Thesis (M.Sc.)--Chulalongkorn University, 2007

Noctiluca scintillans is the main causative red tide organisms in the inner Gulf of Thailand. Generally, this red tide could be observed around the river mouth areas including Chonburi and Petchburi coastal areas. However, the relationship between groups of N. scintillans in the inner Gulf of Thailand has not been known. Therefore, this study aimed to use the application of the molecular genetic technique to investigate genetic variation of N. scintillans. The samples were collected from 3 different locations in the inner Gulf of Thailand (Petchburi, Samotprakarn and Chonburi province), 2 locations from the eastern and southern part of the Gulf of Thailand (Chanthaburi and Chumpron province) and 2 sites from The Philippines and Indonesia. N. scintillans was cultured in ESM-culture medium, fed with Dunaliella. The DNA was extracted by salting out method for molecular genetic study. 48 ISSR primers were screened and 5 primers produced clear, polymorphic, and reliable ISSR profiles (814, SAS 3, 17898A, HB15 and 844A). The PCR product of COX I gene was about 450 bp in size. The analysis of the COX I sequences showed that there was no genetic variation among green N. scintillans samples. For ITS I region, the amplified PCR product was approximately 800 bp in size. The primer ITS_F1 was used to carry out sequencing reaction, 489 bp of DNA sequence were obtained, the sequence consisted of partial sequence of 18s rRNA (471 bases) and some part ITS region (27 bases). The sequence of PCR product of 56 bases were obtained by reversed primers ITS_R2. and contained part of 5.8s rRNA (41 bases) and part of ITS1 region (15 bases). The analysis of sequence obtained from ITS_F1 primers (489 bases) showed no differences among the samples collected from all stations. There was a problem to get the whole sequence of ITS I region of N. scintillans in this study. This might be caused by the variation between multiple copies of the gene within each sample since this gene has been reported that the multiple copies could be occurred.