R2104 1.2 – 1.3 Seed Germination, Harvesting and Storing

Question 1

What is a seed?

Answer 1

A seed is the product of sexual reproduction Formed from ovules as a result of fertilisation. Method by which plants reproduce.

Question 2

State the benefits to a plant of sexual reproduction

Answer 2

Adaptation – survival of the fittest; strongest plants will thrive

Variety – mixing of characteristics gives chance of new and better plants

Survival – can survive harsh conditions as a seed

Volume

Question 3

Testa facts

Answer 3

Seed coat For protection Tough May need damaging before germination - nicking, soaking, soil particles etc.

Question 4

Cotyledon

Answer 4

Seed leaf Provides store of food for germinating seed One seed leaf - monocot Two seed leaves - dicot

Question 5

Hilum

Answer 5

Scar from where attached to ovary

Question 6

Plumule

Answer 6

Part of seed that forms first shoot

Question 7

Epicotyl

Answer 7

Connects cotyledon to plumule

Question 8

Hypocotyl

Answer 8

Connects cotyledon to radicle

Question 9

Radicle

Answer 9

Forms first root

Question 10

Micropyle

Answer 10

Small hole in testa where pollen tube entered ovule. Can be where water enters for germination

Question 11

Horticultural benefits of propagation from seed

Answer 11

Produces variation from which new cultivars can be developed Only method for some species Can get large numbers from one plant Easily stored Can avoid virus transmission as guaranteed sources are available.

Question 12

What are the limitations for propagation by seed?

Answer 12

Some plants may not produce viable seed

Lack of uniformity

Difficult germination

Some seeds don’t store easily

Time to maturity

Question 13

What is a viable seed?

Answer 13

Has the potential for germination when conditions are right. Contains living embryo

Question 14

What is seed dormancy?

Answer 14

When viable seed fails to germinate even when all germination conditions have been met.

Question 15

Describe changes in germinating seed

Answer 15

Takes in water Respiration rate increases Breakdown of food store Rapid cell division Splitting of seed coat/testa Emergence of radicle

Question 16

Describe preparation and storage of Phaseolus vulgaris and Nigella damascena.

Answer 16

Collect ripe seed (when seed pods are brown)

Choose ones that are pest and disease free and true to type

Store pods and capsules in a warm place until they split

Clean the seed so is free from dust and debris (sieve)

Place in paper bag to be kept dry and cool.

Lidded plastic box with silica gel in fridge

Label and date

Question 17

When should seed be harvested?

Answer 17

• As seed ripens (in most cases)
• Seed from dry fruits should be collected on a dry day
• Dry on the plant for as long as possible into the autumn, ideally until the pods become so dry they are crispy
• If this is not possible, uproot the plants and hang them upside down somewhere warm until the pods are completely dry

Question 18

What are recalcitrant seeds?

Give examples.

Answer 18

• Desiccation intolerant – moist/fleshy seed that easily lose their viability if stored for any length of time, even under conditions that are normally conductive to seed longevity, i.e. low moisture content and low temperatures.
• They cannot have moisture content below 20–30% w/o injury.
• Includes many tropical plants such as rubber, coconut, avocado, cacao, lychee, mango and tea.
• Such seeds can only be kept for a year or less.
• Difficult to store and ex-situ conservation is problematic.
• Some species can lose their viability within a week if kept in air, e.g. Salix japonica

1. Aesculus hippocastanum
2. Quercus robur
3. Castanea sativa

Question 19

What are orthodox seeds?

Give examples of vegetables and flowers.

Answer 19

• Dry seed, can be dried to 5% moisture content w/o injury; desiccation tolerant and long lived.
• Longevity depend on species and storage conditions.

Vegetables:

1. Daucus carota
2. Phaseolus vulgaris or coccineus
3. Lactuca sativa

Flowers:

1. Lobelia erinus
2. Nigella damascena
3. Lolium perenne
4. Begonia semperflorens

Question 20

What is seed viability/germination affected by?

Answer 20

• The condition of the seed when first stored
• How long it is stored (viability diminishes over time)
• What seed is being kept
• Whether respiration is controlled (the aim is to slow down respiration. If respiration is not controlled then seeds may use up food needed to produce strong, healthy plants.
• Dormancy – some seeds may become dormant if stored and to promote germination dormancy must be broken

Question 21

Describe preparation and storage of Solanum lycopericum fruits for seed storage.

Answer 21

• Harvesting

Harvest healthy fruit which is free from damage when it is ripe.

• Maceration

Macerate the fruit by pressing the fruit with a board, squashing by hand or scooping out the seeds from the flesh. The pulp can also be fermented in water for a few days e.g. Solanum lycopersicon.

• Separation

The seeds can be separated from the flesh by placing the pulp in a bucket of water. The flesh and dead seeds float and the live seeds sink to the bottom. Seeds can be separated with the use of a sieve.

• Drying

Dry in airy place or in gentle heat; on greaseproof paper or a paper towel

Question 22

Describe the method of storage for orthodox (dry) seeds.

Answer 22

Orthodox (dry) seeds require dry, cool conditions which are provided by placing the seed in a sealed container with silica gel to maintain a dry atmosphere and placing them in a refrigerator at a temperature of 4°C.