IN VITRO REGENERATION OF RHODODENDRONS VIA AXILLARY SHOOT AND SOMATIC EMBRYO INDUCTION

Efficient in vitro regeneration via axillary shoot induction from shoot-tip meristems and somatic embryo formation from leaf explants were studied with six cultivars of Rhododendron L. The cultivars tested significantly showed the highest shoot regeneration on MS medium containing 6 mg/L 2iP. For most of the cultivars a significantly enhanced shoot multiplication in higher isopentenyladenine (2iP) concentrations (8-10 mg/L) combined with 1 mg/L indole-3-acetic acid (IAA) was found. Chromosome diploid number (2n=2x=26) in actively growing shoot apices and a high degree of genetic stability were determined. At concentration 2.5 mg/L thidiazuron (TDZ), the percentage of explants forming embryogenic structures was 70-73%; whereas at concentration of 5 mg/L TDZ, the percentage significantly decreased to 58%. In rhododendrons, somatic embryo induction was observed in the presence of leaf bud formation. Histological analysis demonstrated embryogenic capacity of callus exclusively in the presence of TDZ.