Influence of thidiazuron (TDZ) pretreatment of shoot tips on shoot multiplication and ex vitro acclimatization of Harpagophytum procumbens

The effects of thidiazuron (TDZ) pretreatment of shoot tips on Harpagophytum procumbens shoot proliferation and successive stages of micropropagation, i.e. rooting of regenerated shoots and acclimatization of plantlets to ex vitro conditions, were described in the present study. The best response in terms of shoot proliferation (about seven shoots/explant) and shoot length (3.2 +/- A 0.4 cm) was obtained when explants pretreated with 25 A mu mol L-1 TDZ for 6 h were cultured on Schenk and Hildebrandt medium containing indole-3-acetic acid (IAA) (0.57 A mu mol L-1) and 6-benzylaminopurine (BAP) (8 A mu mol L-1). Under these conditions, a 330 % increase in shoot multiplication over TDZ non-pretreatment culture was achieved and TDZ pretreatment shoots were longer compared to those in control culture (2.6 +/- A 0.3 cm). The TDZ pretreatment did not affect the percentage of rooted shoots, length of roots and number of roots formed per shoot. The rooted plantlets were transplanted from in vitro to pots with soil and grown during 1 year in the greenhouse. The hardening process was difficult and time-consuming. We found that the plants developed from the TDZ pretreated culture were superior to plants from non-pretreated culture in terms of survival rate and morphological features, such as shoot length, leaf size, flowering and earlier root tuberisation. Random amplified polymorphic DNA and inter-simple sequence repeat analyses of pretreatment with TDZ plants showed genetic similarity to non-pretreatment plants. We conclude that applying the strategy of initial explant pretreatment with TDZ may be valuable for the improvement in H. procumbens in vitro propagation.