Wang Chaoying, Xie Yingzan, Ma Lihui
School of Culture and Tourism, Chongqing City Management College, Chongqing, China.
Chongqing Urban Ecosystem National Positioning Observation and Research Station, Chongqing Academy of Forestry Sciences, Chongqing, China.
PLoS One. 2025 Mar 27;20(3):e0319513. doi: 10.1371/journal.pone.0319513. eCollection 2025.
Rhododendron platypodum Diels is an endangered ornamental plant distributed in the high-elevation subtropical regions of China. Known as one of the "queen flower", its population is restricted to three sites in China, with only few individuals. To explore the reasons for poor population regeneration and provide theoretical basis for genetic breeding to support its popularization and application of this native garden tree species, field investigation and artificial pollination experiment were conducted to test the flowering characteristics and breeding system of R. platypodum in Zhaoyun Mountain, Chongqing. The results revealed that: (1) the flowering period of R. platypodum began in mid-April and ended in late May, lasting 36 days, with an average flowering duration of 9.15 days per flower. (2) Pollen viability was highest in the morning and evening, peaking on third day after flowering, while stigma receptivity was highest between the second and third days. (3) The value of hybridization index and the pollen-ovule ratio indicated a partial self-compatibility and facultative outbreeding of this species. (4) Artificial pollination experiments showed no evidence of parthenogenesis or automatic self-pollination, and the fruit set rates for xenogamy, geitonogamy were higher than those for self-pollination, with artificial pollination yielding higher fruit set rate than natural pollination. (5) The primary effective pollinators of R. platypodum were identified as Bombus sp. and Apis cerana sinensis. Our research found that instead of long flowering period, high pollen viability and simultaneous mature of stigma and pollen, high geitonogamy relying on pollinators for effective production and the pollen restriction are more likely to have adverse effects on the population of R. platypodum. Further factors such as limitation in seed dispersal, germination challenges, and environmental requirement for seedlings and saplings may contribute to the endangerment of R. platypodum.
鹿角杜鹃是一种分布于中国亚热带高海拔地区的濒危观赏植物。它被誉为“花中皇后”之一，在中国仅分布于三个地点，个体数量稀少。为探究其种群更新不良的原因，并为遗传育种提供理论依据以支持这种本土园林树种的推广应用，在重庆照云山对鹿角杜鹃进行了实地调查和人工授粉实验，以测试其开花特性和繁育系统。结果表明：（1）鹿角杜鹃的花期始于4月中旬，结束于5月下旬，历时36天，每朵花的平均开花持续时间为9.15天。（2）花粉活力在早晨和傍晚最高，在开花后第三天达到峰值，而柱头可授性在第二天和第三天之间最高。（3）杂交指数和花粉胚珠比的值表明该物种具有部分自交亲和性和兼性异交性。（4）人工授粉实验未发现孤雌生殖或自动自花授粉的证据，异花授粉、同株异花授粉的坐果率高于自花授粉，人工授粉的坐果率高于自然授粉。（5）确定鹿角杜鹃的主要有效传粉者为熊蜂属和中华蜜蜂。我们的研究发现，鹿角杜鹃种群受到的不利影响更可能来自于依赖传粉者进行有效繁殖的高同株异花授粉和花粉限制，而非花期长、花粉活力高以及柱头和花粉同时成熟。种子传播受限、发芽挑战以及幼苗和幼树的环境需求等进一步因素可能导致鹿角杜鹃濒危。
