Abstract
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 (Fst = 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.
Highlights
The flower structure of Toona ciliata Roem (Meliaceae) is characterized by flowers of about 5 mm long
Scoring its mating system helps to understand the reproductive ecology of this species and to imply its natural regeneration
This study investigated mating system of six natural populations in different regions and showed occurrence of selfing or inbreeding in different geographical regions
Summary
The flower structure of Toona ciliata Roem (Meliaceae) is characterized by flowers of about 5 mm long. Stamens with anthers in functionally female flowers seem not to produce fertile pollen This is an alternative to those patterns that avoid selfing and inbreeding by forming sexually diecious plants or employing self-incompatible genes. It is not clear whether such floral development is ubiquitous or not in genus Toona and other genera (e.g., Cedrela and Swietenia) of the Meliaceae[2], and the flowers that remain perfect cannot be excluded. Scoring mating system of T. ciliata is of particular significance to its genetic conservation or sustainable management This species is classified as an endangered species in China[7] it is not in the”Red lists” of the species at risk by the International Union for Conservation of Nature and and Natural Resources (IUCN).
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