Calcium alginate encapsulated synthetic seed production in Plumbago rosea L. for germplasm exchange and distribution

Abstract

Plumbago rosea L. (Plumbaginaceae), is a medicinal shrub commercially exploited for its naphthoquinone principle, plumbagin, extracted from the roots especially for treating skin disorders. As the plant is exploited from the wild without being replenished, conservation of the species becomes inevitable. Synthetic seeds would provide for effective conservation, germplasm exchange and distribution of this species. A reliable protocol for synthetic seed production in Plumbago rosea has been developed encapsulating the axillary buds. The axillary buds from P. rosea cultures established and multiplied using the nodal explants in Murashige and Skoog (MS) medium supplemented with Benzyl Adenine (BA) 1.5 mg/L and Indole 3-Acetic acid 1.0 mg/L, were used for synseed production. The plantlet conversion efficiency was the highest in synthetic seeds developed with sodium alginate 2.5% in modified MS with 0.4 M sucrose and CaCl₂ 100 mM. This combination gave the earliest bud initiation (9.19 ± 0.39 days) and maximum number of shoots per explant (2.31 ± 0.16 shoots). Microshoots from the culture, when inoculated on to MS medium supplemented with Naphthalene Acetic Acid 1.0 mg/L gave the best rooting response with 10.67 ± 0.94 roots per plant and 5.42 ± 0.29 cm root length. This is the first report of synthetic seed production in P. rosea using axillary buds as explant.

Keywords: Conservation; Germplasm exchange; Plumbago rosea; Synthetic seed.

Fig. 1

Culture establishment in MS medium a after 2 weeks in culture, b after 4 weeks in culture; Axillary shoot proliferation in MS + BA 1.5 mg/L + IAA 1.0 mg/L, c after 3 weeks in culture, d after 6 weeks in culture; e and f basal callusing in MS + BA 1.5 mg/L + NAA 1.0 mg/L

Fig. 2

a Synthetic seeds made from nodal axillary buds formed by complexing with SA 2.5% + CaCl₂ 100 mM; b–d regeneration from synthetic seeds after 2, 4 and 6 weeks of culture

Fig. 3

In vitro rooting in MS + NAA 1.0 mg/L, a after 2 weeks in culture, b and c after 6 weeks in culture, d and e ex vitro establishment in red soil and coir pith (2:1) supplemented with AMF 1 g per plant