Comparative Study On Pollination Biology Of Siraitia Grosvenorii And Its Relatives

Siraitia grosvenorii is a dioecy vine in Cucurbitaceae.Due to the medicinal and edible properties,fruits of S.grosvenorii were widely used in food,medicine and health care products,and consequently make it an important economic crop in Guangxi of China.However,the natural pollination process of this plant were found to be seriously limited,leading to the high farming cost that hand pollination was required to make female flowers bearing fruits.For the other species in Cucurbitaceae,the pollination limitation happened in S.grosvenorii was rarely reported.So the comparative study on pollination biology between S.grosvenorii and its relatives will shed light on the mechanism of this pollination limitation.Due to the strong associations of flower shape,flower color,flower volatile substances,flowering phenology and flower nectar with the flower pollinators,the flower morphological characteristics,flower volatiles and flower-seeking insects of S.grosvenorii and of its 11 relatives plant(all from 9 genus of Cucurbitaceae)were systematically researched in this study.The aims of this study were to reveal the reasons of the pollination limitation in S.grosvenorii,and further,to provide basic information for the pollination biology research of Cucurbitaceae plants.The main results of this study are as following:1.Flower morphological characteristics of S.grosvenorii and its relatives.Petals of Lagenaria siceraria var.hispida,Trichosanthes kirilowii Maxim.and L.siceraria(Molina)Standl.are white color,and petals of the remaining 9 species are yellow;Luffa acutangula(Linn.)Roxb.,Luffa siceraria var.hispida,Luffa siceraria(Molina)Standl.and T.kirilowii are nocturnal bloomings,the remaining 8 species are diurnal bloomings;Benincasa hispide Cogn.var.chiehqua How.,Cucurbita moschata(Duch.ex Lam.)Duch.and Luffa cylindrica(L.)Roem.have the largest petal,with size of 70~110 mm,and then,the petal size of L.siceraria,L.siceraria,T.kirilowii.and L.acutangula is 30~50 mm,and the petal size of remaining plants is 20~30 mm.In general,the flower morphologicaland other related features of S.grosvenorii and its relatives have their own characteristics and similarities,and these floral features have a certain internal relationship with their visiting insects,which may affect their respective visiting insects may affect the efficiency of insect pollination.2.Flower volatile constituents of S.grosvenorii and its relatives.The flowers volatile substances were analyzed by GC-MS,the volatile odor substances of S.grosvenorii are mainly terpenes,and the alpha.-Cubebene is the main component of S.grosvenorii's female and male flowers,each accounting for 49.67 % and 67.60 % of the relative content of volatile odor substances.The male and female flowers of L.acutangula and C.moschata have similar volatile constituents,(E)-3,7-dimethyl-1,3,6-Octatriene is the main volatile component of the female and male flowers of L.acutangula,each accounting for96.31 % and 93.12 % of the relative content of volatile odorants;1,4-dimethoxy-Benzene was the main volatile component in the female and male flowers of C.moschata,which accounted for 89.91 % and 62.34 % of the total volatile odorant content;male and female flowers of M.charantia and C.sativus have significant differences in volatile substances,Limonene is the main volatile odorant of M.charantia' female flower,which accounting for 57.38 %,while in male flowers of M.charantia,Indole is the main volatile odor substance,which accounting for 53.49 %;Benzyl alcohol is the main volatile odorant of male flowers of C.sativus,reaching 60.16 %.Since the volatile parts of the flower parts usually have the function of attracting insects,it is speculated that the interspecies differences of volatiles in the flower parts have different effects on the species of flower-seeking insects and the characteristics of flower-seeking behavior of the tested plants.3.Flower-seeking insects of S.grosvenorii and its relatives.It has been observed that in S.grosvenorii and its relatives,such as L.acutangula,L.siceraria,etc.,flower-seeking insects are mainly moths,while plants that bloom during the day,such as M.charantia,L.cylindrica,etc.use bees as the main visiting insects.Further analysis found that there is no strict one-to-one correspondence between species of visiting insects and plant species.For example,when Halictus sp.is observed to visit M.charantia,L.cylindrica,etc.,Nomia chalybeata will visit L.cylindrica,M.charantia and S.grosvenorii male flowers,etc.,but there are differences in the frequency of visits to different plants.For example,when the pollination visits L.cylindrica,the frequency is as high as 2.67 ± 1.11,while the visit to M.charantia is up to 1.05 ± 0.76.In addition,a small number of insect species were found to visit only one plant.For example,Ctenoplectra davidi Vach only visits S.grosvenorii male and female flowers,Macroglossum pyrrhosticta only visits L.acutangula flowers,which are mainly visited at 18 o'clock and 19 o'clock.The frequency of their respective visits was 1.96 ± 0.74 and 0.53 ± 0.75,respectively.The number of species of flower-seeking insects in each experimental plant and the frequency of visiting flowers were investigated.The number of flower-seeking insect species and the frequency of visiting flowers were recorded in S.grosvenorii and L.cylindrica.In general,there are significant differences in the species of flower-seeking insects and their flower-seeking behaviors in experimental plants.4.The characteristic of the antennae sensory of the pollinating insect of S.grosvenorii.C.davidi is an effective pollinating insect of S.grosvenorii.This study found that this bee was unique in flowering and only visited S.grosvenorii in but not to the remaining 11 study plants.In order to explore the formation mechanism of the obligatory foraging behavior of C.davidi,the scanning electron microscopy observation and analysis of the antennae of C.davidi was performed.The results showed that the antennae of C.davidi were knee-shaped.There were 11 types of sensillar on the antenna of C.davidi,namely sensilla trichodea,sensilla chaetica,bud-like sensilla,sensilla basiconica,b?hm bristles,sensilla cavity,sensilla placodea,sensilla campaniformium,sensilla margin,setae,and sensory pore.Specifically,three subtypes of sensilla trichodea and also two subtypes of sensilla basiconica and sensilla chaetica were observed.On theventral surface of flagellum,it was dominated by sensilla chaetica,while were sensilla placodea and sensilla basiconica on the back surface of flagellum.The sensilla placodea was an olfactory organ,which was ubiquitous in Hymenoptera,and was also widely distributed on the back of the F3~F11 whip of antenna of the C.davidi,which may have the function of detecting the location of the host plant.In other words,it plays a key role in locating accurately between the male and female flowers of the S.grosvenorii and helping them complete pollination.The sensilla basiconica was also a olfactory sensor,which can sense the smell of plants.It was preliminarily believed that it may play an important guiding role in accurately positioning the host plant.The male and female flowers of S.grosvenorii have large differences in flower shape,flower color,flower volatile matter composition,flower visiting insect species andfrequency of visiting flowers.In addition,the cultivation of S.grosvenorii focuses on economic benefits,and the artificial destruction of the ratio between male and female plants may be one of the reasons for its pollination limitation in its natural state.