Abstract: [Objective] Poor natural regeneration and over-exploitation have resulted in the continual decline of natural forests and trees of Toona ciliata. In depth studies of genetic diversity and structure of T. ciliata of different provenances are particularly important for conservation, utilization of genetic resources, and the development of future breeding programs for the species.[Method] Sequence-related amplified polymorphism (SRAP) markers were used to investigate genetic diversity of 29 provenances from China and one provenance from Australia of T. ciliata to define the level of genetic diversity and the relationships among different provenances. Samples from China were collected from natural stands. Each provenance was represented by 30 sample trees with a distance of at least 50 m among the sample trees. The Australian provenance was taken from the resources collection nursery of the South China Agricultural University. The POPGENE1.32 software was used for genetic diversity parameters calculation. The NTSYS-pc2.1 software was used for cluster analysis based on the matrix of Nei's genetic distances and the degree of genetic relatedness among provenances was assessed by principal coordinates analysis (PCoA) and MANTEL analysis with GenAIEx 6.5. STRUCTRUE 2.3 was used to analysis the genetic structure. [Result] A total of 505 polymorphic bands were amplified by 24 pairs of primers. The average value of polymorphism information content (PIC) was 0.41. The average value of Nei's gene diversity index (H) was 0.3770. Shannon's information index (I) within provenances ranged from 0.1575 to 0.467 5, the average value was 0.556 9 among provenances. The AMOVA indicated that 79.24% of the total variation was among provenances and 20.76% was within provenances, revealing that provenance selection is important for the breeding of T. ciliata. In STRUCTURE analysis, 30 provenances were divided into two groups. Group Ⅰ included the provenances from central and eastern China. The provenances of southwest and south China and the provenance of Australia formed Group Ⅱ. Isolation-by-distance (IBD) patterns were revealed in the provenances of China by Mantel test. The unweighted pair group method of arithmetic averages (UPGMA) cluster showed that the 30 provenances could be classified into four clusters. Cluster Ⅰ consisted of the 14 provenances from Central China and East China. Cluster Ⅱ consisted of only Lechang provenance. Cluster Ⅲ was composed of provenances mainly from South China and Southwest China, but the two provenances from Guangdong province were not classified into the same cluster. GroupⅣ was composed of provenances from Guangdong (YF) and the provenance of Australia. The result was consistent with biplot of PCoA analysis. [Conclusion] Habitat fragmentation of the natural distribution has led to spatial isolation among populations, low rate of gene exchange and limited gene flow, resulting in geographic variation among provenances. The UPGMA cluster analysis and PCoA analysis demonstrated a clear variation pattern consistent with the geographical trend of T. ciliata. Studies of artificial reproduction should be reinforced while carrying out protection of the original habitat, and collect all current genetic resources and expand the range of collection as far as possible.

Key words: Toona ciliata, SRAP markers, genetic diversity, genetic structure