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Chapter 9 Principles of Propagation by Cuttings. Biology of Propagation by Cuttings Labor costs = up to 80% of cost of propagationLabor costs = up to.

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Presentation on theme: "Chapter 9 Principles of Propagation by Cuttings. Biology of Propagation by Cuttings Labor costs = up to 80% of cost of propagationLabor costs = up to."— Presentation transcript:

1 Chapter 9 Principles of Propagation by Cuttings

2 Biology of Propagation by Cuttings Labor costs = up to 80% of cost of propagationLabor costs = up to 80% of cost of propagation The biology of what actually triggers adventitious root formation is largely unknown!The biology of what actually triggers adventitious root formation is largely unknown!

3 Biology of Propagation by Cuttings Adventitious root & bud formationAdventitious root & bud formation –Stem and leaf-bud cuttings only need to produce adventitious roots –Root and leaf cuttings need to develop both adventitious buds & adventitious roots

4 Biology of Propagation by Cuttings Dedifferentiation - the ability of previously developed, differentiated cells to initiate cell divisions & form new meristems = adventitious roots and budsDedifferentiation - the ability of previously developed, differentiated cells to initiate cell divisions & form new meristems = adventitious roots and buds

5 Biology of Propagation by Cuttings Adventitious root formation (natural)Adventitious root formation (natural) –Corn: brace roots

6 Biology of Propagation by Cuttings Adventitious root formation (natural)Adventitious root formation (natural) –Dracena or Ficus: aerial roots

7 Biology of Propagation by Cuttings Adventitious root formation (natural)Adventitious root formation (natural) –2 types: 1.) Preformed (latent) root initials - develop naturally on the stem and lie dormant Ex: willow, hydrangea, poplar, coleus, marigold, tomato, Swedish ivy, pothosEx: willow, hydrangea, poplar, coleus, marigold, tomato, Swedish ivy, pothos 2.) Wound-induced roots - develop only after the cutting is made in response to wounding. Formed “de novo” (= “anew”)

8 Preformed root initials-Coleus

9 Preformed root initials-Pothos

10 Preformed root initials- Swedish Ivy

11 Preformed root initials-tomato

12 Preformed root initials-willow

13 Biology of Propagation by Cuttings Order of events to produce wound-induced rootsOrder of events to produce wound-induced roots –1.) outer, injured cells die –2.) a necrotic plate forms and seals the wound (suberin) = cork and gum blocks xylem –3.) parenchyma cells (callus) form behind plate –4.) cells near the vascular cambium divide and produce adventitious roots

14 Biology of Propagation by Cuttings Exact location of origin of adventitious roots (still unclear!)Exact location of origin of adventitious roots (still unclear!) –Herbaceous plants = originate outside and between vascular bundles Note: in carnation, roots hit fiber sheath in stem and cannot penetrate and must grow down through stem until they emerge from the base of the cuttingNote: in carnation, roots hit fiber sheath in stem and cannot penetrate and must grow down through stem until they emerge from the base of the cutting –Woody perennials = originate from cambium or young phloem

15 Biology of Propagation by Cuttings Direct root formation from vascular tissueDirect root formation from vascular tissue Indirect root formation from callusIndirect root formation from callus Difficult-to-root species often have a ring of sclerenchyma cells that block root penetration.Difficult-to-root species often have a ring of sclerenchyma cells that block root penetration. Difficult-to-root species often produce callus first and then roots from the callus (Indirect root formation)Difficult-to-root species often produce callus first and then roots from the callus (Indirect root formation)

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20 Biology of Propagation by Cuttings Origin of new shoots and roots in leaf cuttings from:Origin of new shoots and roots in leaf cuttings from: –Preformed 1° meristems - cells still meristematic (rare) Ex: piggyback plant, kalanchoe –Wound-induced 2° meristems - dedifferentiated cells Ex: African violet, begonia

21 Biology of Propagation by Cuttings Limiting factor in leaf cutting propagation is the formation of adventitious buds NOT adventitious roots!Limiting factor in leaf cutting propagation is the formation of adventitious buds NOT adventitious roots! Ex: rubber tree leaf roots readily but never forms adventitious shoots

