Seeds Flashcards
What is a seed?
A seed is the product of sexual reproduction.
Seed is produced from a fertilised ovule following pollination.
What is the function of the fruit?
The function of the fruit is to protect and distribute the seeds.
A fruit is defined as the ovary containing the seeds.
What is the definition of propagation?
The horticultural practise (ie; human controlled) method of increasing plants in number.
What are the external parts of the French Bean called?
Testa - tough hard outer coating of the seed. Protects the seed.
Hilum - Area outside of the testa where the seed was attached to the ovary. No function. It’s a scar.
Microphyle - This is a small pore in the testa opposite the tip of the radicle. Water enters via the micropyle during imbibition which is the first stage of germination.
What are the internal features of the French bean? (Phaseolus vulgaris)
Cotyledon - a cotyledon is a seed leaf. In Dicots there are 2 and in monocots there are 1.
Plant embryo - Occupies the buik of the seed interior. It is made up of Radicle, hypocotyl, epicotyl, cotyledons and plumule.
Plumule - Part of seed which will form the first shoot which will become stem & leaves.
Epicotyl - part of the seed which is above the cotyledons. It will form the stem and leaves.
Radicle - part of the seed which will form the first root. First part of seed to grow and pushes down into the soil to anchor the plant and access water.
What is the botanical name for French Bean?
Phaseolus vulgaris
What are the benefits to the plant of sexual reproduction by seed?
Because genetic material is being mixed there is more variation.
Variation gives the plant a better chance of survival, because they are not all the same. So less chance of extinction.
Seeds are dispersed by various means - can be dispersed far away from the parent plant by wind or animal. Gives them greater chance of survival not in shadow of parent plant, also different habitats increases chance of survival.
Less risk of transfer of pests and diseases compared to vegetative reproduction - therefore greater chance of survival.
A way of creating lots of offspring which can colonise an area quickly as some plants release 1000s of seeds. Especially weeds.
They can remain dormant when conditions of growth are unsuitable. Eg. over winter for some trees and shrubs.
What are the Horticultural benefit for propagation by seed?
Genetic variations create new cultivars which can boost sales of bedding and vegetable plants. The grower can hand pollinate and select certain characteristics.
Growers can select cultivars that resist certain pests and diseases, so yields are higher.
Growers can create F1 cultivars by inbreeding parents for characteristics and then crossing them so all the same first generation. This means uniform germination, same height, colour and hybrid vigour.
They can be stored easily for long periods of time.
Get large numbers of plants relatively cheaply.
Only method for some annuals and biennials.
Can avoid virus transmission. (virus’ not normally found in seed).
What are the limitations of propagating from seed?
They may not come true to type due to variation. (some plants will come true to type if they are self pollinated - eg. beans, tomatoes, peas)
Some will not produce viable seed. (Seed that will germinate.
Lack of uniformity (unless they are F1 Hybrids)
Some seeds do not store easily (recalcitrant seeds such as oak and horse chestnut).
Some have various types of dormancy and are difficult to germinate. Knowledge for specific types of dormancy for specific plants is required.
What 3 vegetable plants are usually propagated from seed?
Daucus carota (carrot) Solanum lycopersicum (tomato) Phaseolus vulgaris (French bean)
What bedding plant is usually propagated from seed?
Lobelia erinus ‘Sapphire’
What annual is usually propagated from seed?
Nigella damascena. (love in a mist)
What lawn seed is usually sown from seed?
Lolium perenne (perennial rye grass)
What tree is usually propagated from seed?
Quercus robur - English oak
Which herbs are propagated from seed?
Chives, coriander and basil.
What are the benefits of propagation by seed? (for the gardener)
Produces variation from which new cultivars can be produced.
Is the only available method for some species. (Phacelia tanacetifolia - green manure)
May get large numbers of seed from each plant, therefore large numbers of plants.
Seed can easily be stored.
Can avoid virus transmission.
Can sow seeds when gardener wishes. ie. for timed flowering/cropping.
Economical
Germination rates fairly certain for vegetables.
What are the limitations of Propagating plants from seed?
Open pollinated seeds will probably not come true to parent.
Takes a long time to maturity. (Compared to grafting an apple tree)
Germination may be complicated and require certain environment conditions.
Some plants may not produce viable seed.
Some seeds do not store easily. (recalcitrant)
Takes up space to grow from seed.
Lack of uniformity in resulting plants. (unless F1 hybrid)
Seeds may have a dormancy mechanism that must be overcome.
What does seed viability mean?
This is the ability of a seed to germinate under ideal conditions.
The seed is viable if it contains a living embryo and will germinate if conditions are right.
Different seeds remain viable for different lengths of time if stored correctly.
Eg. parsnip can remain viable for up to 1 year, cucumber is 10 years.
