DNA EXTRACTION AND RAPD MARKERS TO ASSESS THE GENETIC SIMILARITY AMONG GELIDIUM-SESQUIPEDALE (RHODOPHYTA) POPULATIONS

A simple method developed for genomic DNA isolation from fungus was te sted on the red alga, Gelidium sesquipedale (Clem.) Born et Thur., whi ch is commercially exploited for its high sulfated polysaccharide (aga r) content. This method is faster, cheaper, and less toxic than conven tional phenol/chloroform methods. Random amplified polymorphic DNA (RA PD) amplifications were performed successfully without the necessity o f purifying the DNA. RAPD markers were used to investigate the genetic similarity among three natural populations of G. sesquipedale from so uthern Portugal. Bulked-genomic DNA samples of 15 different individual s were made in each population. These can be conceived of as a sample of the population DNA. Of the 62 primers screened, 41 produced bands a nd 22 revealed polymorphisms. Genetic similarities among populations w ere high. Populations that are further away from each other have the l owest similarity coefficients, whereas the intermediate Ingrina popula tion, located on the south coast, showed higher genetic similarity wit h the Odeceixe population located on the southwest coast, than with th e Sao Rafael southern population. This suggests a higher genetic flow between Odeceixe and Ingrina or the result may be a founder effect in the sense that the species has propagated from the east coast to the s outh coast of Portugal. We conclude that the use of this isolation met hod with RAPD analysis is appropriate to characterize the genetic vari ability of this commercial species along its geographical distribution . Large sample sizes can be screened at a relatively low cost. Finding genetic markers for commercial populations of C. sesquipedale may be of industrial interest.