Level 2 Horticulture Science Plant Propagation US 20556 10 Credits – Internal Assessment
Contents • Asexualvssexual Propagation • Sexual propagation (seed sowing)- overview • Seed structure • Germination • Respiration • Seed requirements • Seed Dormancy • Seed Vigour and Viability • Seed sources
Asexualand Sexual Propagation • AsexualPropagation - using one parent plant to produce a new individual that is a clone (genetically identical) • Key words: offspring, new individuals, parent plant(s), • Sexual Propagation – recombination of the genes to produce a new individual that is a genetically different (also known as sexual reproduction) In Angiosperms -This always involves flowers and always results in seed. In Gymnosperms/ ferns and Moses this results in spores Question – if a plant self pollinates is it sexual or asexual propagation?
Seed sowing - Contents To understand seed sowing technique we will be looking at: • Seed structure • Germination • Respiration • Seed requirements • Seed Dormancy • Seed Vigour and Viability Seed Sowing Menu
When two varieties of plant are crossed together (sexual propagation) the combining of different genetics results in a plant that is hetrozygous for many genotypes. This often means that a particular trait receives both of the varieties traits • Hybrid vigour
Seed sowing – seed structure Three parts to a seed • Seed coat • Endosperm • Embryo ‘A seed is a plant in a box with it’s lunch’ Seed Sowing Menu
Seed sowing – seed structure • Seed coat -the outer covering of a seed helps protect the embryo from injury and drying out. Seed coats can be thin and soft as in beans or thick and hard as in walnuts or coconut seeds. • Endosperm, a temporary food supply, is packed around the embryo in the form of special leaves called cotyledons or seed leaves. These are often the first parts visible when the seed germinates. • Embryo – the ‘baby’ plant. Seed Sowing Menu
Two different situations: • Cotyledon(s) appear above ground as first leaves (seed leaves) • Cotyledon(s) remain below the ground
Seed sowing – Seed Structure • There are two types of plants that produce seeds: Monocotyledons and Dicotyledons Seed Sowing Menu
Seed Structure Seed Sowing Menu
Germination • Starts when the seed begins to absorb water • Ends when the new plant is able to get all its’ energy from photosynthesis.
Germination – the process • The seed absorbs water until it swells and smoothens its exterior wrinkles. • Swelling continues until the coat of the seed bursts open. • Food stored in cotyledons or endosperm soaks up water and soluble substances dissolve in it. • Respiration begins thus energy and raw materials are supplied by food for cell division and growth. • A radical appears first and then a pumule.
Respiration • During respiration (in plants and animals) energy is released from sugar (glucose) by a series of chemical reactions. The sugar is broken down into carbon dioxide and water in a process which uses oxygen.
Respiration in seeds • INPUTS OUTPUTS • Match your list to the following. • Allows seed to swell and break seed coat • Required for respiration • Speeds up the various chemical processes
Seed requirements • Seeds don’t get re-assessment opportunities. Once they begin to germinate they either survive or die. • Seeds need the WOW factor to survive (water oxygen, warmth). Soil, light, CO2 are only for ‘grown-up’ seeds • A seed is a plant in a box with it’s lunch – but no dinner – if a seed is in the packet too long it will run out of lunch and die.
Seed dormancy • Dormant seeds are seeds that are in ‘sleep’ mode waiting for the correct conditions to begin germination. • These conditions include WOW, but also physiological changes in the seed that determine when the seed will germinate. • Many seeds will not germinate until they have been exposed to a cold period (been in the ground over winter). • Other seeds will not germinate until the testa has been damaged (damage may occur from scratching – exposure to stomach acid – attack form micro organisms in the soil) • Seed dormancy aids a species' survival by delaying germination so that 'overall germination' is dispersed over time.
Seed Storage and Viability • Germination requirements = WOW • Seed storage needs to get rid of the Ws. i.e. an environment that is cool and dry! • Why can we not store seeds in a oxygen free environment? • Seeds have limited viability (ability to germinate) because in storage they are undertaking respiration and slowly consuming their energy supply. • For this reason seed packets have expiry dates
Seed vigour • Seed vigour describes the ability of a seed to germinate quickly. Seed storage and genetics determine seed vigour.
Seed Sources • Commercial retailers Saving your own How to save tomato seedsVideo instructions – tomato seeds Seed swap groups Check out the seed savers website
End – Sexual Propagation • Back to Main menu