Genetic diversity analysis of Toona sinensis natural populations in southwest Zhejiang based on SSR markers

To protect scientifically and exploit reasonably Toona sinensis natural genetic resources, and unravel molecular genetic background of T. sinensis natural populations in southwest Zhejiang.

Sixteen polymorphic SSR markers were used in this study to evaluate the genetic diversity, to analyze the extent of genetic differentiation and population genetic structure of 156 materials collected from five T. sinensis populations in southwest Zhejiang.

1) A total of 110 alleles were detected in 156 samples from 16 SSR loci, the average number of alleles (N_a) and effective allele number (N_e) per locus were 6.88 and 2.48, respectively, and different alleles were unevenly distributed in 156 T. sinensis individuals. The PIC value was 0.04-0.79, with an average of 0.45; 2) The average values of the Shannon's information index (I) and the Nei's gene diversity (H) of 16 loci were 0.99 and 0.49, respectively. The average values of inbreeding coefficient in population (F_is) and total inbreeding coefficient in population (F_it) were -0.02 and 0.03, respectively. The average value of genetic differentiation coefficients (F_st) was 0.05, and only 5% of genetic variation was due to different populations. The average value of gene flow (N_m) was 4.82. Analysis of molecular variance (AMOVA) showed that genetic differentiation among 5 populations was mainly due to variation within overall individuals (95%), and slight variation among populations (5%). No variation occurred among individuals within populations; 3) Genetic difference and UPMGA cluster analysis showed that Nei's genetic identity of 5 populations were 0.93. The genetic relationship between Kaihua and Changshan populations was closest with Nei's genetic identity of 0.97 and the variations between Longyou population and other 4 populations was relatively high; 4) Genetic structure analysis showed that there was no most appropriate K value. A certain number of T. sinensis materials from 5 populations were distributed in 3 sub-groups while maximal value of ΔK was 3.

Overall, the genetic diversity of T. sinensis natural resources in southwest Zhejiang is relatively rich at the individual level. There were a low inbreeding level and outcross took place frequently. The extent of genetic differentiation among 5 populations were at a very low level, there were frequent gene exchange among populations and most of variations existed within individuals. Only small variation existed among the 5 populations and they had not formed independent genetic structure. Most of T. sinensis germplasms were with narrow genetic background, while only small number of germplasms were with complex genetic background.