Chapter 9

1. 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

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

6. Biology of Propagation by Cuttings • 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)

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

25. Biology of Propagation by Cuttings • Auxins • 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: 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.

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

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

44. Biology of Propagation by Cuttings • 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

46. Biology of Propagation by Cuttings • 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)

49. Biology of Propagation by Cuttings • 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: • 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