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Principles of Propagation by Cuttings

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1 Principles of Propagation by Cuttings
Chapter 9 Principles of Propagation by Cuttings

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

3 Biology of Propagation by Cuttings
Adventitious 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 buds

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Adventitious root formation (natural) Corn: brace roots

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Adventitious root formation (natural) Dracena or Ficus: aerial roots

7 Biology of Propagation by Cuttings
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, 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 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!) 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 cutting Woody perennials = originate from cambium or young phloem

15 Biology of Propagation by Cuttings
Direct root formation from vascular tissue Indirect root formation from callus 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)

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20 Biology of Propagation by Cuttings
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! 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 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 effect Leaves effect rooting! Presence of leaves increases rooting

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Auxins IAA - naturally occurring (identified in 1935) IBA NAA Exogenous IBA or NAA increases endogenous IAA or increases tissue sensitivity to IAA synthetic

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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
Cytokinins 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
Gibberellins 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.

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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 cuttings Selection and maintenance of stock plants (for cuttings) Select material that is easy to root (physiologically juvenile) 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)

38 Fagus sylvatica (beech)

39 Biology of Propagation by Cuttings
Manipulate 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, pine Girdling and etiolation best for rooting apples

43 Biology of Propagation by Cuttings
CO2 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 production

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Note: 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 shoots Lateral vs. Terminal shoots: For softwood cuttings, chose terminal shoots For semi-hardwood cuttings, chose lateral shoots Basal portion of a shoot best More physiologically juvenile More preformed root initials

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Flowering 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: If deciduous: Hardwood = when dormant Softwood = after Spring flush Semi-hardwood = early summer If evergreen: Broad-leaf = cutting after a flush completed (semi-hardwood) -Spring to fall 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! Days from budbreak Hours of sunlight Degree-day chilling or heating units Can also use “phenology”- the art of observing life cycle phases or activities of plants (and animals)

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For efficient use of personnel: Difficult-to-root plants are taken in winter Easy-to-root plants are taken in spring and summer

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

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Auxins Middle eastern/European practice - put a grain seed in the split end of a cutting. Seed releases auxin as it germinates and stimulates rooting An IBA +NAA auxin combination is better than either alone 2 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 NAA

53 Biology of Propagation by Cuttings
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”)

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

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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)

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Wounding 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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Manipulation of the environment around cuttings: Water/humidity Minimize transpirational losses Water uptake is proportional to the water content in the medium Xylem/tracheids typically blocked after cut so wounding increases diffusion of water into the cutting

60 Biology of Propagation by Cuttings
Methods to maintain atmospheric water Enclosures (tunnels or coldframes) Simple and low-cost 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) Contact system Lay poly. directly on leafy cuttings after watering in

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Intermittent 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

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Fog 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
Temperature Optimum = °F for temperate species Optimum = °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) Low light best for rooting woody plants (20-30 W/m2 = umol/m2/s) Moderate light best for rooting herbaceous plants ( W/m2 = umol/m2/s)

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


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