REPRODUCTIVE BIOLOGY OF A RARE, FLY-POLLINATED ORCHID, BULBOPHYLLUM TIANGUII, IN SOUTH CHINA

Bulbophyllum tianguii, an endangered orchid species, is predominantly distributed on the surface of karst stone mountains or the stems of humus trees in South China.To better understand the reproductive biology of the B. tianguii, we investigated the breeding system and pollination biology in natural populations.The flowering period of the B. tianguii population extended from late March to early April, and anthesis of a single flower usually endured 5-6 days.Floral scent analysis indicated that 2-methyl-1-butanol and leaf alcohol were the major compounds produced by B. tianguii.The breeding system was self-compatible and facultatively outcrossing, requiring pollinators.The only pollinator identified for B. tianguii was Sarcophaga carnaria, a species of fly.However, its visiting frequency is extremely low (0.005 visits/flower/h).The hinged labellum of these flowers functioned as a fulcrum.When pollinators entered the flower, they were propelled in a way that ensured contact with the column area.It plays a key role in the pollen dispersal.Natural fruit set for B. tianguii were merely 2.5% and 2% in the natural populations.Low reproductive rates in B. tianguii were found to be a consequence of few species of pollinators and their low visiting frequency.Pollen limation may be a crucial factor underlying the endangered of B. tianguii.Artificial pollination and the release of pollinators represent effective strategies for increasing the fruit yield to B. tianguii.