Obtaining spores for the production of Saccharina latissima : seasonal limitations in nature, and induction of sporogenesis in darkness

When cultivating the kelp Saccharina latissima, knowledge on the availability of seeding material for the production is essential. Applying a spore seeding approach requires spores from the reproductive organs of the fertile sporophytes (sori). As sori are generally not present during the time of seeding in late summer, the production of spores (sporogenesis) can be artificially induced by removing the meristematic part of the sporophyte and keeping the sporophyte under short day, temperate, and nutrient-replete conditions. Only limited information is available on the effect of light intensities including darkness on the sporogenesis of S. latissima. This study examined the natural pattern of sporogenesis in S. latissima from Middelfart, Denmark, and the effect of four different light regimes (0, 20, 60, or 120 μmol photons m−2 s−1) on the artificial induction of sporogenesis in S. latissima. Natural reproductivity and availability of spores in Denmark peaked in early winter, with 86% of the population being reproductive in November. Reproductive material was available from October until late spring, but with a variable spore release from 11 × 103 to 1.2 × 106 spores cm−2 sori. The artificial induction of sporogenesis was optimal in darkness with > 90% of sporophytes developing sori after 49 days, with an average spore release density of 1.15 ± 0.38 × 106 spores cm−2 sori. The results confirmed that S. latissima in Denmark follows the general pattern of reproduction of S. latissima in North Atlantic regions and demonstrated for the first time that sporogenesis in S. latissima can be efficiently induced in darkness.