Population Genetics Research Of Melia Azedarach In Three Different Types Of Forest

Melia azedarach is a superior native tree species for forestation in Xuzhou,Jiangsu province,China.It is also a occasional species in warm temperate deciduous broad-leaved forest.We conducted a study on the genetic diversity of Melia azedarach populations based on SSR molecular markers,to understand what genetic changes had happened with undergrowth vegetation during the process of plantations succession,and how did human activities effect the genetic diversity of native tree species.The results showed that:(1)14 SSR loci produced a total of 90 alleles in\6 Melia azedarach populations,the number of alleles at each loci(NA)ranged from 3 to 13,each loci produced 6.429 alleles on average.Observed heterozygosity(Ho)ranged from 0.133 to 0.738,with a mean of 0.416.Expected heterozygosity(HE)ranged from 0.166 to 0.677,the average is 0.462.Average genetic diversity(Hs)ranged from 0.161 to 0.646,with a mean of 0.419.Total genetic diversity(HT)ranged from 0.166 to 0.677.with an average of 0.461.Polymorphism information content(PIC)ranged from 0.068 to 0.155,the average is 0.418.Those data showed that the level of genetic diversity of Melia azedarach sampled around Xuzhou was quite low,because of genetic drift and inbreeding depression caused by habitat fragmentation.(2)The QSM population showed the highest level of genetic diversity(HE=0.5245),while the GJC population showed the lowest(HE=0.2485).16 Melia azedarach populations could be divided into 2 clusters,the first cluster contained populations in Xuzhou city,GJC,TZC and HL village.The second cluster contained populations in Huangzangyu Provincial Nature Reserve and NYC village.The coefficient of gene differentiation(FsT)was 0.2097.10.775%of genetic variation existed among groups,10.198%existed among the populations,and 79.027%existed within populations(P<0.001).It indicated that genetic differentiation among Melia azedarach populations was obviously large.(3)The level of genetic diversity of Melia azedarach populations sampled in plantations of different ages had significant difference(P<0.05),which was positively correlated with the ages of plantation and was negative correlated with canopy density.It was possibly because that plantations produced increasing habitat heterogeneity in the process of succession,which provides more living space for Melia azedarach.Besides,we found that the level of genetic diversity of Melia azedarach populations varied in different succession stages.(4)The level of genetic diversity of Melia azedarach populations was negative correlated with urbanization degree of villages,indicating that human activities had a severe negative impact on genetic diversity of Melia azedarach populations.It is also proved that some Melia azedarach populations in backvelder should be well protected,because it's genetic diversity was quite high.