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Stimulation of sexual reproduction was conducted for strain improvement of the agarophyte, Gracilaria fisheri under cultivation. Thirty sporelings from tetraspores with initial height of 2 cm were cultured in 1 L aeration tube flasks under different levels of salinity: 10, 20 and 30 ‰; light intensity: 20, 40 and 60 µmol photons•m-2•s-1; carbon dioxide: 0 and 1%; and concentrations of two plant hormones, 6-benzyladenine and auxin: 0.00, 0.05, 0.10 and 0.50 mg•L-1, separately tested. Formation of reproductive cells was examined from the external surface of the seedlings every week. The results showed that cystocarps were recognized at all levels of salinity and light intensity; the fastest development was at the week 2nd at salinity 20 ‰ and light intensity of 60 µmol photons•m-2•s-1. Cross sections of thalli exhibited completely male structures and cystocarps. Under supplemention with carbon dioxide, 6-benzyladenine and auxin, the formation of sexual reproductive cells in the seaweed was not found. This study suggests that salinity and light intensity could be used for stimulation of sexual reproduction of G. fisheri, while carbon dioxide and the two plant hormones used might inhibit the formation of sexual reproductive cells in this algal species.
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