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SEED PRODUCTION AND TECHNOLOGY
What is a seed?
Seeds are mature, fertilized ovules. Ovules are structures of seed plants containing the female
gametophyte with the egg cell, all being surrounded by the nucellus and 1-2 integuments. A seed
(in some plants, referred to as a kernel), therefore, 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 (conifers and related families or clades) and angiosperm (flowering 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. A seed consists of an embryo, stored food and a seed coat.
The term seed also has a general meaning that predates the above; anything that can be sown or
any propagation material. For example in Irish potato, what is sown or propagated is tuber; in
sweet potato, is vine; in cassava, is stem; in banana, is sucker; in ornamentals, is stem cuttings.
Seeds are the principal means of regeneration of most woody plants. They serve as the delivery
system for the transfer of genetic materials from one generation to the next. The part of a tree’s
life cycle that involves seed formation, maturation, dissemination, and germination is a complex
yet fascinating chain of events, many of which are still poorly understood. However, some
knowledge of these events is necessary for successful collection, production and utilization of
seeds.
Importance of Seed
Introduction
Seeds have been an important development in the reproduction and spread of flowering plants,
relative to more primitive plants like mosses, ferns and liverworts, which do not have seeds and
use other means to propagate themselves. This can be seen by the success of seed plants (both
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gymnosperms and angiosperms) in dominating biological ecological niches on land, from forests
to grasslands both in hot and cold climates.
Crop productivity
Seeds are the principal means of regeneration of most annual and perennial flowering plants.
They serve as the delivery system for the transfer of genetic materials from one generation to the
next.
Seeds play a pivotal role in agriculture. Increase in agricultural production is the key to economic
growth in many countries.
 Seed constitutes the main propagule for plant growth.
 Modern/new agricultural information is disseminated through seed. For example, new
seed is released with the recommended crop husbandry (from land preparation, planting,
control of diseases, insects and weeds, harvesting, post harvest handling and marketing).
Agricultural research findings are disseminated through seed.
 Seed is the main vehicle for the dissemination of plant pests. Seed-borne pathogens, such
as fungi, bacteria and viruses are serious constraints to crop productivity. In worst-case
scenario, seed-borne diseases can be disastrous and even life threatening. Infected seeds
are at risk of being contaminated with mycotoxins and undergo changes in nutritional
value.
Seed-borne diseases can be harmful in several ways:
1. Seed-borne inoculum can reduce seed germination to various degrees, give rise to preand post emergence seedling mortality and progressive disease development in the field
and thereby reduce the yield and quality of the crop
2. Imported seed lots carrying disease propagules may introduce devastating diseases or
new strains of a pathogen into new regions
3. Infected seeds have reduced shelf life
Nutritional and Economic
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 Many seeds are edible and the majority of human calories come from seeds, especially
from cereals, legumes and nuts.
 Seeds also provide most cooking oils, many beverages (e.g. coffee) and spices and some
important food additives. In different seeds, the seed embryo or the endosperm dominates
and provides most of the nutrients. The storage proteins of the embryo and endosperm
differ in their amino acid content and physical properties. For example, the gluten of
wheat, important in providing the elastic property to bread dough is strictly an endosperm
protein.
 Seeds are also eaten by animals, and are fed to livestock. Many seeds are used as chicken
feed.
 Some seeds are also poisonous. One of the deadliest poisons, ricin, comes from seeds of
the castor bean. Other poisonous seeds are those of yew, apple, chestnut and peach.
 The world's most important clothing fiber grows attached to cottonseed. Other seed fibers
are from kapok and milkweed.
 Many important nonfood oils are extracted from seeds. Linseed oil is used in paints. Oil
from jojoba is in the cosmetic industries.
 Seeds are the source of some medicines including castor oil, tea tree oil and the
discredited cancer drug, Laetrile.
 Many seeds have been used as beads in necklaces and rosaries including, Chinaberry and
rosary pea. However, the latter two are also poisonous.
 Resin from Clusia rosea seeds are used to caulk boats.
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CHAPTER 1: REPRODUCTIVE PROCESSES IN PLANTS
Introduction
Plant growth originates within the buds in regions known as meristems. In the meristems, cell
division and elongation occur, and these processes produce tissues that soon develop into
specific plant parts. Vegetative meristems give rise to parts such as stems, leaves, and roots,
while reproductive meristems give rise to floral organs that ultimately produce fruits and seeds.
Within any meristem are minute primordia that resemble knobby outgrowths or ribbed inverted
cones. Although hardly distinguishable to the naked eye, the configurations of the primordia
become visible when the bud scales are removed and examined under magnification. As growth
proceeds, the configurations enlarge and differentiate into recognizable plant organs.
FLORAL INDUCTION
Vegetative growth of plants occurs until they are ready to flower. At that stage, certain external
stimuli can trigger floral induction, a physiological change that permits the development of
reproductive primordia. This change may precede actual flowering by several days, weeks, or
even months.
Temperature Stimuli
For floral induction to occur, many plants require exposure to low temperatures. This process has
been called vernalization. In its narrowest sense, vernalization means the promotion of flowering
in some winter cereals by cold treatment of the moistened or germinating seeds. In its broader
sense, vernalization means the induction of flowering in any winter annual, biennial, or even
perennial species through exposure to low temperature. For example, rye (Secale cereale), a
winter annual, and perennial ryegrass (Lolium perenne) both must undergo prolonged exposure
to low temperatures before they can produce flowers. Sugar beets and carrots are examples of
biennial species that grow vegetatively the first year, after which they are vernalized by exposure
to winter temperatures.
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In the chrysanthemum and tomato, floral induction is accomplished by repeated exposure to low
night temperatures, separated by periods of higher temperature. This phenomenon occurs in
many plants and has been called thermoperiodism.
Day-Length Stimuli
In many species, floral induction occurs in response to day length, or photoperiod. Thus, plant
species have been categorized according to their day-length requirements as short-day, long-day,
intermediate-day, or day-neutral; however, it is really the length of the night, or dark period, that
is the critical factor that influences flowering.
Long-day plants include most cereal grains, clover, hibiscus, and Irish potato. Some short-day
plants are chrysanthemum, tobacco, poinsettia, sweet potato and strawberry. Intermediate day
plants include climbing hemp weed, wild kidney bean, Indian grass, and broom corn. Among the
day-neutral plants are tomato, field bean, zinnia, dandelion, and chickweed.
The photoperiod requirements for flowering may be qualitative or quantitative. Some short-day
species such as the Biloxi variety of soybean are unable to flower except under short-day
treatments; in other short-day species, such as sunflower, flowering is hastened by the
appropriate short-day conditions, although it eventually occurs without them.
Chemical Stimuli
Certain natural and synthetic chemical substances can cause floral induction. Some are auxinlike
compounds-for example, indoleacetic acid, naphthalene acetic acid, or the common herbicide,
2,4-dichlorophenoxyacetic acid (2,4-D). At certain concentrations, gibberellic acid may also
cause floral induction. It promotes flowering of long-day plants held in short-day conditions;
however, it inhibits flowering of short-day plants under the same conditions. Other substances
known to cause flowering or to increase flower production are cytokinins, ethylene, acetylene
and ethylene. In contrast, maleic hydrazide inhibits flowering.
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