The inflorescence stalk: A source of highly regenerative explants for micropropagation of geophytes

The commercialization of new breeding lines, disease-free plants and potentially useful selections of geophytes, is often hampered by their low natural propagation rate. This can be solved by micropropagation. The source for explants commonly used for the establishment of in vitro cultures is the bulb, corm or other perennating organ. Inflorescence stalks have been found to be a useful alternative source for overcoming the problem of contamination found in explants from underground organs. In addition, by using the inflorescence, the selected stock plant is not destroyed. Gladiolus, Nerine, Narcissus, Ornithogalum, Allium and Brodiaea cultures have been established in vitro from inflorescence explants. Gladiolus (Iridaceae) explants isolated from the floral stem just below expanding florets still enclosed by the bracts, were highly regenerative in the presence of NAA and kinetin. In Nerine (Amaryllidaceae), the tissue which was found to regenerate buds in the presence of 2,4-D and BA was taken from the junction between peduncle and pedicels of an emerged inflorescence which was still enclosed in its spathe. In Narcissus (Amaryllidaceae) the floral stalk of young non-emerged inflorescences in non-dormant bulbs, regenerated buds in the presence of NAA, BA, elevated phosphate and adenine sulphate. The number of buds regenerated, depended on the position in the young floral stem from which the explant was taken and on the duration of bulb storage at low temperature. In Allium, however, only the tissue between the pedicels was regenerative. In Brodiaea and Ornithogalum the stalk as well as the pedicel-peduncle junction were highly regenerative. The potential of expediently isolated explants from inflorescence stems for an efficient micropropagation system will be discussed.