Abstract
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.
Highlights
In Europe, the cultivation of seaweed is currently being developed toward a more viable and economically sustainable industry, which can provide biomass for a wide range of applications (Zhang and Thomsen 2019)
The fraction of the fertile sporophytes capable of releasing spores varied between 70 and 100% from November to May, but in June and August none of the collected fertile sporophytes released viable spores, and in October it was estimated that only 10% of the total population released viable spores, despite the fact that more than 40% of the total population were bearing sori
The spore release density was highest in November with an average spore release of 1.2 ± 0.41 × 106 spores cm−2 sori (Table 1)
Summary
In Europe, the cultivation of seaweed is currently being developed toward a more viable and economically sustainable industry, which can provide biomass for a wide range of applications (Zhang and Thomsen 2019). A solution for this is to artificially induce sporogenesis by removing the meristem of sporophytes and keeping sporophytes in a short day regime around 10 °C (Lüning 1988; Pang and Lüning 2004; Forbord et al 2012). Maturation can proceed in a light regime with light intensities above 30 μmol photons m−2 s−1 (Lüning 1988; Pang and Lüning 2004; Forbord et al 2012), but as high light intensities have been found to promote sorus formation in S. japonica (Mizuta et al 1999a), optimal light intensities for sorus formation are not well described for S. latissima
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