Temperature effects on graft healing and survival in flare tree peony (Paeonia rockii)

• Temperature is a key external factor influencing graft healing and survival in FTP. • Elevated temperature accelerates and enhances the quality of healing at the graft junction to improve the survival rate of grafts in FTP. • Appropriate temperatures for effectively grafting FPT are 20.3∼22.8 °C (autumn open field), ≥ 15.7 °C (variable-temperature facility), and 22 °C (temperature-controlled facility), by which a recommended protocol can overcome seasonal limitations on grafting duration, and enhance the propagation efficiency in the industry. Grafting used in the commercial propagation of common tree peony (CTP, Paeonia suffruticosa ) in China and Japan is required urgently to systematically investigate the flare tree peony (FTP, P. rockii ), as FTP exhibits distinct biological characteristics from CTP. In this study, through grafting FTP ‘Jingyun Guan’ as the scion onto the rootstocks of the seedlings from Chinese herbaceous peony ( P. lactiflora ), P. ostii ‘Feng Dan’, and P. rockii , respectively, we investigated the effects of rootstock origins and ambient temperature on graft healing and survival under open field, variable temperature facility, and controlled temperature facility. The results indicated that ambient temperature significantly affected graft healing and survival rate, whereas the rootstock types had a lesser effect on them. Morphological and anatomical observations of ‘Jingyun Guan’/ ‘Feng Dan’ grafts showed that elevated ambient temperature promoted callus growth, new cambium formation, and vascular tissues differentiation at the graft junction, ultimately improving the survival rate. Our results revealed that the appropriate temperature for grafting was between 20.3∼22.8 °C (survival rates 93.3 %∼96.7 %) in open field, ≥ 15.7 °C (survival rates ≥ 90 %) in variable temperature facility and 22 °C (survival rates ≥ 93.3 %) in controlled temperature facility, by which a protocol to propagate FTP was established and will be of significance for improving the production efficiency of emerging FTP cultivars.