Preliminary Studies On Flowering Control By Means Of Photoperiod And Induction Of A Novel Varied Flower In Petunia Hybrida 'Fantasy'

Flowering control is an important technology involved in floriculture, in whichmanipulating photopedod is easy and without environmental pollution. With development ofthe protected cropping industry, digitization and standardization in floriculture is inevitable. Aquantitative understanding of photoperiod is necessary to meet this tendency. Petunia (Petunia×hybrida Vilm.-Andr.) is one of the most important bedding plant and potted plant in the world, andthe cultivar 'Fantasy' is fit to be used in Chinese cities. Conclusions drawn from the studies on petunia'Fantasy' could be directly used in guiding mass cultivation.The research of floral development has always been the hotspot and the front ofdevelopmental biology. Petunia, as a model plant, is of great importance in this area.However, the lack of floral developmental mutants, and the unknown signals mediate leadto mutant have been blockages to further research. Study on the varied flower of petunia'Fantasy' induced by specific environment could initiate subsequent research.The results are as follows:①Five patterns of induced phase change have been established, which could beused as guidance for experiments and reference for analysis in juvenile studies.②Petunia 'Fantasy' is a long day (LD) plant, it appeared as facultative or obligate ofLD according to the environment. Plants tended to have an upright habit with increase in heightand crown diameter under LDs and a compact habit with increase in branch number under short days(SDs). Accordingly, LDs should be provided to accelerate floriculture by inducing flowering of petunia'Fantasy', while short days provided to improve quality by lower plants height.③Transferring plants between SD and LD according to leaf number or growing weeks ofseedling, it is concluded that the juvenile phase of petunia 'Fantasy' ended at the 6-8 leafstage, the process of which could be accelerated by LDs. Take the premise that plant qualityof petunia 'Fantasy' is of the first importance, also reducing the waste of energy is inconsideration, it is suggested that cultivate under SDs before the 6-8 leaf stage, and underLDs thereafter. The process of juvenility study is simplified by light transferring resting on growing weeks of seedling, simultaneously, a reliable parameter for floriculture isprovided by observation on leaf number.④It is concluded from the experiment of light transferring that limited inductivephotoperiod (LIP) of petunia 'Fantasy' is 3 weeks. Compared with continuous LD, LIPreduced plant height significantly without influence on crown diameter and brunchnumber. It is suggested that 3 weeks of LD set on petunia 'Fantasy' after 6-8 leaf stage, bywhich enough LD had been provided for floral induction without waste of energy andharm to plant morphology.⑤The flower bud differentiation process of petunia 'Fantasy' could be divided into7 phases: vegetative growth phase, inflorescence primordium differentiation phase, bractdifferentiation phase, flower differentiation phase, sepal differentiation phase, corolla andstamen differentiation phase, and pistil differentiation phase. The response of flower buddifferentiation of petunia 'Fantasy' to photoperiod started at 5 growing weeks of seedling,that is being at flower differentiation phase under LD and inflorescence primordiumdifferentiation phase under SD respectively.⑥Significant linear relationships existed between each growth characteristics ofpetunia 'Fantasy' and its flower bud differentiation phase, the regression equations are asfollows: y=0.565x+0.43 (crown diameter; R~2=0.9566), y=0.2638x+0.0528(leaf number;R~2=0.8982), y=0.5501x+0.9944(height; R~2=0.8162), and y=0.6863x-0.4946 (growingweeks of seedling; R~2=0.7918). Data indicates that the more sensitive of growthcharacteristics to photoperiod, the more significant relationship between growthcharacteristics and flower bud differentiation phase. Conclusion could be drawn from thedata that it was from inflorescence primordium differentiation phase to flowerdifferentiation phase that petunia 'Fantasy' accepted the floral induction by LDs.⑦Observed by naked eyes, in the deletion (del) varied flower of petunia 'Fantasy',there is no corolla; big differences existed among floral organs, all of which elongation isinhibited; fertility of the flower is lost. While observed by dissecting microscope, there iscorolla in del, loses its vitality at different stages before mature. Moreover, observed byscanning electron microscope, the lost of vitality in corolla could occurred before thestigma of pistil could be merge.⑧Among the treatments combined of different temperature (high temperature, HT;and low temperature, LT)and different photoperiod (LD and SD), the del varied flower obtained in all treatments but HTSD; it formed earlier than wild-type in the sametreatment; it formed earlier under HT than that of LT under LD, also earlier under LDthan that of SD under low temperature. Standardized canonical discriminant functioncoefficients indicate that photoperiod is of most importance in the induction of the delvaried flower.⑨Based on analysis of floral development genes, an imaginary draft of thephotoperiod function on the development of the del varied flower of Petunia hybrida'Fantasy' was drawn.⑩Discrimination protocol of the flower type was established based on this study, bywhich 90％of the original grouped cases were correctly classified. According to thetemperature and photoperiod under which petunia 'Fantasy' grows, the flower type of avisible flower bud of this plant should be predicted by the discriminant, which makes itpossible for further research on the del varied flower of petunia 'Fantasy'.