LONG-TERM EFFECTS OF THIDIAZURON ARE INTERMEDIATE BETWEEN BENZYLADENINE, KINETIN OR ISOPENTENYLADENINE IN MISCANTHUS-SINENSIS

The thidiazolylurea derivative thidiazuron has been reported to be con siderably more effective than benzyladenine in promotion of in vitro s hoot formation in a number of dicotyledonous species. In the present s tudy, axillary shoots of Miscanthus sinensis (Thunb.) Anderss.'Gigante us' that had been subcultured four times on modified Murashige and Sko og medium with 20 mu M benzyladenine were transferred to media with be nzyladenine, kinetin, isopentenyladenine or thidiazuron at concentrati ons of 0.01, 0.1, 1, 10, 30 or 100 mu M and grown over four subculture s. Shoot and root formation stabilized after the first subculture and results from the three subsequent subcultures are presented. The commo n effects of cytokinins, i.e., promotion of axillary bud growth, inhib ition of root formation, reduced stem growth and delay of senescence, were observed for all four cytokinins. In a descending order regarding shoot formation, the four cytokinins at the optimum concentration cou ld be ranked as follows: benzyladenine, thidiazuron, kinetin and isope ntenyladenine. Benzyladenine and thidiazuron had optimum effects at th e same concentration with regard to axillary shoot formation but thidi azuron induced a significantly lower number of shoots than benzyladeni ne. The number of roots, shoot size and percentage of chlorotic shoots were also the same for benzyladenine and thidiazuron. When transferri ng shoots from benzyladenine or thidiazuron medium to rooting medium, shoots previously grown on thidiazuron became taller and formed fewer roots than shoots previously grown on benzyladenine.