an advanced generation of an open pollinated population composed of a group of selected inbred clones or hybrids. The concept of artificial or synthetic seed is shown in Figure 1.

1. APOMIXIS

Development of seed without fertilization. When the seed formation occurs without sexual fusion, the process is known as apomixis. This occurs by several mechanism, however all apomitic seed have genetic material only from the female plant Apomixis may or may not require pollination and pollen tube germination to initiate seed formation, however sexual union.

1. OVULE DEVELOPMENT

The development of ovule occurs within the ovary, which provides a location for nurture and development of the female gametophyte, its sexual fusion with in the male gametophyte, and embryo development, survival, and eventual regrowth (Fig. 1). Ovule growth begins as a small outgrowth within the nucellus. As megasporogenesis and megagametogenesis continue, the region of the nucellus that is to become the ovule enlarges and differentiates into definite morphological characteristics. Secondary outgrowths, or collars (integuments), soon appear around the periphery of the nucellar outgrowths and envelop it. These usually consist of the inner and outer integuments and ultimately become the testa (seed coat) of the mature ovule.

1. VEGETATIVE PROPAGULE

Vegetative propagation or asexual propagation is the method of propagating plants with the use of organs other than the seed and spore. In contrast to sexual propagation, the union of the male and female sexual gametes (fertilization) is not a requisite to the production of new plants. Hence the word “asexual”, which means “without sex” or “not sexual”.

1. SEED

A seed is defined as a ‘mature ovule’ or a reproductive unit formed from fertilized ovule, consisting of an embryo, reserve food and a protective cover.

Seed is the basic input in agriculture upon which other inputs are applied. A good vigorous seed utilities all the resources and realized as a reasonable output to the grower. It is wealth to the farmer, it is the yesterday’s harvest and tomorrow’s hope. Good seed in good soil realize good yield.

Seeds exhibit a great range of variation in shape, size, colour and behaviour. The most essential factor for the success of plantation is the ready availability of quality seeds. The quality of seed is totally responsible for the future return / performance of each and every seedling.

1. FRUITS

Fruit is a part of a flowering plant that derives from specific tissues of the flower, mainly one or more ovaries.

1.1. Types

1.1.1. Fleshy

1.1.1.1. Simple fleshy fruits

Develop from a flower with a single pistil.

1. FLOWERING

The flowering goes through a phase of vegetative growth producing more stems and leaves and a flowering phase where they produce the organs for sexual reproduction.

1.1. Synchronisation in flowering

Synchronous flowering refers to the phenomenon of coincident, simultaneous flowering of all population of a given species in a large region.

1. INFLORESCENCE

An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches.

1.1. Types of inflorescence

Inflorescences can be simple or compound.

1.1.1. Simple inflorescence

Inflorescence of sessile disc florets forming the capitulum

1.1.1.1. Indeterminate

Indeterminate simple inflorescences are generally called racemose. The main kind of racemose inflorescence is the raceme. The other kind of racemose inflorescences can all be derived from this one by dilation, compression, swelling or reduction of the different axes. Some passage forms between the obvious ones are commonly admitted.

