eChapters

• The seed production of varieties and hybrids should be carried out carefully by following various techniques in the region where they are well adopted.
• The various factors affecting quality seed production includes,
  1. Agro climatic factors / Ecological factors - edaphic and climatic factors
  2. Production factors
  3. Post harvesting handling of seed
  4. Seed quality control factors

1. DEFINITION

Seed deterioration is defined as deteriorative changes occurring with time that increase the seed’s vulnerability to external challenges and decrease the ability of the seed to survive

The important events involved in seed development and maturation include

• Pollination
• Fertilization
• Development of the fertilized ovule by cell division
• Accumulation of reserve food material
• Loss of moisture content

A seed (in some plants, referred to as a kernel) is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes the process of reproduction in seed plants (started with the development of flowers and pollination), with the embryo developed from the zygote and the seed coat from the integuments of the ovule. In broad sense, seed is a material which is used for planting or regeneration purpose. Seed technological point of view, seed may be sexually produced matured ovule consisting of an intact embryo, endosperm and or cotyledon with protective covering (seed coat). It also refers to propagating materials of healthy seedlings, tuber, bulbs, rhizome, roots, cuttings, sets, slips, all types of grafts and vegetatively propagating materials used for production purpose. Quality seed, therefore, can be defined as the seed which fulfills the minimum requirements of getentic and physical purity, seed germination and vigour freedom from weeds and other crop seeds and other relevant seed standards.

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.

Drying is an important unit operation in seed processing in order to maintain seed ability and vigor . it is advocated that seeds should be harvested soon after they attain physiological maturity to obtain better quality seeds and to minimize field losses. The traditional method of sun drying is inadequate, uncontrolled and time bound, which may not meet the high demand of quality seeds in time. Hence artificial drying, the effect of certain drying parameters like seed moisture content, drying air temperature, airflow rate, depth of seed loading and time of exposure on drying characteristics and viability of seeds are to be determined for safe and economical drying of seeds.

1. SEED DRYING

The process of elimination of moisture from the seed is called drying.

2. STAGE OF MOISTURE ELIMINATION

The moisture from the seed is eliminated in 2 stages

1. Surface moisture of the seed that initially removed by the drying air.
2. The removal of the moisture in the surface cause an imbalance in the moisture potential in the surface of the seed and the inner portion of the seed which leads to the migration of moisture from the inner organ to the surface.

The migration of moisture to the surface is slower than the evaporation and a moisture gradient is developed in the kernel. Elimination of moisture from the seed depends upon the relative humidity and temperature of the environment surrounding the seed.

Vegetable seed drying is the most critical stage for any shop floor activities. Only properly dried seed will be taken for processing and all the other activities from seed receipt to storage. Seed producers harvest the seed which will have more moisture than packaged seed. For example onion seed harvested when its moisture at 60% but eventually dried to 10-12% for safe storage and packaging. Seed drying is highly skilled and specialized activity without affecting the seed quality. Proper drying procedures are vital for storage and field performance of seed lots. Drying prevents germination of the seed, the growth of bacteria and mould and it reduces the conditions for development of insects. The moisture content of a seed is influenced by the humidity of the air because they are very hygroscopic in nature. The more moisture in the air, the higher the moisture content of the product. If seed are harvested during warm, humid weather, the moisture content of the seed will be high because the relative humidity of the air is high as well. It is necessary to dry the seed before it can be stored safely. The method of drying depends on the local conditions (climate, season, volume of the seed, type of seed etc)

Vegetable seed drying is the most critical stage for any shop floor activities. Only properly dried seed will be taken for processing and all the other activities from seed receipt to storage. Seed producers harvest the seed which will have more moisture than packaged seed. For example onion seed harvested when its moisture at 60% but eventually dried to 10-12% for safe storage and packaging. Seed drying is highly skilled and specialized activity without affecting the seed quality. Proper drying procedures are vital for storage and field performance of seed lots. Drying prevents germination of the seed, the growth of bacteria and mould and it reduces the conditions for development of insects. The moisture content of a seed is influenced by the humidity of the air because they are very hygroscopic in nature. The more moisture in the air, the higher the moisture content of the product. If seed are harvested during warm, humid weather, the moisture content of the seed will be high because the relative humidity of the air is high as well. It is necessary to dry the seed before it can be stored safely. The method of drying depends on the local conditions (climate, season, volume of the seed, type of seed etc)

1.1 Problem
    1.    Compare the seed quality at different physiological maturity stages
    2.    Compare the seed recovery in acid and fermentation method

1.2 Materials
    ·    Tomato fruits – 4 batches
    ·    Plastic bucket/ Beaker
    ·    Water

In tomato seed extraction is the very important operation. Tomato seed can be extracted by following way.

