A Study Of Effective Pollinators For The Dioecious Vine Siraitia Grosvenorii(Cucurbitaceae)

Pollinator-limited fruit production is widespread in animal-pollinated crops.Siraitia grosvenorii(Cucurbitaceae),one dioecious vine endemic to Southeast Asia,has been cultivated and widely used as a medicinal plant.In its major cultivated area in China,its fruit production depends on artificial hand-pollination.To investigate potential pollinators for this crop,here we studied pollination characteristics in a population of Siraitia grosvenorii in Yongfu County,Guilin,Guangxi Province.Differences of floral traits between female and male plants including floral phenology,rewards,odor composition,and particularly pollinator effectiveness were compared.Major results of its pollination system are:(1)Siraitia grosvenorii is dioecious,seed production relying on pollinator visits,absent of agamospermy.(2)The flowering phenology of this species was generally from mid-June to late September,with several peaks.Single flowers lasted one day in males,and 1-2 days in females.The androecium is fleshy with short filaments and broad anthers and consists of two pairs of connate stamens and a fifth single stamen.Female flowers resemble male flowers as the gynoecium that three fleshy two-lobed stigmas borne on a thick style looks like the androecium.Male flowers provide pollen,nectar and oil reward,but female flowers only oil to visitors.The main chemical components of the oil secretion are esters,aldehydes,aromatic hydrocarbons,alkanes,alkenes,ketones,free fatty acids,ethers,and alcohols.Floral scent released by Siraitia grosvenorii mainly consists of ethyl carbonate,acetal,toluene and 2-Butene,2-(1-ethoxyethoxy)-,(E)-,those also appear in the main components of the oil drop.(3)The visitors mainly included bees,butterflies,and flies.Bee visitors to male flowers were Apis mellifera,Ceratina flavipes,Ctenoplectra davidi,and Bombus bee,Xylocopa bee,Halictus bee species.Female flowers are only visited by Ctenoplectra davidi(female).Our comparison of the pollination efficiency among different visitors showed that only female oil-collecting bee Ctenoplectra davidi was the effective pollinator.In summary,our investigation in the field population indicated that those visitors only visiting male plants could not delivery pollen,functioning as nectar or pollen thieves.To promote fruit production in this dioecious crop with a specialized pollination system,hand pollination or promotion of the Ctenoplectra bee populations is needed.