What are the four key requirements for seed germination?
- Moisture
- Temperature
- Oxygen
- Light/dark
Why is moisture needed for germination?
Required for imbibition to break testa and provide water for biological processes involved in growth and cell division.
What is average temperature needed for seed germination? Are there any exceptions?
Average germination for many seeds is 15-21 degrees C.
Varies between species.
Lettuce goes dormant over 25 degrees.
What is oxygen needed for in seed germination?
Required for respiration of carbohydrates stored in seed to fuel cell division and growth.
Why is light/dark significant in germination of seeds?
Can trigger or prevent germination depending on seeds.
Salad - Lactuca sativa need light
Nigella damascena need dark
Not all species are light sensitive.
What changes take place in a germinating seed?
Imbibing of water. (taking in of water) Water slowly enters through the microphyle and testa.
Rising respiration rate. Aerobic respiration occurs & rapidly rises as cell division and growth continues.
Breakdown of food store - to provide energy for cell division.
Rapid cell division for the growth of the radicle (root) and plumule (shoot)
The splitting of the seed coat more fully with water absorption
Emergence of the radicle.
Emergence of the plumule..
What are the two different types of germination called?
Epigeal and hypogeal.
What type of germination occurs with Phaseolus vulgaris? (French bean)
Epigeal - cotyledons grow above ground.
What type of germination occurs with Vicia faba? (Broad beans)
Hypogeal - cotyledons stay below ground.
What is the botanical name for Broad beans?
Vicia faba
How can the horticulturalist provide ideal moisture conditions for germination?
Water compost before sowing, or carefully after so as not to disturb the seeds.
Soak seed prior to sowing so as to soften the coat. Eg. Lathyrus odoratus
Important not to overwater, as this will reduce oxygen available and could cause seed to rot.
Cover seed with lid or glass to retain moisture.
Irrigation - stand trays on capillary matting, sand beds or use a mist bench.
How can the horticulturalist provide ideal temperature conditions for germination?
Ambient temperature can be provided in a greenhouse with hot water pipes, or electric heater.
Localised heat in the form of electric cables in a bottom heat mat or a sealed propagation unit with a lid is an economical way of providing heat where needed.
High temperatures can be lowered with shading, ventilation or damping down (seeds like lettuce become dormant over 25 degrees.
How can the horticulturalist provide ideal oxygen levels for germination?
Open compost which has a good air filled porosity.
Allows oxygen to reach the seed for respiration to occur. Add sharp sand, vermiculite or perlite.
Do not compact the soil when sowing.
Do not over sow as there will be competition for oxygen.
How can the horticulturalist provide ideal light conditions for germination?
Keep uncovered by compost in an open position so that they receive light. Vermiculite covering allows some light through but helps with moisture absorption.
Artificial lighting
How can the horticulturalist provide ideal dark conditions for germination?
Closed cabinets
Seed covering with compost and depth of covering.
Place a sheet of toughened glass over the tray and then cover the glass with newspaper.
Describe what seed dormancy is?
Dormancy is demonstrated when a viable seed fails to germinate even though all conditions have been met.
The seed may have a physiological or physical dormancy. Eg. Lathyrus odoratus hard seed coat.
Important to note use of word ‘viable’ - as a non viable seed is dead and will therefore never germinate.
What is the purpose of seed dormancy?
This ensures germination does not occur when favourable conditions will not be sustained. (Eg in Winter
What is meant by the term physical dormancy?
Physical dormancy – a thick or impervious seed coat prevents water from entering seed. ‘Physical’ is something that can be seen overtly like the seed coat.
What is meant by the term physiological dormancy?
Physiological dormancy – requires a period of time spent under specific environmental conditions eg chilling or requires exposure to light to break dormancy. ‘Physiological’ means functions happening within the seed which cannot be seen.
How can you break physical dormancy of a seed?
Scarification - deliberate damage to the seed coat to allow water to enter. Lathyrus odoratus - soak before sowing to soften the coat, or nick the seed with a knife.
How can you break physiological dormancy?
Stratification - some seeds need a period of cold before they germinate, which would happen naturally in the wild. The grower will place seeds in a bag of moist sand or vermiculite and keep in a sealed container in the fridge for 1-2 months.
This process breaks down the chemicals within the seed that inhibit germination and stimulates embryo development.
When is a seed ready to harvest and what should you check when harvesting seeds?
Most seeds must be harvested when they are fully ripe. (there are some exceptions)
Seed must be prepared for storage by cleaning off any debris and checking for damage/disease.
Cleaning & checking prevents pests or diseases being harboured in the stored seed.
Cleaned seed easier to store - takes up less space.
