1. Vegetative (Asexual) Propagation Used extensively (in hort) to propagate plants that aren’t easily propagated by seed Kinds of vegetative propagation –Cuttings –Layering –Tissue culture –Specialized structures (bulbs, etc.) –Grafting and budding

2. All vegetative propagation methods use a piece of one plant (propagule) to reproduce another (identical) plant All plants that are propagated from one original plant are part of a clone (clonal propagation)

3. Cuttings are (in general) the easiest, the cheapest, and the most widely used forms of vegetative propagation Stem cuttings are the most common type of cutting used

4. The goal in propagating by stem cuttings is to replace the missing part (root system) Two processes are required: Dedifferentiation - the ability of a differentiated cell to initiate cell division Redifferentiation - formation of a growing root

5. Redifferentiation requires: Cells competent to form a root meristem (root initial) Development of a root initial into a functioning root (determinism)

6. Plants from which stem cuttings can be taken Annuals, biennials, herbaceous perennials (most are easy-to-root) Woodies (range from easy-to-root to hard-to-root)

7. Types of rooting on stem cuttings (based on the type of roots that develop) Preformed roots and latent root initials - present when the cutting is taken from the stem Wound-induced roots - not present when the cutting is made (cutting the stem into pieces causes a wound reaction that stimulates rooting)

8. Preformed roots or latent root initials Develop while still attached to the parent plant Usually lie dormant till stems are made into cuttings Are often associated with nodes Are common in certain genera (e.g., Salix, Hydrangea, Ribes, Populus)

9. Wound-induced roots (anatomical events) Dedifferentiation - differentiated cells prepare to divide Formation of root initials from dividing cells Root primordia formation - the apex becomes organized Root emergence through the stem

10. Both wound-induced and preformed roots are adventitious: New (de novo) growing points (root meristem) form on established structures (e.g., a stem) Roots arise other than by normal development of the seedling Or, simply - a root developing where one isn’t expected

11. Origin of adventitious roots in a stem Herbaceous: near a vascular bundle Woodies: –Easy-to-root species (spp.): near the vascular cambium “directly” –Hard-to-root spp.: often requires an intervening callus phase (“indirectly”)

12. Time of adventitious root formation in juvenile and mature leaf-bud cuttings of Ficus pumila treated with IBA * *Davies FT et al. (1982) Amer J Bot 69:804-811.

13. Callus and rooting Callus is an irregular mass of dividing parenchyma cells Relationship to rooting: –Formation of callus and roots are independent events in easy- to-root spp. –Callus formation is often a precursor to root formation in hard-to-root spp

14. Direct root formationIndirect root formation dedifferentiation root initials callus formation cell differentiation vascular strand formation competent root-forming cells From Fig. 9-10, Hartmann 2002

15. Root Initials Root Primordium Root Emergence apex organization differentiation, vascular connections From Fig. 9-10, Hartmann 2002