Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chapter 7 Principles of Propagation by Seed. Germination process-Germination process- –Seed must be viable = embryo alive and capable of germination –Seed.

Similar presentations


Presentation on theme: "Chapter 7 Principles of Propagation by Seed. Germination process-Germination process- –Seed must be viable = embryo alive and capable of germination –Seed."— Presentation transcript:

1 Chapter 7 Principles of Propagation by Seed

2 Germination process-Germination process- –Seed must be viable = embryo alive and capable of germination –Seed must receive: WaterWater Proper temperatureProper temperature OxygenOxygen Light (depending on species)Light (depending on species) –Primary dormancy must be overcome = after-ripening. Often removed by environmental conditions

3 Phases of germination

4 Principles of Propagation by Seed Phases of Germination:Phases of Germination: –I.) Water uptake By imbibition = a physical process in seeds with a permeable seed coatBy imbibition = a physical process in seeds with a permeable seed coat Occurs whether seed is alive, dead, dormant or non-dormantOccurs whether seed is alive, dead, dormant or non-dormant First minutes = rapid uptakeFirst minutes = rapid uptake Followed by hours of slow uptakeFollowed by hours of slow uptake Seeds generally do not wet uniformlySeeds generally do not wet uniformly Volume of seed increasesVolume of seed increases

5 Principles of Propagation by Seed Phases of Germination:Phases of Germination: –I.) Water uptake (continued) Leakage: amino acids, sugars, proteins,... Since cell membranes are not fully functional yetLeakage: amino acids, sugars, proteins,... Since cell membranes are not fully functional yet Quantity leaked is proportional to seed qualityQuantity leaked is proportional to seed quality High leakage means the seed is susceptible to attack by insects, fungi, and bacteria (can be measured by an electrical conductivity meter)High leakage means the seed is susceptible to attack by insects, fungi, and bacteria (can be measured by an electrical conductivity meter)

6 Imbibition & Lag Phase Fresh Weight

7 Principles of Propagation by Seed –II.) Lag phase Mitochondria matureMitochondria mature Proteins are synthesized (enzymes are activated)Proteins are synthesized (enzymes are activated) Food reserves are metabolizedFood reserves are metabolized Enzymes loosen cell wallsEnzymes loosen cell walls

8 Principles of Propagation by Seed –III.) Radicle emergence Result of cell enlargementResult of cell enlargement Food reserves continue to be usedFood reserves continue to be used Enzymes degrade certain cell walls to permit exit of the radicleEnzymes degrade certain cell walls to permit exit of the radicle GA promotes enzymatic cell wall hydrolysis and radicle emergenceGA promotes enzymatic cell wall hydrolysis and radicle emergence ABA inhibits enzymatic cell wall hydrolysisABA inhibits enzymatic cell wall hydrolysis

9 Radicle emergence

10 Principles of Propagation by Seed Use of storage reservesUse of storage reserves –Proteins in protein bodies In cotyledons and endospermIn cotyledons and endosperm Enzymes (proteinases) are required to break down proteins into amino acidsEnzymes (proteinases) are required to break down proteins into amino acids Proteinases synthesized during imbibitionProteinases synthesized during imbibition

11

12

13 Principles of Propagation by Seed –Starch In endosperm (in grain crops)In endosperm (in grain crops) Order of events:Order of events: –Imbibition –GA in embryo & scutellum (protective sheath around cotyledons in monocots) translocated to the aleurone layer –Aleurone layer = a secretory cell layer that surrounds the endosperm –Enzymes are synthesized (  -amylase) –Enzymes convert starch to glucose & maltose sugars and then transported to the embryo for use in development and growth –Note: these sugars are important in beer making!

