基于形态及分子标记的濒危植物夏蜡梅自然居群的遗传变异研究

比较了濒危植物夏蜡梅(Sinocalycanthus chinensis)大明山、大雷山、龙须山3个居群的果实与种子的形态变异,采用ISSR分子标记技术分析DNA序列的变异,综合评价夏蜡梅3个居群的遗传变异。结果如下:果实性状中,果柄长、果实长、果实重、每果种子数等指标均以大明山居群最大、大雷山居群次之、龙须山居群最小,它们之间差异显著(P<0.05)。种子重、种子长、种子宽、种子厚等指标均以大雷山居群最大,与大明山居群和龙须山居群差异显著(P<0.05)。基于果实形态特征的表型分化系数(VST)在0.5518—0.9750之间,平均为0.8930,所有果实形态指标的变异大部分存在于居群间。基于种子形态特征的VST在0.1669—0.8678之间,平均为0.6240,除种子长外,其他种子形态指标的变异也大部分存在于居群间。ISSR分析表明,3个居群的多态位点百分率、Shannon信息指数、Nei基因多样性均是大明山居群最高、龙须山居群次之、大雷山居群最低。居群间的遗传分化系数(GST)为0.6050。基于ISSR分子标记数据的聚类结果显示大明山居群先与龙须山居群聚在一起,再与大雷山居群相聚,这与基于种子性状特征的聚类结果相似,而与基于果实性状特征的聚类结果不同。3个居群的种子形态特征变异系数与遗传多样性水平具有显著的正相关,且基于果实形态特征估算的VST要高于GST,而基于种子形态特征估算的VST仅略高于GST,表明夏蜡梅不同居群间的种子形态变异主要由遗传变异所造成的,而环境因子在果实形态变异中起了重要作用。Mantel检验显示3个居群基于分子标记数据的遗传距离矩阵和基于果实及种子形态特征的欧氏距离矩阵之间的相关性不显著,表明果实与种子在居群间出现的表型分化除了受遗传因素影响外,还受到其它环境因子的强烈影响。

Genetic variation among populations of the endangered Sinocalycanthus chinensis based on morphological traits and ISSR profiles

Sinocalycanthus chinensis, the only representative of the Sinocalycanthus genus belonging to the Calycanthaceae family, is an endangered shrub endemic to China. A combination of morphological traits and molecular markers may be the most reliable method to assess genetic variation among populations of this species. To provide crucial information for establishing strategies for the management and conservation of this species, the genetic variation among three populations of S. chinensis was assessed based on the morphological traits of fruits and seeds and on inter-simple sequence repeat (ISSR) profiles. We obtained the following results: fruit stalk length, fruit length, fruit weight, and seed number per fruit varied significantly among the three populations (P<0.05) with the highest values in the Damingshan(DMS) population, intermediate values in the Daleishan (DLS) population, and the lowest values in the Longxushan (LXS) population. Seed weight, seed length, seed width, and seed thickness were greatest in the DLS population, and were significantly higher than their respective values in the DMS and LXS populations (P<0.05). The phenotypic differentiation coefficient (V_ST) based on the morphological traits of fruits varied from 0.5518 to 0.9750, with a mean of 0.8930. All the variation existed among populations. The V_ST based on the morphological traits of fruits varied from 0.1669 to 0.8678, with a mean of 0.6240. Except for seed length, all the variation existed among populations. The percentage of polymorphic loci, Shannon informative index, and Nei's gene diversity were highest in the DMS population, intermediate in the LXS population, and lowest in the DLS population. The genetic differentiation coefficient (G_ST) among populations was 0.6050. The clustering results based on ISSR data showed that DMS and LXS populations were clustered into one group, and the DLS population joined to that group. The dendrogram was similar to that based on the morphological traits of seeds, but differed from that based on the morphological traits of fruits. There was a significant positive correlation between the mean variation coefficient of seeds and the genetic diversity indices, while there was no correlation between the mean variation coefficient of fruits and the genetic diversity indices. The V_ST based on the morphological traits of fruits was higher than the G_ST estimated from ISSR data, while the V_ST based on the morphological traits of seeds was similar to the G_ST estimated from ISSR data. This suggested that the morphological variations among seeds might be caused by genetic variations, while environmental factors might play important roles in forming the morphological variations among fruits. A Mantel test showed that there was no significant correlation between the genetic distance matrix based on the ISSR profile and the Euclidean distance matrix based on the morphological traits of fruits or seeds. This indicated that the variations among the morphological traits of fruits and seeds may be mainly affected by environmental factors, as well as genetic factors.