Effects of temperature and light on early sporophyte development of <i>Saccharina japonica</i> and <i>S. latissima</i> (Phaeophyta)

Abstract Saccharina japonica is common aquaculture species in Asia, whereas S. latissima is cultivated in North America and Europe. This study aims to select superior strains using breeding techniques for high‐temperature tolerance and faster development at the early sporophytic stage. Qualitative experiments were conducted to observe the reproduction and early development of sporophytes under different temperatures (5, 10, 15, and 20°C) and light conditions (5 and 40‐μmol photons m −2 s −1 ) for 20 days after male and female gametophytes were crossed. Two female (F05 and F15, S. japonica ; FB and FO, S. latissima ) and male (M06 and M14, S. japonica ; MB and MO, S. latissima ) gametophyte strains in each species were used. No inter‐specific crosses were made. Four possible intraspecific crosses were cultured. Regardless of the species, the development of sporophytes was observed earlier at 10°C than all other temperatures (5, 15, and 20°C). No sporophytes were observed at 20°C during the experiment. The crosses of F15xM14 ( S. japonica ) and FBxMB ( S. latissima ) showed higher thermal tolerance and rapid development of sporophytes than other crosses. These results suggest that optimal reproduction and early development of sporophytes can vary from species to species of the same genus and even between strains of the same species.