14 aleurone layer

15

16

17

18 Principles of Propagation by Seed –Lipids Oil bodies in endosperm & cotyledonsOil bodies in endosperm & cotyledons Oils = triacylglycerides (glycerol & fatty acids)Oils = triacylglycerides (glycerol & fatty acids) Glyoxysomes are organelles found ONLY in seeds! They process stored oils.Glyoxysomes are organelles found ONLY in seeds! They process stored oils. Fatty acids are high energy compounds used in the glyoxylate cycle to produce sucroseFatty acids are high energy compounds used in the glyoxylate cycle to produce sucrose Sucrose is then transported to the embryo for use in development and growthSucrose is then transported to the embryo for use in development and growth

19 Canola Seed Oil

20

21

22 Principles of Propagation by Seed Measures of germination:Measures of germination: –Germination percentage (%) = number of seedlings produced in a specified time –Germination rate - T 50 value = # of days required to achieve 50% germination of the seed lot

23 Germination curve

24 Standard seed germination curve

25 Seed vigor

26 Principles of Propagation by Seed Environmental factors influencing germination:Environmental factors influencing germination: –1.) Water - threshold water potential = amount of water needed by the seed for radicle emergence Rate of water movement in soil depends on:Rate of water movement in soil depends on: –Texture (pore space) –Packing (pore space) –Closeness of seed/soil contact Water with high salt content can counter-balance the effects of water imbibition (this is a problem in California with subirrigated fields and high water evaporation)Water with high salt content can counter-balance the effects of water imbibition (this is a problem in California with subirrigated fields and high water evaporation)

27 Principles of Propagation by Seed Seed primingSeed priming –Regulates water imbibition of seeds –Charles Darwin suggested this possibility in 1855! –Polyethylene glycol (PEG) used today (aerated) –Starts metabolic processes without radicle emergence –Seed is re-dried for short-term storage at cool temperatures –Results in uniform germination –Used on bedding plant plug production (annuals)

28 Seeds primed and pregerminated in aerated PEG

29 Effects of seed priming on germination

30 Principles of Propagation by Seed –2.) Temperature The MOST important environmental factor that regulates TIMING of germinationThe MOST important environmental factor that regulates TIMING of germination Boil-treat seeds to control disease. This won’t damage the seed as long as the seed is DRYBoil-treat seeds to control disease. This won’t damage the seed as long as the seed is DRY Store seed at low temperatures to prolong viabilityStore seed at low temperatures to prolong viability Temperature affects germination percentage and germination rateTemperature affects germination percentage and germination rate Germination rate increases with an increase in temperature (up to a point)Germination rate increases with an increase in temperature (up to a point) Germination percentage is constant in the mid- temperature range and low on either endGermination percentage is constant in the mid- temperature range and low on either end

31 Principles of Propagation by Seed Temperature ranges:Temperature ranges: –Minimum - lowest temperature for germination –Maximum - highest temperature for germination –Optimum - a range where the greatest percentage of seedlings are produced at the highest rate

32 Principles of Propagation by Seed Temperature categoriesTemperature categories –Cool-temperature tolerant - native to temperate zones prefer °F Ex: broccoli, cabbage, carrot, peas, alyssumEx: broccoli, cabbage, carrot, peas, alyssum –Cool-temperature requiring - native to a Mediterranean climate. No germination if > 77 °F Ex: celery, lettuce, onion, delphiniumEx: celery, lettuce, onion, delphinium

33 Principles of Propagation by Seed Temperature categories (continued)Temperature categories (continued) –Warm-temperature requiring - native to subtropical and tropical regions Must be > 50°F for sweet corn & tomatoMust be > 50°F for sweet corn & tomato Must be > 60°F for beans, pepper, cucumbers, cottonMust be > 60°F for beans, pepper, cucumbers, cotton

34 Principles of Propagation by Seed Temperature categories (continued)Temperature categories (continued) –Alternating temperatures Day/night temperature fluxes are better than constant temperaturesDay/night temperature fluxes are better than constant temperatures Used in seed testing labsUsed in seed testing labs 18°F (10°C) difference often used18°F (10°C) difference often used Imbibed weed seeds deep in soil do not germinate since there is little temperature flux, however, they will germinate if the soil is cultivated and seeds are brought to the surface where there is temperature fluxImbibed weed seeds deep in soil do not germinate since there is little temperature flux, however, they will germinate if the soil is cultivated and seeds are brought to the surface where there is temperature flux

