| As one of the most important economic marine macroalgae, Saccharina japonica plays a vital role in the national economy and people’s lives. Cultivar selection and breeding are very important for the cultivation of S. japonica; however, the genetic relationships among various cultivars are unclear and the commerical names in market are always confusing. People often distinguish one cultivar from another by their morphological characteristics and economic traits, such as colour, length and so on, which makes it hard to guarantee the preservation and utility of germplasm resources. Therefore, SSR technique was applied to study the genetic diversity and relationships of 15 main cultivars(20 individuals per cultivar) of S. japonica obtained from 7 nurseries in Shandong Province. 15 out of 88 SSR primers were selected in the experiment. A total of 94 alleles were generated across all samples, among which 25 are unique, with allele numbers ranged from 3 to 17 per primer. All of the 15 cultivars exhibited relatively high standard of genetic diversity, as revealed by the average of the Nei’s genetic diversity(H) and the Shannon’s Information index(I) being 0.466 and 0.862, respectively. At the cultivar level, C12 showed the highest genetic diversity(H:0.488;I:0.888) and 202 showed the lowest(H:0.305;I:0.506). Genetic distance among 15 cultivars ranged from 0.007 to 0.547, and genetic identity ranged from 0.579 to 0.993. Based on genetic distance among cultivars, the phylogenetic tree was constructed by using UPGMA method. It was clearly suggested from the dendrogram that all cultivars could be divided into three groups: cultivar C033 was clustered into the first group, cultivar 205 and 202 were closer to each other and clustered as the second group, the last one was constituted by other 12 cultivars. Analysis of molecular variance(AMOVA) revealed that 11.39% of variation resided among cultivars, while 88.61% within cultivars. The total Gst value was 0.128 and the gene flow(Nm) was 1.702, indicating a intermediate genetic differentiation and a certain amount of gene flow among all 15 cultivars. When applying AMOVA to 12 cultivars except 202, 205 and C033, the variance among cultivars(95.97%) was especially higher than it within cultivars(4.03%), with total Gst value was 0.059 and the gene flow(Nm) was 3.970, implying low genetic differentiation and relatively high gene flow among these 12 cultivars. All the results showed that the 15 cultivars of S. japonica had a relatively high genetic diversity level which was beneficial to adapt to the changeable environment, however, some of the cultivars might be mixed with each other, as indicated by their genetic distance and genetic variation. Fortunately, some effective SSR markers had been found in this experiment, which may be helpful in strain identification.In the northern part of China, parental sporophytes of the farmed seaweed S. japonica that are used for releasing spores are selected from the farmed population. The recirculated-cold water system is applied to produce seedlings of S. japonica(artificially cooled from 24 to ca. 7℃ ℃). The less the days to culture the seedlings, the lower the production cost. Since the parental plants are maintained on longlines in the sea, elongation of maintenance of them in the water will have to face up to the rising temperature in the summer(from 20 to 25℃). For S. japonica, there has been no study to elucidate the effect of the rising temperature on the ability of sorus to release spores and the performance of gametogenesis as well as the growth of the resulted sporophytes. In the present study, we used two strains “205†and “C033†as the subjects, arranged five temperatures and four culture periods in combination to study the impact. The results indicate that,(1) spore release failed at 24℃, but showed no apparent difference from 20 to 23℃;(2) germination rates of spores from sorus cultured on day 12 and 16 under the same temperature were higher than that of day 4 and 8;(3) female gametophytes and the resulted sporophytes from sorus cultured at 23 were much smaller than that from 20℃-22 at the same℃ culture time;(4) under identical conditions, both female gametophytes and the resulted sporophytes were the smallest on day 16 in all culture trials;(5) size of gametophytes were positively co-related with the size of sporophytes. In summary, sorus of the parental plants are apparently in stressed conditions when in temperature higher than 23 or℃ incubated for more than 16 days at temperature from 20-23℃. |
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