Effect of constant and alternating temperature regimes on post-dormancy development of herbaceous peony

Understanding the mechanisms of chilling accumulation in dormant herbaceous peony is essential for the development of successful techniques for flower production. In this research, dormant containerized plants of 'Sarah Bernhardt' (SB) were placed in dark cooling chambers with constant temperatures of 2, 6, 10 and 20°C in October 2012. After 2-17 weeks of storage, six plants from each treatment were transferred weekly to a greenhouse. In 2013-2014, dormant plants of SB and 'Katherine Fonteyn' (KF) were exposed to diurnal alternating temperature regimes in the dark: (1) 16 h at 2°C and 8 h at 10°C; (2) 8 h at 2°C and 16 h at 10°C; (3) 16 h at 2°C and 8 h at 15°C; (4) constant 2°C. After 2-18 weeks of storage, the plants were transferred to a greenhouse. Records of storage conditions (soil and air temperature) and parameters of plant development were organized in a large database. Temperature regime during the storage period greatly affected dormancy release and stem elongation. We estimated a quadratic regression of maximal stem length on storage conditions. Efficiency of low chilling temperatures was enhanced by the effect of higher temperatures, applied during the diurnal cycle. We argue that (1) in peony, internal mechanisms interconnect with chilling requirements for dormancy release, and (2) chilling accumulation under diurnal fluctuations of natural soil temperatures might consist of two stages: the major one occurs under low soil temperatures at night, while the second stage responds positively to moderate higher day temperatures. New data on peony dormancy and growth processes will help to optimize cut-flower production of ornamental geophytes in warm regions and under forcing conditions.