Influences of Pre-chilling on the Growth and Development of Flower Buds and Cut-flower Quality of Forced Tree Peony.

Abstract

This study was undertaken to clarify the influences of pre-chilling on the growth and development of flower buds and the cut-flower quality of tree peony forced for December shipping. 1. The growth and development of flower buds were accelerated and the number of petals was increased by the pre-chilling treatment. At the end of the pre-chilling period, stamen primordia were forming in some plants of 'Hanakisoi' and 'Shimadaijin' and pistil primordium was appearing in 'Suminagashi'. Concurrently, a mass of undifferentiated tissue appeared between the developing petals and stamens. This indicates that there is a period when the differentiation of both petals and stamens proceeds simultaneously. 2. The sprouting or flowering of plants in pre-chilled plots was earlier than that in non-pre-chilled ones. Flowering percentages were 100% in control plots of 'Jitsugetsunishiki', 'Yaezakura' and 'Yachiyotsubaki', and 83% in control plots of 'Shimadaijin' and 'Suminagashi', and also 83% in pre-chilled plot of 'Jitsugetsunishiki'. In 'Hohki' and 'Kamatanishiki', flowering percentages were low or 0%, regardless of the pre-chilling treatment. In 'Kaoh', flowering percentage was 0% in control plot, whereas it was 50% in pre-chilled plot. 3. Cultivars in which the flowering percentage exceeded 80% by December usually had satisfactory leaf expansion and stalk elongation and adequate flower quality even though the plants were not pre-chilled. Hence, they were marketable. The number of petals on flowers from pre-chilled plants tended to decreased by anthesis, especially in 'Suminagashi'. These results indicate that 'Jitsugetsunishiki', 'Yaezakura', 'Shimadaijin', and 'Suminagashi' rarely need a pre-chilling treatment for their flowers to be marketable by December. Based on the effect of pre-chilling on flowering percentage, it is presumed that tree peony cultivars used for December market were classified into 3 flowering percentage groups: 1) improved, 2) lowered, and 3) no or small change. It is proposed that the pre-chilling treatment reduced the number of petals per flower because pre-chilling favored the differentiation of stamens at the expense of petals.