35 Principles of Propagation by Seed Aeration effects on germinationAeration effects on germination –Oxygen uptake is proportional to the amount of metabolic activity –Oxygen diffuses through water slowly therefore waterlogged soils slow/inhibit germination

36 Principles of Propagation by Seed Light effects on germinationLight effects on germination –Involves quality (wavelength) and photoperiod (duration) –Light-sensitive seed are generally small in size or are epiphytes (grow on other plants) Ex: alyssum, begonia, coleus, orchidsEx: alyssum, begonia, coleus, orchids

37 Principles of Propagation by Seed Light effects on germinationLight effects on germination –A few plants have germination inhibited by light Ex: amaranthus, allium, phloxEx: amaranthus, allium, phlox –Some require dark to germinate Ex: calendula (pot marigold), delphinium, pansyEx: calendula (pot marigold), delphinium, pansy –Some require a specific daylength Ex: birch, hemlockEx: birch, hemlock

38 Principles of Propagation by Seed Disease during germinationDisease during germination –Damping-off Pythium ultimumPythium ultimum Rhizoctonia solaniRhizoctonia solani Botrytis cinereaBotrytis cinerea Phytophthora spp.Phytophthora spp. –Drying, salts and excess heat at the soil surface can also look like damping off Optimum growth between 68-86°F Pb. on warm-requiring seeds Secondary pathogens

39 Damping-off in tomato & soybean

40 Principles of Propagation by Seed Dormancy - regulation of germinationDormancy - regulation of germination –Quiescent seeds - only need to be imbibed and an appropriate temperature for germination. NO dormancy! –Primary dormancy - a type of dormancy where seeds will not germinate despite adequate environmental conditions –Secondary dormancy - induced under unfavorable environmental conditions

41 Principles of Propagation by Seed Dormancy is important to propagators because it allows storage, transport and handling of seedDormancy is important to propagators because it allows storage, transport and handling of seed After-ripening - changes in the dry seed during storage that allow the seed to germinate following favorable conditionsAfter-ripening - changes in the dry seed during storage that allow the seed to germinate following favorable conditions

42 Principles of Propagation by Seed Types of Primary DormancyTypes of Primary Dormancy –Exogenous dormancy - factors outside the embryo (seed coat or parts of the fruit) Inhibits water uptakeInhibits water uptake Physical restriction on embryo expansion or radicle emergencePhysical restriction on embryo expansion or radicle emergence Controlling gas exchange (O 2 /CO 2 )Controlling gas exchange (O 2 /CO 2 ) Preventing leaching of internal inhibitorsPreventing leaching of internal inhibitors Supplies inhibitors to the embryoSupplies inhibitors to the embryo

43 Principles of Propagation by Seed –Exogenous physical dormancy (“seed coat”) Outer integument becomes hard or fibrous during dehydration and ripening (Ex: coconut, honeylocust, Kentucky coffeetree)Outer integument becomes hard or fibrous during dehydration and ripening (Ex: coconut, honeylocust, Kentucky coffeetree) In drupes (cherry, peach, etc.). Have a hardened endocarp (“pit” or “stone”)In drupes (cherry, peach, etc.). Have a hardened endocarp (“pit” or “stone”) In nature, hard seed coats are softened by:In nature, hard seed coats are softened by: –Microorganisms –Passage through an animal’s digestive tract –Abrasion -freeze/thaw –Fire

44 Principles of Propagation by Seed –Exogenous chemical dormancy In fleshy fruitsIn fleshy fruits Contain chemical inhibitors such as ABA (Ex: citrus, cucumbers, apples, pears, grapes, etc.)Contain chemical inhibitors such as ABA (Ex: citrus, cucumbers, apples, pears, grapes, etc.) Desert plant fruits have chemical inhibitors that must be leached away by rains that then provide enough water for germination and seedling developmentDesert plant fruits have chemical inhibitors that must be leached away by rains that then provide enough water for germination and seedling development

