True aloe (Aloe vera) and krantz aloe (Aloe arborescens) are currently being used for the extraction of cosmetic and nutraceutical active ingredients (Cardarelli et al., 2017; Espinosa-Leal and Garcia-Lara, 2019). Krantz aloe has a wide geographical distribution in the African continent, with populations in South Africa, Botswana, Swaziland, Lesotho, Mozambique, Zimbabwe, Mapaura and Timberlake, and Malawi. Although krantz aloe is common within its range, human activity has caused a negative impact on populations (Smith et al., 2008). Wild populations of aloe species are currently threatened as a result of their continuous collection for transplantation to private gardens or the extraction of active ingredients (Maundu et al., 2006). Conventional propagation using lateral shoots and rhizome cuttings is not able to fulfill the increasing market demand for aloe (Cristiano et al., 2016).
In vitro tissue culture represents a promising alternative to wild collections of krantz aloe plants and conventional propagation by allowing the production of multiple plants for their reintroduction to the wild and fields, and production of active metabolites to be optimized (Espinosa-Leal et al., 2018). Although some reports exist on the in vitro tissue culture of krantz aloe (Bedini et al., 2009; Cardarelli et al., 2017; Kawai et al., 1993), the establishment of cultures from plant explants has proved difficult because of the long response times of the explants and their release of polyphenols, resulting in the need for constant subcultures (Bedini et al., 2009).
Seeds are an alternative explant for in vitro culture establishment. True aloe seeds are not commonly used as a means of propagation (traditional and in vitro) because of their scarcity in nature and low GPs of 0% to 25% (traditional) and 60% to 70% (in vitro) (Cristiano et al., 2016). Studies have investigated the optimization of germination conditions for bitter aloe (Aloe ferox) and krantz aloe in petri dishes without substrate and with filter paper, which have shown that the use of karrikinolide (KAR1)-rich SSW either as a priming treatment or a watering solution promotes seed germination (Bairu et al., 2009; Kulkarni et al., 2013). Studies have demonstrated that SSW can also promote seedling vigor, including leaf and root length and number (Demir et al., 2018). Hydration of seeds before sowing is another method for improving germination (Demir et al., 2018; Khan, 1992). However, the effect of SSW and SI, separately and combined, on the in vitro germination of krantz aloe under aseptic conditions using Murashige and Skoog (MS) culture media (Murashige and Skoog, 1962) as a standard substrate has not been investigated previously. Therefore, the objective of this work was to evaluate the effect of SI with water and the addition of SSW to the culture media on the in vitro germination and initial seedling development of krantz aloe.
Bairu, M.W., Kulkarni, M.G., Street, R.A., Mulaudzi, R.B. & van Staden, J. 2009 Studies on seed germination, seedling growth, and in vitro shoot induction of Aloe ferox Mill., a commercially important species HortScience 44 751 756
Bedini, C., Caccia, R., Triggiani, D., Mazzucato, A., Soressi, G.P. & Tiezzi, A. 2009 Micropropagation of Aloe arborescens Mill: A step towards efficient production of its valuable leaf extracts showing antiproliferative activity on murine myeloma cells Plant Biosyst. 143 233 240
Cardarelli, M., Rouphael, Y., Pellizzoni, M., Colla, G. & Lucini, L. 2017 Profile of bioactive secondary metabolites and antioxidant capacity of leaf exudates from eighteen Aloe species Ind. Crops Prod. 108 44 51
Chumpookam, J., Lin, H.-L. & Shiesh, C.-C. 2012 Effect of smoke-water derived from burnt dry rice straw (Oryza sativa) on seed germination and growth of papaya seedling (Carica papaya cv. Tainung No. 2) HortScience 47 741 744
Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) 2019 Appendices. Apendices I, II and III. 26 May 2020. <https://cites.org/eng/app/appendices.php>
Coons, J., Coutant, N., Lawrence, B., Finn, D. & Finn, S. 2014 An effective system to produce smoke solutions from dried plant tissue for seed germination studies Appl. Plant Sci. 2 1 5
Cristiano, G., Murillo-Amador, B. & De Lucia, B. 2016 Propagation techniques and agronomic requirements for the cultivation of barbados aloe (Aloe vera (L.) Burm. F.): A review Front. Plant Sci. 7 1 14
Demir, I., Ozden, E., Yıldırım, K.C., Sahin, O. & van Staden, J. 2018 Priming with smoke-derived karrikinolide enhances germination and transplant quality of immature and mature pepper seed lots S. Afr. J. Bot. 115 264 268
Demir, I., Ozuaydin, I., Yasar, F. & van Staden, J. 2012 Effect of smoke-derived butenolide priming treatment on pepper and salvia seeds in relation to transplant quality and catalase activity S. Afr. J. Bot. 78 83 87
Espinosa-Leal, C. & Garcia-Lara, S. 2019 Current methods for the discovery of new active ingredients from natural products for cosmeceutical applications Planta Med. 85 535 551
Espinosa-Leal, C.A., Puente-Garza, C.A. & García-Lara, S. 2018 In vitro plant tissue culture: Means for production of biological active compounds Planta 248 1 18
Gupta, S., Hrdlička, J., Ngoroyemoto, N., Nemahunguni, N.K., Gucký, T., Novák, O., Kulkarni, M.G., Doležal, K. & van Staden, J. 2020 Preparation and standardisation of smoke-water for seed germination and plant growth stimulation J. Plant Growth Regulat. 39 338 345
Kawai, K., Beppu, H., Koike, T., Fujita, K. & Marunouchi, T. 1993 Tissue culture of Aloe arborescens Miller var. natalensis Berger Phytother. Res. 7 S5 S10
Kulkarni, M.G., Amoo, S.O., Kandari, L.S. & van Staden, J. 2013 Seed germination and phytochemical evaluation in seedlings of Aloe arborescens Mill Plant Biosyst. 148 460 466
Ma, F., Cholewa, E., Mohamed, T., Peterson, C.A. & Gijzen, M. 2004 Cracks in the palisade cuticle of soybean seed coats correlate with their permeability to water Ann. Bot. 94 213 228
Martínez Richart, A.I. 2019 Aloe arborescens. The IUCN red list of threatened species 2019: E.T110688013A110688030. 27 Apr. 2020. <https://dx.doi.org/10.2305/IUCN.UK.2019-1.RLTS.T110688013A110688030.en>
Maundu, P., Kariuki, P. & Eyog-Matig, O. 2006 Threats to medicinal plant species: An African perspective, p. 47–62. In: S. Miththapala (ed.). Conserving medicinal species: Securing a healthy future. IUCN: Ecosystems and Livelihoods Group, Asia, Colombo, Sri Lanka
Santini, B.A., Rojas-Aréchiga, M. & García Morales, E. 2017 Priming effect on seed germination: Is it always positive for cacti species? J. Arid Environ. 147 155 158
Shao, S., Meyer, C.J., Ma, F., Peterson, C.A. & Bernards, M.A. 2007 The outermost cuticle of soybean seeds: Chemical composition and function during imbibition J. Expt. Bot. 58 1071 1082
van Staden, J., Sparg, S.G., Kulkarni, M.G. & Light, M.E. 2006 Post-germination effects of the smoke-derived compound 3-methyl-2H-furo [2,3-c]pyran-2-one and its potential as a preconditioning agent Field Crops Res. 9 98 105
Varela, R.O. & Albornoz, P.L. 2013 Morpho-anatomy, imbibition, viability and germination of the seed of Anadenanthera colubrina var. cebil (Fabaceae) Rev. Biol. Trop. 61 1109 1118