Callus Cultures of Spilanthes acmella L.: Initiation, Selection of Suitable Explants and Growth Optimisation

Callus could be induced from the leaf, stem, petiole and root explants of Spilanthes acmella using MS medium supplemented with 2,4-D, picloram and NAA. Callus induced on MS with the addition of NAA usually accompanied with the formation of hairy roots. MS + 0.5 mg/L 2,4-D and MS + 0.5 mg/L picloram were the two most suitable media for induction of fine, soft and friable callus from the leaf explants. The optimum conditions for production of callus were to maintain the cultures at 25°C and continuous lighting with an intensity of 25 µE m^-2s^-1. The callus biomass increased at every subculture cycle on either MS + 0.5 mg/L 2,4-D or MS + 0.5 mg/L picloram and became constant or reduced after the 7th or 8th subculture cycles. The petiole-derived callus cultured on MS + 0.5 mg/L picloram changed from compact texture to friable type and the colour became yellowish brown after several subcultures.