On 22nd November 2023, Klaus-Otto Lüning passed away and with him a restless and inspiring person of seaweed research. Klaus was a free spirit and enthusiastic algae researcher with boundless energy and a good sense of humour, who never bowed to convention, refused to be forced into any system, motivated many students and colleagues and gave inspiring lectures. When Klaus entered the room, it was quickly filled with a special intensity that was impossible to escape. He managed to captivate the ignorant and those new to algae and convince them of the beauty of these ’plants’, but also of their scientific importance.

Li, Xiaodong, Wang, Yanjun, Xiao, Luyang, Huang, Ershuai, Liu, Xiao, Shan, Tifeng and Pang, Shaojun. " Saccharina sporophytes settling on kelp cultivation rafts come from wild intertidal populations and not from the farmed cultivars" Botanica Marina, 2024. https://doi.org/10.1515/bot-2023-0096

Yarish, C., Pang, S., Lu, S. et al. Xiugeng Fei (1932–2022). J Appl Phycol (2024). https://doi.org/10.1007/s10811-023-03171-0

Li, X.D., Zhong, C.H., Jin, Z.H. et al. Genetic structure, major chemical component contents and agronomic characters of the principal cultivars of the kelp Saccharina japonica in the largest kelp production province in China. J Appl Phycol 35, 763–772 (2023). https://doi.org/10.1007/s10811-023-02905-4

Phlorotannins are among the most important defensive molecules in kelp. They have been majorly identified in brown algae so far. Type III polyketide synthase (PKS) is regarded as one of the enzymes catalyzing a major step in the biosynthetic pathway of phlorotannins. In this study, a type III PKS gene (sjPKS1) is characterized from the economic brown alga Saccharina japonica sporophyte. It contains 7 exons and 6 introns. The sjPKS1 open reading frame consists of 1245 nucleotides encoding a protein of 414 amino acids. The sjPKS1 are 87%, 83%, and 82% identical to that of Ectocarpus siliculosus, Sargassum binderi, and Sargassum fusiforme at the nucleotide level, respectively. While the amino acid sequences of sjPKS1 share more than 90% identity to that of the three brown algae species. The sjPKS1 expression at 200 µmol photons m−2 s−1 was significantly higher than at 20 and 50 µmol photons m−2 s−1 in sporophytic seedlings, so did the content of soluble phlorotannins inside the plants. Seven motifs in response to light are identified in the 5′ flanking region of sjPKS1 and two potential transcription factors are predicted by screening yeast one-hybrid library.

Undaria pinnatifida is the commercially second most important brown alga in the world. Its global annual yield has been more than two million tonnes since 2012. It is extensively cultivated in East Asia, mainly consumed as food but also used as feed for aquacultural animals and raw materials for extraction of chemicals applicable in pharmaceutics and cosmetics. Cultivar breeding, which is conducted on the basis of characteristics of the life history, plays a pivotal role in seaweed farming industry. The common basic life history shared by kelps determines that their cultivar breeding strategies are similar. Cultivar breeding and cultivation methods of U. pinnatifida have usually been learned or directly transferred from those of Saccharina japonica. However, recent studies have revealed certain peculiarity in the life history of U. pinnatifida. In this article, we review the studies relevant to cultivar breeding in this alga, including the peculiar component of the life history, and the genetics, transcriptomics and genomics tools available, as well as the main cultivar breeding methods. Then we discuss the prospects of cultivar breeding based on our understanding of this kelp and what we can learn from the model brown alga and land crops.

Use of cultivars with certain agronomical traits has been throughout the development history of kelp Saccharina japonica farming in China. Pursuit of high yield had been on top of all the parameters. However, in recent years, demand for better blade quality has steadily become intensive, especially in the northern farming region of this country. In this article, we report a newly bred, intraspecific hybrid E25 (as designation code), of its biological features and its applicability as a potential cultivar in the related farming region. A fully grown sporophyte of E25 could reach 4–5 m in length, 0.6–0.8 m in width, and 3–5 kg in fresh biomass depending on the farming zones and growing density within ca. 7-month cultivation period from November to May–June of next year. Unlike most of the cultivars or naturally grown sporophytes, sporophyte of E25 lacks fascia in the middle of the strip and possesses smooth blades. It has thicker ruffled undulate margins on both longitudinal sides and relatively low water content in its blade. Due to its much higher chlorophyll a content, blanched product is greener than most of the other cultivars, much favored by the processing industry. Seedling production of E25 relays on a pair of vegetatively propagated unialgal male and female gametophytes. High polymorphic microsatellite markers could accurately identify its uniformed genotype and distinguish it from other conventional cultivars. The first filial sporophytic generation of E25 (E25-F1) maintains the same yield level as its parent, reaching 23–25 kg m−1 cultivation rope, but with larger deviations in individual sizes as reflected by its higher coefficient of variations (CV).

