Establishment of a practical tissue culture for producing hairy roots of Valeriana officinalis L. via Agrobacterium rhizogenes

Valerian (Valeriana officinalis L.) is used in traditional medicine for its root or rhizome as a mild sedative and tranquilizer in many countries. In order to evaluate the potential production of hairy root of V. officinalis under in vitro conditions the regeneration of V. officinalis via indirect organogenesis and also Agrobacterium-mediated transformation was conducted. Leaves, stems and roots of in vitro plants were used as the explants for indirect organogenesis. The highest callus formation frequency was achieved on a medium supplemented with (0.1 mg/L Kin + 2 mg/L 2,4-D) for leaf and root explants (100%) and (0.1 mg/L Kin + 10 mg/L 2,4-D) for stem explants (100%). Furthermore, the highest percentage of shoot regeneration was obtained on a medium containing 0.5 mg/L NAA + 2 mg/L BAP (60.00%) in leaf-derived calli. Hairy roots of valerian were obtained following co-cultivation of leaf, stem and root-derived callus with Agrobacterium rhizogenes strains AR15834 and LBA 9402. As a result, the LBA9402 strain appeared to be better than the AR15834 strain in terms of both mean of hairy root formation (68.62%) and production of the respective hairy root (90%). The optimal growth of the hairy roots occurred on selective MS medium containing 20 mg/L rifampicin and 250 mg/L cefotaxime without any plant growth regulators. This study revealed that rapid growth of the hairy roots of V. officinalis may offer an attractive alternative to the exploitation of this valuable medicinal plant species via optimizing tissue culture technique.   Key words: Valeriana officinalis, indirect organogenesis, rolB gene, Agrobacterium rhizogenes, hairy roots.