22 Biology of Propagation by Cuttings Root cuttings –Need to develop adventitious shoots first & then adventitious roots develop from the adventitious shoot –Works best on plants that sucker –Ex: apples and crabapples (Malus), lindens (Tilia), blackberries/raspberries (Rubus) –Note: root cuttings produce adventitious shoots from interior tissue. If you have a periclinal chimeric plant (i.e.: a thornless blackberry), if you propagate this plant by root cuttings, you will get plants with thorns

23 Biology of Propagation by Cuttings Polarity of cuttings –Distal = end nearest the shoot tip shoots –Proximal = end nearest the crown (shoot/root junction) roots –Note: the opposite occurs on root cuttings Distal roots Proximal shoots –Polar movement of auxin is an ACTIVE transport process (will work against gravity if cutting inverted)

24 Biology of Propagation by Cuttings Hormonal control of adventitious root& bud formationHormonal control of adventitious root& bud formation –Specific root-forming factor discovered by Went in 1929, called, “rhizocaline” –Buds effect rooting! No buds or dormant buds either inhibit rooting or have no effectNo buds or dormant buds either inhibit rooting or have no effect –Leaves effect rooting! Presence of leaves increases rootingPresence of leaves increases rooting

25 Biology of Propagation by Cuttings AuxinsAuxins –IAA - naturally occurring (identified in 1935) –IBA –NAA –Exogenous IBA or NAA increases endogenous IAA or increases tissue sensitivity to IAA synthetic

26 Biology of Propagation by Cuttings Root initiation has two stages:Root initiation has two stages: 1.) root initiation –A.) auxin-active: auxin is required for root formation –B.) auxin-inactive: auxin not required for roots 2.) Root elongation - auxin not required

27 Biology of Propagation by Cuttings CytokininsCytokinins –zeatin, kinetin, 2iP, TDZ, BA or BAP –High auxin/low cytokinin ratio favors adventitious rooting –Low auxin/high cytokinin ratio favors adventitious buds/shoots –Difficult-to-root plants often have HIGH cytokinin levels

28 Biology of Propagation by Cuttings GibberellinsGibberellins –GA (Japan, 1939) –Causes stem elongation –Inhibits adventitious root formation (may block protein production) but depends on the stage of rooting Ethylene and Abscisic Acid produce variable responses.Ethylene and Abscisic Acid produce variable responses.

29 Biology of Propagation by Cuttings Other compounds: –Salicylate = phytohormone (contains salicylic acid = active ingredient in aspirin) from Salix –Growth retardants/inhibitors Ancymidal = Arrest Paclobutrazol = Bonzi Uniconazole Enhance rooting by acting against GA Reduce shoot growth, therefore less competition against root production None used commercial to improve rooting

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36 Biology of Propagation by Cuttings Classification of plant rooting responses 1.) Plant has all the essential endogenous substances including auxin. When given proper environmental conditions, roots will form 2.) Plant has all the essential endogenous substances EXCEPT auxin is limiting. Exogenous auxin application will cause rooting, given proper environmental conditions 3.) Some endogenous substances are limiting other than auxin, therefore external application of auxin has little response

37 Biology of Propagation by Cuttings Factors affecting regeneration of plants from cuttingsFactors affecting regeneration of plants from cuttings –Selection and maintenance of stock plants (for cuttings) Select material that is easy to root (physiologically juvenile)Select material that is easy to root (physiologically juvenile) Rejuvenate stock material by serial grafting, hedging or micropropagation (serial culturing)Rejuvenate stock material by serial grafting, hedging or micropropagation (serial culturing) Cone of juvenility (oak and beech leaf retention is an indicator of more juvenile areas)Cone of juvenility (oak and beech leaf retention is an indicator of more juvenile areas)

38 Fagus sylvatica (beech)

39 Biology of Propagation by Cuttings Manipulate the environmental conditions and physiological status of the stock plantManipulate the environmental conditions and physiological status of the stock plant –Water status: take cuttings in the morning when plant material is turgid –Temperature: Higher temperatures (54- 80°F) better for rooting (however, only a minor role)

