The Study On Hybridization Between Bauhinia Variegata And Bauhinia Purpurea

Bauhinia variegata and Bauhinia purpurea belong to the genus Bauhinia of Caesalpiniaceae,which are commonly used as ornamental trees in Lingnan.They were taken as experiment materials in this study to carry out preliminary research on the selection of parental pollen and stigma receptivity,hybrid compatibility,the separation of flowering period of interspecific hybridization and so on,which the culture conditions of pollen in vitro germination and the preservation conditions of pollen were screened by single factor method,the pollen viability of different flowering stages were tested comparatively by TTC and in vitro germination,the stigma receptivity was detected by benzidine-H₂O₂ method,the growth status of pollen after artificial pollination were estimated with fluorescence microscopy and the flowering periods were regulated by plant growth regulators.These studies will lay foundations for hybridization and its excellent hybrid cultivars of Bauhinia variegata and Bauhinia purpurea in the future.The main results are as follows:1.The optimal culture conditions for pollen in vitro germinationThe optimal culture conditions pollen in vitro germination of Bauhinia variegata pollen were cultured in the solid medium with 15%sucrose+0.06%H₃BO₃+1%agar and at27?for 2h,which optimal germination effect was obtained.There was no significant difference in pollen germination with 0.01%-0.05%concentration of CaC l₂.Both of the concentration from 0.01%to 0.05%of MgSO₄ and KNO₃ inhibited the germination of the Bauhinia variegata pollen.2.Pollen viability and its storage conditionsThere were significant differences in pollen viability among different flowering stages of Bauhinia variegata and Bauhinia purpurea.In all flowering stages,fresh flowers just opened that day had the highest pollen viability,which were most suitable for artificial pollination.Taken the fresh flowers just opened that day as the research object,the pollen viability of Bauhinia variegata was 81.37%and 51.27%respectively by TTC and in vitro germination,and the pollen viability of Bauhinia purpurea was 96.03%by TTC.The pollen viability of Bauhinia variegata and Bauhinia purpurea in different storage conditions were significantly different,and both of their optimal storage conditions were4?with silicone,which preservation time was 30 days and 60 days respectively.The pollen viability of Bauhinia variegata and Bauhinia purpurea were almost inactivated after storage for 30 days and 60 days,which decreased to 2.71%,17.79%respectively.3.The stigma receptivityDuring dew bud to fresh flowers just opened that day of Bauhinia variegata and Bauhinia purpurea,stigma holds strong receptivity.Especially,the loose buds of Bauhinia variegata and its variants,the fresh flowers just opened that day of Bauhinia purpurea reached the strongest stigma receptivity.4.Observations of pollen tube growth situation by fluorescence microscopyMost pollens could attach and germinate on stigmas of the intraspecific hybrids of Bauhinia purpurea and the interspecific hybrids of Bauhinia purpurea×Bauhinia variegata,and then some pollen tubes could reach the middle of style,while a spot of pollen tubes could pass through the whole style,enter into the ovule to achieve fertilizat ion.The research indicated that the intraspecific hybrids of Bauhinia purpurea and the interspecific hybrids of Bauhinia purpurea×Bauhinia variegata had certain hybrid compatibility,accompanied by callose reaction,as well as pollen tube bending,knot,winding,abnormal slender,mid-tail spiral,the top of the expansion,reverse germination and other anomalies.It was concluded that a major obstacle of Bauhinia variegata and Bauhinia purpurea is before fertilization,and the abnormal growth of pollen after pollination hindered the normal fertilization and reduced the seed setting rate.5.Preliminary study on flowering regulatorThe results showed that the optimized treatment for improving Bauhinia variegata flowering earlier were was 1500mg/L of 6-BA,with an average flowering period predate of35 days and 75%of pollen viability.While that for delaying Bauhinia purpurea flowering was 2000mg/L of PP₃₃₃,which delayed flowering period of 25 days,and the pollen vitality was 92.94%.There were not obvio us effects of plant growth regulators on pollen viability of Bauhinia variegata and Bauhinia purpurea,and their pollen could be selected as male parent to pollinate.6.The results of artificial pollination testThe self-pollination and parthenogenetic o f Bauhinia variegata and Bauhinia purpurea were not fruitful,and it was inferred as cross-pollination.In 2016,the natural seed setting rate of the campus and nursery Bauhinia variegata flowering period were 7.00%and 4.00%,respectively.In 2017,the natural seed setting percentage of the campus early flowers Bauhinia variegata and blooming Bauhinia purpurea were 5.00%,4.00%.There was a significant difference in the ovaries and hybrid compatibility with different hybrid combinations of different color s.Affinity from high to low,respectively,intraspecific hybridization of Bauhinia variegata:Bauhinia variegata var.candida×deep purple flower of Bauhinia variegata>pink flower of Bauhinia variegata×Bauhinia variegata var.candida>Bauhinia variegata var.candida×pink flower of Bauhinia variegata>deep purple flower of Bauhinia variegata×Bauhinia variegata var.candida>deep purple flower of Bauhinia variegata×deep purple flower of Bauhinia variegata;intraspecific hybridization of Bauhinia purpurea:pink flower of Bauhinia purpurea×deep pink flower of Bauhinia purpurea>pink flower of Bauhinia purpurea×white flower of Bauhinia purpurea>pink flower of Bauhinia purpurea×red/purplish red/violet flower of Bauhinia purpurea;interspecific hybridization:pink flower of Bauhinia purpurea×pink flower of Bauhinia variegata>pink flower of Bauhinia variegata×pink flower of Bauhinia purpurea>Bauhinia variegata var.candida×pink flower of Bauhinia purpurea>pink flower of Bauhinia variegata×violet flower of Bauhinia purpurea.In 2016,harvested intraspecific hybridization combination of pink flower of Bauhinia purpurea×deep pink flower of Bauhinia purpurea,pink flower of Bauhinia variegata×Bauhinia variegata var.candida mature pods 13 and 1 respectively;obtained 68 hybrid seeds that their germination rate and the seedling rate were 16.18%and 0 respectively.In2017,respectively,harvested intraspecific hybridization combination of pink flower of Bauhinia purpurea×deep pink flower of Bauhinia purpurea,interspecific hybridization combination of pink flower of Bauhinia purpurea×pink flower of Bauhinia variegata hybrid fruit 1 and 14,and their hybrid seeds were 9 and 111.