In vitro shoot multiplication and rooting of wild Paeonia officinalis L., subsp. officinalis

Paeonia officinalis L., subsp. officinalis, is a herbaceous peony spontaneously growing on rocky slopes, up to 1,800 m of altitude, from Southern France to Albany, that includes Tuscan and Emilian Apennines. Its propagation occurs by rhizome or seeds under natural growing conditions; however, seeds need a couple of years to germinate. The aim of the present research was to set up a protocol for the in vitro propagation of this species, useful for its reintroduction in the natural environment, and suitable at nursery level. The combined effect of 6-benzyladenine (BA) and polyvinylpyrrolidone (PVP) was investigated on shoot multiplication of single shoots and small shoot clusters, in agarized culture media. A two-step rooting procedure was used, providing one-week culture of shoots in complete darkness on media enriched with indole-3-butyric acid (IBA) and their transfer to auxin-free media. Agarized media or perlite soaked in liquid media were used for both root induction and elongation phases.Complete culture survival was obtained with 1.0 g L-1 PVP and the use of small shoot clusters as explants. BA at 2.0 mg L-1 gave the maximum mean shoot multiplication (2.7) from a single shoot at the 3rd subculture; however, very short shoots were produced by shoot clusters after three further subcultures. BA at 1.0 gL(-1) allowed a constant multiplication (about 2:1) of well-elongated shoots regardless of the explant type. The multiplication rates reported here are quite low, but comparable to data available in the literature for in vitro grown shoots of wild herbaceous P lactiflora. The maximum rooting percentage (50%) was obtained in liquid media, for shoots from 1.0 mg BA treated with 2.5 mg L-1 IBA, although not different from other IBA treatments (1 and 5 mg L-1 ). The present results are promising with regard to the in vitro phases. However, they also suggest further research in improving rooting and achieving successful acclimatization of healthy plants. If this goal is reached, micropropagation might represent an alternative vegetative propagation method for the reintroduction in the natural environment of this species, and its release at nursery level as plant for gardens.