The genus Dracaena includes 113 species (The Plant List, 2018) of woody stemmed foliage plants in the tropics (Bailey, 1949). Dracaenas are evergreen shrubs or trees most frequently characterized by long linear leaves of significant decorative and horticultural values. Most species are grown as potted indoor plants and propagated for commercial purposes (Jones and Luchsinger, 1986; Vinterhalter and Vinterhalter, 1997). Besides their ornamental value, some species including Dracaena arborea and D. mannini (Okunji et al., 1996), D. cochinensis (Nong, 1997), D. draco (Mimaki et al., 1999), and D. loureiri (Ichikawa et al., 1997) also possess several medicinal properties and are used as an herbal remedy in traditional medicine.
The Gabal Elba dragon tree, also known as the Nubian dragon tree (Dracaena ombet Heuglin ex Kotschy & Peyr.; Asparagaceae) is an evergreen tree capable of reaching heights of 2 to 4 m. The branches are dichotomous, short, and spreading, with thick, rigid, and sword-shaped leaves. The leaves are clustered as rosettes at the ends of the dichotomous branches (Bari, 1968). The mature fruits are edible and eaten by local people as a supplement to their meagre diet, and the resin obtained from the trunk is used in traditional medicine [International Union for Conservation of Nature (IUCN), 1998]. Steroidal saponins from D. ombet (El-amin et al., 2002; Moharram and El-Shenawy, 2007) possess analgesic and anti-inflammatory properties (Moharram and El-Shenawy, 2007). Dracaena ombet is distributed in the coastal mountainous regions of the Red Sea, mainly in Gabal Elba, Egypt (Ghazali et al., 2008), with scattered populations in Saudi Arabia, Sudan, Ethiopia, Somalia, and Djibouti (IUCN, 1998). It has experienced population declines throughout its range and scattered individuals remain in inaccessible areas (Bos, 1997; El-Azzouni, 2003; Friis and Lawesson, 1993; Kamel et al., 2015). The subpopulations on the Red Sea Hills and Gabal Elba in Egypt and Sudan are particularly threatened (El-Azzouni, 2003). On the basis of the assessment of the World Conservation Monitoring Center (1998) using a now-outdated set of criteria (Version 2.3), D. ombet has been categorized as endangered in the IUCN Red List of Threatened Species (IUCN, 1998). In northern Sudan, D. ombet populations have completely vanished from Erowit, the only area where they are known to have existed in that country (El Azzouni, 2003). Overgrazing, overcutting, droughts, and attack by parasitic pests or diseases have contributed to the decline. Scanning and transmission electron microscopy revealed the association of pathogenic fungal species in leaf spots of D. ombet (Baka and Krzywinski, 1996). Field-based observations suggest that 80% of the D. ombet population in Gabal Elba may soon be extinct, making it critically endangered (Kamel et al., 2015).
Conventional propagation of the genus Dracaena is achieved through cuttings (Vinterhalter and Vinterhalter, 1997), but some species such as D. draco and D. ombet are mainly propagated by seeds. Although the seed production in D. ombet may be high, many seeds do not germinate. Moreover, vegetative propagation of D. ombet is difficult. Ghazali et al. (2008) attempted to propagate D. ombet using the newly vegetative axillary buds, but no rooting occurred, and the propagation failed. In vitro propagation methods have been developed for a few ornamental Dracaena sp., including D. surculosa (Miller and Murashige, 1976; Liu et al., 2010), D. deremensis (Badawy et al., 2005; Blanco et al., 2004; Debergh, 1976), D. fragrans (Debergh, 1975, 1976; Debergh and Maene, 1981; Lu, 2003; Vinterhalter, 1989; Vinterhalter and Vinterhalter, 1997), D. sanderiana (Aslam et al., 2013; Beura et al., 2007), and D. marginata (Chua et al., 1981; El-Sawy et al., 2000). However, propagation of ornamental Dracaena sp., still relies on imported cuttings as a commercial practice.
An alternative approach is to propagate and conserve D. ombet through tissue culture techniques. Tissue culture facilitates the rapid production of propagules from several species that are difficult to propagate using conventional techniques as well as the conservation of endangered and threatened plant species (Fay, 1992; Sarasan et al., 2006). Although D. ombet is an endangered species of economical and medicinal importance, to our knowledge, tissue culture techniques have not been used to propagate and conserve this species. The aim of this study was to develop in vitro propagation methods for D. ombet to conserve this critically endangered species.