45 Principles of Propagation by Seed Endogenous dormancyEndogenous dormancy –Morphological dormancy Rudimentary embryo = araliaceae (ginseng), papaveraceae (poppy), ranunculaceae (anemone)Rudimentary embryo = araliaceae (ginseng), papaveraceae (poppy), ranunculaceae (anemone) Linear embryo = ericaceae (rhododendron), annonaceae (pawpaw)Linear embryo = ericaceae (rhododendron), annonaceae (pawpaw) Overcome by:Overcome by: –Alternating temperatures –Treat with KNO 3 or GA

46

47 Principles of Propagation by Seed Endogenous dormancy (continued)Endogenous dormancy (continued) –Physiological dormancy Non-deep = after-ripening. Fresh seeds of herbaceous plants (annuals and many perennials) lose dormancy during standard storageNon-deep = after-ripening. Fresh seeds of herbaceous plants (annuals and many perennials) lose dormancy during standard storage PhotodormancyPhotodormancy –Seeds require either light or dark conditions –Involves phytochrome (in most plants) which is photoreversible –There is often an interaction between light and temperature –Light requirement can sometimes be offset by cool temperatures or alternating temperatures (Ex: lettuce seed, can germ. in dark if temp. below 73°F)

48 Principles of Propagation by Seed Endogenous dormancyEndogenous dormancy –Physiological dormancy Photodormancy (continued)Photodormancy (continued) –Seed coat or underlying endosperm act as light sensors (if removed, light control disappears) –Hormones (GA) can overcome a light requirement –Red > far-red in natural sunlight (2:1) therefore phytochrome is active (P Fr form) and seed stimulated to germinate –Under foliage, far-red light penetrates more than red light, therefore phytochrome is inactive (P r form) and seeds fail to germinate –Red light does not penetrate soil as deeply as far-red light, therefore light-sensitive seeds stay dormant until they get closer to surface (Ex: weed seeds)

49 Lettuce seed is light sensitive Dark Light

50

51

52

53 Tanada effect Exposed to red light (phytochrome active) Exposed to far- red light (phytochrome inactive)

54 Principles of Propagation by Seed Endogenous dormancyEndogenous dormancy –Physiological dormancy Intermediate/deep physiological dormancyIntermediate/deep physiological dormancy –Stratification (moist-chilling) –Must be aerated –Moisture should be constant –Temperature should reflect the plant’s native habitat for the winter/spring (≈ ºF) with a minimum of 23ºF –Time for seed-chilling requirements are related to bud- chilling requirements!

55 Effects of stratification on germination

56 Seeds hormone levels during stratification

57 Effects of vernalization/stratification on seedling development

58 Principles of Propagation by Seed Endogenous dormancyEndogenous dormancy –Physiological dormancy Intermediate/deep physiological dormancy (continued)Intermediate/deep physiological dormancy (continued) –For intermediate dormancy, if embryo is removed from the seed, it will readily germinate (dormancy is mostly seedcoat) and moist-chilling time required is short –For deep dormancy, an excised embryo will not germinate readily nor will it form normal plants (physiological dwarfs) and these seeds require a long moist-chilling period (> 2mo.)

59 Principles of Propagation by Seed Double dormancyDouble dormancy –Seed has two kinds of dormancy –Ex: a rudimentary embryo & seed coat dormancy = morphological dormancy & physical (exogenous) dormancy ThermodormancyThermodormancy –Different from thermal inhibition –Once exposed to high temperatures, will not germinate when temperatures return to the optimal germination range Ex: lettuce in summer, therefore often primed (in PEG) at cool temperatures to allow germination prior to sowingEx: lettuce in summer, therefore often primed (in PEG) at cool temperatures to allow germination prior to sowing

60 Principles of Propagation by Seed Advantages of seed dormancyAdvantages of seed dormancy –Seedling survival - permits germination only when the environmental conditions are favorable –Creates a “seed bank” - not all seeds for a species germinate in a single year. Spreads germination out over time –Synchronize germination - for a particular time of year –Seed dispersal - especially after being carried in the digestive tract of animals

61 Summary of types of germination

62 Epigenous seed germination

63

64

65 Hypogenous seed germination


Download ppt "Chapter 7 Principles of Propagation by Seed. Germination process-Germination process- –Seed must be viable = embryo alive and capable of germination –Seed."

Similar presentations


Ads by Google