The brown alga Undaria pinnatifida (Harvey) Suringar is an economically important kelp species native to the Northwest Pacific and has been extensively farmed as human food in East Asia for more than half a century (Yamanaka and Akiyama, 1993). It is also an important resource for extracting biologically active compounds such as fucoidans which have diverse applications in pharmaceutical and cosmetic industries (Zhao et al., 2018; Yoo et al., 2019). Its annual yield worldwide has been more than two million tons since 2012 (http://www.fao.org/fishery/species/2777/en). Nowadays U. pinnatifida has become a cosmopolitan species due to its worldwide spread in recent decades, attracting increasing public attention (South et al., 2017). It has been listed as one of the world's 100 worst invasive species (Lowe et al., 2000), and in Europe has been regarded as one of the top 10 worst invasive species (Gallardo, 2014).

In aquaculture of the kelp Saccharina japonica, hybrid cultivars could improve both the yield and quality of the farmed products. Hybrid cultivars refer to the diploid macroscopic offspring resulted from crossing a pair of haploid vegetative gametophyte cell lines. When these two cell lines are derived from individuals that are geographically isolated, the adult sporophytic offspring mostly remain immature in their second year of growth from June to September in the sea. The absence of sori in the adult sporophytes of the hybrid during this period prevents them from being used as parental ones for releasing spores to produce “summer seedlings” in hatchery. This is due to the seasonal restriction of hatchery operation which requires the availability of matured sori exclusively in August in the temperate zone in the northern hemisphere. The reasons for appearance of nonsporulating adult individuals has never been investigated although raising adult sporophyte in land-based tank filled with recirculated cold water at 10 °C has been a routine operation in hatchery enterprises in the subtropical zone in the south region of China for more than 20 years. While in the north region of China, parental sporophytes have been always raised in the sea until they are used for hatchery. From 2017 to 2019, we have conducted a series of culture experiments, both in beakers with isolated thallus in incubators and in large concrete tanks with intact individuals, trying to understand this phenomenon and look for a solution. The results showed that, (1) the hybrid cultivars demonstrated a feature of photoperiodic short-day plant and that it could form sorus within 25 days when exposed to SD at higher temperature (18 °C); (2) the hybrid cultivar maintains unique genetic structures different from the conventional ones as revealed by use of ten polymorphic microsatellite markers; (3) the sensitivity of the hybrids to the shortening of day-length differs in at least 10 days among individuals and could be inherited to its offspring; (4) sori induction in the intact adult sporophytes could be achieved within a month when supplied with SD, applicable to all current cultivars including the hybrids. The discovery and solution presented in this article has opened a gateway to utilization of hybrid cultivars in the giant kelp farming industry in China.

Sporophyll development is an important biological process which is crucial to reproduction of the sporophyte of the brown alga Undaria pinnatifida. However, the molecular foundation underlying this process is largely unknown due to lack of genomic information in this important alga. Full-length transcriptome, which covered male and female gametophytes at vegetative and gametogenic phases, and the blade, stipe, immature and mature parts of the sporophyll of sporophytes, was obtained for the first time through single molecule real-time sequencing in this study. After removing potentially polluted sequences derived from microorganisms, we obtained a total of 61,181 transcripts with average and N50 length being 1639 and 1815 bp, respectively, and annotated 21,915 of them (35.8%). By using the full-length transcriptome as reference, we performed Illumina sequencing to analyze the difference of gene expression among different developmental stages of the sporophyll and validated the results by quantitative real-time PCR. A large number of transcripts related to flagellar components and fucoidan biosynthesis as well as a few transcripts coding for meiotic nuclear division protein were found to be significantly upregulated with development of the sporophyll, and thus the over-expression of them is likely essential for the sporophyll to perform its biological function. These findings contribute to our understanding of sporophyll development in U. pinnatifida at the transcriptional level.

