Abstract
Osmanthus serrulatus Rehder (Oleaceae) is an endemic spring-flowering species in China. It is narrowly distributed in the southwestern Sichuan Basin, and is facing the unprecedented threat of extinction due to problems associated with natural regeneration, habitat fragmentation and persistent and serious human interference. Here, the genetic diversity and population structure of 262 individuals from ten natural populations were analyzed using 18 microsatellites (SSR) markers. In total, 465 alleles were detected across 262 individuals, with a high polymorphic information content (PIC = 0.893). A high level of genetic diversity was inferred from the genetic diversity parameters (He = 0.694, I = 1.492 and PPL = 98.33%). AMOVA showed that a 21.55% genetic variation existed among populations and the mean pairwise Fst (0.215) indicated moderate genetic population differentiation. The ten populations were basically divided into three groups, including two obviously independent groups. Our results indicate that multiple factors were responsible for the complicated genetic relationship and endangered status of O. serrulatus. The concentrated distribution seems to be the key factor causing endangerment, and poor regeneration, human-induced habitat loss and fragmentation seem to be the primary factors in the population decline and further genetic diversity loss. These findings will assist in future conservation management and the scientific breeding of O. serrulatus.
Highlights
Osmanthus serrulatus Rehder is an evergreen shrub or small tree with long and slender pedicels and weeping flowers that bloom in spring, which distinguishes it from other species [1,2]
Ex situ conservation of as many individuals as possible via seeds or branches could be used as an auxiliary measure to establish a germplasm resources library to preserve the genetic diversity, by providing sufficient materials for germplasm innovation and possible reintroduction of this endemic species in the future. This is the first study to perform an analysis of the genetic diversity and population structure of O. serrulatus in southwestern Sichuan using 18 SSR markers
Our results show high adaptability and evolutionary potential in the natural O. serrulatus populations
Summary
Osmanthus serrulatus Rehder is an evergreen shrub or small tree with long and slender pedicels and weeping flowers that bloom in spring, which distinguishes it from other species [1,2]. Our previous work on O. serrulatus indicated that persistent human interference and increasing habitat fragmentation were the major external factors posing a critical threat to its wild populations [3], while its characteristic functional androdioecy [4], seed germination every other year [5], and unique habitat requirements [6,7] might be the internal factors leading to a dramatic decline in the population and slow regeneration of the natural habitat These findings play a crucial role in new Osmanthus cultivar breeding and highlight subtropical forest biodiversity patterns and mechanisms in China. Despite research efforts in regard to the phylogeny and evolution [9,10], genetic diversity and population structure [11,12,13,14] of O. fragrans (Thunb.) Lour., there is an urgent need to explore the genetic relationships of O. serrulatus with neutral markers, e.g., microsatellites, to obtain a better understanding of its genetic diversity and population structure
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