1. Fermentation methods: Red ripe fruits should be picked and crushed in non metallic pots. Profuse foam formation indicates that fermentation is completed. Fermentation of seed material should not be prolonged beyond 72hr to get seed of high germination. Preferably the seed should be washed free of pulp after 48hr require temperature uses.
2. Acid treatment methods: In case of urgency seed may be washed by using 1.0 to 1.5 liters of 35 to 38% concentrated HCL/g tomato fruit pulp. Fermentation is completed in about 30 minutes. Clean seed are obtained by stirring and washing procedure are quickly as possible.
3. Alkali treatment methods: In case Alkalie 10% sodium bicarbonate is mixed in equal volume of pulp or 300 g washing soda dissolve in 4 liter of boiling water is sufficient for 4 liter fruit pulp.
4. Mechanical methods: It is used for large scale operations put the ripe fruits into the mechanical seed extractor for crushing and separation of the seed and gel from the pulp. By acid 0.8% solution of acetic acid for 24hr at or below 21⁰C (1kg seed/10 liter of acetic acid).

1. SEED EXTRACTION

The processing of seeds starts from the extraction of seed material from the plant parts. The seed removal in dry fruits is known as threshing, while that of wet fruits is known as extraction.

2. METHODS OF SEED EXTRACTION

2.1. Dry extraction

Dry extraction is done either manually or mechanically. Manual extraction is by beating with pliable bamboo stick or by beating against a hard surface. Threshers are used for mechanical extraction. In this, care should be taken to avoid mechanical injury. Eg. All agricultural crops.

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.

Fumigation is a method of pest control that completely fills an area with gaseous pesticides to suffocate or poison the pests within. It is utilized for control of pests in buildings, soil, seed, and grain produce. It is also used during processing of goods to be imported or exported in order to prevent transfer of exotic organisms. Fumigants are chemical compounds in gaseous form that enter the body of insect through the spiracles spread all over via trachea and tracheoles. The important fumigants are Methyl bromide, Ethylene dibromide, Aluminium phosphide, Ethyl formate, Hydrogen cyanide, Chloropicrin etc.

1. SEED CLASSES

Generation system of seed multiplication is nothing but the production of a particular class of seed from specific class of seed up to certified seed stage. The choice of a proper seed multiplication model is the key to further success of a seed programme, which basically depends upon

Seed germination

It is defined as the emergence and development from the seed embryo, of those essential structures, for the kind of seed in question, indicates its ability to produce a normal plant under favourable conditions. The seedlings devoid of an essential structure; showing weak or unbalanced development; decay or damage affecting the normal development of seedling are not considered in calculating the germination percentage.

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.

Introduction

Germination is the growth of a plant contained within a seed; it results in the formation of the seedling, it is also the process of reactivation of metabolic machinery of the seed resulting in the emergence of radicle and plumule. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. The seed of a vascular plant is a small package produced in a fruit after the union of male and female reproductive cells. All fully developed seeds contain an embryo and, in most plant species some store of food reserves, wrapped in a seed coat. Most seeds go through a period of dormancy, where there is no active growth; during this time the seed can be safely transported to a new location and/or survive adverse climatic conditions until circumstances are favourable for growth. Dormant seeds are ripe seeds that do not germinate because they are subject to external environmental conditions that prevent the initiation of metabolic processes and cell growth. Under proper conditions, the seed begins to germinate and the embryonic tissues resume growth, developing towards a seedling. In short, seed germination is the ability of a seed to develop in to a normal plant under favourable conditions in the soil (ISTA, 1985) or the process by which the dormant embryo wakes up and begins to grow is known as seed germination.

Seed Health Testing

Science of determining the presence or absence of disease causing agents such as fungi, bacteria and viruses and insects in the seed samples.

Seed Borne disease

The seed primordial or the maturing seed may be infected either (i) directly from the infected plant through the flower or fruit stalk and the seed stalk or directly from the seed surface, or (ii)infection from outside may be introduced through stigma or ovary wall or pericarp, and the flower or fruit stalk, and later through the seed coat. A pathogen may penetrate several of these parts of the seed and in turn infect them. The infestation /contamination of the seed may occur during harvesting, threshing and processing. Visualizing the importance of seed borne diseases the Central Seed Certification board has prescribed certification standards for foundation and certified seed for several diseases.

The pathogen may carry with the seeds in three ways.

• Admixture: Pathogens are independent of seeds but accompany them. They are mixed with health seeds during threshing.
• External:The pathogen may be present on seed surface as spores, oospores and chlamydospores.
• Internal: Pathogens establish within the seed with definite relationship with seed parts.

1. INTRODUCTION

Seed health refers to the health status of a seed. Sowing healthy seeds of high quality is our concern to improve crop yields, thus increasing food production. It has a great concern to farmers and seed producing agencies where the disease is high and average yields are low and where more food is needed to feed the ever-increasing population. So, it is important to test the seeds for disease organism before they are sown in the field and to avoid harmful organisms traveling from infected to non-infected areas within a country or across international boundaries.