AgrawalV.SardarP.R.2007In vitro regeneration through somatic embryogenesis and organogenesis using cotyledons of Cassia angustifolia VahlIn Vitro Cell. Dev. Biol. Plant43585592
AslamJ.MujibA.SharmaM.P.2013In vitro micropropagation of Dracaena sanderiana Sander ex Mast: An important indoor ornamental plantSaudi J. Biol. Sci.206368
AzizM.A.OoiH.L.RashidA.A.1996In vitro responses of Dracaena fragrans cv. Massangeana to growth regulatorsPertanika J. Trop. Agr. Sci.19123127
BadawyE.M.HabibA.M.A.El-BanaA.YosryG.M.2005Propagation of Dracaena fragrans plants by tissue culture techniqueArab J. Biotechnol.8329342
BaileyL.H.1949Manual of cultivated plants. MacMillan New York NY
BariE.A.1968Sudan p. 59–63. In: I. Hedberg and O. Hedberg (eds.). Conservation of vegetation in Africa south of the Sahara. Acta Phytogeogr. Suec
BosJ.1997Dracaena p. 76–79. In: S. Edwards S. Demissew and I. Hedberg (eds.). flora of Ethiopia and Eritrea the National Herbarium Addis Ababa University Ethiopia and Department of Systematic Botany Uppsala Sweden
DewirY.H.AldubaiA.A.El-HendawyS.AlsadonA.A.SeliemM.K.NaidooY.2018Micropropagation of buttonwood tree (Conocarpus erectus) through axillary shoot proliferationHortScience53687691
DewirY.H.MurthyH.N.AmmarM.H.AlghamdiS.S.Al-SuhaibaniN.A.AlsadonA.A.PaekK.Y.2016In vitro rooting of leguminous plants: Difficulties, alternatives, and strategies for improvementHort. Environ. Biotechnol.57311322
DewirY.H.SinghN.MngomezuluS.OmarA.M.K.2011Micropropagation and detection of important triterpenes in in vitro and field grown plants of Syzygium cordatumJ. Med. Plants Res.530783083
El-MahroukM.E.DewirY.H.OmarA.M.K.2010In vitro propagation of adult strawberry tree (Arbutus unedo L.) through adventitious shoots and somatic embryogenesisPropag. Ornam. Plants109398
GhazaliU.El BailyH.DoraA.ArkeebH.H.AoudM.OssmanG.MansourM.El-NemeryH.2008The globally endangered Dracaena ombet monitoring and assessment project in Gabel Elba protected area Egypt. Final report. Conservation Leadership Programme Egypt. 18 Sept. 2018. <http://www.conservationleadershipprogramme.org/media/2014/11/2007_Egypt_DMAP-Project_Final-report.pdf>
Gonzalez-ArnaoM.T.Lazaro-VallejoC.E.EngelmannF.Gamez-PastranaR.Martinez-OcampoY.M.Pastelin-SolanoM.C.Diaz-RamosC.2009Multiplication and cryopreservation of vanilla (Vanilla planifolia ‘Andrews’)In Vitro Cell. Dev. Biol. Plant45574582
HyndmanS.E.HasegawaP.M.BressanD.A.1982The role of sucrose and nitrogen in adventitious root formation on cultured rose shootsPlant Cell Tissue Organ Cult.1229238
IchikawaK.KitaokaM.TakiM.TakaishI.S.IijimaY.BoriboonM.AkiyamaT.1997Retrodihydrochalcones and homoisoflanes isolated from Thai medicinal plant Dracaena loureiri and their estrogen against activityPlanta Med.63648656
International Union for Conservation of Nature1998Dracacena ombet. The IUCN red list of threatened species. 21 Apr. 2018. <https://www.iucnredlist.org/species/30395/9535978#bibliography>
JonesS.B.LuchsingerA.E.1986Plant systematic. 2nd ed. McGraw-Hill New York
KamelM.GhazalyU.M.CallmanderM.W.2015Conservation status of the endangered Nubian dragon tree Dracaena ombet in Gebel Elba national park, EgyptOryx49704709
LiuJ.-X.DengM.HennyR.J.ChenJ.-J.XieJ.-H.2010Regeneration of Dracaena surculosa through indirect shoot organogenesisHortScience4512501254
LuW.2003Control of in vitro regeneration of individual reproductive and vegetative organs in Dracaena fragrans cv. Massangeana Hort. - Regularities of the direct regeneration of individual organs in vitroActa Bot. Sin.4514531464
MimakiY.KurodaM.IdoA.KameyamaA.YokusukaA.SashidaY.1999Steroidal saponin from the aerial parts of Dracaena draco and their cytostatic activity on HL 60 cellsPhytochemistry50805813
NemethG.1986Induction of rooting p. 49–64. In: Y.P.S. Bajaj (ed.). Biotechnology in agriculture and forestry Vol. 1. Trees I. Springer-Verlag New York NY
SarasanV.CrippsR.RamsayM.M.AthertonC.McMichenM.PrendergastG.RowntreeJ.K.2006Conservation in vitro of threatened plants—progress in the past decadeIn Vitro Cell. Dev. Biol. Plant42206214
ShaikS.DewirY.H.SinghN.NicholasA.2010Micropropagation and bioreactor studies of the medicinally important plant Lessertia (Sutherlandia) frutescensS. Afr. J. Bot.76180186
The Plant List2018Dracaena. 30 Aug. 2018. <http://www.theplantlist.org/1.1/browse/A/Asparagaceae/Dracaena/>
VinterhalterD.VinterhalterB.1997Micropropagation of Dracaena species p. 131–146. In: Y.P.S. Bajaj (ed.). Biotechnology in agriculture and forestry 40: High-tech and micropropagation VI. Springer-Verlag Berlin Germany
World Conservation Monitoring Centre1998Dracaena ombet. The IUCN Red List of Threatened Species 1998: E.T30395A9535978. 21 Apr. 2018. <http://dx.doi.org/10.2305/IUCN.UK.1998.RLTS.T30395A9535978.en>