Efficient protocols for the micropropagation of tree peony (Paeonia suffruticosa 'Jin Pao Hong', P. suffruticosa 'Wu Long Peng Sheng', and P. × lemoinei 'High Noon') and application of arbuscular mycorrhizal fungi to improve plantlet establishment

Tree peony (Paeonia sect. Moutan) is a famous ornamental crop worldwide that is difficult to propagate. The present study provides efficient protocols for the micropropagation of three economically important tree peony cultivars (Paeonia suffruticosa 'Jin Pao Hong', P. suffruticosa 'Wu Long Peng Sheng', and P. × lemoinei 'High Noon'). For optimal shoot multiplication, different concentrations of GA3 were added into woody plant medium (WPM) (double strength Ca2+) containing 1.0 mg l−1 BAP; 0.5 mg l−1 GA3 yielded the highest multiplication rate with more than 4 shoots per explant for the three cultivars. For better rooting, different polyamines (putrescine, spermine, or spermidine) were added individually to half-strength MS medium containing 1.0 mg l−1 IBA. 5.0, 1.0, and 1.0 mg l−1 putrescine produced the optimal rooting for 'Jin Pao Hong' (100%), 'Wu Long Peng Sheng' (100%), and 'High Noon' (80%), respectively; each rooted shoot had 4-6 roots measuring 4-6 cm in length. Poor survival rates during acclimatization were obtained for 'Jin Pao Hong' (52.6%), 'Wu Long Peng Sheng' (40.1%), and 'High Noon' (64.0%) when the plantlets were grown in uninoculated vermiculite/peat/perlite sterilized substrate; in contrast, 'High Noon' plantlets inoculated with Glomus mosseae showed a high survival rate (83.4%) and vigorous growth. The protocols reported in this study can be used for rapid and large-scale propagation of the three tree peony cultivars. Furthermore, this study raises interesting possibilities for stimulating the in vitro rooting of tree peony cultivars through polyamine application and for improving the ex vitro establishment of tree peony plantlets through arbuscular mycorrhizal fungi inoculation.