Introduction

In 1990, the magnitude of fungal diversity, that is, the actual number of species worldwide, was estimated conservatively to be at least 1.5 million. Of the 1.5 million estimated fungi, it has been estimated that 14,000 species produce fruiting bodies of sufficient size and suitable structure to be considered macro-fungi which can be called mushrooms. Of these, about 50 % or 7,000 species are considered to possess varying degrees of edibility and more than 3,000 species from 31 genera are regarded as prime edible mushrooms. To date, only 200 of them are experimentally grown, 100 economically cultivated, approximately 60 commercially cultivated and about 10 have reached an industrial scale of production in many countries (Hawksworth, 2001). Of the 14,000 species of mushrooms in the world, around 700 have known for medicinal properties. Thus, mushrooms have vast prospects as sources of medicines. The early herbalists were more interested in the medicinal properties of mushrooms than in their basic value as a source of food. Humankind has constantly searched for new substances that can improve biological functions and thereby make people fitter and healthier. About 3.5 billion people worldwide, all over half of the world populations rely on plant-based medicines and dietary supplements for their primary health care. Of the plant materials involved in medicines or health tonics, quite a few are fungi. The practice of using fungi as herbal medicines can be traced in different early records of the ‘materia medica’. The earliest book on medicinal materials the “Shen Nongs Herbal” recorded the medicinal effects of several fungi such as Ganoderma lucidum, Poria cocos, Tremella fuciformis, Polyporus umbillatus and other unidentified fungi. The most famous of all work on the traditional medicines “Pen Ts’ao Kang Mu” which was compiled by Li Shi-Zhen of the Ming Dynasty recorded the medicinal fungi totaling more than twenty species, including Ganoderma lucidum, Poria cocos, Polyporus umbellatus, Lentinula edodes, Termitomyces albuminosus, Auricularia auricula, Pleurotus ostreatus, Armillaria mellea etc. A very unique insect-infecting fungus, Cordyceps sinensis, was for the first time taken as a medicinal fungus in the book “Essentials of Materia Medica”. There have been new discoveries and developments in the field of medicinal fungi, which have greatly enriched the treasure house of our traditional medical and medicinal sciences. As a result of large number of scientific studies on medicinal mushrooms in the past three decades, the traditional uses of many mushrooms have been confirmed and new wider uses found. Some traditionally important and leading medicinal fungi in the Oriental medicines are presented below

Introduction

Spices have played a very important role in shaping the history of human culture and civilization. Spices condiments and aromatic plants were the first articles traded by ancient people. These prompted the foreigners to the land of spices. Among spices, seed spices is a group well distributed over different agro-climatic regions in India covering major part in semi-arid to arid region largely in Rajasthan and Gujarat. The other states where one or more of seed spices grown are Haryana, Punjab, M.P., Bihar, U.P., West Bengal, Orissa, Tamil Nadu and Karnataka. The seed spices are grown in different parts of the world covering mainly Mediterranean region, South Europe and Asia. These crops were introduced to India from Mediterranean and Central Asian region, perhaps a long time ago. Today India enjoys the position of largest producer and exporter in the world for these crops. The country is bestowed with immensely rich land races diversity in seed spices crops. Much of the country’s agro-biodiversity is in the custody of farming community who followed age old farming systems. However the land races are being lost due to expansion of agriculture production in the frontier areas or replacement with the improved cultivars. Hence, scientific management of these valuable resources on different dimensions of activities in India viz. survey and collection, characterization, evaluation, documentation and conservation has assumed prime importance today. Out of the total 20 seed spices grown in India the ten are prominent. These important seed spices are divided into major and minor group of seed spices. The crops covered as major seed spices are coriander, cumin, fennel and fenugreek, whereas, ajowan, dill, nigella, celery and anise constitute minor group. The semi-arid to arid region is considerably rich in plant biodiversity of seed spices and it is required to conserve the natural wealth of these crops. The increasing loss of plant diversity owing to numerous natural and manmade causes calls for immediate efforts for its collection and safeguard.

Introduction

Potato is a wonder crop that can be grown under diverse range of agro-climatic conditions. Short duration; high yield per unit area and time and wide flexibility in planting and harvesting time are important virtues of potato that enable its inclusion in intensive cropping systems.

Potato is not an Indian crop but is a native of high Andean region of South America. It was introduced in India perhaps in 16^th or early 17^th century by either the Portuguese traders or the British missionaries. The present day cultivated potatoes (tetraploid, 2n=4x=48) in most of the world represent Solanum tuberosum spp. tuberosum and S. tuberosum spp. andigena, although it’s numerous diploid (2n=2x=24) relatives are still under cultivation in and around its primary and secondary centers of origin in South America (Pandey and Sarkar, 2005). The great Irish famine in the 19^th century, caused by late blight disease, nearly wiped out all the earliest potato introductions in the Europe and dramatically changed the potato cultivation and production scenario in rest of the world.

