中国特有濒危植物夏蜡梅的交配系统

Mating system of Sinocalycanthus chinensis(Cheng et S.Y.Chang) Cheng et S.Y.Chang,an endangered,indigenous species in China

夏蜡梅Sinocalycanthus chinensis具有局限的地理分布、片断化的生境、较小的种群规模和特殊的遗传结构,研究其交配系统,将为评估造成其目前这种遗传结构的内因、明确夏蜡梅遗传衰退机制和制定保护策略提供重要依据。通过野外观察、实验室检测和人工控制交配实验等研究,结果表明:夏蜡梅从开花到散粉雄蕊和退化雄蕊呈直立到平展再到合拢状的动态变化,当花药处于最平展状态时,柱头成熟具有粘性,可授性最强;说明夏蜡梅雌蕊先熟,雌雄配子存在一定的时空隔离,仅发育后期可遇。花粉胚珠比(P/O)、杂交指数(OCI)和人工控制交配实验的结果较为一致,表明夏蜡梅的交配系统为以异交为主的混合交配系统,部分自交亲和,完成授粉需要传粉者。综合种群结构、遗传结构和交配系统,夏蜡梅种群内遗传多样性降低而种群间遗传分化加剧最重要和直接的原因是生境的破坏、种群规模变小而导致的近交或自交比例增加。人工控制交配实验结果进一步表明,远交和混合授粉即用含有天台种群的花粉进行授粉具有显著的远交优势,远交结实率高达79.6%,平均每果实结实9.1粒种子,平均每胚珠结实0.75粒。因此,人为地促进2种群间的基因流将有利于夏蜡梅自然种群的恢复和遗传多样性的增加,对夏蜡梅保护策略的制定有重要参考价值。

Sinocalycanthus chinensis（Cheng et S.Y.Chang） Cheng et S.Y.Chang has a narrow geographic distribution,a fragmented habitat,a small population size,and a special genetic structure.It is indigenous to China,and due to its non-contiguous habitat and geographic isolation,several small regions have come into existence based on reproductive characteristics resulting in a very restricted distribution,mainly confined to Lin′an and Tiantai of Zhejiang Province.Genetic diversity for S.chinensis is relatively low in not only natural populations but also in artificially-cultivated populations;however,there is a definite genetic differentiation between the two geographically isolated Lin′an and Tiantai populations.The primary objectives of this study were to define the relationships among mating systems and genetic structures,to provide reasons for genetic degeneracy,and to develop successful conservation strategies in natural populations of S.chinensis.The floral biology and mating systems were assessed through field observations（including flower size,development and opening process）,lab detection（including pollen quantity and viability,pistil receptivity and the number of ovules）,and,for the Lin′an population,artificial pollination experiments（including natural pollination,emasculation,directly bagging selfing,artificial selfing,geitonogamy,xenogamy,outbreeding and two different mixed pollination）.Results of the field observation and lab detection showed that during bloom and pollen dispersion,stamen and staminode development changed from erect to explanate to folding with pistil receptivity reaching a peak when the stamens were at the explanate stage.Also,pistil receptivity was 7 to 8 d,lasting from the small bud stage until the pistil wilted,with pollen viability of more than 40%.In artificial pollination experiments：（1） outbreeding had the highest seed set（79.6%） with seed number per fruit of 9.1 and per ovule of 0.75;（2） mixed pollinations of geitonogamous pollen and outbreeding pollen had seed set of 55.0% with seed number per fruit of 7.3 and per ovule of 0.60;（3） mixed pollinations of xenogamous inbreeding pollen and outbreeding pollen had seed set of 64.3% with seed number per fruit of 7.5 and per ovule of 0.61;（4） geitonogamy had seed set of 19.6% and seed number per fruit of 6.7,whereas xenogamous inbreeding had seed set of 32.3% and seed number per fruit of 5.3;and（5） no fruits were produced with natural selfing under a bag,but artificial self-pollination with pollen from the same flowers had seed set of 49.6%.Also,from a pollen-ovule（P/O） ratio of 11740 ∶ 1,an outcrossing index（OCI） of 3,and artificial pollination experiments,the mating system showed xenogamy with partial self-compatibility（a mixed-mating system） requiring pollinators.Additionally,results of artificial pollination,using pure or mixed pollens from the Tiantai population,showed outbreeding had the highest seed set as well as seed number per fruit（9.1） and per ovule（0.75）.Thus,from field and lab observations,S.chinensis was protogynous with temporal and spatial isolation of male and female gametes within the same flower,there was some potential for self-compatibility;meanwhile,pistil receptivity and pollen viability increased reproductive success during pollination.Additionally,combining population structure,genetic structure,and mating system,an increased percentage of self-pollination and inbreeding,due to habitat destruction and decreased population size,caused low genetic diversity and high genetic differentiation.Also,pollination tests using pollen from the geographically isolated populations,showed strong outbreeding advantages meaning artificially accelerating gene exchange among isolated populations could contribute to increase population size and genetic diversity.Finally,artificial outbreeding using pollen of geographically isolated populations for species conservation as well as intercropping with S.chinensis seeds,seedlings,or adult trees,could be undertaken.