40 Primrose

41 Biology of Propagation by Cuttings –Light: photoperiod/irradiance/quality specifically as they influence CHO’s accumulation. If photoperiod stimulates floral development, this will reduce rooting (photomorphogenic response) Etiolation of stock plants = exclusion of light Banding on stock plants = localized light exclusion (Velcro™) Shading = growing stock plants under reduced light conditions. Reduces the production of lignins and phenolic metabolites normally used to make lignins instead are used to make roots

42 Biology of Propagation by Cuttings Girdling - constricting the stem, blocking downward translocation of CHO’s, hormones, etc. Good on sweetgum, sycamore, pineGirdling - constricting the stem, blocking downward translocation of CHO’s, hormones, etc. Good on sweetgum, sycamore, pine Girdling and etiolation best for rooting applesGirdling and etiolation best for rooting apples

43 Biology of Propagation by Cuttings CO 2 enrichment = mixed responses but if photosynthesis increases, then increase in CHO’s which helps supply developing roots with energy.CO 2 enrichment = mixed responses but if photosynthesis increases, then increase in CHO’s which helps supply developing roots with energy. CHO’s do NOT regulate rooting but provide developing roots with energy. A high C/low N ratio favors root production over shoot productionCHO’s do NOT regulate rooting but provide developing roots with energy. A high C/low N ratio favors root production over shoot production

44 Biology of Propagation by Cuttings Note: for hardwood cuttings, it is best to select slow-growing lateral shoots over fast-growing terminal shootsNote: for hardwood cuttings, it is best to select slow-growing lateral shoots over fast-growing terminal shoots

45 Biology of Propagation by Cuttings Selection of shootsSelection of shoots Lateral vs. Terminal shoots:Lateral vs. Terminal shoots: –For softwood cuttings, chose terminal shoots –For semi-hardwood cuttings, chose lateral shoots Basal portion of a shoot bestBasal portion of a shoot best –More physiologically juvenile –More preformed root initials

46 Biology of Propagation by Cuttings Flowering vs. Vegetative shootsFlowering vs. Vegetative shoots –If easily rooted, it does not matter –If difficult to root, select vegetative shoots

47 Biology of Propagation by Cuttings Seasonal timing:Seasonal timing: –If deciduous: Hardwood = when dormantHardwood = when dormant Softwood = after Spring flushSoftwood = after Spring flush Semi-hardwood = early summerSemi-hardwood = early summer –If evergreen: Broad-leaf = cutting after a flush completed (semi- hardwood) -Spring to fallBroad-leaf = cutting after a flush completed (semi- hardwood) -Spring to fall Narrow-leaf = hardwood best (late fall through winter)Narrow-leaf = hardwood best (late fall through winter)

48 Biology of Propagation by Cuttings If you do research in this area (even as a nurseryperson), you should reports finding based on PHYSIOLOGICAL characteristics and NOT calendar dates!If you do research in this area (even as a nurseryperson), you should reports finding based on PHYSIOLOGICAL characteristics and NOT calendar dates! Days from budbreakDays from budbreak Hours of sunlightHours of sunlight Degree-day chilling or heating unitsDegree-day chilling or heating units Can also use “phenology”- the art of observing life cycle phases or activities of plants (and animals)Can also use “phenology”- the art of observing life cycle phases or activities of plants (and animals)

49 Biology of Propagation by Cuttings For efficient use of personnel:For efficient use of personnel: –Difficult-to-root plants are taken in winter –Easy-to-root plants are taken in spring and summer

50 Biology of Propagation by Cuttings Treatment of Cuttings:Treatment of Cuttings: –Storage of cuttings Stick immediately orStick immediately or mist and hold overnight in a refrigerator (40- 48°F)mist and hold overnight in a refrigerator (40- 48°F) Long-term storage in a refrigerator with high humidity (+ ethylene inhibitors)Long-term storage in a refrigerator with high humidity (+ ethylene inhibitors) Long-term duration depends on CHO reservesLong-term duration depends on CHO reserves

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52 Biology of Propagation by Cuttings –Auxins Middle eastern/European practice - put a grain seed in the split end of a cutting.Middle eastern/European practice - put a grain seed in the split end of a cutting. Seed releases auxin as it germinates and stimulates rootingSeed releases auxin as it germinates and stimulates rooting An IBA +NAA auxin combination is better than either aloneAn IBA +NAA auxin combination is better than either alone 2 forms of auxin2 forms of auxin –Acid = water-insoluble, dissolve in alcohol or base (KOH) –Salt = water soluble form (typically a potassium salt) Bacteria and light destroy natural IAA but not IBA or NAABacteria and light destroy natural IAA but not IBA or NAA