Unlike in European Countries 80% of the potato is grown in India under short day conditions as a short duration crop i.e. 70-90 days. The tubers are exposed to high temperatures during planting (September-October) and harvesting (February-May). The crop is irrigated and suffers mid day water stress. The potato varieties introduced from Europe were unsuitable for growing under the above conditions. Systematic potato research in India spanned over the last half-a-century of the 20^th century in the past millennium. The Central Potato Research Institute (CPRI), which was established in 1949, has bean mainly responsible for tremendous growth of potato production in the country. The indigenous technological advances made it possible to extend potato cultivation in almost all part of the country. Now in India, compared to the production, area and yield of potato in 1949-50, the increase over the same period was 1513%, 559% and 270% respectively (Naik and Thakur, 2007). According to the FAO, potato production worldwide stands at 329 million tones and covers more then 19 million ha.

Introduction

Chilli is one of the most important spice and condiment of daily use in all most all the Indian houses. The fresh and dry fruits are the rich source of Vitamin A (292 IU) and Vitamin C (111 mg/100g). Its pungency not only improves the taste of the different preparations but also improve their storability. The colour of the fruits is due to the presence of the pigment capsanthin and pungency and acridity is due to the presence of alkaloid oleoresins knows as capsaicin (C₁₈ H₂₇ O₃ N). The capsaicin has a very good medicinal importance and also having importance for the pharmaceuticals industries for preparation of the different types of the drugs, because of the presence of the antioxidants like Vitamin A, C and P (Rutin). The green and red sweet pepper, bell pepper, Pimiento (heart shape) and cherry pepper are used in the fresh market processing industries for stuffing pickling and dehydrated processed meat. It is used as green as well as dry powder, pickles, salad and for industry to prepare the medicines for external and internal uses.

Introduction

The traditional approach to transferring genes from wild to cultivated species is based on interspecific hybridization followed by selection of hybrids that combine the trait with the cultivated genetic background. This breeding strategy is achieved by various backcross generations in which the selected hybrids at each generation are crossed back to the cultivated genotype with the aim of reducing the wild genome and its undesirable traits. The use of molecular markers has allowed this breeding approach to be greatly improved, since these markers directly reveal genetic variability through DNA analysis (Staub et al. 1996), and therefore their detection is not influenced by environmental effects. Since the development of numerous molecular markers for plant genometatic analysis, the possibility to select the genotype instead of the phenotype has been closely examined, leading to the concept of molecular marker-assisted selection (MAS; Paterson et al. 1991). The basic concept of MAS for crop improvement has been well discussed by Collard et al. (2005) which is most appropriate for this chapter. The most widely used markers suitable for MAS are RFLP, RAPD, AFLP, and SSR. Their common origin is point mutation or chromosome rearrangements that were accumulated during the evolution of the species without negatively influencing their survival and reproduction. The choice of the most suitable markers for MAS can differ and depends on the labor required for their detection, possibility of revealing single or multiple loci, dominant or co dominant nature and costs.

Introduction

Carrot (Daucus carota L., 2n=2x=18) is a cool-season root vegetable grown all over the world in temperate as well as sub-tropical climates. In India, it is cultivated over an area of 24,000 hectares with an annual production of 3,50,000 metric tones with a productivity much lower (14.58 t/ha) than the world average (22.17 t/ha) as per FAO, 2004. Carrots are used for human consumption as well as for animal feed. Carrot can thus be used for augmenting fresh fodder supply to milch animals during the lean winter in Kashmir (Hussan and Ahmed, 1999). Carrot has a significant place as an ingredient in soups and sauces and in dietary composition and also as a salad. A sweet preparation called Gajar Halwa is very famous dish in North India. Besides canning, it is also used in preparation of pickles. It is also exported in the form of fresh roots to the countries like Kuwait and Sharjah. Carrot is a rich source of á and â- carotene. The total carotenoid content in the edible portion of carrot roots ranges from 6.00 to 54.80 mg/100g. The yellow and orange coloured roots contain relatively more carotenoid. Carrot roots contain protein, fat, carbohydrate, minerals (especially Ca, Mg, Na, K, Cu, S etc.) besides vitamin A, B₁, B₂, nicotinic acid and vitamin C. In carrot roots, sucrose is the most abundant with endogenous sugar contents 10 times than those of glucose and fructose.