Undaria pinnatifida, a kelp species native to East Asia, has become cosmopolitan and drawn increasing attention due to its worldwide spread in recent decades. Floating fragments of this alga were found washed ashore on Sylt in 2016, the first record of this species in Germany. Thalli attached to local oyster reefs were detected in 2017. The genetic relationship between the floating and attached thalli on Sylt, as well as their relevance to the populations from northern Europe and native regions, was hitherto unknown. Here, 10 microsatellite markers were used to assess relationships between the recently established population on Sylt and five other northern European populations in France (Brittany, West English Channel), the Netherlands and England (Plymouth, West English Channel) plus three natural populations in China. Almost no genetic differentiation was detected between the floating and attached populations on Sylt, but they were genetically distinct from all the other studied northern European populations. The very low genetic diversity revealed in the new founder populations of Sylt suggests that they came from genetically similar parents. The marked reduction in both the number of alleles and heterozygosity in the northern European populations, as compared with the Chinese ones, is typical of founder effects in recently populated regions. Prominent genetic divergence was found between most of the northern European populations except those within Brittany and Sylt. Further studies will focus on identifying the putative source populations that might be found on shellfish farms, in local marinas or the benthic habitats around Sylt Island.

Although the original Saccharina japonica populations in China are assumed to have been accidentally introduced from Japan in 1920s, few investigations have been performed to prove it. Genetic structure analysis is expected to shed light on this question. In the present study, 11 highly polymorphic microsatellite markers were employed to analyze the genetic structure of representative populations of S. japonica in the Northwest Pacific, including the four varieties from Japan. Populations from China had a much lower level of genetic diversity than the ones from Japan in terms of the number of alleles, private alleles and locally common alleles, and the values of heterozygosity, suggestive of the founder effect in the introduced populations. Both the Bayesian model-based and genetic distance-based analyses revealed three major clusters: (1) S. japonica var. japonica, var. religiosa, and var. ochotensis from Hokkaido, as well as the populations from Korea and Russia; (2) populations from China; and (3) var. diabolica. Saccharina japonica var. diabolica harbored the highest number of private alleles, with three of them having a frequency of 1.00 at three loci, which have the potential to be used as specific markers to distinguish this variety from others. Significant genetic differentiation was found between almost all the populations except for a few cultivated populations from China. Populations from China were most closely related to S. japonica var. japonica, which was in turn most close to var. religiosa and the Korean population. The microsatellite markers used in this study were shown to be polymorphic enough to decipher the subtle genetic structure of S. japonica, including the different varieties.

The giant kelp farming industry in China, with an annual production of 1.4 million t (dry weight, DW) in a farming area of 130,564 ha, depends on a safe and constant supply of sporelings each year that are nurtured in ca. 20 commercial hatchery enterprises in Shandong and Fujian provinces in the north and south, respectively. Extension of the kelp growing period in the sea relies on the use of the so-called summer sporeling. Its production is based on using recirculated cold water (5–10 °C) to allow gametogenesis to happen and thereafter the young sporophytes to grow in summer when the ambient seawater temperature (above 20 °C) is too high. This allows sporophytic sporelings to be transferred to open water in early autumn, 2 months earlier than naturally occurring plants in coastal populations. Although historically commercially viable and successful, there have been few reports to describe this hatchery process. In this case study, the entire process of a commercial hatchery manipulation in the 2015 production season at Lvshun, Dalian, northern China, is presented, including pre-treatment of parental plants, control of spore release, and control and adjustment of solar irradiance and temperature at different developmental stages of the plants as well as the nutrient supply regime over the entire course. Analyses of the data and process in this report is expected to shed light on future optimization of the technique as well as providing useful clues for other farmed kelp species in other regions of the world.

