In vitro callus induction and indirect organogenesis of Brucea mollis Wall. ex Kurz - A potential medicinal plant of Northeast India

The present investigation was carried out to develop an efficient protocol for in vitro propagation of Brucea mollis Wall. ex Kurz, an important medicinal plant, confined to only Karbi Anglong district of Assam. The plant is extensively used to cure malaria. Due to several natural factors like inefficient pollination, seed dispersal mechanisms and anthropogenic activities, the plant is facing extinction. Through indirect organogenesis from leaf and internode explants on MS (Murashige and Skoog) media, callus induction was achieved at a maximum (100%). However, the minimum time (7-15 days) was observed for induction of callus on B5 as compared to MS media. The color and texture of the callus varied depending on the type of explants as well as the concentrations of growth regulators used in both the media. Best response for percentage of callus induction (100%) was obtained from the leaf explants on MS media, when the media was supplemented with the four combinations of growth regulators, i.e., (i) BAP (8.88 μM) + NAA (1.61 μM), (ii)BAP (8.88 μM) + NAA (2.68 μM), (iii) BAP (8.88 μM) + 2,4-D (2.27 μM) and (iv) BAP (8.88 μM) + 2,4-D (4.54 μM). While in the case of internode explants, maximum (100%) percentage for callus induction was obtained with BAP (8.88 μM) + NAA (1.61 μM) and BAP (8.88 μM) + NAA (2.68 μM). Multiple shoot regeneration was achieved from the callus of all the three types of explants when transferred to shoot regeneration media (both MS and B5 media) supplemented with BAP, NAA, Kinetin and IBA at different concentrations and combinations. The maximum percentage of shoot regeneration (100%) from the calli of all explant types were obtained with the combination of BAP, NAA and IBA. However, the best response in terms of minimum number of days taken to regenerate shoots and maximum shoot length was obtained using the leaf explants at BAP (8.88 μM) + NAA (2.68 μM) + Kinetin (13.95 μM) on MS media. The regenerated shoots were cultured for rooting on half strength media supplemented with IBA and NAA singly, and the highest rooting percentage was achieved when MS media was supplemented with 14.76 μM IBA. About 60% of the plantlets survived during acclimatization and were successfully transferred to the field. The regeneration protocols standardized for B. mollis could be found most effective for mass propagation of the medicinally important plant as well as its conservation.