53 Biology of Propagation by Cuttings Note: early bud-break and shoot growth of rooted cuttings is important to overwinter survival of:Note: early bud-break and shoot growth of rooted cuttings is important to overwinter survival of: –Acer (“maple”) –Cornus (“dogwood”) –Hamamelis (“witchazel”) –Magnolia (“magnolia”) –Prunus (“cherry”) –Rhododendron (“rhododendron”) –Stewartia (“stewartia”)

54 Biology of Propagation by Cuttings Mineral nutrition of cuttings during rootingMineral nutrition of cuttings during rooting –N required for nucleic acids –Zn is a precursor to auxin Leaching of nutrients:Leaching of nutrients: –Mist can severely leach nutrients from leafy cuttings Easily leached: N & MnEasily leached: N & Mn Moderately leached: Ca, Mg, S, KModerately leached: Ca, Mg, S, K Slowly leached: Fe, Zn, P, ClSlowly leached: Fe, Zn, P, Cl

55 Biology of Propagation by Cuttings Should you add fertilizer to the mist?Should you add fertilizer to the mist? –No! –It will inhibit rooting –Causes salt build-up or cuttings and equipment –Increase algae (which reduces aeration and causes problems with sanitation)

56 Biology of Propagation by Cuttings WoundingWounding –Increases callus (which can yield roots) –Increases ethylene which promotes adventitious root production –Increases the penetration of exogenous auxins into the cutting

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59 Biology of Propagation by Cuttings Manipulation of the environment around cuttings:Manipulation of the environment around cuttings: –Water/humidity Minimize transpirational lossesMinimize transpirational losses Water uptake is proportional to the water content in the mediumWater uptake is proportional to the water content in the medium Xylem/tracheids typically blocked after cut so wounding increases diffusion of water into the cuttingXylem/tracheids typically blocked after cut so wounding increases diffusion of water into the cutting

60 Biology of Propagation by Cuttings Methods to maintain atmospheric waterMethods to maintain atmospheric water –Enclosures (tunnels or coldframes) Simple and low-costSimple and low-cost Problem: heat is trapped. Shade the plastic or use white poly.Problem: heat is trapped. Shade the plastic or use white poly. Best for difficult-to-root species requiring extended time for rooting (avoid nutrient leaching)Best for difficult-to-root species requiring extended time for rooting (avoid nutrient leaching) –Contact system Lay poly. directly on leafy cuttings after watering inLay poly. directly on leafy cuttings after watering in

61 Biology of Propagation by Cuttings Intermittent mistIntermittent mist –Developed in the 1940’s –Lowers air temperature (OK) –Lowers leaf temperature (OK) –Lowers medium temperature (not good), so should use with bottom heat –Ex: Mist-O-Matic

62 Biology of Propagation by Cuttings Fog systemsFog systems –Maximize humidity –Water particles stay suspended in air –Reduces foliage wetting and nutrient leaching – Reduces disease –Best on difficult-to-root cuttings –Helps to acclimate plantlets from tissue culture

63 Biology of Propagation by Cuttings TemperatureTemperature –Optimum = 66 - 77°F for temperate species –Optimum = 78 - 90°F for tropical species –A 10°F drop between day/night is best –Too high air temps. increase budbreak and elongation of new shoots (not good) –Root initiation is stimulated by inc. temps. –Bottom heat best for root initiation then remove from heat for root development

64 Biology of Propagation by Cuttings Light (irradiance)Light (irradiance) –Low light best for rooting woody plants (20-30 W/m 2 = 80 - 120 umol/m 2 /s) –Moderate light best for rooting herbaceous plants (90-100 W/m 2 = 360 - 400 umol/m 2 /s)

65 Biology of Propagation by Cuttings Light (photoperiod)Light (photoperiod) –Long-days or continuous light is best Light (quality)Light (quality) –More red light than far-red light Photosynthesis is not required for root formation as long as CHO’s are adequatePhotosynthesis is not required for root formation as long as CHO’s are adequate


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