A Century of Progress with Vegetative Plant Propagation

Gesneriaceae. Root cuttings were used for various fruit crops, horseradish (Armoracia rusticana P. Gaertn., B Mey. & Scherb.), and others. It was known that when shoots were regenerated adventitiously, as with root cuttings or leaf cuttings, traits (such as variegation), which are associated with chimeras were lost (Bailey, 1896). Humidity control was not nearly as good as today s mist and fog systems, but other methods were used and considered very important for leafy cuttings (Bailey, 1891, 1896; Corbett, 1902). Transpiration was minimized by reducing leaf area of cuttings. Nathaniel Ward invented the glass-covered terrarium, known as the Wardian case in 1829 (Hershey, 1996). Therefore, small, high humidity cases had been in use for over 70 years when ASHS formed. Various types of frames and boxes covered with glass sashes and plates were used to maintain a high relative humidity for rooting leafy cuttings 100 years ago. There were problems with cutting rot in these propagation cases, then called damping-off (Bailey, 1891, 1896; Corbett, 1902). Today, damping-off is considered a seed or seedling disease (Agrios, 1997; Hartmann et al., 2002). Because of the stagnant air environment, Botrytis was likely one of the pathogens involved. Today there is an acute awareness of the importance of strict sanitation to reduce losses associated with diseases in the propagation bed, but sanitation was not a major concern of plant propagators a century ago (Bailey, 1891, 1896; Corbett, 1902). They were aware that damping-off and other important plant propagation diseases were caused by fungi (Bailey, 1891, 1896). Bailey (1896) wrote that “there is no complete remedy” for these propagation diseases. He advocated avoiding both crowding plants and a stagnant, moist environment; as well as reducing watering and using well-drained media. These remain excellent recommendations. The importance of the use of bottom heat for cuttings was well known and widely used a century ago (Bailey, 1891, 1896; Corbett, 1902). For outdoor propagation, these authors advocated burying hardwood cuttings , such as those of grape (Vitis spp.), upside-down to insulate and protect the buds from low winter temperatures. The butts of the cuttings (proximal ends) were covered with 5 to 7.5 cm (2 to 3 inches) of sand and the Spring sun would warm them, stimulating rooting. Bottom heat also was provided in greenhouses by flues or heating pipes, by burning a lamp that heated a tray of water under the propagation medium or where the lamp s heat was distributed to the medium by means of a heat funnel, by heating and recirculating hot water, or by fermenting manure (Bailey, 1891, 1896). None of these methods had thermostatic control and the need for a higher temperature for root initiation than for root elongation had not yet been discovered (Preece, 1993) . Layering techniques were well-established (Bailey, 1891, 1896; Corbett, 1902). Layering methods in use when ASHS formed were tip layering, trench layering, mound (stool) layering, serpentine layering, and air layering. This area of propagation has changed little in the past century, except for modern use of polyethylene to wrap air layers. Because there have been so few changes in layering methods, the history of layering in the last hundred years is not described in this paper. Grafting is another vegetative propagation technique that has changed little over the last century. The importance of vascular cambium alignment and callus growth between the scion and understock was well understood a century ago (Bailey, 1891, 1896; Corbett, 1902). One hundred years ago, propagators were t-budding, plate budding (including H-budding), flute budding, and chip budding. Grafting techniques included whip and tongue grafting, root grafting done as a form of whip grafting, saddle grafting, side grafting, splice grafting, veneer grafting, cleft grafting for topworking trees, wedge grafting, bark grafting, inlaying, seed grafting, and approach grafting (inarching). Plants were double-worked, suggesting an awareness of the importance of interstocks to overcome any localized graft incompatibility or to overcome weak and poor growth (Bailey, 1896). At that time, interstocks were called first scions; the second scion was grafted to the first scion. Propagators I thank librarian Kathy Fahey, Morris Library, Southern Illinois University Carbondale for her help finding some of the more obscure references, as well as those that were cited incompletely in referenced works. She added greatly to the thoroughness of this manuscript. I thank Linda Preece for listening to me think out loud as I developed and improved this manuscript. Some of the most important advances in the history of cloning plants were made during the last 100 years. These have made commercial plant propagation more efficient. This paper is focused on when and how these discoveries were made and when they were adopted by the plant propagation industry. For example, within five years of the discovery of auxin there were three commercial products being manufactured for rooting of cuttings, including Hormodin and Rootone. I took two primary approaches in researching this paper. Original research articles were searched and plant propagation books and United States Department of Agriculture (USDA) and agricultural experiment station bulletins throughout the past century were perused. The articles provide information about when discoveries were made and the books and bulletins are used as benchmarks to determine when new practices were adopted by the horticultural industry. It is difficult to determine specifically when some of the new methods, such as the use of steam to disinfest propagation media, had become widely adopted by the propagation industry. Some papers, bulletins and books specifically discuss commercial adoption of these new techniques. In other cases, the time when these practices initially appeared in reference/text books and bulletins can be interpreted as an indication of when they were adopted by commercial propagators. There have been two recent papers on the history of plant propagation (Geneve, 2001; Mendel, 1992). Much of the paper by Geneve (2001) focuses on the ancient history of plant propagation rather than advances during the last century. There is some overlap between this present paper and the manuscript by Mendel (1992). This present paper covers a longer history than the seventy years (about 1920–1990) discussed by Mendel.