Study On Breeding System And Pollination Accuracy Of Tirpitzia Sinensis Hemsl

As a bridge connecting the sexual reproduction of plants,breeding system is crucial to reveal the maintenance mechanism of species diversity and the mutual adaptation between flower morphological characteristics and pollinators.The heterostylous plants have been thought to improve compatible pollination between floral morphs within species and promote cross pollination.However,relevant examples are scarce,and the micro and macro mechanisms of improving pollination accuracy are still unclear.Tirpitzia sinensis(Hemsl.)Hallier is typically heterostylous,disturbs in karst areas with a long flowering period and beautiful flower shape.T.sinensis is ideal to explore the adaptive significance of heterostylous plants and has potential ecological and horticultural value.To explore the breeding system of T.sinensis,the morph ratio and the flowering phenology was counted,the floral morphological characteristics and nectar traits(volume,concentration and composition)were measured,the number of pollen in single flower and P/O ratio and pollen surface ornamentation were measured,the pollen viability and stigma receptivity were measured at different flowering time,the outcrossing index was calculated and artificial pollination treatments was performed.In order to explore the microscopic and macroscopic evidence of improving the pollination accuracy,the pollen deposited on the stigma from intramorphic and intermorphic with control treatment and emasculation experiments was quantified.The pollen germination rate and pollen tube length among intramorph,intermorph pollination treatments from two morphs were measured.Results are showed as follows:(1)The plant number of the long-styled morph(L-morph)and short-styled morph(S-morph)in natural populations had no significant difference.The flowering period of T.sinensis usually lasted from May to August,and the single flowering period lasted for about 3 days.There was no significant difference in the single flowering period between L-morph and S-morph.The leaf length,leaf width,sepals length,sepal width,petals width and tube depth of S-morph were significantly larger than those of the L-morph.The flower length and petal length of L-morph are significantly larger than the S-morph.Pistil length,anther length,pollen number of single flower and P/O ratio of L-morph is significantly larger than those of S-morph.The pistil length of S-morph was significantly greater than that of L-morph,The other traits were not significantly different between the two morphs.The pollen volume of S-morph was significantly larger than that of L-morph,and the pollen surface ornamentations of the two morphs were different.The stigma surface areas and surface ornamentations of the two morphs were not different.The pollen viability on the first day of flowering was significantly higher than that of the second day,while the stigma viability of the first and second day of flowering had no significant difference.The nectar volume secreted during night was significantly higher than that of the day in S-morph.There was no significant difference in the nectar volume between the day and night in L-morph.The nectar mainly contained sucrose,glucose and fructose,and the content of sucrose was the highest,followed by glucose,and fructose was the lowest.(2)The main visiting insects of T.sinensis were the Macroglossum,Bombus,Apis and Xylocopa.The hawkmoth conducted effective pollination when probing nectar.The bumblebee and the carpenter bee mainly robbed nectar,and the honeybee mainly gathered pollen.The visit rate of hawkmoth was the highest.The visiting time was usually lasted from 17:00 PM to 20:00 PM.The removed pollen number of L-morph was significantly more than that of the S-morph of hawkmoth.The percentage of compatible pollen was significantly more than that of incompatible pollen in the L-morph deposited by hawkmoth.The percentage of compatible and incompatible pollen were not significantly different in S-morph deposited by hawkmoth.The seed set of intermorphic pollination treatment was significantly higher than that of control,intramorphic,self-crossing,autogamatic,and emasculated treatments in S-morph of T.sinensis.The seed sets between the control and intermorphic pollination treatments were not significantly different in the L-morph of T.sinensis,and they were significantly higher than that of self-crossing,autogamatic,and emasculated pollination treatments.The seed sets of self-crossing,autogamatic,emasculated treatmentswere zero.The results indicated t T.sinensis was intramorphic outcrossing and self-incompatibility.(3)The ratio of incompatible pollens deposited on the stigma was significantly higher than that of compatible pollens in natural populations.The ratio of compatible pollen deposited on the stigma was significantly increased in L-morph with emasculation treatments,but not in S-morph.Pollen germination rate and pollen tube length with the intramorphic pollination treatment could significantly lower than those of intermorphic pollination treatment.In this study,a series of experiments on the breeding system of the dimorphic T.sinensis were carried out The effective pollinators and its pollination efficiency were determined.The floral characteristics of T.sinensis,especially the nectar traits,were defined.It provided accurate macroscopic and microscopic evidence for the promotion of pollination accuracy in heterostylous plant.It also provides scientific basis for the protection of germplasm resources,and the introduction and cultivation of wild varieties to horticultural varieties.