Differential responses to in vitro bud culture in mature Robinia pseudoacacia L. (black locust).

Buds excised from the stems of five dormant, mature (20- to 30-year old) black locust (Robinia pseudoacacia L.) trees were placed on MS basal medium with various levels of 6-benzylaminopurine. In all treatments, bud explants from two of the trees produced shoots which could be subcultured. Whole plants were obtained from cultures of these two trees. Explants from two other trees became vitrified or produced callus, respectively, when cultured on medium containing between 0.032 and 1.0 μM 6-benzylaminopurine; subculturable shoots were only obtained when the buds from these trees were cultured on medium containing 3.2 μM 6-benzylaminopurine. No shoot cultures which could be subcultured were obtained from the fifth tree used in these experiments. The whole plants produced in these experiments were transferred to a greenhouse, and were phenotypically normal five months after culture initiation (three months after transfer to the greenhouse).