Enhancement of growth and regeneration efficiency from embryogenic callus cultures of Oncidium ‘Gower Ramsey’ by adjusting carbohydrate sources

The embryogenic callus was induced from shoot apex tissues of Oncidium ‘Gower Ramsey’, and the derived callus cultures maintained more than 5 years were viable in growth and exhibited high regeneration capability. Combination levels of exogenous 2,4-dichlorophenoxyacetic acid (2,4-D) and thidiazuron (TDZ) could stepwise change granular and yellow callus into more friable or compact morphotypes. In the 16-h photoperiod culture, the influences of various carbohydrate sources including sucrose, maltose and trehalose were assessed on formation and development of protocorm-like body (PLB) from the embryogenic callus. Histological observations showed a unicellular origin for these PLBs. The growth of plantlets regenerated on half-strength Murashige and Skoog (MS) medium supplemented with maltose or trehalose was significantly better than those regenerated on sucrose. Approximately, 6000 PLBs could be generated in 2 months from an initial culture of 1 g callus fresh weight, and then more than half of the PLBs developed into plants in 4 months after two subcultures on the medium supplemented with 20 g/l trehalose.