The Reproductive Biology Of Rhododendron Excellens Hemsl.et. Wils.

Rhododendron excellens Hemsl.et.Wils. belongs to Subsect. Maddenia, Sect. Rhododendron, Subg. Rhododendron in the genus of Rhododendron. We studied the characteristics of floral syndromes, breeding system, pollination biology and seed germination characters of R. excellens for better understanding the reproductive traits, ecological adaptation and discussing conservation implications of R. excellens.1. Floral phenology and traits. R. excellens is an evergreen low shrub with 2 m height. The flowering period can last one month, from earlier May to earlier June. The petal color is green on the first day of flowering, and changes white gradually later. Compare to other species of Rhododendron, pollen viability is low, and the maximum is only reaching up to 84.43%. The stigma receptivity is keep receptive over flowering period. Meanwhile, the stamens curved towards deep of petal during eraly flowering period indicating promoting cross-pollination and avoiding sexual interference.2. Pollination biology. Honeybees (Apis cerana) are the specialized pollinators. Honeybees are very active on sunnay days and the visitation rate would become nearly 0 on cloudy or rainy days. Different time within single flower gives rise to different visitation rate. On the basis of observations, honeybees'visitation rate to green petals in the first day is much higher than white ones in later days, indicating higher male fitness in early flowering time than later within a flower.3. Breeding system. The breeding system of R. excellens is partial self-compatible, outcrossing dominant and needing pollinators. Supplemental pollination showed that seed set from self pollen supplemental treatment is significantly lower than out cross pollen supplemental treatment. Finally, the analysis of inbreeding depression showed that seed number other than seed weight was significantly affected by inbreeding depression.4. Comparative studies on seed germination traits. Temperature treatments showed that 25℃/15℃is the best condition for seed germination. Seed germinating from cross pollination is significant higher than self pollination at Ganbazi, whereas no significant difference at Banpozhai. Compared to seeds collected in 2009, Seed germination rate is significantly higher from seed collected in 2010.