Optimized in vitro rooting procedure for Eulophia streptopetala Lindl: an indigenous southern African plant

Orchids (Orchidaceae) exhibit an incredible range of diversity in shape, size and colour of their flowers thus providing exotic beauty as ornamental plants. In addition, some are utilized as herbal medicine, food or spice. Although they are found in almost all habitats: grassland, marshes, savannas, scrub and occasionally also in fynbos, some of the species are threatened with extinction due to the destructive and indiscriminate harvesting in their natural habitat for use as herbal medicine as well as for ornamental plant trade. Due to the outbreeding nature of orchids, micropropagation techniques have been used for over 40 years for production of clonal plants as well as for conservation purposes. Eulophia streptopetala Lindl. an epiphytic orchid which grows in eastern and southern Africa is in danger of extinction in the wild. Tissue culture protocols for E. streptopetala have previously been developed but with low in vitro rooting success. The current study aimed at optimizing in vitro rooting and ex vitro survival of in vitro generated shoots. In this study, shoots multiplied from in vitro germinated seedling-derived explants were used. All shoots were elongated on Murashige and Skoog (MS) media with vitamins for this investigation. MS medium (with vitamins) containing indole butaric acid (IBA) and indole acetic acid (IAA) at 0.5, 1, 2 and 3 mg L^-1 alone or in the presence of 2 g L^-1 activated charcoal (AC) were considered for in vitro rooting of E. streptopetala shoots. The shoots were assessed after 4 weeks of in vitro rooting and survival after acclimatization. However, acclimatization of in vitro rooted plantlets MS with 3 mg L^-1 IAA showed the highest rate of survival (80%). Root lengths of in vitro rooted plantlets were also influenced by the type of growth regulator considered. This optimized protocol should enhance in vitro propagation and conservation of Eulophia streptopetala Lindl.