Male adventitious roots of Rumex thyrsiflorus Fingerh. as a source of genetically stable micropropagated plantlets

Rumex thyrsiflorus Fingerh. is one of the few dioecious plant species that have sex chromosomes. The chromosome constitution of females is 2n = 12A + XX and 2n = 12A + XY1Y2 of males. It is a medicinally important plant species and has also been the object of studies on the structure and function of sex chromosomes and sex ratio. An efficient plant regeneration protocol was developed from karyologically stable male roots that had been derived from a long-term liquid culture. The root segments were grown on MS medium supplemented with the following plant growth regulators: 2.4-D, NAA, kinetin, BAP and TDZ. The highest frequency (81.73 %) of adventitious shoot formation (16.27 shoots/explant) was obtained on MS + 0.5 mg/l TDZ. Regenerated shoots were successfully rooted on ½ MS + 2 % sucrose + 0.5 mg/l IBA and acclimated to in vivo conditions. Histological analysis revealed indirect (via callus) adventitious shoot formation. The cells of the morphogenetic callus were surrounded by a fibrillar structure that was similar to the extracellular matrix. Molecular analysis based on genetic sex markers confirmed that all of the root explants were male. The genetic stability of the regenerated plantlets was confirmed using random amplified polymorphic DNA analysis. This is the first report concerning the micropropagation protocol for R. thyrsiflorus Fingerh. from male roots derived from a long-term liquid culture, which offers a unique opportunity to obtain true-to-type plants of the same sex.