Pre-chilling promotes flowering in Paeonia lactiflora ‘Taebaek’ without flower bud abortion

Abstract

This study was conducted to prevent flower bud abortion in forcing culture of herbaceous peony. When dormant rootstocks of Paeonia lactiflora ‘Taebaek’ were subjected to dormancy-breaking treatment (0°C for 6 weeks) in November, this could hasten flowering in early spring. However plants chilled in August, September, or October produced abnormal flowers or resulted in flower bud abortion. To prevent flower bud abortion, we placed the dormant rootstocks at five pre-chilling treatments for 2 weeks in mid-September and October. The treatment conditions were 0°C for 2 weeks (C0, control), natural chilling in an open field for 2 weeks (NT), pre-chilling at 15°C for 2 weeks (P15), 15°C for 1 week → 10°C for 1 week (P15 → 10), and pre-chilling at 10°C for 2 weeks (P10). After these pre-chilling treatments, all of the plants were placed under a cold regime of 0°C for 6 weeks in order to break dormancy. In the C0 and NT treatments, a great numbers of flower buds were aborted from their stems. On the other hand, the P15 → 10 and P10 treatments increased to 74.7 and 81.0% for flowering, respectively. Pre-cooling treatment accelerated the growth of flower buds compared to the C0 or NT treatments. To promote blooming in the autumn season, rootstocks were also placed into three treatments (C0, NT, and P10) in early July. While the C0 and NT treatment were unable to produce flowering at all, the treatment P10 induced more than 80% flowering of plants. From these results, pre-chilling at treatment 10°C for 2 weeks was recommended as the optimum treatment to promote flowering without flower bud abortion in forcing culture for winter or autumn flowering.