Interspecific Compatibility And The Relationship Among Bruguiera Gymnorrhiza, B. Sexangula And B. Sexangula Var. Rhynchopetala

Bruguiera genus plants, including B. gymnorrhiza, B. sexangula and B. sexangula var. rhynchopetala, are the major mangrove species in China. The morphological traits of three mangrove species are similar and some of traits of B. sexangula var. rhynchopetal are quite similar to B. sexangula while others to B. gymnorrhiza. Some researchers suggested that B. sexangula var. rhynchopetala is a variation of B. sexangula while others suggested that it was a hybrid species of B. gymnorrhiza and B. sexangula. Here flower morphologic traits, manual pollination, ISSR molecular marker and comparison of DNA sequence were investigated to study the degree of genetic variation, the relationship of the three species and taxonomic position of B. sexangula var. rhynchopetala. All the work was summarized as follow:(1) Comparison of floral morphologic traits: The stigma was almost equal to the petal in B. sexangula var. rhynchopetala, but higher in B. sexangula and lower in B. gymnorrhiza before blossoming. The relative length of stigma to the petal is 1.007±0.015, 1.056±0.021 and 0.847±0.023 respectively. Two tails t-test indicated that the data were extremely notable difference.(2) Interspecific compatibility: Pollen viability was greater than 90% in the three species by acetocarmine stain. Few of pollen tubes could be observed in pistillary cord and reached to the ovary when B. sexangula, B. gymnorrhiza and B. sexangula var. rhynchopetala crossed with each other which suggested that the three mangrove species were interspecific incompatibility.(3) ISSR analysis of Genomic DNA: eighteen ISSR primers which could produce clear loci were screened from eighty one primers. Total 142 loci were amplified and 109/142(76.2%) of ISSRs were polymorphic. Nei's genetic similarity (GS) between B. gymnorrhiza and B. sexangula was 0.43, that of B. gymnorrhiza and B. sexangula var. rhynchopetala was 0.50 and that of B. sexangula and B. sexangula var. rhynchopetala was 0.55. Dendrogram based UPGMA showed clustering of B. sexangula and B. sexangula var. rhynchopetala into a loose group and B. gymnorrhiza into a single group.