Hermaphroditic gametophyte production and an intact male life cycle were investigated in Undaria pinnatifida. Zoospore-derived hermaphroditic gametophyte could give rise to male sporophytes which showed the same morphological appearance but with smaller biomass than normal cultivated sporophytes. Male sporophytes were shown to discharge only male zoospores. In this investigation, male spores derived from the male sporophytes and female spores derived from female parthenosporophytes were crossed to produce the hybrid sporophytic offspring. The latter contained both alleles of homozygous parental sporophytes when analyzed by use of eight polymorphic microsatellite markers, further confirming the success of cross. Thus, line crossing by use of unisexual sporophytes will be expected to replace unisexual gametophyte line crossing in breeding practice in the future in this commercially farmed seaweed.

Seedling production of brown alga Saccharina japonica in China happens in recirculated cold seawater to provide sufficiently large young plants for open sea cultivation when the seawater temperature drops below 20℃. In order to clarify whether there was a variety contamination problem in the sharing recirculated cold water system when more than one variety was produced in this investigation,a female gametophyte clone was used to test whether hybrid sporophytes could be obtained at the inlet of the water system and inside the seedling culture tanks, using parthenogenetic sporophytes as the control. Four microsatellite loci were used to further analyze the genotypes of the sporophytes. Results showed that the sporophytes obtained at the water inlet and inside the seedling production tanks were composed of alien genes indicating clearly the presence of variety contamination. Thus,this paper suggested that an independent water system was required to cultivate the parental plants in order to maintain purity and superior characteristics of each variety.

Undaria pinnatifida is an important economic brown alga in East Asian countries. However, its genetic and genomic information is very scarce, which hinders further research in this species. A high-density genetic map is a basic tool for fundamental and applied research such as discovery of functional genes and mapping of quantitative trait loci (QTL). In this study the recently developed specific length amplified fragment sequencing (SLAF-seq) technology was employed to construct a high-density genetic linkage map and locate a sex determining locus for U. pinnatifida.

The annual life cycle of the brown seaweed Undaria pinnatifida (Harvey) Suringer comprises a macroscopic diploid sporophyte stage and a microscopic haploid gametophyte stage. In 2011, an unusual zoospore-derived monoecious gametophyte isolate (designated as line 10-5-3) of U. pinnatifida was observed. To understand this phenomenon, a comprehensive screening of eighty-two previously identified male gametophyte cultures, isolated from three randomly selected cultivars (lines 10, 7, and 5) was performed. Thirty-six of the isolates developed both antheridia and oogonia on the same filamentous fragment in a standard gametogenesis test (SGT: 18°C, 60 μmol photons/(m2∙s)). Selfing of the monoecious gametophyte or crossing it with a normal male gametophyte both gave rise to morphologically normal sporophytic offspring. However, crossing resulted in a much higher fertilization rate (89.7%). The hybrid and selfed sporophytic offspring were grown to maturity in flow tanks at an ambient temperature of 10–18°C over a period of 69 days. Active zoospores were released from both types of mature sporophylls. The majority of these developed into male gametophytes, while 15%–20% developed into the observed monoecious structures on the same filament. Using PCR amplification it was found that all the monoecious gametophyte isolates and the sporophytic offspring resulting from the selfing and crossing lacked the femalelinked microsatellite sequence (a part of the locus Up-AC-2A8, GenBank accession No. AY738602.1), indicating their male nature. U. pinnatifida is an invasive species in some regions and the implications of the above findings for this species in nature are briefly discussed.

During sexual reproduction of seaweeds, spermatozoid (sperm) discharge is triggered by chemical messengers (pheromones) released by the female gametes. The chemotactic ability of the sperm ensures fertilization success. Using unialgal male and female gametophyte material under designated standard gametogenesis testing (SGT) conditions, the potential life-span of the sperm of two seaweeds, Saccharina japonica and Undaria pinnatifida, was assessed by their ability to fertilize eggs. Results show that within 20–30 min after being discharged, sperm of both species could complete fertilization without an apparent decline in fertilization rate. Although fertilization rate 60–120 min after sperm discharge dropped significantly in both species, some sperm were viable enough to fertilize the eggs. In S. japonica, at 12°C, some sperm were able to fertilize eggs up to 12 h after discharge. In both species, egg discharge rates (EDR) in the male and female mixed positive controls were significantly higher than those of all the sperm-testing groups. Doubling the seeded male gametophytes of S. japonica in the SGT tests significantly increased the EDR, further confirming the effect of the presence of the male on the female in terms of facilitating egg discharge from oogonia.