Reproductive Ecology Of Phalaenopsis Pulcherrima(Orchidaceae), A Species Endemic To East Asia

Phalaenopsis pulcherrima (Lindl.) J.J. Sm., an endecmic species to East Asia, is an evergreen perennial herb of the genus Phalaenopsis in Orchidaceae family. P. pulcherrima is one of the important parent-species in the hybridation of Phalaenopsis for its high ornamental value in patterns and colors of flower. However, recently, P. pulcherrima has already become an endangered species due to overexploitation and loss of its natural habitat. Understanding the characteristic of reproductive system of P. pulcherrima is essential for the conservation of P. pulcherrima. In this study, we explored the reproductive characteristics of P. pulcherrima by investigating its flowering phenology, breeding system, pollination biology and the factors of reproductive success in a natural forest of Wangxia of Hainan Island, China. Our main findings were as follows:(1) The paper explored flowering phenology characteristics and analyzed the relationship with reproductive success.The flowering period of the P. pulcherrima populations was from late May to early October, lasting120-138days, while the flowering duration of individual plants was39-69days. The typical flowering process for a flower could be divided into four periods:"Bud flowering stage","Initial flowering stage","Full flowering stage", and "Fade flowering stage". The life span of a single flower was significantly shortened with emasculated and pollinated treatments (P<0.01), and the rostellum would be gradually curved and coalesced with the stigma after the pollination within9.79±2.32hours. And the flowering curves had a multimodal peak period, which was a so-called "Multiple bang" pattern. The synchrony index was an average0.53. P. pulcherrima had a lower relative flowering intensity ranging from10%to30%.The onset time of flowering was negatively correlated with the duration of flowering and the flower number (P<0.01), and negatively correlated with the fruit set ratio. The duration of flowering was positively correlated with the flower number but negatively correlated with the fruit set ratio(P<0.01). The flower number was positively correlated with the fruit set ratio (P<0.01). The flowering synchrony index was negatively correlated with the onset time, but positively correlated with the duration of flowering and the flower number.(2)The paper analyzed the difference of different pollination treatments, and explored the mating system of populations. No automatic pollination or apomixes were observed in P. pulcherrima. P. pulcherrima with autogamy and xenogamy treatments showed significant difference in the fruit volume and dry weight (P<0.01), but not in the fruit set rate (P>0.05). Seed embryo rate of autogamy fruits was16.08±17.75%, significantly lower than xenogamy fruits (96.21±4.97%,P<0.01). The data analysis results refered that P. pulcherrima had the characteristic of early-acting inbreeding depression. And P. pulcherrima had a mixed mating system and outcrossing was the primary mating mode. Outcrossing and selfing rate of P. pulcherrima population were91.92±4.13%and8.08±4.13%, respectively.(3) The pollinators had been determined, and the characteristics of reproductive success had been explored. Some species, i.e., Amegilla zonata, Amegilla leptocoma, Nomia punctulata, and Apis florea were observed to visit P. pulcherrima. Of these species, A. zonata and N. punctulata had the highest visit frequency. No pollinator was observed at night. The pollinarium removal rate in2011(57.13±2.54%) was significantly higher than in2012(46.31±5.07%), possiblely result from the between-year differencese in weather conditions, habitat characteristics, pollinator efficiency. Pollinarium deposition rates in2011(16.83±1.44%) was slightly higher than in2012(16.56±2.83%).(4) Preliminarily explored and analyzed the influence to P. pulcherrima by accompanying rewarding plant species. Forty rewarding plant species had been recorded within and outside of the study plots, of these plant,23species showed a higher or equal length of flowering period with P. pulcherrima. There were eleven rewarding plant species sharing main pollinators and eight of them co-occuring with P. pulcherrima in plots. Helicteres angustifolia and Hedyotis consanguinea were the two species which had the largest number of individuals and the most extensive distribution. Through regression analysis on the ratio of flower number and the pollinarium removal and deposition rate of P. pulcherrima, the results showed that "Magnet species effect" existed between P. pulcherrima and the former two plant species.(5) The paper analyzed the characteristics of insect-pest, and explored the influence to reproductive success by the insect-pest. Eight pest-insects had been recorded, and the insects causing the most severely damage to P. pulcherrima were the larva of Lye sp.1(Lycaenidae) and the adult of Chr sp.1(Chrysomeloidea). The main pest period was from early June to early August, and the pest proportion of2011was significantly higher than that in2012at single flower, inflorescence and individual level, but significantly lower at fruit level.