College of Forestry and Landscape Architecture, South China Agricultural University, Guangdong, 510642, China.
Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, South China Agricultural University, Guangdong, 510642, China.
Sci Rep. 2020 Oct 12;10(1):16998. doi: 10.1038/s41598-020-74123-8.
Most initially perfect flowers of Toona ciliata Roem subsequently develop into functionally unisexual flowers and their relative positions in the same inflorescence could enhance the outcrossing system in this species. Here we investigated the mating system of this species. We used eight nuclear microsatellite markers and investigated the progeny of 125 mother trees from six populations naturally distributed in South China, with sample sizes ranging from 64 to 300 seeds. The multilocus outcrossing rate was 0.970 ± 0.063, and the single locus outcrossing rate was 0.859 ± 0.106, indicating the pattern of predominant outcrossing. Selfing was present in one population, but biparental inbreeding occurred in five populations. Inbreeding was absent in maternal parents, and correlations of selfing among families or among loci were generally insignificant. Positive correlation of paternity at multiple loci was significant in four populations, but was not consistent with the results at single loci. Population substructure occurred in male similarity between outcrosses only in one population. Population genetic differentaitaion was significant (F = 34.5%) and the effects of isolation-by-distance at the eight loci were significant among the six populations. These results provide evidence that self-comptability and inbreeding naturally occur in T. ciliata and indicate that inbreeding avoidance is necessary during genetic improvement and breeding of this endangered tree species.
香椿最初的完全花随后发育为功能上的单性花，它们在同一花序中的相对位置可以增强该物种的异交系统。本研究调查了该物种的交配系统。我们使用了 8 个核微卫星标记，对分布在中国南方的 6 个种群的 125 棵母树的后代进行了调查，样本大小从 64 到 300 颗种子不等。多座位异交率为 0.970 ± 0.063，单座位异交率为 0.859 ± 0.106，表明存在主要异交的模式。一个种群存在自交，但五个种群存在双亲的近交。母本中不存在自交，家系间或座位间的自交相关性通常不显著。四个种群中多个座位的亲缘关系呈正相关，但与单个座位的结果不一致。只有一个种群的雄性相似性中存在异交的亚群结构。六个种群之间存在显著的遗传分化（F=34.5%），八个位点的隔离-距离效应显著。这些结果表明，香椿中存在自交亲和性和近交，这表明在遗传改良和濒危树种的繁殖过程中，避免自交是必要的。
