2104 - Significance of Seed Propagation & Seed Structure

Question 1

What is a seed?

Answer 1

A seed is the structure that forms from a fertilised, ripe ovule of an angiosperm or gymnosperm plant.
It is a product of sexual reproduction.

Plant benefits:
Genetic variation between each seed allows the plant population to adapt to environmental conditions or changes within it.

Question 2

Horticultural Benefits of Propagating from Seed

Answer 2

• Genetic variation will lead to new cultivars (plant breeding)
• Greater chance of some individuals being disease resistant
• Greater chance of some individuals being drought or cold hardy
• Large number of plants can be produced from one
  (collection and prorogation of own stock, easier.cheaper to produce large quantities of plants)
• Easy to store and transport
• Less risk of disease transfer (than cuttings)
• Some species may only be propagated by seed

Question 3

Horticultural Limitations of Propagating from Seed

Answer 3

• Genetic variation = lack of uniformity
• some seed had complex dormancy mechanism, which makes germination difficult, requires expertise.
• Not all seed is viable, nor do all plant produce viable seed.
• Seed loses viability over time
• Woody perennials can take years to reach maturity
• Recalcitrant (unorthodox) seed won’t store for long

Question 4

Dicot seed parts - structure

Answer 4

Testa - seed coat
Radicle - forms first root
Micropyle - entry point for water (germination), gaseous exchange
Hillum - seed attachment point to the ovary
Hypocotyl - joins radicle to cotyledons
Cotyledon - seed leaves or storage
Epicotyl  - joins cotyledons to plumule
Plumule - become first true leaves

Question 5

Plant examples propagated by seed - Vegetables

Answer 5

Vegetables:
Daucus carota
Solanum lycopersion

Question 6

Plant examples propagated by seed - Annuals

Answer 6

Annuals:
Helianthus annuus
Lobelia erinus

Question 7

Plant examples propagated by seed - Lawn Grasses

Answer 7

Lawn Grasses:

Lolium perenne

Question 8

Plant examples propagated by seed - Woody plants

Answer 8

Woody plants:

Fagus sylvatica

Question 9

Plant examples propagated by seed - Seasonal bedding

Answer 9

Seasonal Bedding:
Calendula officinalis
Nigella damascena

Question 10

Plant examples propagated by seed - Others

Answer 10

Glasshouse salads, Herb production, green manures, garden wild flower meadows

Question 11

Seed collecting checklist

Answer 11

• Collect at correct stage of ripening
• Healthy Plant
• Free of P&D
• Plant that is true to type
• Note the provenance of parent plant
• label seed batches accurately

Question 12

Dry Seed collecting

Answer 12

Phaseolus vulgaris

Harvest:
Removing pods from plants as the ripen with sterile secateurs. On a dry day to avoid infections. Place in a dry container and label. Location, Date etc…

Separate:
Spererate seeds from pod and leave to dry on newspaper for 7-10 days turning regularly.

Clean:
Clean the seed by removing debris by hand or using a sieve

Grade:
Grade and reject any seeds clearly not viable, diseased or too small

Store and Package:
In dry cool conditions in a paper bag or plastic box with a silica gel sachet.
Labelled with Genus, Species, Cultivar, Date collected, provenance.

Question 13

Fleshy fruit seed collecting

Answer 13

Solanum lycopersicon

Harvest: removing dry skinned, ripe, P&D free fruit from plant using clean secateurs.
Remove from stalk, place in fresh water.

Macerate:
Macerate the fruit by pulping it through a sieve without damaging the seed.
(soak in water for a few days to seperate the pulp from the seed)

Clean:
Clean the seeds by washing in a sieve

Dry:
Dry the seed by placing onto wax-paper and place in a warm dry place for 1-2 weeks.

Clean:
Clean the seed by removing debris or using a sieve

Store:
In a dry paper bag or plastic box with a silica gel.
Label with Genus, Species, cultivar, Date collected, site/provenance.

Question 14

Recalcitrant / Orthodox Seed

Answer 14

Recalcitrant:
Quercus roubar, Aesculus hippocastanum

Very short viability, few months, ussually fleshy and moist.
(lots of stored energy for long seedling length before reaching light)

Orthodox:
Phaseolus vulgaris, Solanum lycopersicum

Most species, medium to long term viability 2 - 10 years. Dry seeds.

Question 15

Seed Storage - Temperature

Answer 15

Seed viability is usually extended as temperatures fall to around 3-5c.
Aerobic respiration rate in the seed is greatly reduced.

Question 16

Seed Storage - Moisture

Answer 16

Most orthodox seed will remain viable if kept in a low-humidity environment.
Reduce the chance of moisture being taken up through the micropyle and beginning the process of germination.

Recalsitrant seed must be kept in cool and moist conditions. Boxes of moist coir.

Question 17

Seed Storage - Age of Seed, P&D

Answer 17

Seed viability reduces with age.

Presence of P&D, especially rodents in grain store.

Question 18

Seed Storage - co2, o2 concentration

Answer 18

Increasing the co2 concentration can prolong seed viability by reducing the rate of respiration.

Conversely, increasing the o2 concentration in seed storage can decrease seed viability by increasing the rate of respiration.

Storage is often in a Nitrogen rich atmosphere.

Question 19

Germination requirements

Answer 19

Water:
required to rehydrate the seed.
Oxygen: 
required by the seed for respiration
Suitable Temperature:
is required for cell activity spp dependant.
Light:
Some seedlings require light to germinate, and therefore are best left uncovered.

Primula vulgaris, Begonia semperflorens

Question 20

Process if Germination

Answer 20

• seed take sup water through the micropyle
• respiration rate increases as temperature level increases
• Respiration allows energy to be released from the cotyledon storage
• Rapid Cell division follows form the meristematic tissue
• Testa splits and the Radicle emerges