Effects of Temperature and Light Intensity on the Early Growth of Tetrasporophytes and Gametophytes of Agarophyton vermiculophyllum

The aim of this study is to examine the physiological characteristics of an agarophyte Agarophyton vermiculophyllum (Ohmi) Gurgel, J.N. Norris et Fredericq in the early life stage of tetrasporophytes (2n) and gametophytes (n) to select appropriate seedlings for mariculture. Growth experiments were carried out at the combinations of four temperatures (20, 25, 30, and 35°C) and three light intensity levels (20, 60, and 100 μmol photons m-2 s-1) in the two ontogenetic stages: discoid holdfasts and erect sporelings. Holdfast areas and sporeling lengths of tetrasporophytes and gametophytes were estimated after 14 days in culture. Relative growth rates (RGRs) for holdfast areas were 7.08–28.38% day-1 for tetrasporophytes and 11.58–23.67% day-1 for gametophytes. At 35°C, holdfasts of tetrasporophytes survived with RGRs of 7.08–23.28% day-1 but those of gametophytes died. Maximal holdfast growth of tetrasporophytes occurred at 30°C and 100 μmol photons m-2 s-1, which were different from gametophytes (25°C and 100 μmol photons m-2 s-1). RGRs of tetrasporophytic sporelings were 2.93–11.11% day-1 and were between 0.78–10.82% day-1 for gametophytes. Maximal growth of A. vermiculophyllum sporelings occurred at 25°C and 60 μmol photons m-2 s-1 for tetrasporophytes, and at 20°C and 100 μmol photons m-2 s-1 for gametophytes. In conclusion, the present results indicate that carpospores could be used as resources of spore-seedling methods having genetic diversity for mass field cultivation because tetrasporophytes showed higher-temperature tolerance and faster-growing ability than gametophytes of A. vermiculophyllum in the discoid holdfast and sporeling stages.