In vitro propagation and ex vitro rooting of Caralluma edulis (Edgew.) Benth. & Hook. f.: An endemic and endangered edible plant species of the Thar Desert

Abstract

Caralluma edulis (Edgew.) Benth. & Hook. f., (family Asclepiadaceae), rich source of antioxidants, is an edible and nutraceutically important plant of the extreme arid regions of the Thar Desert. Anthropogenic activities on established sand dunes, habitat destruction and harvesting/grazing of complete plant prior to its reproductive maturity restrict the propagation by sexual means. Poor reproduction and seed set have put adverse pressure on native populations of this endemic and slow multiplying plant of Indian Thar Desert. Though it is categorized as endangered plant species, there is need for revision of its status as this species can be spotted rarely in its habitat. There is also need for development of non-conventional methods for propagation and conservation of C. edulis. Therefore, in vitro methods are good alternative for multiplication, propagation and germplasm conservation of this nutraceutically important plant. We used nodal segments obtained from field grown plants as explant for culture initiation. Murashige and Skoog (1962) medium containing 6-benzyladenine (BA) (2.0mgl−1)+additives proved optimum for axillary shoot bud induction and produced 3–4 shoots. Shoots were amplified by repetitive transfer of original explant and by subculturing of in vitro raised shoots on various concentrations of cytokinins (BA and Kinetin [Kn]) alone and in combination with auxin (α-naphthaleneacetic acid [NAA]). A high rate (35.30±1.55 per culture vessel) of shoot multiplication was achieved on MS medium fortified with 0.5mgl−1 BA+0.5mgl−1 Kn+0.1mgl−1 NAA and additives. In vitro produced shoots were rooted under in vitro as well as ex vitro conditions. Half strength MS medium containing 1.5mgl−1 indole-3-butyric acid (IBA) was optimal for root induction under in vitro conditions. More than 95% shoots were rooted ex vitro, when in vitro raised shoots were treated with IBA (300mgl−1) for 4min. Rooted plantlets by both methods were hardened under different conditions of humidity and temperature in the greenhouse. The percentage survival rate of ex vitro rooted plants was higher (97.1±2.02%) in comparison to in vitro rooted plants (87.6±2.45%). The described protocol can be efficiently used for the large scale propagation and conservation of germplasm of this edible, endemic and endangered plant.