Genetic variation of Avicennia marina in the costal area of Vietnam was examined using microsatellite and AFLP markers. By using five microsatellite loci a total of 21 alleles were detected. The average number of alleles per locus per population ranged from 1.667 to 3.000. The observed heterozygosity varied from 0.180 to 0.263, with an average of 0.210 indicating relatively low level of genetic variation comparing to the previous studies on A. marina in the worldwide range. The expected heterozygosity was larger than the observed heterozygosity leading to positive inbreeding coefficients in all the six populations. Highly significant departures from Hardy-Weinberg Equilibrium were detected in four populations. AFLP analysis revealed a total of 386 loci, of which 232 (60.1%) were polymorphic. In congruent with microsatellite markers relatively low levels of genetic variation were detected at both gene and nucleotide levels ( H = 0.086; π = 0.0054). Reduced level of genetic variation was found in the central population, and in the southern populations. Both microsatellite and AFLP markers revealed large genetic differentiation ( F ST = 0.262 and 0.338, respectively) indicating strong genetic structure among regional populations.Pairwise genetic distance by AFLP showed two populations in the north and the other two in the south are closely related each other.

Genetic variation of the mangrove genus Kandelia (Rhizophoraceae) in the South China Sea region, in four populations in Vietnam and in one population each in Iriomote, Japan, and Bako, Borneo, was evaluated using microsatellite markers. A total of 54 alleles in the six populations were detected by using four microsatellite loci. The two northern Vietnamese populations (Don Rui and Xuan Thuy) showed a high allelic diversity (40 alleles in total) and a high level of gene diversity (H E = 0.773 on average). In contrast, the two southern Vietnamese populations (Can Gio and Ngoc Hien) showed low allelic diversity (11 alleles in total) and a low level of gene diversity (H E = 0.244 on average). There was only one allele common to the two regions. The Iriomote population was genetically related to the northern Vietnamese populations, while the Bako population was related to the southern populations. The findings and the morphological observations indicate that these two genetically differentiated vicariant lineages represent two different species groups, Kandelia obovata Sheue, Liu, and Yong for northern Vietnam and Japan and Kandelia candel (L.) Druce for southern Vietnam and Borneo. The difference in the amount of genetic variation shows that these two species experienced a different adaptive process during the past glacial ages.

No abstract

Mangroves are constituent plants of tropical and subtropical intertidal forest communities. In order to assess their genetic variations and understand the contributing factors determining their genetic structures, we investigated sequence variation of the matK (maturase K) region of plastid DNA in three widely distributed species, Avicennia marina, Kandelia candel and Lumnitzera racemosa , taking samples from multiple populations in Vietnam and samples from Okinawa. These three species have different types of seeds/propagules with regard to vivipary, size and other characteristics and are expected to have different migratory potentials. Generally, variation within a population was low, probably reflecting unstable habitats of mangroves. In contrast, we found very different patterns of differentiation between populations of the three species. In A. marina , we recognized three groups of geographic lineages that were moderately separated while in K. candel , two distantly separate geographic lineages were found. No genetic variation was found in the total population of L. racemosa from Okinawa to southern Vietnam. We discuss possible factors, such as properties of propagules, zonation and natural disturbances, that may influence the genetic structures of mangrove species.

The study of AFLP analysis in Kandelia obovata, one of the major mangrove species in Japan, revealed the existence of a unique fragment showing stuttered peaks. We cloned this fragment and found a novel microsatellite locus. We report the method used for isolation and the polymorphic nature of this locus among the populations on Iriomote Island.