Abstract:

With cotyledonary petiole and hypocotyl explants, the shoot regeneration frequencies of three turnip (Brassica rapa L. ssp. rapifera) cultivars were examined. To achieve a high-frequency regeneration system, the hormone combination of thidiazuron (TDZ) and naphthaleneacetic acid (NAA) was compared with combination of benzyladenine (BA) and NAA on shoot regeneration. The results show that cotyledonary petioles were the best explant and that Murashige and Skoog (MS) medium containing 7.0 mg·L^-1TDZ and 1.0 mg·L^-1 NAA was suitable recipe for getting high-frequency shoot regeneration. Based the recipe, the effects of AgNO3 concentration, seedling age, pre-culture time of 2,4-dichlorophenoxyacetic acid (2,4-D) were investigated to optimize the shoot regeneration system. The results suggseted that petiolate cotyledon with seedling age of 5 d cultured in MS medium containing TDZ 7.0 mg·L^-1 + NAA 1.0 mg·L^-1 + AgNO3 5.0 mg·L^-1 followed by pre-culture with 2,4-D 1.0 mg·L-1 for 2d can be induced with highest-frequency regeneration. The highest shoot formation rate was about 90%. The rooting percentage of shoots was 100% on MS supplemented with 0.1 mg·L^-1 indole-3-butyric acid (IBA). The 95% rooted shoots survived in a greenhouse.

Key words: turnip, Brassica rapa, TDZ, AgNO3, regeneration