Asia minor, Afghanistan, North West India, Iran and Turkey are the centers of origin of carrot. As per Encyclopedia Britannica, carrots have originated from Afghanistan, Punjab and Kashmir with secondary centers in Ethiopia and North America. The European carotene carrot (syn. Western carotene carrot, temperate carrot) has been derived from the Asiatic anthocyanin containing forms of carrot (syn. Eastern anthocyanin carrot, tropical carrot). Afghanistan is the centre of diversity of the purple coloured carrot (anthocyanin carrot) and as such this country is suggested as the primary centre for origin. Integration between the Asiatic and European carrots has given the present day forms which are fleshy, smoother, less forked and better coloured.

Punjab and Kashmir are also considered as primary centre of origin with secondary centers in Ethopia and North America. It is still found in its wild form in Himachal Pradesh and Kashmir valley where wild animals especially brown bear feed on its roots. People still eat the wild carrots in some parts of Kashmir (Yawalkar, 1980). In north India highly coloured types of carrots are found which are not available in Europe. The colour of carrot ranges from absolute colourless to light lemon, light orange, orange and deep orange, light purple, deep purple and almost black. It is also an indication of this region being a primary centre of origin of carrot.

Introduction

Turnip is an important root crop which is very popular particularly in northern India. It is a cool season crop mainly grown as a fall or winter crop in the hills and winter crop in the plains. Turnip (Brassica rapa L. syn. Brassica compestris var. rapa) belong to family Brassicaceae. It has a chromosome number of 2n=2x=20. Two main centers of origin have been indicated. The Mediterranean area is considered to be the primary centre of origin of European type/temperate types. While Eastern Afghanistan with adjoining areas of Pakistan is considered to be another primary centre with Asia Minor, Transcaucasus and Iran as secondary centre. The parents of cultivated turnip are found in the wild form in Russia, Siberia and Scandnavia. It was cultivated by the ancients and ranked next to grapes and cereals in Italy. It was introduced in England probably in 1590 and United States in 1606 (Yawalkar, 1980). Turnips are now cultivated throughout the world.

Turnips are botanically biennial herbs, but are cultivated as annual root crops for both animal and human consumption. The turnip root contains 41.6% moisture, 6.2 g carbohydrates, 0.5 g protein, 0.2 g fat, 0.04 mg thiamin, 0.04 mg riboflavin, 43 mg ascorbic acid, 30 mg Ca, 40 mg P and 0.4 mg Fe per 100 g of edible portion. The turnip green contains 15,669 IU vitamin A per 100 g (Aykroyd, 1963). Turnip is grown for its enlarged root as well as for its foliage. Extra seedlings from thinning are often used as greens. The fresh roots are consumed in salads or cooked as vegetable or used in pickles. The young leaves contain high amount of ascorbic acid and iron, rank second in vitamin A content and are cooked as greens.

The fleshy thickened underground portion of turnip is actually the hypocotyl. The colour and shape of this underground portion vary with the cultivars and the roots are flat globular to top-shaped and long. The colour of under ground portion may be white or yellow, while that of above ground portion may be red, purple, white, yellow or green. A distinct tap root and secondary roots arise from the lower part of the swollen hypocotyl. Thickening begins in the central part of the hypocotyle, followed by the upper and lower parts. Normally, the roots attain edible maturity in 40-80 days depending on cultivar and climatic conditions.