Floral Development And Chilling Requirements Of Paeonia Lactiflora Cultivars

As an indigenously famous flower in China, peonies (Paeonia lactiflora Pall.) for cut flowers and potted plants have a huge market with big potential. However, peonies typically bloom in April to June, and usually last for1-2weeks. In order to prolong the marketing period and to improve profitability, a forcing culture has become a feasible way. In this experiment, we study early-flowering cultivar ’Da Fu Gui’,’Dong Fang Hong’, mid-season flowering cultivar ’Zi Feng Yu’and late-flowering cultivar’Qing Wen’,’Tao Hua Fei Xue’, and research their flower bud differentiations and chilling requirements for growth and flowering. Based on these researches we further systematically investigate’Da Fu Gui’, and figure out relationships between its growth and chilling requirements or heating requirements, between bud maturity degree and flowering, between plant ages and flowering. We also discuss the problem about a high proportion of flower bud abortion in forcing culture from the perspective of floral development. The results are as follows:(1) All peony cultivars in field in Beijing began with the formation of leaf primordia in early June. In late August, bract primordia began to form in all cultivars’renewal buds which reveal the beginning of the generative stage. In late September, sepal primordia formed in all cultivars’renewal buds. The apical meristems began to produce petals in early October and form stamen primordia in late October. In the middle of November, pistil primordia formed in all cultivars except’Tao Hua Fei Xue’. As the temperature decreased and soil became frozen, differentiation ceased in the late November. The pace of differentiation has no direct relationship with flowering date, the cultivars’differentiation are dependent on their speed of reproductive differentiation (early September-late November). Cultivars (terminal floral bud) entered dormancy with different proportion of petal primordia, stamen primordia, pistil primordia and a few leaf primordia, and the bud maturity degrees of cultivars were’Da Fu Gui’=’Qing Wen’>’Zi Feng Yu’>’Tao Hua Fei Xue’. Axillary meristem (form axillary floral buds) grew later than apical meristem (form terminal floral buds), their bract primordia typically differentiated after the apical meristem entered petal primordia, and most of axillary floral bud entered dormancy with petal primordia.(2) Chilling requirements vary among Paeonia cultivars. Under condition with low temperature2±1℃,’Qing Wen’,’Da Fu Gui’and’Dong Fang Hong’ needed chilling treatment for7-10weeks,’Zi Feng Yu’and’Tao Hua Fei Xue’needed chilling treatment for10weeks which is enough for breaking dormancy and getting more flowers. Cultivars’chilling requirements have no relation with flowering date, bud emergence speed could be used as a standard to estimate the dormancy breaking. The main reason of decrement of the number of flowers per plant is the planting environment instead of excessive chill (chilling duration was extended from13weeks to22weeks).(3) The duration of the chilling treatment had significant effect on the time taken for sprouting to occur, Increasing chilling (4-13weeks) or over chilling (16-22weeks) would lead to the reduction of heat requirements for flowering from23751(chilling treatment for4weeks) down to13084growing degree hours (GDH)(chilling treatment for22weeks).(4) Although mix-bud of ’Da Fu Gui’could emergence in leaf, bract or sepal primordia stage after chilling treatment, it has no relation to flowering responses, since bud emergence was not affected by bud maturity and maturity or immaturity in Paeonia’Da Fu Gui’can be evaluated by flowering responses. When bud differentiation enters early petal primordia stage (petal has1-2layers), they could flower after chilling treatment. It would be better if the peonies were moved into cold room in from the late October to middle November in Beijing. In Beijing, peonies could be available for market as early as late January.(5) Flower quality and numbers of’Da Fu Gui ’per plant is affected by its ages. Flower quality and numbers reached the maximum in the second year and began to decrease in the third year. Different potted-age plants had no significant difference in chilling response.(6) Flower bud abortion of Paeonia lactiflora can occur at any development stage in the shoot growth cycle and the proportion of bud abortion is closely related to cultivars. Using Paeonia’Qiao Ling’as an example, the aborted flower buds were divided into4stages. In forcing culture, the aborted buds in stage1from shoot elongation to flower bud appearance are developed from buds whose differentiation retarded than normal ones. Aborted flower buds in late stages are mostly caused by culture environment.