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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.
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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
All vegetative propagation methods use a piece of one plant (propagule) to reproduce another (identical) plantAll plants that are propagated from one original plant are part of a clone (clonal propagation)
Cuttings are (in general) the easiest, the cheapest, and the most widely used forms of vegetative propagationStem cuttings are the most common type of cutting used
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
Redifferentiation requires: • Cells competent to form a root meristem (root initial) • Development of a root initial into a functioning root (determinism)
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)
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)
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)
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
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
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”)
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.
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
From Fig. 9-10, Hartmann 2002 Direct root formation Indirect root formation dedifferentiation callus formation cell differentiation vascular strand formation competent root-forming cells competent root-forming cells root initials
From Fig. 9-10, Hartmann 2002 Root Initials apex organization Root Primordium differentiation, vascular connections Root Emergence
