The effects of plant growth regulators on shoot formation, regeneration and coloured callus production in Echinocereus cinerascens in vitro

Protocols were established for micropropagation and coloured callus production of Echinocereus cinerascens, a cactus that is highly in demand for the horticultural industry. An efficient micropropagation system facilitates rapid shoot production of this threatened species. The present study investigates the effects of the plant growth regulators NAA and BAP on shoot and coloured callus induction. Shoots were produced from axillary buds and coloured callus from stem explants cultured on Murashige and Skoog (MS) medium supplemented with different concentrations of NAA and BAP (0.5, 1.0, 1.5, 2.0 mg l(-1)) applied singly and in combinations. The medium that resulted in the highest mean number of shoots produced was MS supplemented with 2.0 mg l(-1) NAA and 1.5 mg l(-1) BAP. In general, media with combinations of BAP and NAA were more effective than NAA or BAP alone in inducing shoots. NAA alone resulted in significantly fewer shoots than BAP alone. Most stem explants produced coloured callus in all treatments. Green callus was induced in over 80 % of explants in all treatments in which the hormones were applied singly, while yellow callus was induced in 80-100 % of explants in half of the treatments with hormone combinations. In contrast, the occurrence of pink callus was less prevalent than green and yellow callus. Pink callus was induced in 3-40 % of explants when treatments were added with single BAP or NAA and in 7-63 % of explants treated with combinations of BAP and NAA.