Introduction
Over the past hundred years, vegetative plant propagation has undergone remarkable changes. From simple methods used in the early 1900s to advanced micropropagation techniques, each innovation has shaped modern horticulture. John E. Preece’s 2003 review traces these developments and their impact on the industry.
Early Techniques in 1903
At the formation of the American Society for Horticultural Science (ASHS) in 1903, propagators already used hardwood, softwood, semihardwood, leaf, and root cuttings. Grafting, layering, bulb division, and rhizome separation were also practiced. However, humidity control relied on glass cases and sand beds, and sanitation was minimal. Diseases such as damping-off were common and difficult to manage.
Sanitation and Disease Control
One of the first major advances was the introduction of steam disinfestation for soils and propagation media in the early 1900s. By the 1920s, steaming became a standard method for reducing soilborne pathogens. Later refinements emphasized pasteurization rather than sterilization, preserving beneficial microbes. Sanitation of tools, containers, and work areas became central to successful propagation.
Mist and Fog Systems
Reducing transpirational water loss was long recognized as critical for rooting leafy cuttings. The invention of mist and fog systems in the 1940s and 1950s represented a major breakthrough. Intermittent mist increased survival rates, reduced wilting, and allowed for large-scale propagation. Fog systems later improved efficiency by lowering disease incidence and reducing water use.
Juvenility and Phase Change
By the mid-20th century, researchers established that juvenile plant tissues root more easily than adult tissues. This understanding led to practices such as coppicing, hedge rows, and rejuvenation techniques that provided propagators with material better suited for vegetative cloning.
Auxins and Rooting of Cuttings
The discovery of auxins transformed propagation by cuttings. Indole-3-butyric acid (IBA) and naphthaleneacetic acid (NAA), synthesized in the 1930s, remain the most effective and widely used rooting compounds today. Auxins enabled species previously difficult to propagate to be rooted reliably, revolutionizing commercial production of ornamentals, fruit trees, and forestry species.
Micropropagation
The development of tissue culture techniques marked a turning point in plant propagation. Early experiments with orchid seed germination (Knudson, 1922) evolved into full-scale micropropagation by the mid-20th century. The introduction of Murashige and Skoog (MS) medium, cytokinins such as benzyladenine (BA), and somatic embryogenesis opened new possibilities for mass clonal production. Today, commercial micropropagation provides millions of pathogen-free plants for agriculture, forestry, and floriculture.
Escaping Pathogens
Vegetative propagation techniques also became tools for disease elimination. Meristem culture, combined with thermotherapy, proved effective for producing virus-free stock in crops such as potato and dahlia. These practices significantly improved crop health and yields, setting the stage for large-scale clean planting material programs worldwide.
Conclusion
A century of innovation—from sanitation and mist systems to auxins and micropropagation—has transformed vegetative plant propagation into a sophisticated science. While traditional methods remain important, advances in biotechnology, automation, and environmental control promise to further enhance efficiency and reliability in the future.