Micropropagation of Aroids

This web page is only meant to be an introduction to the tissue culture propagation technique known as micropropagation for some of the plants composing the family Araceae L. It is an update to an article (Hyndman, 1987) originally published in Aroideana , the journal of the International Aroid Society . The present work is not meant to be a review of all the current and past literature on the subject. A planned review of extensive protocol descriptions for the in vitro culture of all reported aroid species is in progress, so do check back periodically for an update. For more detailed perspectives of plant tissue culture on the web, refer to Plant Tissue Culture Information Exchange and Plant Tissue Culture Research at the University of Minnesota.

Introduction

Some years ago, Mr. David Burnett of Sydney, Australia, became the first author to bring a very rare and beautiful aroid, Alocasia guttata var. imperialis N.E. Brown, from the brink of obscurity back into the horticultural limelight by using a plant tissue culture technique known as micropropagation. He then made propagules available to the collectors around the world. In Burnett's landmark work on the Alocasia (Burnett, 1984), he describes the colorful history of this remarkable species and how it had become so rare that it was only known to exist in a single collection. It was very rare in it's native Borneo as well . The micropropagation of Alocasia guttata var. imperialis N.E. Brown using a procedure known as shoot tip culture was successful. Since that time, a once very rare species is now available and enjoyed by many collectors of aroids. From this experience many people learned what a powerful tool tissue culture can be for the conservation and preservation of endangered aroids, and how very advantageous the technique can be to the collector of rare aroids as well. The purpose of this web page is to introduce and explain the basics of aroid micropropagation, the plant tissue culture technique used for propagation, and to provide information for anyone who may be interested in applying this technique to propagate some of their favorite aroids.

Historical Advantages and Disadvantages

An aroid, Amorphophallus konjac K. Koch, was actually the first monocotyledon to be reported in the literature as having been successfully tissue cultured (Morel and Wetmore, 1951). In fact, the authors reported the first successful propagation of an Amorphophallus by tissue culture in that same paper with the production of adventitious shoots from callus derived from tuber tissue grown on a defined salts medium to which B vitamins and a synthetic auxin were added. Comparable results with Sauromatum guttatum Schott were mentioned as well.

Since those early years in plant tissue culture history, numerous reports about the micropropagation of aroids have appeared in the literature. Table 1 lists some of these reports for some of the genera of the Araceae L. Generally, these reported techniques can be applied to related species and genera. The hobby tissue culturist can apply these techniques quite effectively to the propagation of rare aroids. Alternatively, an aroid collector could contract a willing commercial laboratory to propagate a limited number of plants. When participating in a micropropagation program, the aroid collector must observe one important caution: the demand for collectors' aroids is very small, as compared to commercial cultivars, therefore, the propagation of only a very few high quality specimens should be contemplated. When this one caution is observed, the advantages of aroid micropropagation include:

the production of potentially disease free plants,
the conservation of endangered species and rare cultivars,
the potential of creating new cultivars,
and the international shipment of aroids with much reduced quarantine restrictions.

Producing Disease Free Aroids

Hartman (1974) was the first to report the use of micropropagation for the purpose of producing disease free aroids. He carefully dissected out the shoot tips, which consisted of the apical meristem and a leaf primordium, and subsequently cultured them on a chemically defined medium. He was able to produce Caladium bicolor, Xanthosoma sagittifolium, and Colocasia esculenta plants free of dasheen mosaic virus. In 1981, the Agricultural Research Center, Apopka, Florida, released an improved variety of Dieffenbachia maculata cv. Perfection given the cultivar name of 'Perfection-137B' (Chase et al., 1981). Using a micropropagation system as the cornerstone of his disease indexing program, Knaus (1976) selected D. maculata 'Perfection-137B' on the basis of the freedom of systemic pathogens, including dasheen mosaic virus, and on the basis of superior horticultural characteristics. These same micropropagation techniques can be used quite effectively to get disease free plants in other species of aroids as well. Just because an aroid is micropropagated does not mean that it is automatically disease free, or somehow immune to diseases. Micropropagated aroids are no different from any other aroid in their ability to resist diseases. They may only be considered to be disease free if they have been specifically tested for the pathogen in question.

