| Trachycarpus nanus Beccari,which belongs to family Arecaceae and genus Trachycarpus,is a dioecious perennial shrub without aboveground stems.The species is narrowly distributed in west to northwest of Yunnan province of China.Although it has been recorded as the second threatened plant in China,the study of the species conservation biology is still scarce.In the present study,the seed ecophysiological and conservation genetics of this species were studied to elucidate the endangered mechanism of T.nanus.Furtheremore,some management and conservation strategies to protect species germplasm of this species were proposed based on the results.The main results and conclusions are as follows:1.Seed ecophysiology of T.nanusSeed biological characteristics,optimum germination conditions,dehydration sensitivity and storage features of T.nanus were tested.Seed of T.nanus consists of seed coat,endosperm and embryo.The pericarp is attached to the seed coat and is difficult to separate.Endosperm is hard and milk-white.The embryo is linear,lateral and biased toward the navel.The seed 1000-grain weight was 254.34±5.31 g and the initial moisture content was 41.91±0.46%.The optimum germination temperature for seed germination was 25?.Photoperiod had no effect on the final germination percentage of T.nanus.The seeds of T.nanus were non-dormant The highest germination rate was 76.5%.The seeds were intermediate which can tolerate partly of dehydration.The critical water content of seed was about 7%.In addition,the dehydration rate could affact seed viability.Although there was no siginificantly influence of seed vigor when seed stored at 4?for a short term,the storage inhibit seed germination perceantge and prolong the germination time.2.Conservation genetics of T.nanus based on SSRs markersWe analyzed the genetic diversity,genetic structure and population demography dynamics of 120 individuals from 6 T.nanus populations based on 7 microsatellites(SSR)loci.The results indicated that a total of 58 alleles were identified with a mean value of 8.286 alleles per locus.The species exhibited a low levels of genetic diversity(Na=3.571,Ne=2.053,Np=7.833,Ra=3.540,Ho=0.129,He=0.338)at the species level but high genetic differentiation(FST=0.23,P<0.001)among populations.The inbreeding coefficient(FIS)was 0.633,suggesting a significant inbreeding in the 6populations of T.nanus.The AMOVA analysis revealed that 76.99%of the genetic variation was partitioned within populations.PCoA and UPGMA cluster analysis indicated that the 6 populations could be divied into two groups,of which one group was only consisted of DZS population,and another group was constituted of population HDZ,MDZ,YJA,LJS and JZS.However.,the structure analysis showed that the optimal K-value was 3,of which population DZS and JZS were included in group one,population JZS was included in group two,and population HDZ,MDZ and YJA were included in the final group.The Mantel test analysis indicated that genetic distance and geographic distance were not correlated(P>0.05).The historieal and contemporary gene flow between populations were extremely low.Furtheremore,there was no obvious evidence showed that populations of T.nanus suffered of the bottleneck effect recently.3.Endangered mechanism and conservation strategies of T.nanusBased on the above results,we may conclude that the species has low levels of genetic diversity,high genetic differentiation among the populations and high inbreeding within population.These factors caused the species's endangered status.Therefore,we proposed that strengthen the in situ protection of the existing field populations of T.nanus and their habitats.Priority protection should be given to population DZS and YJA which had more private alleles.Meanwhile,artificial seedling for raising population size of T.nanus in the wild and establishing new populations was also a viable way.Moreover,we also suggest develop the utilization of T.nanus to its future conservation. |
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