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Summary of section 4-6
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Provides the summary of all the content in test 2 in crop production 214
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Section 4.1: Principles of seed propagation:Processes involved:
Breeding- Crossing of 2 selected parents. Selecting seedling with desired
characteristics.
Must have arisen in cultivation
Must have clear characteristics
Characteristics must be obtained during propagation
Seed Morphology:
What is a seed?:
A seed is a mature ovule consisting of the following:
₋ Embryo (offspring)
₋ Food reserves
₋ Within a protective covering
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,Embryo:
Represent new plant generation
Develops after sexual union of male and female gamete during fertilization
Basic structure:
Axis with growth points at each end:
1. One for the shoot
2. One for the root
3. One or more cotyledons attached to embryo
What is a cotyledon?
Cotyledons are the first parts to emerge out of a seed. They contain reserve food material that
provides nourishment to the developing seedling.
Function:
Stores food for the growing embryo.
Number of cotyledons in embryo is used to classify plant:
Monocotyledonous:
Single cotyledon
Examples: Coconut, palms or grasses
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,Dicotyledonous:
Beans or peach: have 2 cotyledons.
Gymnosperms: As many as 15 cotyledons.
Seed Germination:
- Morphologically, the protrusion of radicle marks the end of the germination phase
- Physiological level:
End of germination is a transition point characterized by the loss of desiccation tolerance
and on the molecular level a switch from the germination program to the seedling growth program
occurs
Before germination can happen:
Seed must be viable
Appropriate environmental conditions
Dormancy must be overcome
Germination = Phase of activation of metabolic machinery of the embryo and embryo growth, till
protrusion of radicle (embryonic root) through seed coat. Protrusion of radicle marks the end of the
germination phase.
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, STAGE 1 - Embryonic differentiation (Histo):
• Rapid increase in weight
• Cell division
STAGE 2 - Cell expansion:
• Largest increase in seed size due to deposition of food reserves
STAGE 3 - Maturation drying:
• Rapid loss of seed weight due to water loss
• Stop metabolic activity
Vivipary seeds:
Viviparous germination: process in which the seeds germinate while being attached to the parent
plant. The viviparous germination is seen most prevalent in mangrove plants.
Recalcitrant seeds
Are seeds that do not survive drying and freezing during ex-situ conservation. These seeds cannot
resist the effects of drying or temperatures less than 10 °C (50 °F); thus, they cannot be stored for
long periods like orthodox seeds because they can lose their viability eg. mango, avocado, lychee
and coffee.
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