THIDIAZURON - A POTENT CYTOKININ FOR WOODY PLANT-TISSUE CULTURE

Thidiazuron (TDZ) is among the most active cytokinin-like substances for woody plant tissue culture. It facilitates efficient micropropagation of many recalcitrant woody species. Low concentrations (<1 muM) can induce greater axillary proliferation than many other cytokinins; however, TDZ may inhibit shoot elongation. In some cases it is necessary to transfer shoots to an elongation medium containing a lower level of TDZ and/or a less active cytokinin. At concentrations higher than 1 muM, TDZ can stimulate the formation of callus, adventitious shoots or somatic embryos. Subsequent rooting of microshoots may be unaffected or slightly inhibited by prior exposure to TDZ. The main undesirable side effect of TDZ is that cultures of some species occasionally form fasciated shoots. The high cytokinin activity and positive response of woody species to TDZ have established it as among the most active cytokinins for in vitro manipulation of many woody species.