Plant Growth Regulation 33: 19–23, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 19 Micropropagation of the endangered Aloe polyphylla A.L. Abrie & J. van Staden ∗ Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal Pietermaritzburg, Private Bag X01, Scottsville, 3209 South Africa ( ∗ author for correspondence) Received 10 January 2000; accepted in revised form 21 March 2000 Key words: aloe polyphylla, benzyladenine, conservation, micropropagation Abstract A rapid propagation protocol was establish for the highly endangered Aloe polyphylla (Schönland ex Pillans). Seed was germinated in vitro on Murashige & Skoog 1962 medium [6] with or without sucrose. Plantlets were cultured on medium containing benzyladenine only, or a combination of BA and NAA. After initial problems with browning, the explants rapidly formed axillary and adventitious buds. Maximal shoot formation was obtained on MS medium containing 1.0 mg l −1 BA. Some shoots rooted spontaneously on MS medium, but the rooting percentage was improved with a 0.5 mg l −1 IBA supplement. Rooted plantlets were acclimatized to greenhouse conditions. The success of this project indicates that micropropagation can be a useful tool in the conservation of this endangered species of the genus Aloe. Abbreviations: BA – benzyladenine; 2,4-D – 2,4-dichlorophenoxy acetic acid; IAA – indole-3-acetic acid; IBA – indole-3-butyric acid; Kin – kinetin; MS – Murashige & Skoog (1962) medium; NAA – ∝-naphthyl acetic acid; TDZ – thidiazuron 1. Introduction Little work has been published on the micropropaga- tion of Aloe species, largely because of the diffi- culties in establishing primary explants in culture. Aloe explants secrete phenolic substances that lead to browning and often death of the explant [7, 10]. Most previous work has focussed on species with medicinal or cosmetic properties [3, 5, 7, 10]. A large number of aloes have ornamental value and several of these are threatened in the wild. In southern Africa 46 Aloe species are listed as endangered, vulnerable or rare in the Red Data list [4]. Aloe polyphylla is one of the rarest and most unique of all the Aloe species. The arrangement of the grey-green leaves is the plant’s most striking feature, consisting of five spirals with 15 to 30 leaves in each spiral. These can be twisted in a clockwise or anti- clockwise way [8]. The species has a very restricted distribution and only occurs on the steep basaltic mountain slopes of Lesotho, at high altitudes of above 2000 m. This area receives over 1000 mm of rain and the plants are often under snow in winter [11]. Despite the prohibition on the removal of plants and seed from Lesotho, collection continues and numbers are declining rapidly. The cultivation of Aloe polyphylla is hampered by the special soil and moisture require- ments of the plant and transplanted specimens usually die [8]. A successful micropropagation method can provide a reliable source of plants to small scale farmers in the Lesotho region and for conservation purposes. 2. Materials and methods Seeds were obtained from Ecoscape Nursery, Santa Cruz, USA, decontaminated and used to establish in vitro plantlets. The seeds were scarified using sand- paper or a scalpel blade prior to treatment. Seeds were decontaminated in 70% ethanol, for 2 min, followed by a 10 min rinse in 1% NaOCl solution. The seeds were then rinsed thoroughly in sterile distilled water. Decontaminated seeds were aseptically transferred to