Also important to make sure the seed is not contaminated by other seeds - eg. wildflower seed may contaminate grass seed.
How to harvest Phaseolus vulgaris seeds? (French Beans)
On a dry day.
Ensure pods are fully ripened - brown and papery. Rattle sound.
Remove pods from plant.
If conditions wet, remove entire plant and hang upside down in a warm dry room to finish drying.
Save seeds from the healthiest plants which are true to type. Do not save any seeds which look different, damaged or marked.
Leave seeds in a clean dry tray in a warm room to dry out. (Not too hot or direct light)
How to harvest seeds from Nigella Damascena? (Love in a mist)
On a dry day.
Select a healthy pest and disease free plant.
Seedpods should be completely dry - brown and papery.
Look as if they are about to split.
Cut off the entire seed head into a paper bag which is labelled with species name and date.
Place pods in the seed bag in a dry place for the seeds to ripen.
Check when pods are all open, empty entire contents into a seed tray.
Separate the seeds from the chaff with a fine sieve (finer than the seed) Or winnow on a gentle breeze.
How to pack and store Phaseolus vulgaris harvested seeds?
Package up securely in labelled envelopes with cultivar and date.
Keep stored in a cool, dry location.
Paper envelopes can be stored in a plastic box with a silica gel packet.
Exclude mice!
How to package and store Nigella Damascena harvested seeds?
Package up securely in labelled envelopes with cultivar and date.
Keep stored in a cool, dry location.
Paper envelopes can be stored in a plastic box with a silica gel packet.
Exclude mice!
How to harvest tomato seeds Solanum lycopersicum?
Pick fully ripe fruit true to type and healthy.
Do not save fruit that looks markedly different to the rest of the fruit.
Cut off individual fruits into a labelled bag or tray.
If fruits not ripening, they can be cut and placed with a banana!
Cut open tomatoes, and scoop out seeds and pulp and place in a jar of water.
Leave in a warm dry place to ferment.
Fermentation removes compounds which inhibit germination, and destroys seed borne diseases.
After a few days a layer of mould can be seen. Open jar and remove mould.
Tip seeds into a sieve and clean with running water.
Place seeds back in a jar of water. Any which float are not viable and can be removed.
On a commercial scale tomato fruit are macerated by machine to release the seed and their gelatinous gel.
How to dry, and store harvested Solanum lycopersicum seeds? (tomato)
Drain viable seeds in a sieve, and spread rinsed seeds in a single layer on greaseproof paper to dry out in a warm dry place - away from direct sunlight.
Package up securely in envelopes which are labelled with the species, variety name and date.
Keep stored in a cool dry place. Seeds can last for 6 years.
Seeds stored in envelopes can be kept in an air tight container with a silicon gel packet to absorb any excess moisture.
What is an Orthodox seed?
A dry seed.
A seed which can withstand drying and storage as they age slowly.
Ageing is slowest when conditions are cool and dry.
Can be stored for long times.
Eg. Phaseolus vulgaris, Nigella damascena, Solanum lycopersicum, Lobelia erinus, Daucus carota.
What is a recalcitrant seed?
Recalcitrant seed is moist and fleshy. Cannot withstand drying and freezing temperatures as they have a high water content. Requires cool, moist storage conditions. Can only be stored for short periods. Eg. Quercus robur (Oak) Horse Chestnut.
What are the horticultural benefits of propagation from seed?
New cultivars boost sales.
F1 hybrids can be created - form uniform offspring.
Relatively cheap.
Easy to store.
Growers can breed disease resistant varieties
Can avoid virus transmission.
What are the limitations of propagating from seed, compared to vegatative propagation?
Dormancy - many seeds require a particular treatment to break the dormancy before they will germinate. Grower needs to know specific requirement.
May not come true to type - the same as the parent plant.
Some do not produce viable seed.
Some do not store easily - recalcitrant.
How to harvest recalcitrant seeds?
Example of recalcitrant seed - Quercus robur - Oak.
When harvesting the seed should be true to type, free from pathogens, undamaged, and of reasonable size.
Seeds are collected when they are ripe in the autumn and fall from the trees.
Seed can be placed in a polythene bag to ensure it does not dry out with plant name & location & date.
After removing the husks from the seed it can be mixed with either moist peat, sand or vermiculite and placed in a polythene bag.
Seed should be stored in rodent proof containers no longer than 3-4 weeks. Or in the refrigerator 4-5 degrees.
What happens to a seed stored over time?
Over time the food is slowly metabolising, and may use up food reserves.
Seeds can also become over dry and non viable over time.
Viability decreases over time.
How does the storage temperature affect the viability of seed germination?
If too hot seeds may dry out, and become non viable.
Cool temperatures slows respiration to promote longevity in storage.
Viability decreases as temperature increases.
