Aloes grow in a wide range of habitats and are an important group of medicinal plants in Africa. Traditionally, the harvesting of plant parts was sustainable and limited to household use. Currently, many Aloe species are threatened in Africa as a result of commercial use (Maundu et al., 2004). Pfab and Scholes (2004) reported that harvesting only one adult plant annually from a population of 100 Aloe peglerae produces an extinction probability of 100%. This means harvesting of only 0.12% or less of the mature plants of A. peglerae per year can be considered as sustainable. Aloe ferox is another widely harvested South African species (Sachedina and Bodeker, 1999). The bitter yellow juice and gel obtained from the leaves of this species are used as a laxative and for healthcare products, respectively (Van Wyk et al., 1997). Newton and Vaughan (1996) estimated that in 1990, A. ferox leaves were officially harvested from ≈10 million plants for 400 t of bitters. They also reported that there was an unofficial trade of another 300 t of bitters, suggesting a need for the safeguarding of this species. The export details of A. ferox extract from South Africa between 1994 and 2003 is documented by Knapp (2006). Overall, the value of the A. ferox industry in South Africa is estimated to be R150 million (U.S. $15 million) per year. Government and private sectors are expanding this industry for the benefits of rural communities as a result of the increasing demand for A. ferox bitters and gel (Shackleton and Gambiza, 2007).
At present, A. ferox is not vulnerable in the wild. However, there is concern that overharvesting of leaves, although this does not harm the plant, may affect growth, flowering, and make the plant less resistant to drought (Donaldson, 1989; Newton and Vaughan, 1996), which can lead to local extinction (Van Wyk and Smith, 1996). Pfab and Scholes (2004) emphasized that sustainability can never be achieved without ex situ cultivation.
Tree and shrub species of Aloes are propagated through stem cuttings, which are dried and planted. A more or less similar method is adopted for suckering species in which small plantlets are detached from the mother plant that are dried and planted. However, seed propagation is more feasible and recommended for survival of rare species (Van Wyk and Smith, 1996). If this species has to be propagated on a large scale by means of seed or tissue culture methods, then currently there is no basic information available on these aspects. Aloes are succulent and warm-climate plants, where both temperature and water play an important role in establishing them. This study was therefore conducted to examine 1) the effects of different temperatures, growth-promoting substances, and watering frequencies on seed germination and seedling growth of A. ferox; and 2) to assess the applicability of an in vitro propagation protocol developed for other Aloe spp.
Bairu, M.W., Stirk, W.A., Doležal, K. & Van Staden, J. 2007 Optimizing the micropropagation protocol for the endangered Aloe polyphylla: Can meta-topolin and its derivatives serve as replacement for benzyladenine and zeatin? Plant Cell Tissue Organ Cult. 90 15 23
Bairu, M.W., Stirk, W.A., Doležal, K. & Van Staden, J. 2008 The role of topolins in micropropagation and somaclonal variation of banana cultivars ‘Williams’ and ‘Grand Naine’ (Musa spp. AAA) Plant Cell Tissue Organ Cult. 95 373 379
Baxter, B.J.M., Van Staden, J., Granger, J.E. & Brown, N.A.C. 1994 Plant-derived smoke and smoke extracts stimulate seed germination of the fire-climax grass Themeda triandra Environ. Exp. Bot. 34 217 223
Chukwujekwu, J.C., Fennell, C.W. & Van Staden, J. 2002 Optimisation of the tissue culture protocol for the endangered Aloe polyphylla S. Afr. J. Bot. 68 424 429
Donaldson, J. 1989 Criteria for listing on Appendix I and Appendix II. Test of the applicability of the criteria 88 89 Munoz M.C. (comp.). Aloe ferox—Proposed revision of Resolution Conf. 9.24 (CoP12 Com.1.3)
Hardegree, S.P. & Emmerich, W.E. 1990 Partitioning water potential and specific salt effects on seed germination of four grasses Ann. Bot. (Lond.) 66 587 595
Knapp, A. 2006 A review of the trade in Aloe ferox with a focus on the role of the European Union A TRAFFIC Europe report for the European Commission Brussels, Belgium
Kulkarni, M.G., Sparg, S.G., Light, M.E. & Van Staden, J. 2006 Stimulation of rice (Oryza sativa L.) seedling vigour by smoke–water and butenolide J. Agron. Crop Sci. 192 395 398
Maundu, P., Kariuki, P. & Eyog-Matig, O. 2004 Threats to medicinal plant species—An African perspective Proc. of a global synthesis workshop on Biodiversity and Species Extinctions: Managing Risk in A Changing World. IUCN, World Conservation Congress Bangkok 17–25 Nov
Murashige, T. & Skoog, F. 1962 A revised medium for a rapid growth and bioassays with tobacco tissue cultures Physiol. Plant. 15 473 497
Pfab, M.F. & Scholes, M.A. 2004 Is the collection of Aloe peglerae from the wild sustainable? An evaluation using stochastic population modelling Biol. Conserv. 118 695 701
Rodríguez-García, R., Jasso de Rodríguez, D., Gil-Marín, J.A., Angulo-Sánchez, J.L. & Lira-Saldivar, R.H. 2007 Growth, stomatal resistance transpiration of Aloe vera under different soil water potentials Ind. Crops Prod. 25 123 128
Saks, Y. & Ish-shalom-Gordon, N. 1995 Aloe vera L., a potential crop for cultivation under conditions of low-temperature winter and basalt soils Ind. Crops Prod. 4 85 90
Shackleton, C.M. & Gambiza, J. 2007 Growth of Aloe ferox Mill. at selected sites in the Makana region of the Eastern Cape S. Afr. J. Bot. 73 266 269
Sheng-zuo, F., Li-yi, S. & Xiang-xiang, F. 2006 Effects of NaCl stress on seed germination, leaf gas exchange and seedling growth of Pteroceltis tatarinowii J. For. Res. 17 185 188
Sławomir, B. & Wiktoria, R. 2002 Sugars as a metabolic regulator of storage protein mobilization in germinating seeds of yellow lupine (Lupinus luteus L.) Acta Physiol. Plant. 24 425 434
Van der Bank, H., Van Wyk, B-E. & Van der Bank, M. 1995 Genetic variation in two economically important Aloe species (Aloaceae) Biochem. Syst. Ecol. 23 251 256
Van Staden, J., Jäger, A.K., Light, M.E. & Burger, B.V. 2004 Isolation of the major germination cue from plant-derived smoke S. Afr. J. Bot. 70 654 659