Conservation of Endangered Species and Rare Cultivars

Another very important use of micropropagation is in the conservation of endangered species and rare cultivars. Sara Oldfield indicated in her 1983 Aroideana article that the propagation of rare aroid species can be an important aid to conservation. Micropropagation can serve in this role very well by making it possible to use a single plant as the progenitor of many clones in a relatively short period of time, thereby making the plant more available to collectors. Collecting pressure on wild populations is then reduced as was explained above for Alocasia guttata var. imperialis N.E. Brown

Potential of Creating New Cultivars

In a past issue of Aroideana, Marcel Lecouffe (1981) explained how he had discovered a new cultivar of Caladium humboldtii which he named 'Marcel' from a micropropagated population. When the first author was commercially micropropagating Alocasia 'Black Velvet', a new Alocasia ,probably from Borneo, he discovered an individual plant among the larger population of clones that had larger and thicker leaf laminae, thicker petioles, and more robust growth overall. Additionally, there are a number of new syngonium cultivars in the foliage plant industry that are mutations from tissue cultured Syngonium podophyllum 'White Butterfly'. Several patented and trademarked cultivars having red pigmentation in their leaves are produced by Agri Starts, Inc., a micropropagation company in Apopka, Florida. All of these aroids are examples of micropropagation serving as a source of new cultivars. The mechanism of this phenomenon is not entirely understood. It is generally referred to as somaclonal variation (Larkin et al, 1981).

International Shipment of Aroids

Micropropagation also can be a useful means of shipping aroids internationally. Aroid plantlets growing in sterile containers, free of pests and diseases, have few quarantine restrictions at the port of entry. Once the micropropagated aroids arrive at their destination they can be either propagated further or removed from their sterile conditions to be grown on to full sized plants.

Micropropagation is Not a Panacea

With all of these advantageous uses of micropropagation for the aroid collector, we must keep in mind that this propagation technique is not a cure-all for the problems that might beset our plants. For example, a particular species that is difficult to propagate by more conventional methods such as by cuttings or by seed, may be just as difficult to micropropagate. Micropropagation is more likely to produce less desirable plants due to somaclonal variation than it is to produce uniquely desirable new cultivars. For a more detailed discussion of the disadvantages of micropropagation, refer to Dr. Maciej Hempel's informative web page from Sydney, Australia, "Does micropropagation influence plant quality?"

Aroid Micropropagation for the Hobbyist Tissueculturist

Micropropagation can be done at home with the use of very simple and inexpensive equipment, both home made and purchased, so that anyone interested in trying to micropropagate their favorite aroids can do so. The first step is to gather as much information as you can by going to your local library to find the literature about the techniques used for the specific genus or species you are interested in. Examples are listed in Table 1. Some of the books that reveal greater detail about the applied and basic aspects of plant tissue culture science are listed in Table 2. Then refer to the plant tissue culture web pages, like those mentioned above, to get further insights regarding micropropagation at home. Dr. Acram Taji of the University of New England, Armidale, New South Wales, Australia, has a very informative web page entitled "Plant Tissue Culture for Home Gardeners" that covers the subject very well. Rick Walker has a very informative web page about "Tissue Culture in the Home Kitchen". Although Rick describes how to do carnivorous plant tissue culture, he clearly explains through text and photographs many of the same techniques, media, and equipment necessary for the home micropropagation of aroids as well. Several companies offer plant tissue culture equipment, supplies, and cultures, such as those in Table 3. Most of these companies have representatives specializing in customer service and technical support that can help with basic questions and suggestions about home micropropagation.

Literature Cited

Burnett, D. 1984. The cultivated Alocasia. Aroideana 7(3 and 4).

Chase, A.R. et al. 1981. Perfection-137B, a pathogen-free selection of Dieffenbachia maculata derived through tissue culture. Circular S-280, Florida AES, IFAS, University of Florida, Gainesville.

Hartman, R.D. 1974. Dasheen mosaic virus and other phytopathogens eliminated from caladium, taro, and cocoyam by culture of shoot tips. Phytopath. 64: 237-240.

Hyndman, S.E. 1987. The advantages of tissue culture for the aroid collector. Aroideana 10(3): 7-10.

Knauss, J.F. 1976. A tissue culture method for producing Dieffenbachia maculata cv. Perfection free of fungi and bacteria. Proc. Florida State Hort. Soc. 89: 293-296.

Larkin, P.J. and W.R. Scowcroft. 1981. Somaclonal variation -- a novel source of variability from cell cultures. Theor. Appl. Genet. 60: 197-214.

Lecoufle, M. 1981. Caladium humboldtii and it's cultivar 'Marcel'. Aroideana 4(4): 114-115.

Morel, G. and R.H. Wetmore. 1951. Tissue culture of monocotyledons. Amer. J. Bot . 38:138-140.

Oldfield, S. 1983. Trade in endangered species. Aroideana 6(3): 83-84.